2 speed mini bike clutch

2 speed mini bike clutch DEFAULT

US3610062A - Automatic mini-bike transmission - Google Patents

Oct. 5, 1971 5, J, HOFF 3,610,062


AUTOMATIC MINI-BIKE TRANSMISSION 1 Filed Dec. 5, 1969 2 Sheets-Sheet 2 INVENTOR. STEPHEN J. H OFF BY WM ATTORNEYS United States Patent AUTOMATIC MINI-BIKE TRANSMISSION Stephen J. Hoff, Richmond, Ind., assignor to Comet Industries, a division of Holfco, Inc., Richmond, Ind. Fil d Dec. 3, 1969, Ser. No. 881,665 Int. Cl. F16d 23/10; F1611 9/00 US. Cl. 74217 C 3 Claims ABSTRACT OF THE DISCLOSURE An automatic two-speed transmission for mini-bikes and other light-weight vehicles. A first centrifugal main clutch on the engine shaft drives parallel chains to highand low-speed sprockets on a jack shaft which is chainconnected to the drive-wheel. The low-speed sprocket drives the jack shaft through a one-way, roller low clutch of sturdy 4-roller construction, which allows the jack shaft to overrun when the high drive engages. The high-speed sprocket drives the clutch shoes of a second centrifugal high clutch which has its clutch drum fixed to the jack shaft. The high-clutch shoes are primarily centrifugally responsive, but are arranged to have limit d self-energizing action and thereby to maintain smooth engagement and release as transition changes occur during shifts. The combination gives reliably predictable shifts in response to driver control of engine speed, and smooth transitions between low drive and high drive.

The jack shaft assembly comprises a continuously slotted shaft on which the clutches, sprockets, a brake drum, and supporting bearings are mounted in axially adjustable relation to adapt such assembly for versatile application to different bike structures and for use as a modification kit on existing bikes.

BACKGROUND OF THE INVENTION This invention relates to an automatic transmission and more particularly to an automatic two-speed transmission for use in light weight vehicles such as mini-bikes.

Mini-bikes in their simplest form comprise an internal combustion engine which is connected through a centrifugal main clutch to a drive train to the rear wheel, which train may include a jack shaft. The present invention utilizes a jack shaft continuously connected by a drive chain to the rear drive wheel. The engine-driven centrifugal main clutch drives high-speed and low-speed drive sprockets connected by chains at different speed ratios to high-speed and low-speed driven sprockets on the jack shaft. The low-speed driven sprocket is connected to the jack shaft through a roller clutch of sturdy 4-roller construction which allows the jack shaft to overrun the low-speed drive train when the high speed drive train is operative. The high-speed driven sprocket is connected to the shoe assembly of a secondary or high-speed centrifugal clutch, and the drum of that clutch is fixed on the jack shaft to drive such jack shaft when the high speed clutch is engaged. A brake is desirably provided on the jack shaft.

Two'speed automatic transmissions for use in minibikes and similar light weight vehicles have Previously been proposed. The present invention relates to the type of transmission shown in US. Pats. Nos. 2,463,100 and 3,436,977, and constitutes an improved transmission of that general type. The transmission in accordance with the present invention has smoother and more predictable and reliable operating characteristics, especially in shifting between low and high speeds, which increases safety and gives a smoother ride and a much longer operating life.

Pat. No. 3,436,977 employs a roller clutch having a plurality of small rollers. I have found that improved results are obtained with a 4-roller clutch in which the rollers are each positively spring pressed to clutching position and operate between sturdy and solid races. Pat. 3,436,977 employs a centrifugal clutch in the high-speed drive train which has sprag-type clutch shoes mounted on the counter shaft, that is, on the element which i driven by the clutch, and has its drum fixed to the highspeed sprocket, that is, to the element which drives the clutch. This is the rational arrangement in that the centrifugally responsive clutch shoes rotate with the jack shaft and the driven wheel which undergo a continuous speed increase in the transition from low-speed drive to high-speed drive. This arrangement, as taught by the aforesaid patents, utilizes clutch shoes which are each connected to its supporting hub at a point displaced by a large angle from the center of pressure of the shoe face in a direction such that the said center of pressure is ahead of the point of support in the direction of drive rotation, which gives a high degree of self-energization in the clutch action. It has been found that such arrangement as taught by the aforesaid prior patents, gives a harsh clutching action and especially a clutching action which is unpredictable so that the bike rider cannot know or control when shifts will occur between high and low drive, especially when the bike is being ridden over rough terrain, when control is especially needed for safety.

The present invention overcomes this unpredictability and lack of control. In the present invention the mounting arrangement of the shoes and drum is reversed from that just described and a differently-acting clutch is used. The counter shaft fixedly carries the clutch drum, that is, the driven element of the clutch, and the shoes are carried with the high speed sprocket so that they rotate with the engine, which is the driving element and which tends to undergo a speed reduction in the transition from lowspeed drive to high-speed drive. The shoes are mounted on the hub of the sprocket in a manner such that each shoe is driven at a point near to or ahead of the center of pressure of its clutch face. This provides a limited amount of self-energization or wedging action between the shoe and drum and the clutch engagement depends on and is responsive to a combination of both centrifugal action and self energization. The engagement is primarily centrifugal, in response to a high speed at which the shoes are driven by the engine. As they engage, their speed tends to decrease and the limited self energization maintains engagement in a smooth relationship through the transition from low speed drive to high speed drive. The result is a progressive clutch action, both on engagement and disengagement; and this combines with the action of the sturdy roller clutch to give improved and controllable operating characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated in the accompanying drawings, which show a preferred embodiment, and in which:

FIG. 1 is a plan view of a two-speed automatic transmission assembly in accordance with the invention, partially in section and with portions broken away;

FIG. 2 is a sectional view of the low speed driven sprocket and roller clutch, taken on the line 22 of FIG. 1;

FIG. 3 is a sectional view of the centrifugal driven clutch, taken on the line 3-3 of FIG. 1; and

FIG. 4 is an end view of the jack-shaft assembly, showing the brake and the mounting bracket.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the mini-bike drive assembly shown in FIG. 1, the gasoline engine 14 of a mini-bike is supported by conventional means on the frame 12 of the bike. The engine shaft 15 carries the hub 30' of a centrifugal main clutch 22 having drive shoes 32 which are normally disengaged but which under centrifugal force move outward into engagement with a driven clutch drum 34, in known manner. Such drum 34 is carried by a sprocket hub 36 rotatable on a bearing sleeve 38 carried by the motor shaft 15 and fixed to the hub 30. The sprocket hub 36- carries a fixed low-speed sprocket 40 and a fixed high speed sprocket 42, which are conveniently of the same size as shown and may have, for example, twelve sprocket teeth.

A counter shaft or jack shaft 48 is mounted on frame members 12 by means of ball bearings 50 and 51. The inner races of the bearings carry the jack shaft, while the outer races are fixed in mounting plates 44 which are adjustable on and bolted to mounting brackets 46 welded or otherwise secured to members of the bike frame 12. The jack-shaft 48 is a continuous length of slotted shaft and the bearings and other elements are adjustably mounted thereon and secured by collars and set screws so that the assembly is readily adapted to fit various bike assemblies and to be supplied as a kit for application to existing bikes.

The jack shaft assembly includes a final drive sprocket 52 which in use is connected by a chain to a sprocket on the drive wheel of the mini-bike. Outward from such sprocket and adjacent the outer face of bearing 50, the jack shaft also carries a brake drum 54 arranged to be engaged by a brake band 56 carried by a mounting stud 57 on the mounting plate 44 for the adjacent bearing 50.

A low-speed driven sprocket 60 and a high speed driven sprocket 62 are mounted on the other end of the jack shaft 48, inside the bearing 51 in alignment with the high and low speed sprockets 40 and 42 carried by the motor shaft 15. When the parts described above are mounted for use, the low speed sprockets 40' and 60 are connected by a low-speed chain 100-, and the high speed sprockets 42 and 62 are connected by a high-speed chain 102.

