VERY rough noises - 1982 GPZ 750

Hello I am Felix from Holland.

I have some issues with my 82 GPZ that I cannot diagnose.

I rebuilt the top end. It ran perfectly when I fired it up. I rode up and down the street, satisfied with myself and parked it.
After a week, I started it again and it suddenly started making VERY rough noises. I immediately shut it down and gathered it would be a top end problem. So I opened it up to check. Everything 100% perfect.

So now I have tried to rotate the crank by hand. It does not rotate nicely. It has some rough spots that I can pull through without much force but it does not sound nice. It feels rough and you can hear some grinding.

Now I was wondering what can this be? It seems like a sudden failure not a gradual one. ..

Any ideas?

Thanks

Felix

Felix, check the compression, throttle open.
Remove cam cover and see if oil is up there!
Check valve clearance (I think your engine has under-bucket shims, I would normally think that a shim has slipped out)
Check worm drive for Tacho.
Check chain-tensioner is adjusted and locked
This is a start!
RegardZ.

Hi,

Thanks for your reply. I checked all the above items and I am beginning to become quite sure the top end is ok.
compression is there, timing is perfect, chain is taut, clearances no problem.

Rotation was also difficult without head. The noise seems to come from below.

Dropped the oil pan in the mean time. I can see upward but do not know what to look for.

When I rotate the rear wheel (in gear), everything rotates freely up to the clutch (i.e. exterior basket - I removed the clutch linings).
When I rotate the clutch interior basket (counterclockwise, i.e. normal direction), I have the same grinding noise.

Strange thing: when I rotate the crank (cw), I come to the ' grinding point ' noise - then I turn a LITTLE back (no noise here), after which I can rotate again for a while until the same happens.

So I begin to suspect somewhere between crank and clutch exterior basket.... What could it be???


Thanks again

Felix

I suspect you have a bearing down. Can you rotate the engine without the bike in gear? Roy

I will try. Next step for me is a stethoscope...

But one more thing - this most definitely was a sudden failure. And I think bearings do not fail suddenly, but gradually.... Would this narrow down the possiblities?


Thanks

Felix

This may sound stupid but could you remove the chain from the rear wheel?

FKK wrote: Hi,

Thanks for your reply. I checked all the above items and I am beginning to become quite sure the top end is ok.
compression is there, timing is perfect, chain is taut, clearances no problem.

Rotation was also difficult without head. The noise seems to come from below.

Dropped the oil pan in the mean time. I can see upward but do not know what to look for.

When I rotate the rear wheel (in gear), everything rotates freely up to the clutch (i.e. exterior basket - I removed the clutch linings).
When I rotate the clutch interior basket (counterclockwise, i.e. normal direction), I have the same grinding noise.

Strange thing: when I rotate the crank (cw), I come to the ' grinding point ' noise - then I turn a LITTLE back (no noise here), after which I can rotate again for a while until the same happens.

So I begin to suspect somewhere between crank and clutch exterior basket.... What could it be???


Thanks again

Felix

You may have dropped something down in the bottom end when you rebuilt the top and now it's eating a bearing or primary gear. :ohmy: