Fine Tuning the Clutch

By: Mrviper700

The 2 biggest tools in fine tuning your clutching heat and you tach. A hot clutch is telling you, " I am very inefficient and wasting power!" If your front clutch is hot, you know you need to work on that front, same goes for the rear but the whole trick in this is to find the best all around set up which gives you decent clutch temps and all the characteristics your looking for such as back shift for on and off the gas, twisty trails require this, long lake racing doesn't. That means tune the clutch's to what kind of riding you do 90 percent of the time and just deal with the other 10%, win or lose because setting the sled up for the 10 percent will result in a very unhappy owner. You cant have the best drag set up and the fastest sled top speed on the lake, cant happen with a snowmobile clutch. To get one thing you must give up something else in another area.

You will want to usually set up your sled to leave from a stop to full throttle holes hot at the peak torque output of the engine, this will be lower then your peak hp number is. You want to load the engine at peak torque rpm and then let it build the rpm up to your peak hp rpm.

1.) start off with your rpm being adjusted correctly, all this is done basically with the primary clutch.

2.) you tailor or control the shift with your helix and spring combo it acts to fine tune the up shift created by the primary overcoming the spring with the centrifugal force being generated by the flyweights.

Lets add this, lets just say you brought your sled here and we take it out to the test field, here's what I would look for when riding it.

1.) Where does the sled engage the belt at? is it too high or too low for the engine work and or traction available?, I would guess at 42-4500rpm on snow for your particular sled.
2.) When rapidly accelerating the sled what does the tach do, is it a clean rapid sweep up to the peak torque output of the engine?
Or does it gain rpm then actually lose rpm for a short bit and then begin to climb? doing this is a result of over shifting, meaning the clutches are getting ahead of the engine, can be caused by too steep of a helix start, too weak of a secondary spring, way too much traction for the engagement speed and thus pulling the motor way down from peak torque.

3.) After getting out about 400ft is the tach climbing up to peak hp and does it stay there? if it does good your getting a decent straight shift profile, if it doesn't then it needs attention, you'd start to look at the spring rates and profile of the weight your using.

4.) After its wide open does the tach stay on peak and if you encounter a snow drift or what ever increases drag on the sled does the sled lose rpm? If it stays on target, good, if it falls this is a sign of not back shifting and keeping the engine on peak, can be caused by too steep of a secondary helix finish angle, along with too soft of a secondary spring setting, or too soft of a secondary spring, meaning you need a stiffer rate.

5.) After I made this 750ft or so pass on the sled, stop the sled and its time to open up the clutch cover, is the primary hot? can I hold my hand on the sheave face for more then 3-4 seconds without instinctively pulling away cussing? Can I do the same to the secondary? heat means your slipping the belt, needs either more weight, less shift out tension on primary spring (another sign will be over revving of rpm on peak)

for every problem you encounter there is 3 ways to fix it, one will be better then the other and will do something different then the other 2, key is finding the best one that applies to you and your riding style and hangs onto the belt with the least amount of waste!

This process is GENERAL, its meant to give you a idea of what to look for and what maybe to cure the problem, As Turk said continuous wide open passes will heat up the clutch's, and belt, especially a 8dn, they like to hold the heat once hot. I tune then let it cool, and retune, this process can last a hour if I guess right, or all day!!

By: Mrviper700

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