The low speed sprocket 60' is carried by the outer ring 59 of a roller clutch 64 having a hub 65 keyed to the jack shaft 48, as indicated at 67. As shown in FIG. 2, clutch 64 has four roller bearings 66 spaced 90 apart and each positioned between a ramp on the heavy ring 59 and the hub 65. Each roller 66 has an associated spring 63 pressing it into a position of clutching engagement between its ramp and the hub 65. The clutch is arranged to transmit drive from the sprocket 60 to the jack shaft during low-speed drive but to permit the hub 65- and jack shaft 48 to overrun the low speed driven sprocket 60 when the jack shaft is driven at a higher speed by the high speed sprocket 62.

The high speed sprocket 62 is arranged to transmit drive to the jack shaft 48 by means of a centrifugal clutch 68, the characteristics and arrangement of which are of prime importance to the two-speed operation. The clutch 68 includes a hub 70 which carries the sprocket 62 and is mounted for rotation on a bearing sleeve 71 carried by the jack shaft 48. As best seen in FIG. 3, each shoe 78 has an inner face 74 which normally bears against the peripheral surface of the hub 70, and each shoe is provided with a radially extending socket 80 which receives a driving lug 82 fixed on the hub 70. Preferably, the driving lugs 82 and sockets 80 are positioned at the center, circumferentially, of the shoes, and hence at the centers of pressure of the clutch faces, or slightly forward of such centers in the direction of rotation.

The ends of the shoes 78 carry cross pins 79, between which tension springs 84 are connected to bias the two shoes 78 inward to a retracted or disengaged position. Under centrifugal force, the shoes 78 move outward into engagement with the drum 86. The lugs 82 and sockets 80 remain in engagement in all operative positions of the shoes 78 relative to the hub 70. The clutch drum 86 is fixed to a hub 88 which is keyed to the jack shaft 48 by a key 89, so as to be mounted coaxially with and engageable by the shoes 78.

With the engine 14 idling and the engine shaft 15 rotating at idling speed (e.g., up to 1000 r.p.m.), the shoes 32 of the centrifugal main clutch 22 will be retracted and no drive will be transmited from the engine to the clutch drum 34 and drive sprockets 40 and 42. When the engine is accelerated to the engaging speed for which the main clutch 22 is designed, for example 1900 r.p.m., the clutch shoes 32 are thrown outward by centrifugal force to en gage the drum 34 and drive it and the two sprockets 40 and 42. The high-speed centrifugal clutch 68 will be in dis engaged condition below its designed engaging speed, and drive will be through the low-speed sprocket 40, the lowspeed chain the low-speed driven sprocket 60, and the low-speed clutch 64. In such clutch, the rollers 66 are spring-pressed into one-way (forward) clutching engagement between the ring 59 and the hub 65, and rotation of sprocket 60 will therefore transmit driving torque to the jack shaft 48. The jack shaft 48 will rotate the drive sprocket 52 to transmit drive to the drive wheel at the low speed ratio determined by the relative sizes of the low speed sprockets 40* and 60. As here illustrated, the sprockets 40 and 60 have 12 and 24 teeth respectively, and the sprocket 60 rotates at one-half the speed of the sprocket 40 The bike is accelerated in the low speed drive until the high-speed clutch reaches its predetermined engagement speed, for example, a speed of 2700 r.p.m. for the hub 70 and its sprocket 62. As shown, such sprocket has the same number of teeth (12) as the driving sprocket 60, so that the hub 70 is rotated at engine speed. At the engagement speed of the high speed centrifugal clutch 68, its shoes 78 will engage its drum 86 to engage high-speed drive. When full engagement is reached, the high speed sprocket 62 will drive the jack shaft at engine speed, at a high-speed drive ratio of 1:1. When the high speed drive rotates the jack shaft at any speed higher than the low-speed clutch 64, the rollers 66 of such low speed clutch will allow the hub 65 to freely overrun the lowspeed sprocket 60.

In the transition from low to high speed, the shoes 78 first move under centrifugal force into initial engagement with the drum 86, which will be rotating, under lowspeed drive, at half the speed of the shoes 78. Engagement will tend to increase the speed of the drum and reduce the rotational speed of the engine and shoes, and hence will tend to reduce the centrifugal force tending to cause engagement. But the limited or soft self-energizing action of the shoes will maintain the engagement and progressively increase it. A smooth transition to full engagement will occur, to fully establish high speed drive. Shifts between the 2:1 low drive and the 1:1 high drive will be responsive to engine speed, which the driver controls, rather than to jack shaft speed which may vary with changes in the surface on which the bike is being driven and on traction engagement between the drive wheel and the ground.

When engine speed decreases below the predetermined engagement speed the reduction of the centrifugal force on the shoes 78 or the high speed clutch 68 causes such shoes to disengage from clutch drum 86, thus disengaging the high speed drive. Overrunning of the low speed clutch will then cease and driving torque will then again be transmitted to the jack shaft 48 by such low speed clutch 64. Again, in this shift from high to low drive the limited self energizing action of the high-speed clutch shoes will ensure a smooth transition in the shift.

Ellicient braking action will be provided by engagement of the brake band 56 about the brake drum 54 fixed on the jack shaft 48 and hence rotating at jack shaft speed rather than wheel speed. The brake is actuated in conventional manner, by means of a manual brake control (not shown) acting through the control cable 96.

The automatic transmission according to the invention is adapted to be utilized either as original equipment on a mini-bike as manufactured, or as a kit for application to existing mini-bikes. Such a kit may include all of the parts shown in FIG. 1, except only for the engine 14 and its from the sprockets 40 and 42 when mounted on the engine shaft. The several parts on the jack shaft are all adjustably mounted thereon to suit the positions of the mounting brackets, the engine, and the rear wheel.

I claim:

1. An automatic two-speed transmission for mini-bikes and the like having an engine shaft and a drive wheel or the like, comprising a main clutch,

high-speed and low-speed drive sprockets adapted to be clutched to said engine shaft by said main clutch to be driven thereby,

high-speed and low-speed driven sprockets coaxial with a jack shaft for transmitting drive to the drive wheel, means to connect said driven sprockets respectively to said drive sprockets to provide highspeed and low-speed drive trains,

one of said low-speed sprockets being connected in its drive train by a one-way roller clutch arranged to transmit drive in the low-speed drive train and to overrun when the high-speed drive train is engaged, and

2. The invention as set forth in claim 1 in which said drive engagement is a short distance ahead of said circum- 6 ferential center of contact pressure in the direction of drive rotation.

3. An automatic transmission kit for a mini-bike or the like having a frame, an engine supported thereon having a shaft, and a drive wheel, comprising high-speed and low-speed drive sprockets adapted to be mounted on and driven by the engine shaft,

a jack shaft adapted to be mounted on the frame for rotation on an axis between the engine and the drive wheel,

high-speed and low-speed driven sprockets adapted to be connected respectively to said drive sprockets,

said low-speed driven sprocket being arranged for mounting on said jack shaft by a one-way roller clutch arranged to permit said jack shaft to overrun said driven sprocket,

and said high-speed driven sprocket being arranged for mounting on said jack shaft and connected with the shoe assembly of a centrifugal clutch, said centrifugal clutch having a clutch drum arranged for mounting on said jack shaft coaxially with and engageable by said shoe assembly, said shoe assembly comprising a pair of clutch shoes, 2. driving hub for said shoes, each shoe having a drive socket therein and the hub having drive lugs engaged in said sockets, the drive engagement between each lug and its shoe being adjacent the circumferential center of contact pressure between the shoe face and the drum, the shoes of the high-speed centrifugal clutch being constructed and arranged to make initial engagement with their clutch drum in response to centrifugal force and to have limited self energizing action in response to such initial engagement, and thereby to maintain and progressively increase engagement to establish high speed drive, such self energizing action being limited to effect a smooth transition as said engagement occurs.

References Cited UNITED STATES PATENTS 2,488,892 11/1949 Arzt 74-217 (B) X 3,247,727 4/1966 Digby et al 19245 X 3,436,977 4/ 1969 Gredell 74-217 (C) 3,461,994 8/1969 Dallman et al. 192105 (BA) LEONARD HALL GERIN, Primary Examiner US. Cl. X.R.

74217 (S); 192-105 (CD)

Sours: https://patents.google.com/patent/US3610062A/en

Centrifugal Clutch, 3/4" Bore Go-Kart Mini-Bike Clutch 12 Teeth 35 Chain Clutch GoKart Used Primarily on Mini Bikes and Go Karts (black)


You are buying (1) brand new 3/4" bore Centrifugal Clutch With Pulley.

