Stripped cam drive sprocket???

[misterdimwiddy]

I am looking at a TRX motor which apparently has stripped the cam chain drive gear but not damaged any valves?

http://www.ebay.co.uk/itm/Yamaha-Trx-85 ... 4aca719d89

Anyone any idea how this gear could strip without breaking the chain and bending at least some valves?

If the cams siezed in the head (poor lube?) maybe there would be enough force to strip this gear but it can't be an easy thing to destroy.

Wanting a spare track motor to build over winter.

Anyone on here experienced this failure?

[alextrx850]

Big issue here is that the crank has seized so hard that the cams and chain has stripped the crank teeth trying to stop...
You are going to need the crank, most likely the valves would be ok as the pistons stopped so fast ...the motor seized rock solid..might have been on the track...check the wordage there, the cam sprockets are ok..it's the crank.
Nasty.

[misterdimwiddy]

Sounds feasible Alex.

Does suggest total lubrication failure and a right mess internally.

Amazed that the valve gear/cams would have the momentum required to damage the crank through the chain. It's allturning pretty fast I suppose so lots of destructive energy available.

I'll leave it; was only hooked in by the bargain price!

[alextrx850]

True mate, seen the crank sprocket strip before on this forum,..the top end might be an option, however the overall issues inside may not just extend to the crank, you have cam shafts,counter balance shafts ect,..all without much lube..
It would have been the heaviest requirer like the crank that went first.
Sad that another pump is gone.

[dixonj]

I am looking at a TRX motor which apparently has stripped the cam chain drive gear but not damaged any valves?

http://www.ebay.co.uk/itm/Yamaha-Trx-85 ... 4aca719d89

Anyone any idea how this gear could strip without breaking the chain and bending at least some valves?

If the cams siezed in the head (poor lube?) maybe there would be enough force to strip this gear but it can't be an easy thing to destroy.

Wanting a spare track motor to build over winter.

Anyone on here experienced this failure?

Yes I had this happen to my bike when I first bought it. If you type in the search function trx won't go this will give you all the info. Bent nine valves and snapped ones rocked some valve guides also think the cause was over tightened cam caps.

[dixonj]

http://www.trx850.com/phpBB_forum/viewt ... =37&t=6627 here you go