transmission set up/variator shimming

50cczip racer

Well-Known Member
i was going to post this in the clutch topic but feel its worthy of its own thread
ive had interesting results from playing around with shimming the variator,using or removing shims from the centre bush to space out the variator for better acceleration or top speed and more importantly taking up wear and production tolerances from belt to belt.when a thin shim is added the belt seems to sit lower in the front pulley allowing better acceleration but add just a little too much and the belt spins, removing shims or machining 0.5 mm off the bush can provide extra top speed which can be seen on the variator pulleys if you mark them with black marker pen youll see the belt rides higher using the pulleys full range. Hebo document this process in there crank assembly instructions and supply 2 shims ? do any other manufacturers state any set up info
ive seen as much as 2 bhp lost on my belts that have been used for only 1 and a half hours this could be adjusted back with shimming and roller changes but i feel that once the belts get to this stage for racing use its best to start again with a new belt and return to your original settings,i found this out after regular dyno testing before and after races and after refitting a new belt got my original power back after the belt had been run in.
has anyone found better results from polini or malossi overrange belts ive never tried the polini belts as yet but heard they are better than malossi
sprinters and racers please share your experiences.
 
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I picked up a package of shims to try them out. I think I understand the idea of changing the position of the variator faces. Where do you put the shims? between the bushing and the outer face or inner face? does it matter? Is the belt always aligned with the rear pulley or can it be improved by moving the variator farther away or closer to where it rests against the electric start gear? I'm going to experiment with several belt sizes as well from different scooters. I want to learn how to tune a transmission perfectly. I see that it's done so poorly sometimes.
 
shims

shims go between the centre bush and the outer pulley (only if you have enough spline to still slide the outer pulley onto) if not then machine 0.5 or 1.0mm off the bush but only if you have shims to replace the removed material if it doesnt work,it may be perfect spacing to start with
 
we do this regularly whenever we use a new belt or or just resetting the old one, the idea here is to shim only as much washer to let the belt sit in the lowest position without letting the belt slip, to do this you must have an array of washers with different thicknesses.

the lower the belt sits at the front vario the better the acceleration gets, as for using less washers for more top speed i think that's not true, think for a while even if it had no washers the belt will only travel to the maximum point where the vario is capable of (as the engineers made it) so if the scooter lacks top speed it's either the vario design is to blame or you just haven't got enough gear or RPM to pull you at the big end.

we do some modifications to the vario & rear pulley (torque driver) to achieve a taller final gear ratio for a bit more top speed, i can't discuss nor give out any details of how we do it but a clever tuner knows what i'm talking about. we don't take our transmission for granted there's plenty of things to do to improve it's performance from the manufacturer.
 
tiba_karotsu said:
Ss for using less washers for more top speed i think that's not true, think for a while even if it had no washers the belt will only travel to the maximum point where the vario is capable of (as the engineers made it) so if the scooter lacks top speed it's either the vario design is to blame or you just haven't got enough gear or RPM to pull you at the big end.
Tiba, this is offcourse not true.
Simply because the variator has the same angle all over, independent of how far the weights/rolls are in the variator.
So if you start out with your belt "higher" in the variator it will end up at an higher position too (offcourse only when the belt is long enough).

If it's a/the solution to a topspeed problem is a totally different track though:)
 
the rear pulley also limits the amount of travel the belt does at the vario, even if the belt starts higher at the front vario then the belt also descends down a bit at the rear pulley & when the belt hits rock bottom at the rear pulley you end up with the belt maxing out at the same position as it did with the correct washers installed, unless you put too much washer then that will affect top speed performance.
 
tiba_karotsu said:
the rear pulley also limits the amount of travel the belt does at the vario, even if the belt starts higher at the front vario then the belt also descends down a bit at the rear pulley & when the belt hits rock bottom at the rear pulley you end up with the belt maxing out at the same position as it did with the correct washers installed, unless you put too much washer then that will affect top speed performance.
True, offcourse:)

All depends on wether or not you still "have some belt left over".
 
removing washers or machining the bush definately gives more top speed this is something i have done regularly in the workshop to many customers scooters who have asked for a little more top end for road use this can be confirmed by using a black marker pen to show you how high the belt is travelling up the pulley ive seen as much as 8 mph on a near standard 50cc scooter but this was a shim too far as the acceleration was rubbish but had it been fitted with a 70 kit or race clutch would have probably been acceptable
i think its just a case of taking up the available free play in the belt some scoots might not have any but others will but as far as racing or sprinting is concerned the loss of accelleration is not acceptable and any extra top speed is achieved with gear kits.
 
Yuo can get extra belt travel at the rear puley by machining the tracks where the drive pins slide a bit (on polini speed drive only 1 mm if you don't want to mess with the retaining grease o-ring). But even 1 mm gives some extra travel at front. If you overhaul your pulley lots of times you can get the o-ring out and stretch your opening until the spring coils totaly stops it. That will give you much more top speed but you have to get grease in all the time...
 
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