This clutch is used primarily on Mini Bikes and Go Karts but can be also used for other applications.


It is important to have the correct gear ratio for the tire size for proper operation of your clutch or torque converter. A improper gear ratio will make the clutch or belt slip and cause damage to the unit very quickly.

To determine the gear ratio necessary for your go kart or mini bike you must know the limit of your top speed. When using a clutch to drive your go kart the top speed on flat terrain is 35mph, if the terrain is hilly or the weight of the driver is high the top speed should be 25mph. Mini bikes work best with a top speed of 25mph for all terrain.

When using a torque converter with a go kart you may go as high as 45mph on flat terrain and 35mph on hilly terrain. For mini bikes 35mph is the top speed when using a torque converter.

Use our calculator below to determine the top speed and gear ratio for your tire size. Input the tire diameter, highest engine rpm, number of teeth on your clutch or torque converter jack shaft and the number of teeth on the axle sprocket. If you go higher than the recommended mph then the possibility of excessive slipping of the clutch or belt may cause early failure.

Changing the tire size will dramatically change the top speed so if you are going to a larger tire size you must correct the gear ratio for proper operation.


Centrifugal Clutch

3/4" Bore

3/16" Key way

Pulley accommodates 1/2" ABS Belt Style

Package includes:

1x Clutch

Sours: https://www.amazon.com/Centrifugal-Clutch-Go-Kart-Mini-Bike-Primarily/dp/B07KXP2736
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Max-Torque Dual Sprocket Clutch 12T #35, 2 Speed Mini Bike Go Kart - Made in USA

$66.95Buy It Now24d 0h, Click to see shipping cost, 30-Day Returns, eBay Money Back Guarantee

Seller:stevbmi✉️(74,655)99.1%, Location:Versailles, Ohio, Ships to: US & many other countries, Item:141065203113Max-Torque Dual Sprocket Clutch 12T #35, 2 Speed Mini Bike Go Kart - Made in USA. Max-Torque Dual Sprocket Clutch for Two Speed MiniBikesProduct Specs:Max-Torque dual sprocket centrifugal clutchUsed on two speed Mini-Bikes 3/4" bore, dual 12 tooth 35 chain sprocketsWill NOT work with double wide chain, you must use 2 strands of single wide chainShoes style: WedgeSpring: GreenPositive Grab: 2100 RPM Part Number: 400905Check out our other items. Buy In Bulk.We have tons of parts available! Local Pickup Address: BMI Karts & Parts 769 E. Main St. Versailles, OH 45380 Powered by SixBit's eCommerce SolutionCondition:New other (see details), Return shipping will be paid by:Buyer, All returns accepted:Returns Accepted, Item must be returned within:30 Days, Refund will be given as:Money back or replacement (buyer's choice), Brand:Does Not Apply, MPN:Does Not Apply

PicClick Insights - Max-Torque Dual Sprocket Clutch 12T #35, 2 Speed Mini Bike Go Kart - Made in USA PicClick Exclusive

  •  Popularity - 30,319 views, 10.2 views per day, 2,959 days on eBay. Super high amount of views. 66 sold, 24 available.
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How To Make Your Own Racing Centrifugal Clutch For Free

DIY simple 2-speed Go-Kart transmission.

There aren't many off-the-shelf options for someone wanting to do this. Let's face it it's a niche item and most people just buy a dirt bike or quad if they're looking for some off road fun. The Torque-A-Verter (TAV) is one popular if slightly expensive solution, though with the demise of the parent company they may be harder to come by. I found one for around AUD$380 and was tempted but I'd still have to build a jack-shaft with 2 bearings and 2 sprockets and chains so the total cost would be well over AUD$450 also, I'm not happy with the life span of the expensive belts when used off-road. Replacing the engine with a motorcycle engine is the next logical option but that can be very expensive and wastes the existing powerplant (though I'm sure it could be put to other uses).

sideview of gearbox
Photo1: DIY 2-Speed Gearbox
after 10hrs thrashing

I decided to make things difficult for myself and DIY. First, I searched around for compatible transmissions out of something else such as ride-on mowers and cement mixers and even industrial washing machines but all of those have their problems and are potentially expensive or hard to find. Next, I looked at designs for geared, belt or chain driven transmissions and their parts costs.


Belts and pulley drives are by far the cheapest to build. Pulleys are less than AUD$10 each and can be probably found for free out of old washers and tumble dryers etc. Belts are available in a vast range of sizes and can be cheap if you choose common form factors. Some transmission designs take advantage of belt slip and use it as a proxy clutch meaning you can do without a "real" clutch if you design your belt tensioning cleverly. This is also the main drawback of belts; in an off-road application dust, mud and constantly changing loads are going to burn through belts quickly. Losing power over rough terrain due to belt slip is a killer.


Geared transmissions are probably the best solution, they're in just about every car on the road. Unfortunately, most vehicle transmissions are way too heavy for what we want to do here and motorcycle gearboxes are integrated, meaning it's a chore to rebuild them in some other form. Also, the individual gears are usually built onto a shaft so stripping them out and re purposing isn't a viable option. Sourcing stand alone gears isn't impossible, a supplier near me has individual gears for AUD$80 each, so it becomes a question of; "from how few gears can you get a functional gearbox?" Not few enough, I need at least six to do what I want here, way too expensive!


The kart already uses two sprockets and a chain to do the job, maybe we can reuse those and save a few bucks? The main problem with chains is keeping them clean and at the right tension and alignment. Costwize this type of system is a bit more expensive than belt and pulley but has the massive benefit of zero slipping and far greater durability, availability is good too. My local supplier sold me 12-tooth sprockets for less than AUD$10ea, the largest 36-tooth cost only AUD$17 which meant I could afford a few spares. The toughest part is understanding the right gauge to use. Most Go-Karts use a ANSI #35 or #40 chain so stick with those if you have them. The Drift-2 comes with a motorcycle gauge 420 which is a half inch pitch but not quite the same as #40 or any European standard. I got 08B which is similar to #40 but a bit wider than 420, I only had to mod one sprocket to match the 420 output from my clutch.

simple gearbox
Simple Gearbox

So with the power transmission technology chosen at last I can move on to the actual gearbox mechanism design. I looked at a few designs for 2-speed transmissions but the one I chose to base my design on is the tried and trusted dog clutch system. The theory is very simple; the input shaft is keyed to a sliding hub that can slide along the shaft and engage with the left or right input sprockets via a toothed clutch. The output shaft has two sprockets keyed to it, one is small for high gear the other larger for low gear. When the input shaft is driven (via a chain) from the centrifugal clutch at the engine, it rotates the sliding hub, engage the hub with the left or right ratio and you drive that ratio to the output shaft of the gearbox. The kart's rear axle has the original 48-tooth sprocket and is connected by chain to the gearbox's output shaft...

Still with me? It's all much clearer in pictures, probably.

Build summary.

I chose this design because it's relatively uncomplicated and cheap, the total cost was a little under AUD$350. The most difficult parts to make were the clutch parts but only because they require some precision and are made of heavier material than I'm used to working with. Also, a lot of threads needed tapping and that takes time and patience.

First I drew up some rough plans with all the parts I needed, at this stage it was mostly to get an idea of what materials and what size sprockets, bearings and shafts I'd have to buy. Here's a set of plans refined from my jumble of notebook scratchings.

Figures 1 & 2: View of parts and assembly

Figures 3 & 4: Dog and Gear selector construction

closeup of clutch
Photo 2: Close-up view of
Clutch & Selector assembly

Simple Clutch

Of the fabricating I started the clutch parts first. I marked out the clutch plates on 6mm thick steel plate and then cut it into a rough circles using an angle grinder and cutting disk then cleaned up on my sanding wheel. In hindsight this was a dumb ass way of doing it but I didn't have an 90mm hole saw and even if I did my drill press wouldn't bore it through 6mm. I had to make 4 plates so yep, it was a chore. With the plates shaped out I went to a local engineering firm to get the hub part fabricated, it is essentially a 50mm round, 20mm wide boss with a 3/4" centre, I got this made for about AUD$10. The engineer couldn't cut internal keyways, so I decided to torture myself and create it myself using my scroll saw and files. This again was a dumb ass way to do it but I probably saved 50+ bucks on this project doing all 5 internal keyways myself in this way. By the end I got so good at it that I could cut one in about 30 minutes flat.

