Troubleshooting Snowmobile Belt Clutch Systems

Tune ups, maintenance, and general help on your sleds

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Troubleshooting Snowmobile Belt Clutch Systems

#1 Post by john » Sun Dec 28, 2008 2:43 pm

Troubleshooting Snowmobile Belt Clutch Systems Worn or dirty pulleys, improper belt fit, poor belt condition or clutch function problems can rob a high- performance snowmobile of its quick acceleration and ability to achieve maximum speed. Following are several signs of trouble a rider can look for, and address, to increase performance and optimize the snowmobile belt clutch system.

Worn or Dirty Pulleys

Foreign material in the clutch components or on the pulley surfaces can have a drastic effect on how the snowmobile belt clutch system functions (See Table 1). Deposits of belt material on the pulley surfaces and engine shaft, and bushing (often referred to as "greasing") can completely disable the system if allowed to build to an extreme. When this happens, the pulley will usually need to be disassembled for thorough cleaning. Periodic cleaning of the surfaces with a suitable solvent (acetone, Loctite Safety Solvent #75559, etc.) is usually sufficient to keep the system functional. (Note: The belt should be removed prior to cleaning the pulleys to avoid contact with the solvents.)

Most of today's premium belts are compounded with materials designed to minimize material deposits. Drives requiring frequent cleaning suggest that another belt construction should be evaluated.

Improper Belt Fit

Poor acceleration or inability to achieve maximum speed can be the result of a poor-fitting belt. This could be due to an excessively worn belt, an improperly applied or out of tolerance new belt, or improperly adjusted drive hardware. Three checks should be made to determine if the belt fits properly: deflection (tension), side clearance on the engine pulley and ride in the countershaft pulley

Most owners' manuals have recommendations on these measurements. In lieu of these values, the following recommendations will yield reasonable results.

For tension, the belt should be easily deflected 1-1/4 inches (no more than 10 pounds force). Significantly less deflection will cause declutching problems while greater deflections could cause slow acceleration (feels like it starts in second gear).

Side clearance on the countershaft (driveN) pulley can be measured with feeler gauges and should be at least .020 inches for proper declutching. Values over .060 can begin to cause slow acceleration. Ride in the driveN pulley should be measured with the belt fully seated; you can work it around with your hand or measure after the drive has been operated over a part of its speed range and then run in the declutched position for a few seconds.

Most manufacturers recommend that the top of the belt ride close to the outside of the pulley. It should not ride in or out of the pulley more than 1/16-inch. Too much ride-in will reduce the overall gear ratio and too much ride-out can cause belt damage or belt turnover.

Poor Belt Condition

Signs of pending belt failure include loose edge cords, significant cracking between the notches, loss of undercord material and excessive glazing or polishing of sidewalls. Belt conditions most likely to affect drive performance are excessive wear and spin burns on the sidewall. The former can cause noticeable degradation in both acceleration and top speed; the latter causes excessive vibration. As a general rule, a belt which looks "well used" should be replaced.

Selecting Replacement Belts

Belt construction materials significantly affect the characteristics of the clutch system. High-performance belts made for aggressive riding require higher axial forces than recreational belts intended for moderately aggressive use. For the non-racing rider, using a recreational belt for its aggressive characteristics normally will not require any changes.

Adopting the high-performance class of belt for sleds calibrated for recreational belt constructions often will require adjustment of existing clutch components or substitution of new components to optimize system performance. These belts need higher axial forces and often demonstrate a tendency to over-rev the engine on hard acceleration.

Clutch Function Problems

Clutch components are subject to wear just like the belt. Primary wear areas are the flyweight pivots and rollers, engine and countershaft bushings, and torque sensitive cam buttons. It is good preventative maintenance to have the pulleys disassembled, inspected, and rebuilt (as required) every year on sleds used for trail riding, more frequently on larger sleds or where aggressive riding is the norm.

Alignment also should be checked during annual clutch inspections and anytime premature belt failures occur. Misalignment falls into two categories: angular and parallel... Angular misalignment results when the engine is cocked in the frame and the crank and jack shaft are not parallel. With parallel misalignment, the engine crankshaft and the jack shaft are parallel but the pulley offset is incorrect.

Each manufacturer has specific alignment procedures and dimensions. Most manufacturers have special tools to measure parallel misalignment. You also can use a straight edge to make sure the edges of the pulleys are parallel and thus the shafts are parallel.

Another cross-check for alignment is to use a heavy permanent felt tip pen and mark the pulleys with 1/2-inch wide marks down the full belt surface (mark both halves). Then run the sled quickly over the entire speed range. If the marks are significantly more worn on opposite sides of the two pulleys, alignment should be checked.

Symptoms and Causes:

Slow acceleration

* Belt worn too narrow
* Pulleys or center not adjusted for belt fit
* Clutch pulleys dirty or worn
* Pulleys not tuned to match belt construction
* Belt sidewalls excessively glazed
* Secondary gearing not complete

Engine's maximum speed it too high during hard acceleration

* Pulleys not tuned to match belt construction
* Clutch pulleys dirty or worn
* Belt sidewalls excessively glazed

Excessive vibration

* Belt has spin burn spots on sidewalls
* Pulleys loose on shafts or not properly mounted
* Excessive wear of pulley components

Clutch engagement rough or not at proper RP

* Clutch not calibrated to belt construction
* Belt too narrow
* Clutch pulleys dirty or worn

System not back-shifting properly

* Driven spring not calibrated properly
* Clutch pulleys worn or dirty

Premature belt failure

* Drive not aligned properly
* Incorrect belt fit
* Worn or dirty pulleys
* Clutch pulleys not calibrated to belt

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