Scooter suddenly started shaking on acceleration and rolls forward at idle

[Neil955i]

WoooWee!
If that ain't a warning to properly torque those 2 CVT nuts!!
CVT parts are one price...but, destroying the splines is a horror phone call from the mechanic!
Yeah, "sorta tight" is not good enough!...
Good reminder.
Stig

Too true Stig.  Some of the guys on here thought I might clean the splines up sufficiently (by picking out the molten aluminium*), but I wasn't brave enough...

* Yes, that IS spelt correctly 

[Ruffus]

Woooouw, you guys over there must be rich😉.
I get in line too, to come to fix it together with Ericson, would bring tools.

Yes, like written, splines properly cleaned, new CVT plus nuts, belt and clutch and deal done.

[Ruffus]

WoooWee!
If that ain't a warning to properly torque those 2 CVT nuts!!
CVT parts are one price...but, destroying the splines is a horror phone call from the mechanic!
Yeah, "sorta tight" is not good enough!...
Good reminder.
Stig

@Stig, this outer front pulley/ pulleys being made from relative soft aluminium/dural, I learned lately at a discussion with an middleaged scooter dealer/ mechanic, is actually a safety feature.

To safe your crankshaft/motor/rear gear from destructive force by a blocked CVT (which as a possibility is taken into consideration by KYMCO engineers) you have a pretty inexpensive (compared to a whole motor) piece, which gives in, in case, and is easy to replace.

[mousejunks]

Here are aftermath photos. 1 broken roller with a flat spot and also a flat spot on the ramp plate. Pulley wear surfaces seem fine with slight grooves, clutch has a bit of glazing and bell has a bit of discolouring from overheating. Belt is good but will be replaced. Otherwise a bit of a clean/sand and it can be put back.

[mousejunks]

Photo 2 of the roller

[Iahawk]

can someone walk me through the process of how a broken roller would cause the clutch to be always engaged? Clutch engagement is RPM dependent...I can see how a broken roller may help open up the front pulley..maybe change the belt position a bit..but why would this engage the clutch? (still on 1st cup of coffee this morning..)

[Ruffus]

Mouse, yes, roller got stuck, chafed off its coat, disintegrated, jumped out, blocked the transmission, rest we know.

Check carefully before asambling, splines, treads  (with new nuts).
If the rear pulley and clutch is visually good and not demaged, take it again. Slight grooves (under 0.5mm) don't matter.

Clutch bell: measure carefully its "roundness" with a caliper. Preferable a digital. Inner diameter is 160mm (tolerance 0.3mm)
Torque front pulley nut 135nm
Torque rear pulley (clutch) 80nm

If you have clutch and rear pulley out,mount the belt already out on you bench between pulleys (as deep as possible), makes it easier to mount front pulley assy correctely.

When you mount all this, before you put the belt on its front pulley, let the motor run and watch the crankshaft whether its running without tumbling.

And this all for a little bit under €3.000,-😊

[Ruffus]

can someone walk me through the process of how a broken roller would cause the clutch to be always engaged? Clutch engagement is RPM dependent...I can see how a broken roller may help open up the front pulley..maybe change the belt position a bit..but why would this engage the clutch? (still on 1st cup of coffee this morning..)

My theory:
Like written above, broken pieces were between belt and front pulley, tensioned belt, clutch engaged.
Maybe also a little bit too small (diameter) rollers.
1/2 mm would make a difference after some yrs.

[mousejunks]

can someone walk me through the process of how a broken roller would cause the clutch to be always engaged? Clutch engagement is RPM dependent...I can see how a broken roller may help open up the front pulley..maybe change the belt position a bit..but why would this engage the clutch? (still on 1st cup of coffee this morning..)

I'm thinking the roller with the flat spot jammed the variator and wouldn't roll back, so the belt was stuck riding in the highest position. This would cause a high ratio and the rear pulley to spin faster, fast enough to engage the clutch and cause the rear wheel to spin at idle.

Photo 3 below of the pulleys and clutch assembly.

[mousejunks]

Photo 4: the splines on the front shaft. They look intact. Same condition as the rear.

[mousejunks]

Photo 5: close-up of the clutch shoes on the clutch assembly. A bit of glazing.

[mousejunks]

Photo 6: close up of the flat spot on the ramp plate.

[Ruffus]

Does not look that bad! New rollers or gliders, sliders too, a rampplate, belt, new nuts and off you go.
If this ramp plate is still straight, I would polish it, brake and smooth the edges and let it be.

Watch for deadplay front pulley/splines.

[mousejunks]

Does not look that bad! New rollers or gliders, sliders too, a rampplate, belt, new nuts and off you go.
If this ramp plate is still straight, I would polish it, brake and smooth the edges and let it be.

Watch for deadplay front pulley/splines.

It's good news for me - the parts to be replaced are relatively inexpensive and the repair job is pretty straightforward. I will complete it when all the parts arrive.

[Ruffus]

Mouse, this ramp plate looks at 2nd view overall a little bit rough to me, IF you get a new one, compare, IF NOT, do a thorough smoothing and polishing on that. Though the inner ingranation looks too rounded to me.
Breaking edges too.

Dr. P or TechPülley gliders/squares in right dimension might be an idea too, to avoid such an event.