With the boss done I drilled my clutch plates. Two of them will attach to the boss the other two will be welded to each of the primary 12-tooth (12-T) sprockets. All of them need 8 holes each for the dog teeth/studs. A total of 32 holes, 16 with tapped M8 threads the other 16 oversized to 10mm, will be the holes that the studs interlock into. I chose to make the studs from M8 high tensile bolts with the heads cut off and trimmed with chamfers so they will slip into the holes better (FIG3-a1). To attach the plates to the boss I used 4 countersunk M8 bolts for each plate (FIG-3b) these maintain a flat plate surface, the boss has 4 corresponding drilled and tapped holes all the way through (20mm). I wasn't sure if the cheap tap set I had would be able to go the distance but they surprised me and it was pretty easy going, I use heavy oil as tap lube which seems to do the job ok.

Video 1: Clutch assembly.

clutch partsclutch parts
Clutch parts; plates, boss and shaft

clutch partsgearbox parts
Input shaft and clutch parts. Input and output shafts

Now the sliding clutch bit is complete, next the other half (halves) of the clutch. I decided to put the studs on the sprocket side of the mechanism because this means they can be threaded into the plate and locked with nuts on the back of the plate for extra strength. I then prepare to weld the plates to the sprockets, to make sure they're square I shave 1mm from the sprocket boss and made the centre hole in the plate a friction fit, in addition I chamfered the outer edge of the boss and plate centre hole so that the weld would be flush with the plate surface when ground back (FIG-3a) then tapped them into place, squared them up tacked, tested and welded. Note; the two primary 12-T sprockets don't need keyways as they're intended to spin freely on the primary shaft, some grease keeps them moving freely (the rotational difference is only 1:3 between them so there's not a huge amount of wear). That's the main fabrication of the clutch done. I tested the clutch on a dummy shaft in my lathe just to see how the clutch would mesh and it all seemed to work as expected.

off the shelf sprocket
Sprocket with 1/2" pilot hole


All the sprockets for this project came with 1/2" pilot holes, I didn't have a 3/4" drill bit so I got the engineer from earlier to drill all of them and provide me with two keyed 3/4" shafts this only cost about AUD$20 which was half the price of a 3/4" drill bit and I got the shafts into the deal, skinflint I am. All I had to do then was more keyways (groan) and tap in 2 threads for each of the locking grub screws. As a side note I would've used 5 12T sprockets instead of the mix of 12T and 15T ones but the place I bought them from only had limited stock available. The input sprocket on the gearbox is a 12-tooth driven by the 10-tooth of the centrifugal clutch, while the gearbox output is a 15-tooth driving the 48-tooth on the axle. It affects my ratios a little but I can live with it and I like the idea of a small sprocket driving a larger one at every stage. High gear is almost the same ratio as the stock gearing, which was 4.8:1 (engine:axle). Low gear multiplies that by a factor of three using a large 36-tooth sprocket driven by a 12-tooth one, so it's something like 14.4:1. With the stock 13" wheels the cart flies in high gear and still gets along pretty quick even in low. I've yet to rig up a speedo to get real numbers but I'm guessing it does about 20km/h in low and 50ish in high. Sitting 6" from the ground it feels a lot quicker.

I made 8 spacers out of some 6mm aluminium, these provide a bit of space between the sprocket teeth and the bearings/saddle which will bolt to the frame later. I also cut some keysteel for each fixed sprocket, I probably could've just put one big key along the secondary shaft but meh, keysteel is cheap I'll redo if it turns into a problem.

gearbox assembled
Assembled Gearbox

Gearbox Frame and Chain

This was pretty straightforward, nonetheless I mocked it up with scrap tube tacked together to get an idea of the chain lengths required. Unfortunately I couldn't get a compact design without one side being a bit slacker than the other, so I had to put a tensioner on the slack side (FIG-2). This is ok as it's probably worth putting a tensioner on both sides so slack can be taken up as the parts age. There's rules about how far apart the centres of sprockets have to be from each other, one guide states that the distance between centres should be no less than the diameter of the larger sprocket, this was good enough for me. Cutting chain is a bit of a bast', chain wants to flop all over the shop especially when your dealing with a 10 foot length which is the minimum length you have to buy at most places. The mockup gearbox frame got me the distance between the shafts and resulting chain lengths so I went ahead an remade it in 30mm square tube (see: FIG-2 and photo right) it's a simple rectangular frame.

Video 2: Tensioner assembly


The tensioner described in FIG2 didn't last very long. It was made from aluminium and with all the grit getting thrown around on the chain was eaten pretty quickly. The idler sprocket in Video 2 (right) is made from some 3mm steel cut into a rough sprocket shape welded to a short section of pipe. This allows two bearings to be inserted which improves stability and wearing a lot. The bearings are a bit of a loose fit, but it works well and has stood up to about 20 hours use without falling apart. Also, I put a large copper washer on the outer side to reduce lateral movement.

Gear Selector

Figure 4 outlines the parts of the selector mechanism, some of this is optional, you can attach the gear stick side to the selector/shifter by cables or a control rod or a combination of the two like I did. The main point of interest here is the selector arm part of the gearbox and how it interacts with the clutch; it's really just a bearing each at the end of two pivoting arms (top and bottom) this way an even force is applied to the inside of the sliding part of the clutch with minimal friction (Photo 2). When the transmission is under rotation shifting the clutch is smooth from one position to the other.

Fitting it to the Kart

I'm not going to give too many tips on this part because I don't think I have the best solution, I tried not to weld to the Drift-2's frame where possible so that I could revert to stock standard if it all went pear shaped. Because of this, I had to compromise the mounting design quite a bit and I'm not quite happy with it yet, it's still a work in progress. Instead, here's a bunch of photos of it fitted to the Kart.

As you can see it was a snug fit behind the seat with about 10mm free. I had to replace the shocks/springs with rigid struts otherwise the gearbox would bash the back of the seat every time you hit a bump. It's ok because the stock springs don't really do a lot in fact with springs fitted the whole back end bounces up and down quite erratically over rough terrain putting a lot of strain on the engine mounts. The ride feels much the same with/without springs in any case. Originally, I'd planned to put the gearbox above the left rear wheel but changed the plans at the last minute because; it would be difficult to mount solidly, and would end up full of sand from the spinning wheel below. Looking at how well it all fits together now, the original plan was mad.

The gear selector goes through cables and back to a control arm which connects to the gear stick. This works quite well, is fully adjustable and makes it a lot easier getting the stick's mechanical motion around to the gearbox. I also made a modification to the steering arm, I remade it with 2 holes, one in the original position and one 20mm closer to the rod for a bit more leverage, this takes some of the feedback out on rough terrain. I used my tried and tested method of chain tensioning on the axle chain: a skateboard wheel, this one was used on my second Kart so at least one part has carried over. The engine and gearbox are separated by another tensioning bolt so that tension on the primary chain can be easily adjusted.

the kartright hand sideleft hand sidegear stick & control rod
The Kart, Gearbox SIDE views, Gear stick with control rod.

Steering arm modGearstick pivotAxle chain tensionerPrimary chain tensioner
Steering arm mod, Gear stick pivot, Axle chain tensioner, Primary chain tensioner.

In Practice

I wasn't sure how this thing would behave but I've tested it a few times now and it works quite well. The low range gear has turned my Drift-2 into a much more usable machine. Now I can power through boggy sand and up hills that it just couldn't handle before. Also, it does awesome tight donuts and spins the wheels way easier. Shifting gears on the go is a little rough occasionally, you have to lay off the power and ease it in. The centrifugal clutch takes up the difference in rotation between the ratios while the Kart coasts. Shifting from low to high while rolling works well but if your rolling too fast and try to shift back into low there's sometimes a bit of audible clash but nothing destructive. Sometimes it's easier to just stop and shift down into low then accelerate off. It's not something you can thrash under full power repeatedly, but then not many transmissions are.

