SKIDOO 850 – 600 CLUTCH pDRIVE SPIDER SHIM PACK  0,020″
NOTE: this is the same shim for the stock 850 turbo summit and 850 turbo comp trail sled.
You hear comments of “jerking” or “tugging” or “surging” on the bottom end, making the clutching period uncomfortable.  This is the primary clutch roller dwelling back and forth over the start angles of the pdrive ramp.  The belt clearance GAP between the sheave and pulley also influences the amplitude of the surging.  Bigger gap makes a bigger amplitude, more energy of a surging feel in the handlebars.  A bigger belt gap of 090″ will make a harder surging on the handlebars than a 065″ belt clearance.

What the shim does is place the spider closer to the drive belt.  You make the belt gap smaller.  Remember the “jerking” or “tugging” or “surging” on the bottom end?  That event is you feeling the flyweight moving against the roller.  The flyweight is dwelling in a location on the ramp storing potential energy until the gap closes and you feel that uncomfortable jolt on the handlebars, and, or sudden track spin.

At engagement speed, the primary clutch rollers are on the start angles of the ramp and flyweight.  The acceleration between 0mph and 20mph (30kmh) is the “clutching” period of the transmission shift.  This “clutching” period is a complained about discussion on the conduct of snowmobiles.

***Lessening the belt gap reduces the stored energy [impact] potential by getting the sheave to touch the belt, earlier in the clutching period.  The roller is doing more work, earlier on the ramp***

If you want the clutching to feel smoother and more comfortable off the bottom end, THEN close up the belt gap.

With a brand-new belt, you can safely close up the belt gap to 0.045″~0.055″.
Try it, I bet you’ll like it.