Light Judder on Take Off

Hi,
Replaces the belt and put in Dr Pully 28 gram sliders. But still have a light judder on take off. Could it be the Clutch pack?

At 16000 miles, no.

Hmmm well the variator isn't perfect. has a bit of wear. Should I be cleaning the clutch pak? thank you!

Sure, you could deglaze the clutch shoes & clutch bell, either by holding the brakes on and running the RPMs up to 4000 RPMs for a few seconds or by removing the Driven Pulley assembl and using emery cloth on the clutch shoes and clutch bell. But if there is/are noticeable grooves in the Drive Pulley sheaves (can you feel them with your fingernail?) you should probably replace them. If you notice a black ring built up near the outer edge of the sheaves that could be belt deposits from the old belt and might be able to be cleaned off or polished away using fine emery cloth. Be careful of the seal at the base of the moveable pulley sheave though.

Try the brake hold trick first.

Tim

Would'nt the brake hold technique potentially burn a notch in the belt, being the belt cannot rotate due to the rear axle being unable to turn because of the held brake? The silver wings belt has such precise specifications I would be afraid to do this. I wrecked a $100 snowmobile belt a couple years ago by trying to get the track to turn while frozen to the sliders. Only took a couple seconds but the damage was done- notch worn into the belt causing the clutch to vibrate and shimmy.

I would try and deglaze the clutch shoes and drum as suggested.
This seems to be the preferred method for this  concern. I believe the belt is turning the clutch drum assembly and the shoes are partially engaging the clutch drum (this is the deglazing part) to clean off the shoes.This also was the method used years ago on automobiles with a standard transmission that had a slight shudder from the clutch assembly on take off.  Howard

Use more throttle on take off which will allow the centrifugal clutch to lock up faster, the judder is usually the clutch slipping.

Cool thanks everybody. I sure it's the sheves but it'll do for now till I get monied up again. 4000 RPM deglaze helped a bit.
Cheers
Mc

If the 4000 RPM deglaze helped a bit now if you use more throttle on takeoff (as exavid advised) you may find it getting smoother as the miles add up. When I first started riding my Silverwing it was jerky when talking off. I did the 4000 RPM deglaze and started using more throttle on takeoff  and I've never had any problems with the clutch glazing up again. Now I only need to deglaze the clutch pads with emery cloth when I change the belt.

The CVT in the Silverwing is a bit different than the ones used in the past on snowmobiles. In them the driven pulley was attached directly to the engine crankshaft. The increasing rpm caused the two halves of the driven pulley to grab the belt and force it out toward the perimeter as it 'shifted' up. In the Silverwing there's a centrifugal clutch between the driven pulley and the engine. The belt is under compression at all times whether idling or full speed so it doesn't slip as you add power. This prevents belt burning as seen on snowmobiles.
The judder is caused by the centrifugal clutch. Starting out slowly with low power engages the clutch very lightly allowing it to slip for a longer period. The slight variation in clutch grip as it slips causes the judder. Much like riding the clutch with a manual transmission in a car. Allowing the clutch to slip is what causes eventual glazing making the clutch friction material smooth as glass resulting in slipping which show up as judder.
With the SW it's better for the machinery to start out with a brisk throttle application, not full throttle but enough to get the bike up to speed reasonably quickly. Once moving over 20mph or so the clutch will be fully locked up and not slipping at all which is much better for it.

Paul thank you for the clear explanation of the workings of the clutch. People are more likely to follow advice if they understand why it will help.

A most excellent post. I will change my take off technique as I don't use much throttle. I deglazed the clutch a bit and so with a bit more umph I bet it smooths it out even more.
cheers
Mc

Exavid my snowmobile has two clutches not dissimilar to the SWing. The working princibles and the mechanics are the same as the SWing. The belt travels proportionally between the main clutch and the secondary clutch, opening and closing them to create the speed to throttle ratio.

Exactly, for many years snowmobiles (or snogos as they're called in NW Alaska) used the driven pulley to control shifting via flyweights but also as the main clutch to grab the belt as the rpms increased from idle. That system did cause a good bit of belt burning because when the track was stiff as the old style tracks would be in cold weather the driven pulley wouldn't have enough power to grip the belt without slowing the engine and causing the pulley to slip on the belt. That's why I stated "in the past" because for many years after snowmobiles became reliable (early 60s) that's the system they used until the late 70s in most brands. The more modern ones use a separate clutch as does the SW and most scooters.
I used to race snowmobiles in Kotzebue, Nome and a couple larger places in Alaska in the early and mid sixties using Yamahas. I did a lot of modifications to mine and other people's. In those days Yamahas and Skidoos as well as Rupps and some other brands ran bogey wheels instead of slide rails on the track. Also leaf springs without shocks was standard equipment. None of them had an instrument panel or brakes. Made it a bit interesting at times my 1972 Yamaha with some engine modifications and big tuned exhaust chambers mounted to the outside of the shroud could make a bit over 80mph. Lots of fun on rough sea ice.
Either way if your centrifugal clutch isn't running fast enough to lock up it will be slipping and burnishing the friction pads. More throttle at starts will prevent that for the most part. The only time the clutch pads are wearing is when the clutch is slipping, not when idling or running fast enough to lock up.

Just wanted to correct you. Your post made it appear like I had no idea how a snowmobile vs. a silverwings clutch worked, thus the drawn out explanation.

Nope, didn't mean to imply any such.