After about 10 hours use the plates are showing some signs of wear around the holes where the studs interlock (slight rounding of the contact edge) but there's no sign of them becoming unusable any time soon, and anyway they can be replaced very cheaply when the do. The studs themselves don't seem any the worse for the abuse, I probably could've got away with fewer per plate maybe 6 or even 4? The transmission is quite noisy which isn't a surprise, it has 4 chains instead of one. Low range is the loudest, I put that down to the tensioner not quite keeping the pressure on. Of course loud is a subjective term it's not like you can't hear the engine over chain noise.

All in all this was a fun and worthwhile project, The first time I tackled a boggy hill (that made the kart cry before) and churned all the way to the top, made it well worth the effort. Donuts and drifting are heaps easier and when I shift back to high gear the Kart feels the same as it did stock, which is great for speeding along long flat spaces. The possibility of future tweaking means this will be something I continue to get fun out of, on and off the dirt track.

Need to know more detail? Try the feedback page to contact me via email.

Update: Drift-2 :: Suzuki GN250 engine conversion.

I'm considering adding a reversing motor to my Kart and will post the details here, check in from time to time.

Just Golf Balls

My mate Semps has started up his own online shop selling a large range of brandname Golf Balls. So, if you're an Aussie and into Golf give him a go. See the Just Golf Balls website. "You can never have enough balls!"

Other Guides.Back to Homepage.

Sours: http://www.thepixelpump.com/widdershins/how-to-2speed-transmission.php

Speed clutch bike 2 mini

Centrifugal Clutches

Go Kart Clutches and Parts

Go Kart Clutch Catalog | Huge selection of Centrifugal Clutches. Go Kart Clutches and Mini Bike Clutches in 5/8", 3/4" and 1" Bore. American made Max-Torque Clutches, Comet Clutches and Hilliard's Extreme Duty Clutches. Centrifugal Clutch Bushings and Sprockets. We also stock Centrifugal Pulley Clutches, Go Kart Clutch Keys, Keystock, Rebuild Kits and Set Screws.

Max-Torque Go Kart Clutch

Centrifugal Clutches

Max-Torque 'SS'
Centrifugal Clutch





CLUTCH 3/4"B 10TOOTH 40/41/420






CLUTCH 5/8"B 10TOOTH 40/41/420


Made in the USA.
5/8" or 3/4" Bore, 3/16" Keyway.
3/16" Key and Set Screws included.

The American Classic 'SS' (Six Shoe) Max-Torque Centrifugal Clutch - The 'SS' is the most popular style centrifugal clutch used by American Go Kart Manufacturers since it's introduction in 1970. It has a broached 3/16" keyway with two set screw holes located 90 degrees apart, tapped 1/4"-28. Recommended key length 1/2". The key and optional set screws are included. The secret to it's success is the ability to take heat without ruining the garter spring. The spring is made from 302 stainless steel and it can take more than twice the heat of music wire used by competitors. The Spring Manufacturer's Institute indicates a maximum temperature for music wire springs at 250 degrees F ... 550 degrees F for #302 stainless steel wire.

Used on 3 to 8 horsepower engines. 10 tooth clutches use #40, 41 and 420 chain. 11 tooth and 12 tooth clutches use #35 chain. Most installations use a 5/16-24 x 3/4" bolt, washer & lock washer. Grease the engine crankshaft and tapped hole for easy removal in the future. Go Karts with rear wheels taller than 15" require a Torque Converter that uses a belt and a chain.

Max-Torque Clutches are designed, engineered and manufactured to deliver exceptional performance. They're unique and original in design and engineering. Others have copied the design, but they're not able to duplicate the performance and reliability engineered into the Max-Torque Clutch. It's exclusive ground sleeve provides a 10 microfinish for smoother bushing contact, less friction and extended life. The stainless steel spring can't rust, assuring more consistent application of shoe pressure. These plus other Max-Torque pioneered features provide the quality Original Equipment Manufacturers (OEM) specify...and you demand. Minimum operating controls, the throttle becomes the single control for engaging or disengaging the power, as well as controlling the operating speed. Speed up the engine and engage the drive train - slow down the engine and it disengages - one control, the throttle does it all.

The standard Max-Torque SS automatic clutch uses six sintered metal clutch shoes. The shoes evenly distribute the centrifugal loading force over 345 degrees of the drum circumference which lessens drum distortion. The smooth non-aggressive engagement action approximates that of an automatic transmission. It's Preset to engage at approximately 2,200 rpm. This protects the operator, as well as the power transmission system during engine cranking, starting and idling. In the event of an overload, the engine will be lugged down to a slower speed, which will automatically disengage the clutch. Once the overload condition has been eliminated, the clutch will reengage and operate normally. Clockwise or Counterclockwise Installation. It will operate with equal efficiency in either a clockwise or counterclockwise rotation. The clutch can be mounted inboard or outboard with no adjustments needed.

It maintains it's appearance. The drum and sprocket have a black oxide finish while the drive and shoe retainer plates are zinc plated. The oil impregnated bronze bushing rotates on a ground sleeve. This configuration, utilizing a high-grade specially formulated oil or grease for bushing lubrication, considerably increases clutch life in high heat conditions over assemblies that use needle bearings. A bushing is more "forgiving" to both heat and contamination than a needle bearing. It can be completely disassembled with snap ring pliers to replace any worn or damaged parts. It works in contamination. The use of sintered metal shoes and a stainless steel garter spring enables the Max-Torque clutch to maintain its efficiency even when contaminated with dirt, oil, or water.

Cent. Clutch Bolt Kit

Clutch Bolt Kit




The Centrifugal Clutch Bolt Kit is used to install a Centrifugal Clutch on an Engine Crankshaft. The Kit includes one 3/8-24 x 1" Bolt with Washers AND one 5/16-24 x 1" Bolt with Washers.

Max-Torque Clutch Logo

Clutch Rebuild Kit

Max-Torque Rebuild Kit
Sprocket & Bronze Bushing


11 TOOTH 5/8" #35 REBUILD



12 TOOTH 3/4" #35 REBUILD



10 TOOTH 3/4" #41 REBUILD


10 Tooth, 04-464 uses 40, 41 & 420 Chain.

Bronze Bushings

Bronze Clutch Bushings







These Bushings are an internal clutch part. They fit inside the clutch, not directly on the engine crankshaft. The Bushing for 3/4" Bore is 7/8" ID. The Bushing for 5/8" Bore is 3/4" ID.

Ronghai 115485

Centrifugal Clutches





CLUTCH 3/4"B 10TOOTH 40/41/420






CLUTCH 5/8"B 10TOOTH 40/41/420


Made in China.
3/16" Key and Set Screws included.

Clutch and Chain

Clutch and Chain Combo







3/4" Bore Centrifugal Clutch and Chain Combo. 12 Tooth Clutch with 3 Feet of 35 Chain or a 10 Tooth Clutch with 3 Feet of 420 Chain. High-Quality Chain with one Masterlink. Made in China.

Clutches Builtin Key

Clone Engine Clutches





CLUTCH 3/4"B 10TOOTH 40/41/420



CLUTCH 3/4"B 10TOOTH 40/41/420


Fits Honda and Clones. 5/8" bore for 35 chain or 3/4" bore for 40, 41 and 420 chain. Built-in Key. Uses no set screws. Requires a 3/16" keyway that goes all the way out to the very end of the engine crankshaft. Will perform clockwise or counter-clockwise. 4" OD, Height 2-1/4"

Max-Torque Clutch Logo

Max Lube Clutches

Genuine 3/4" Bore
Max-Lube Clutches







Made in the USA.
Zerk Bolt Kit 04-8489 included.
The 12 Tooth Clutch uses 35 Chain.
The 10 Tooth Clutch uses 40, 41, 420 Chain.

Max-Lube Clutches were developed in conjunction with Chuck Brister, a major kart manufacturer here in Louisiana, to address one of the most frequent problems with fun karts - lubrication of the clutch bushing. This lube system supplies lubrication directly to the clutch bushing through the keyway of the engine crankshaft utilizing a special zerkbolt fitting which is available only from Max-Torque. Since its introduction in 1992, lubrication problems have been dramatically reduced. Check to make sure your Briggs & Stratton or Tecumseh Engine has a drilled and tapped hole in the end of the crankshaft. The size of the hole should be 5/16" x 24 threads per inch. If your engine does not have this hole, the MAX-LUBE clutch can not be used.

