Centrifugal Clutch Information
- On all fun karts, ATVs and other off road utility vehicles, it is important to understand the limitations of a centrifugal clutch. A centrifugal clutch is designed to provide load free idle of the engine and slippage under excessive overloading of the driven application. These features help protect the engines from damages such as broken crankshafts and starters.
- The centrifugal clutch on a vehicle should be set to engage ABOVE engine idle to ensure safe braking and operation. The clutch obtains its power from engine RPM. The lower the engagement and higher the maintained engine speed, the more torque the clutch can transfer to the driven unit.
- Many higher horsepower vehicles run into a problem with clutch failures as a result of lack of engine speed. A clutch cannot be expected to replace a transmission or torque converter. These units are designed to change ratios based on operating need. The clutch is a single speed unit. If the vehicle cannot run on the same sprocket without the clutch, then it will not be able to run with the clutch.
- A good ratio to stay above for smaller go-karts on pavement would be 6:1. This can be calculated by the driven sprocket divided by the drive sprocket. An example is a 72 tooth rear axle sprocket driven by a 12 tooth engine or clutch sprocket: 72/12=6. This means for every 6 turns of the engine or clutch sprocket, the axle makes one turn. Many customers report a ratio of 10:1 is best for larger go-karts. A torque converter provides a high speed ratio of 6:1 and a low speed ratio of 14:1.
- Should this ratio be unobtainable with only the clutch and axle sprockets, you must use a jackshaft between them to help boost to the proper ratio. To calculate this ratio use the formula below:
- A = engine sprocket teeth
- B = input sprocket teeth on jackshaft
- C = output sprocket teeth on jackshaft
- D = axle sprocket teeth
- (B/A) x (D/C) = overall ratio
- Always remember that off road lugged tires, tall oversized tires, weighted tires, low engine RPM, extra vehicle weight, etc., will have an effect on overall performance of the drive train and result in failures.
- Engagement for clutches vary widely per OEM and application. For proper set up please refer to your OEMs specification. If none are available please follow these basic tips:
- Many sprocket clutches are built standard with 2100 RPM engagements while pulley clutches are set at 1800 RPM. All applications except the list below generally require the engine to idle load free. Consult engine idle specifications to select the correct spring(s) for your clutch. This should be the next higher spring than the engine idle speed.
- FUN KARTS: Clutches should not be lowered past idle nor raised past 2400 RPM for best performance and safety.
- CHIPPER-SHREDDERS: Clutches for electric start units can be lowered to 1200 RPM for best performance and safety.
- ELECTRIC MOTORS: clutches should be set no higher than 2/3 the running speed. For best results, select the next spring BELOW this figure:
- Example: 1750 rpm x .667 = 1167 rpm: use 1000 rpm spring.
- NOISE AT IDLE:
1) Verify proper idle speed per engine manual
2) Adjust idle speed of engine BELOW clutch engagement speed
3) Install new springs in clutch
- OVERHEATING OF DRUM:
1) Not enough torque from engine, increase engine operating speed
2) Lower engagement speed by changing spring(s)
3) Improper ratio: move to a larger one (example: go from 2:1 to 6:1
4) Move up to the next larger series clutch
1) It is important to apply an anti-seize compound to the engine crankshaft prior to mounting the clutch. This prevents the shafts from rusting together
2) Be sure to use a new key of the proper size
3) To secure the clutch to the crankshaft, use a hardened 1 1/2" OD flat washer with a correct size grade 5 bolt and lock washer (not included with clutches)
4) Bolt the clutch securely to the crankshaft, if a torque wrench is available torque the bolt to 14-19 foot pounds for 5/16-24 UNF threads, and 26-35 foot pounds for 3/8-24 USF threads
5) Do not allow the clutch to press onto the crankshaft chamfer, install a spacer so that the clutch secures to a square shoulder
6) Prior to starting the engine, inspect the clutch drum to ensure that it rotates freely on the crankshaft, if it doesn't replace immediately with a new drum assembly
7) Always install belt and chain guards after any work has been done on the drive system
- SPRINGS: to install new springs, place through the "ears" of each shoe, never change the direction of the coil windings and make sure that both ends of the hooks are securely seated into the shoes
- RE-BUILDING: press rotor out of drum with a bearing press, NEVER hit the shaft with a hammer, rebuild as required and press rotor assembly back into the drum, secure with snap ring(s)
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