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CVT Clutching tipsby jimmypsp700, 2005-09-09
Clutch component installation, from More PVT Performance For Polaris-Mayí99
PRIMARY SPRING CHANGE
Increasing the engagement speed is usually accomplished by installing a spring with higher pre-tension in the primary clutch. The flyweights need a higher centrifugal force to overcome the higher pre-tension, and as a result the engine speed will increase before engagement with the belt.
The pressure spring is easy to change.
-After you remove the transmission cover, you remove the belt from the transmission.
-To change the spring you first need to unscrew the center mounting bolt.
-You then unscrew the six bolts holding the cover in place, and you are ready to change the spring.
Getting the cover back on with a stiffer spring can be a hassle. A simple trick is to get a large washer that fits over the center mounting bolt and screw the cover in to where you can install the 6 cover bolts.
MORE CHANGES- WEIGHTS
If you want larger changes in engine speed, you will have to change the flyweights. Lighter flyweights will increase the shift speed, while heavier weights will reduce the shift rpm. Flyweights are designated in grams, and if you wanted a higher shift speed, you might go down from the stock 55 gram weight.
There are 3 flyweights in each primary clutch. They are mounted with short bolts in the movable sheave, and they push against rollers in the center spider.
-To remove the flyweights they need to be away from the spider. If the belt and cover is off this is easy, just push the movable sheave all the way closed.
-If the cover is on, use a large screwdriver as a lever behind the spider and force the moving sheave over.
-Put an aluminum block between the spider and the sheave to hold the flyweights away from the rollers.
You must remember to remove the block again before you start the engine, or it will be flying out of the clutch and cause damage to whatever it hits. It is always a good idea to install the belt and cover before you start up the engine after having worked on the transmission.
TUNING SECONDARY CLUTCH
When tuning the secondary clutch on the PVT you are going to have to remove it in order to modify its performance.
-To remove it, take out the center screw and slide the clutch off the splines on the transmission shaft. No pullers are necessary unless it is rusted to the shaft.
-On the backside of the clutch the helix is held in place by a snap ring. Be careful when you remove the snap ring, because the preload on the torsion spring behind the spider will force it off.
There are a number of reasons why you would want to remove the helix. You may want to tighten or loosen the torsion spring. Tightening the pre-tension by moving to the next mounting hole will increase the shift speed slightly, and improve the downshift in heavy load conditions. You may also want to change the spring altogether. Springs with higher rates increase shift speeds. Larger helix angles increase acceleration, but may reduce the shift speed too much. To correct this there are compound angle helixes which reduce the angle at higher speeds to keep the shift speed up. The 44-36 degree angle helix is a good example. This helix starts out at a 44 degree angle for good acceleration, and ends up with a 36 degree angle for good top-end speed.
BUTTONS AND ROLLERS
The helix angle surfaces slide against a plastic button on the stock PVTís. There is up to 10 percent friction between these surfaces. A Teflon- coated helix reduces the friction, while a rollerized clutch, where the cam rides against ball bearings, eliminates friction altogether. Reducing friction results in a secondary clutch that reacts more quickly to load changes and also accelerates harder out of corners.
Whatever setup you choose, there are a few things to watch for when you mount the helix back on the shaft.
-First, you should notice that there is a tooth missing in the helix spline. This missing tooth has to line up with a spline that has not been cut all the way on the shaft. The helix only goes back on again in this position. The spring goes in first in the preload holes you have selected.
The next step is where 80 percent of first-timers make a mistake!
If you push the helix straight down, you will have no torsional preload, and the machine will bog down on you for the first hundred feet of travel.
-To preload the torsion spring you need to twist the movable sheave up to a 1/3 turn in the counter-clockwise direction and then push the helix down while making sure it engages with the sliding buttons. It sounds tricky, but it really isnít when you get the hang of it. Have a friend help you the first couple of times.
-With the helix pushed down, install the snap ring again.
If you need more help, I sell a clutch tuning handbook that details the PVT systems for both ATVs and snowmobiles. Contact Aaen Performance at (414) 552-8981.
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