Tools Required to Drill Crankshaft: Electric drill, 1/8" drill bit, ruler, hammer, center punch, 1/2" open end wrench.

Max-Torque Supplied Parts: Clutch with built-in key, 5/16" x 24 TPI zerkbolt and washer and two 3/4" diameter washers.

Installation Instructions: Remove the old clutch from the engine crankshaft. Disconnect the spark plug lead and slowly pull the starter handle until the crankshaft keyway is facing upward. Use a ruler to measure a point approximately 7/8" from the outboard end of the crankshaft to the center of the keyway. As shown in the diagram, the width of a nickel will also provide this dimension. Once this point is located use the center punch with a firm hit to make an indentation in the center of the crankshaft keyway. Drill a 1/8" hole at this indentation until the drill bit breaks through the crankshaft bolt hole cavity. Stop drilling. Blow out this 1/8" hole to remove any chips that might remain from the drilling operation. Place the two fibre washers onto the crankshaft, slide the clutch on the crankshaft and secure the clutch with the zerkbolt and washer.

CAUTION: Do not over-tighten the zerkbolt as the hex head will snap off. No more than 15 ft*lbs of torque should be used in tightening the bolt! Using a grease gun give the zerkbolt a full pump of grease. Replace the chain on the clutch sprocket and replace the chain guard.

Other Operating and Use Instructions: Grease the Zerkbolt, with one squirt, after each week of operation. Avoid or eliminate incorrect gearing. The gear ratio between the clutch sprocket and the drive sprocket should be 1 to 6. For example, if your kart has a 12 tooth clutch sprocket the drive sprocket should have 72 teeth. A 10 tooth clutch sprocket would require a 60 tooth drive sprocket. Tires with a diameter exceeding 15 inches tall should not be used. If any of these suggestions are not followed, the clutch will not operate properly and clutch life will be significantly reduced.

Max-Torque Clutch Logo

Zerk Bolt Kit

Max Lube Zerk Bolt Kit




Grease Zerk Assy fits 04-7680 & 04-7681.

Comet Built In Key

Comet Clutches
with a Built-In Key





CLUTCH 3/4"B 10TOOTH 40/41/420


Genuine Comet Clutches. 5/8" bore 11 tooth - 35 chain. 3/4" bore 10 tooth - 40,41,420 chain. Does not use set screws. Requires 3/16" keyway to the end of the crankshaft. Performs clockwise or counter clockwise. Comet Industries. Made in the USA.

Extreme Duty Go Kart Clutch
Hilliard's Clutches

3/4" Bore Hilliard's
LD4S Extreme Duty Clutches







The 12 Tooth Clutches use 35 Chain. The 10 Tooth Clutches use 40,41 and 420 Chain. Made in the USA. Used on American Sportworks Go Karts and many other brands. Universal Application.

The Extreme Duty Sprocket Centrifugal Clutch is ideal for the everyday demands of childrens yard-use go karts. This clutch was designed to be a low-cost upgrade to the stock unit. A thermodynamically designed clutch shoe increases the clutches capacity to absorb heat without damaging the clutch springs, resulting in longer life and better reliability.

All LD4S Series Clutches are loose assemblies and need to be assembled properly to allow the clutch to operate safely. These steps need to be followed to ensure proper installation. Install a bolt and washer on the end of the engine crankshaft. Use a washer that measures at least 1-1/16 inches on the outside diameter. On this LD4S-L long bushing series clutch there is a retaining ring to retain the bronze bearing in the sprocket drum. A bolt and washer are used to retain the hub on the crankshaft. Make sure that the bronze bushing has a minimum of 1/32 of an inch of movement on the crankshaft of the engine, and not more than 1/16. While tightening the bolt be sure to torque the bolt to the engine manufacturers specifications. To tighten the bolt you will need to make sure that the ignition is in the off position, to ensure that the engine won't start. Next, get the bolt tight to the point that you are turning over the motor while tightening the bolt. Then MAKE sure the ignition is off, and pull the pull starter just out far enough to catch the motor. Then continue to tighten the bolt to the proper specification, holding the pull starter out, you will feel the engine want to pull the started cord back in, you need to hold it out until you get the bolt tight. For cases where there is no pull starter, you will need to find a way to stop the crankshaft from turning over. Verify proper alignment of the sprockets and install the chain according to your owners manual. Over tightening the chain or having the chain too slack will cause premature sprocket and bushing wear. Oil the clutch bushing every 4 hours of use. Try to get the oil in between the housing and the bushing. Removal of the bushing from the sprocket is the best way to ensure proper lubrication.

Requires a tapped engine crankshaft so you can screw a bolt into the end of the shaft to hold the clutch on. The Extreme Duty Sprocket Centrifugal Clutch is ideal for the everyday demands of go karts and youth model snowmobiles. It has been engineered to provide long service life even in the most demanding applications. A thermodynamically designed clutch shoe increases the clutches capacity to absorb heat without damaging the clutch springs, resulting in longer life and better reliability. This Extreme Duty centrifugal clutch can handle higher temperatures to offer longer life. Bi-Directional, they can run clockwise or counter clockwise. Disapates heat better, extending clutch life. Built in internal key.

Hilliard Bushing

Hilliard's Extreme Duty
3/4" Bore Clutch Bushings




Hilliard Sprockets

Hilliard's Extreme Duty
3/4" Bore Clutch Sprockets







The Hilliard's Extreme Duty 10 Tooth Clutch Sprockets use 40, 41 and 420 Standard Roller Chain. The 12 Tooth Clutch Sprockets use 35 Chain only.

Noram Style Clutch

3/4" Bore Noram Style
Racing Clutch for 35 Chain


CLUTCH 3/4" #35P 15T



CLUTCH 3/4" #35P 16T


Large 15 and 16 Tooth Sprockets will provide higher top speed than a Standard 12 Tooth Clutch. Trade-off is a loss of low-end acceleration. Made in China.


Pulley Clutches

Max-Torque 3.20" OD
Centrifugal Pulley Clutches










Made in the USA.
Set Screws and Key included.

Imported Pulley Clutch

Imported 3.20" OD
Centrifugal Pulley Clutches







Made in China.

Pulley Clutch 2 Inch

3/4" Bore 2" OD Pulley
Centrifugal Pulley Clutch




Comet Belt Clutch

Comet 1" Bore
Pulley Clutches




3" Outer Diameter - Built-in 1/4" Key.
Genuine Comet Clutch. Made in the USA.


1" Full Bore Clutch


CLUTCH 1" BORE 14T #40/41/420








1" bore all the way through with set screws.

1600 1 Inch Bore

14 Tooth 1" Bore Clutch
Noram 1600 Series Style




14 Tooth Clutch for 40, 41 and 420 Chain.
1" bore all the way through with set screws.


1" Bore Comet
SCS 400 Clutches





CLUTCH 1"B 10TOOTH #40/41/420C


Genuine Comet Clutches for 3 to 7hp engines and rear wheels 15" or shorter. Require a crankshaft with a 1/4" keyway and tapped end so you can screw a bolt into the end of the crankshaft to hold the clutch on. Made in the USA.

Comet Copy 115573

1" Bore Clutch
For 40/41/420 Chain




For 3 to 7hp engines and rear wheels 15" or shorter. Require a crankshaft with a 1/4" keyway and tapped end so you can screw a bolt into the end of the crankshaft to hold the clutch on.

Clutch Key

3/16" Clutch Keys


KEY 3/16" X 1/2"



KEY 3/16" X 3/4"



KEY 3/16" X 1-1/4"


Key Stock

12" Sections of Keystock


KEYSTOCK 3/16" X 12"



KEYSTOCK 1/4" X 12"


Keystock - Cut as Needed.
For crankshafts, jackshafts, pulleys, axles.

Set Screws

Max-Torque Set Screws


SET SCREW 1/4-28 x 1/4



SET SCREW 1/4-28 X 1/4


AS-1414F 1/4" Set Screw

Clutch Maintenance

Keep Your Machine Safe

Oil the bushing that is located in the sprocket at least every two (2) hours of driving time. You'll have to oil the clutch even more often if you have small children, riding in a small area, never going fast enough to engage the clutch all the way. The clutch continues to generate heat until it engages.

