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Tech > General Chassis Set-up

General Chassis Set-up

Reducing the rolling resistance of a snowmobile is also an important area to explore when you are searching for the ultimate top speed. The horsepower required to overcome rolling resistance or drag increases approximately with the square of velocity so small reductions here can provide measurable improvements in top speed.

Good chassis set up starts with accurate alignment of the drive axle, countershaft, suspension system, and chassis.

Use the following procedure to check your sleds chassis set-up:

Remove the rear suspension, driven clutch, tuned pipe and muffler, track and drive axle. Check to see that the spacing of the drive sprockets is correct on the drive axle. The sprockets should be centered in the space between the rows of internal drive lugs on the track.

Use a press or special tool to shift the sprockets. The sprocket indexing should also be checked. The maximum desynchronization should not exceed 1/16in. The drive axle can be chucked in a lathe and spun to observe the spocket "wobble" and run out. Wobble should not exceed .080in. While this amount of wobble might look excessive, it does not affect performance. If wobble is more than allowed, the sprocket or sprockets should be replaced.

Maximum run out should not exceed .020 in. A maximum of .040in can be removed from the sprockets to true the diameter. Do not remove more than the .040in from the diameter of the sprockets or they will start to go out of pitch with the track.

Reinstall the drive axle and see if it is perfectly centered and square with the tunnel and countershaft. If not square to the tunnel or countershaft, you will need to slot the left side mounting holes to enable the axle to be set in square. If the axle is not perfectly centered, use shims to center it.

Reinstall the rear suspension and use a square to see if the runners are square with the drive axle and tunnel. As the runners of the rear suspension are long, any out of square condition will be especially noticable. Make sure that the drive axle is perfectly square before you do this step.

Also remove any end play from the drive axle at this point. Endplay should be a max of .060in and ideally less than .030in.

General Chassis Set-up
1. Align the runners with the drive sprockets. Equal distance on both sides. Shim drive axle to reduce end play. Maximum end play is .060in. Ideally the end play should be less than .030in.
2. Cut ends of tubes and shim as required to align suspension and remove freeplay.
3. Suspension is squared with drive axle.
4. Drive axle is squared with tunnel and countershaft.

Once everything has bee trued and properly aligned, take it all apart and reinstall it with the track in place. Remember to use thread locker on bolts that attach the suspension to the chassis and also make sure that they are all properly torqued.

Finally adjust the track alignment and tension. Track alignment and tension are most critical to top speed. Make certian that the track is aligned so there is equal distance between the slides and guides on either side of the machine. You can sometimes get a little more top end speed out of the sled by running the track a little on the loose side. Be on the lookout for the dirve spockets jumping or ratcheting under hard acceleration.


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