Oiling the clutch is extremely important. If heat damage occurs, the clutch will never disengage and the machine will start taking off by itself as soon as you start the engine. This is very dangerous! You can see heat damage inside the clutch drum, the metal turns from black to a blue color. The clutch must be replaced if it has heat damage and won't disengage. Heat damage is never covered by warranty.

Where do you oil the clutch? Behind the snap ring, next to the sprocket teeth at the end of the clutch. There's an internal bronze bushing behind the snap ring that requires lubrication and it's up to you to put it there each time. With the engine off, squirt several drops of oil behind the snapring while the bushing is warm. You can also oil the clutch before you ride, oil the clutch and give the oil a few mintues to penetrate down into the bushing. If you don't give the oil time to get down onto the bushing, the oil will just fling off, which is the same as not oiling it at all because the oil never reaches the bushing at all. What oil should I use? A good automotive oil like 10W30 or a straight 30 weight oil is perfect. It's a good idea to oil the chain at the same time. If the chain gets kinky from lack of oil it should be replaced before it damages the clutch sprocket. A new chain is cheaper than a new clutch.

The clutch is an automatic transmission that is activated by the increased rpm of the engine. The clutch should not engage when the kart is at idle. The engine manufacturer sets the idle speed of an engine at the factory. The idle speed of the engine is normally around 1,650 rpm +/- 200 rpm. There are several things that can cause the clutch to engage at idle. Because the kart manufacturer does not start each kart after assembly, it's important that the dealer or the kart owner take a couple of minutes to read the owner's manual and review the recommended procedure when starting or servicing a new kart.

Throttle linkage can bend while riding or in transit to the dealer. It is highly recommended to always start the go kart with the rider sitting in the drivers seat with his or her foot on the brake pedal. Make sure they know which foot pedal, the one on the left, is the brake versus the gas pedal. If the driver has to start his/her own kart then place the front end of the kart against a stationary object like a tree or fence post. Once in the kart, you can roll it backwards with your hand or foot to get the kart in a position to drive forward.

During assembly at the kart factory it's possible that too much tension was placed on the throttle linkage causing the engine to idle above 2,000 rpm (the starting speed of the clutch for engagement). Think and stress safety. When you start the go-kart, be in a position where you can shut it off if the clutch wants to engage by itself. Most karts have two shut off switches on them, one on the steering column or steering wheel and the other on the engine itself. Another possibility is to pull off the spark plug wire, which might give you a slight shock.

A Tachometer (available on our Tools Page) can be used on the engine to verify just where the engine idle speed is set. You can't verify the correct rpm by listening to the engine and concluding it is too high or too low.

Habits That Can Ruin A Clutch

Driving too slowly: A clutch starts to engage around 2,000 rpm and will lock up around 2,600 rpm. Driving at full throttle gives the clutch a chance to cool down. Full throttle locks the shoes in the clutch against the drum. When the clutch is not locked up, the shoes slip against the drum causing tremendous heat which dries up the lubrication in the oil impregnated bushing. The tremendous amount of heat generated can also anneal the spring which is the heart of the clutch. If the shoes turn purple from excessive heat more than likely the clutch is ruined and the spring no longer has the ability to pull back the shoes at idle.

Short stop and go driving: The longer you drive at full throttle the better off it is for the clutch, because it gives it a chance to cool off before the next engagement.

Driving with the foot on the brake: This is a problem with new drivers that are unsure of themselves. When riding a go kart for the first time, try to find an open area that has no obstacles that you have to maneuver around until you get used to the brake and gas pedals. The driver must first be able to build up his or her confidence on the kart before putting obstacles in their path. A small back yard is not a good place to learn to drive a go kart. In my opinion, a minimum of three fourths of an acre is the amount of yard needed for a go kart. Teach your child to drive with one foot on the pedal, be it the brake or the gas but not to press on both pedals at the same time. You either want to go or to stop but you cannot do them both at the same time.

Changing the size of the tires: Putting on tires that are larger than what came with the kart will result in clutch problems. Tires exceeding 13 inches in diameter stress out a clutch if the kart is not properly geared for the larger tires. If you are driving on smooth flat terrain than you may be able to get by with 15 inch tires but once you get on hilly terrain, deep grass, then you are putting additional strain on the clutch, which will cause premature wear. Big tires look cool on a go kart but you create your own problem changing to bigger tires when the clutch isn't designed to handle them.

Weight: A centrifugal clutch is designed to be able to move a certain amount of weight. Once the weight limit is exceeded, then the life of the clutch will be shortened. A good rule of thumb is the kart and driver (and passenger when it is a two seat kart) should not exceed 400 pounds. The kart weighs around 150 pounds add to this the driver (and passenger weight, if it is a two seater kart). If you know ahead of time that you will exceed the 400 pounds then buy a torque converter go kart and avoid the problems of burning up the clutch asking it to do more than it was designed for.

Gear ratio: The sprocket on the engine and the one on the rear axle should have a ratio close to 1:6. This means for every tooth on the clutch there are six teeth on the rear sprocket. So if you count 10 teeth on the clutch there should be 60 teeth on the rear sprocket. (12 teeth on the clutch means a 72 teeth rear sprocket). A torque converter has a variable speed system between the driver and the driven pulleys so it can improve upon this ratio, which gives the torque converter an advantage over a straight clutch system. It improves the ratio by approximately 3:1 and can turn larger tires and drive at slower speeds without doing any damage to the clutch system. A torque converter is a more expensive system initially but it will last longer and is more trouble free when maintained.

Restrictions: Don't try and reduce a go kart speed by limiting the travel of the gas pedal or by putting a restrictor in the carburetor to limit full rpm. Either of these methods will result in the clutch slipping, which is self destructive. A clutch needs full rpm to lock up as quickly as possible to be able to start to cool down. To slow down a go kart you would need to purchase a gear reduction unit, which is like training wheels on a go kart until the driver gets use to how the go kart handles. A gear reduction unit can reduce the speed of the go kart in half.

Keep the clutch and chain lubed ... Oiling a stiff, dried out chain is a waste of time.

Don't put oil inside the clutch holes: The holes on the drum are to let the hot air out of the clutch. DO NOT SQUIRT OIL IN THESE HOLES. When oil gets in the drum portion of the clutch it will cause excessive slippage, which means undue heat will be generated.

If your kart has a grease fitting in the crankshaft for lubrication then a shot of grease once a month should be sufficient lubrication. The grease is coming from the inside of the sprocket outward, which is a better way to lubricate the clutch. The keyway in the crankshaft acts as a reservoir for the grease, which cuts down on the frequency needed for maintenance compared to oiling the snap ring area. The chain still needs to be oiled frequently to keep it from kinking up. There are some excellent chain sprays available that are waxy and will not let sand and dirt adhere to them. Dirt and sand will wear the chain as well as the sprockets.

All chains stretch over time. When the chain starts falling off the sprocket then it is time to move the engine forward or backward to take up the slack in the stretched chain. There are four bolts that hold the engine on the motor mount plate. Take an open end wrench and a socket wrench (most likely a 9/16") and loosen the four bolts, pull back the engine until you take up the slop in the chain. Tighten the bolts back again but make sure the two sprockets are perfectly aligned with each other. You don't want the sprockets out of alignment because this will cause the chain to come off or wear the sprockets unevenly. Leave about half an inch of play between the top of the chain and the bottom, don't pull the engine back where the chain is a tight as you can get it. A tight chain can cause the kart to move in neutral with no one in the drivers seat. A tight chain puts friction on the bushing or roller bearing, which could cause it to engage when the engine is idling. A tight chain also wears out the sprocket teeth really fast.

Teach your child how to do the maintenance on the kart and accept responsibility for its upkeep. Every second tank of gas in the kart is about the interval for oiling the chain and the bushing.

Clutch warranty: How long will the clutch last? If it's installed on the engine crankshaft properly, without using the "magic hammer" to pound it on the shaft, using the right length key (half inch) and observing all the hints that are pointed out here, a clutch should last several years. But, if it's improperly installed, driven in abusive conditions (sand, steep terrain, excessive weight in the kart or rear tires taller than 15 inches), the clutch might only last 20 minutes. If the shoes are blued don't bother sending the clutch back for a warranty replacement. Heat damage is not a factory defect, it wasn't sold with blued shoes. If the clutch is abused, the tell tale signs are easy to spot. Go Karts with rear tires taller than 15 inches or an engine larger than 8 horsepower require a torque converter. If your kart has rear rims larger than 6 inches you'll have to install a Torque Converter that uses a belt and a chain. The last number of the tire size is the rim size.

Hints that Help by Max-Torque! There are no rollers in 219 or #35 chains. Roller chain starts at 1/2" pitch chains which are: #40, #41, #420 and #428 and larger chains. The bigger the gap between the connecting roller link plate and the fixed roller link on the #35 chain, the easier it is to get lubrication in where it is needed. Chain binds on the inside of the roller NOT on the outside surface so spraying lube on the outside of the chain doesn’t accomplish much. Getting the lubrication between the pin and the plates is the secret on how to correctly lube the chain. How, when and what you lubricate with is the purpose of this article.

The inside of the clutch, when the engine is idling, acts like a fan drawing air around the drum to keep the shoes cool. Any excess oil on the chain is going to be sucked into the clutch. It will get on the shoes and in the drum and will have to be burnt off before the clutch will work consistently again. Check your blow-by line off the engine to make sure you have a good seal. It is very important to have the line hooked up properly because of where that oil can go and the problems it can cause. Using your blow-by line to lube your chain is not a very good idea and will cause more problems than it is worth.

The oil additives that can give you problems if they happen to get on your disc or in the drum of your clutch are: Slick 50, Dynamite, Energy Release and any oil that has Teflon or Silicone as one of the ingredients. Any oil that says it is anti-friction be very cautious what you use it on because Teflon or silicone are clutch killers. These are excellent internal engine oil ingredients but will give you fits if they get inside the clutch or on the brake disc. They do just what they are intended to do which is to prevent friction -- steel to steel contact. On a clutch and a brake system, you need friction to have them work properly. The bad news is these lubricants impregnate the steel. Sanding or cleaning with a solvent, brake cleaner or gasoline will not help. Once it is in the metal, it is in there forever because the heat will bring these lubricants back to the surface.

Now back to the chain and what to do to get it race ready. We only use a continuous link chain because master links always break at the worst time. Any chain manufacturer will tell you the weakest link on the chain is the master link. To oil our chain, we take it off and clean it with WD-40 and an air hose. I don’t like to use brake cleaner, solvent or gasoline because these will contaminate my oil bath. We then put our chain as well as our sprockets in a coffee can with 2" of 30 weight petroleum base automotive oil AND a 1/2 of a cube of paraffin wax that you can buy at the grocery store. There will be three cubes in the box, only use 1/2 of one cube.

The coffee can will be placed in a frying pan with a 1/2” of water in the bottom of the frying pan which acts then like a double boiler so we do not have direct heat on the coffee can. Now place it on the stove with the heat turned up to medium (180 F degrees ( 64.5C) for 30 to 45 minutes). When the wax melts into the oil you are done and you can now take it off the stove and hang the chain and sprockets over the can to let the excess drip back into the can to reuse many times. Do not bring the oil to a boil because we don’t want to break down the oil, we just want it hot to get the maximum penetration. The oilite bushing manufactures heat their oil up in a closed system, vacuum out the air that draws the oil into the pores of the bushing. In a new oilite bushing, 15% of the weight of the bushing is the oil that is impregnated into the oilite bushing using a vacuum system. The heat will cause the air to come to the surface of the oil. The void around the pin and roller link will be replaced by oil. The paraffin wax when it melts will act like a seal to keep the oil around the pin in the chain and seal the oil into the bushing. Take the chain out of the hot oil after it has soaked for at least 30 minutes and let the oil and wax drip back into the can to reuse the following week repeating the same process. When it has cooled down store the chain and sprockets away in a plastic bag. There is no need to wipe them off just mount the chain back on the kart when you are at the track next week. Put the sprocket back in the drum and you have enough lube in the chain or on the sprocket to last you a weekend of racing.

The oilite bushing used in a clutch contains sufficient oil to self-lube the sleeve upon which it is rotating for many races before it needs to be replenished. The oil comes out in very minute amounts and gets on the inside of the clutch drum, that is why it is a good idea to wipe out the inside of the drum before your final race of the day. Maintenance is very important on all clutches and preventive maintenance will give you consistency in a clutch. As the oil builds up on the shoes of the clutch and in the drum you start getting excessive slippage so now it is time to sand the shoes and the inside of the drum with some 80 grit sandpaper or emery cloth. After you sand the shoes and sand the inside of the drum wipe them off with a clean rag or blow them off with some air. I would only recommend brake cleaner on a steel shoe clutch never on a clutch that has phenolic resin material. Don’t spray it inside a clutch drum unless you have removed the sprocket. The reason they call it BRAKE CLEANER is that is what you should use it on. It is not really a clutch cleaner but if you use it to clean the clutch make sure you avoid getting any near the oilite bushing or roller bearing. You will contaminate the oilite bushing and no lubricant will stay for very long because the brake cleaner is breaking it down too fast. The other thing I observe when walking through the pits and watching crews clean a clutch, if a little spray is good, a ½ of can must be better yet. They end up spraying the inside of the drum containing the sprocket. If it has a bushing, the brake cleaner will dry out what lubrication is left in the bushing, so when it is put back together, the clutch wants to engage at idle on the line waiting to go out on the track. The safest thing to clean a clutch with is a paper towel or a clean rag, some WD-40 and an air hose. Wipe out the inside of the bushing with a paper towel or pull a rag through the bore, put some petroleum base oil on your finger and work it into the bushing. Follow these simple little tricks and a bushing clutch will never give you a problem. Remember a bushing or roller bearing are only functional when you are at idle, if the kart is moving the clutch is acting as ONE piece of steel.

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Page Last Updated: 10/20/2021
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How To Make Your Own Racing Centrifugal Clutch For Free

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twitter announced today that it will be removing its implementation of stories dubbed “fleets.” the feature was either loved or hated by twitter users since its initial release last year.

this short-lived feature, which was released in november of last year, will be removed on august 3. twitter acknowledged the controversial nature of the snapchat/instagram clone with the farewell tweet. notably, there was no fleet from the main twitter account announcing the departure of the feature, only a standard tweet.

in the goodbye, the company said it is working on “new stuff.” one can hope that they add the ability to edit tweets, in addition to the new edit audience and monetization features.

in a more detailed blog post, twitter shared that it hoped fleets would make people more comfortable posting onto twitter. as fleets disappear, some of the fleet creation features, like gifs and stickers, will be implemented into the standard tweets composer.

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Now discussing:

Centrifugal Clutch, 3/4" Bore Go-Kart Mini-Bike Clutch 12 Teeth 35 Chain Clutch GoKart Used Primarily on Mini Bikes and Go Karts (black)


You are buying (1) brand new 3/4" bore Centrifugal Clutch With Pulley.

This clutch is used primarily on Mini Bikes and Go Karts but can be also used for other applications.


It is important to have the correct gear ratio for the tire size for proper operation of your clutch or torque converter. A improper gear ratio will make the clutch or belt slip and cause damage to the unit very quickly.

To determine the gear ratio necessary for your go kart or mini bike you must know the limit of your top speed. When using a clutch to drive your go kart the top speed on flat terrain is 35mph, if the terrain is hilly or the weight of the driver is high the top speed should be 25mph. Mini bikes work best with a top speed of 25mph for all terrain.

When using a torque converter with a go kart you may go as high as 45mph on flat terrain and 35mph on hilly terrain. For mini bikes 35mph is the top speed when using a torque converter.

Use our calculator below to determine the top speed and gear ratio for your tire size. Input the tire diameter, highest engine rpm, number of teeth on your clutch or torque converter jack shaft and the number of teeth on the axle sprocket. If you go higher than the recommended mph then the possibility of excessive slipping of the clutch or belt may cause early failure.

Changing the tire size will dramatically change the top speed so if you are going to a larger tire size you must correct the gear ratio for proper operation.


Centrifugal Clutch

3/4" Bore

3/16" Key way

Pulley accommodates 1/2" ABS Belt Style

Package includes:

1x Clutch

Sours: https://www.amazon.com/Centrifugal-Clutch-Go-Kart-Mini-Bike-Primarily/dp/B07KXP2736

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