Engine Rebuild, timing jump?

[wsman21]

I posted on here back a while ago with a engine noise question. No one could give me any relevant advice that helped fix it, just guesses. I got the manual, the manual says it is most likely the connecting rods and main bearings. I have removed the engine from the bike, removed cylinder heads, clutch, stator, oil pump, shifting mechanism, and about to split the crank case in half to get at the transmission.

Before I began taking the engine apart I knew next to nothing about motorcycle engines. I noticed when taking the camshafts off that the timing wasn't matched up correctly. My brother who seems quite intelligent said it wasn't really possible for the timing in the engine to jump. I don't believe him after what I have learned. What do you say? The timing can jump from 10,000rpm and having a gasket blow on a oil starved engine can it not?

[Trwhouse]

Hi there,
Your brother, I'm afraid, is wrong.
Yes, the timing chain can "jump" the sprockets on the cams (more likely than jumping around the crank sprocket) if the cam chain tensioners weaken or fail.
The tensioners push against the cam chain as the engine runs, keeping the chain taut and keeping the cams and crank in time. That's how it's supposed to work.
But if the chain stretches and wears, from age and from dirty oil and infrequent oil changes and maintenance, it can jump the sprocket teeth if the tensioners also weaken and fail.
These are all things that are reasons for regular oil and filter changes.
Poor engine maintenance from lack of oil changes and lack of valve adjustments at regular intervals lead to these kinds of major engine problems.
You might have investigated this more before you pulled the engine from the frame.
You could have pulled the cylinder head and cylinders from your GS500 engine while the engine was still in the frame. They're designed for that to be done.
Now though, you can certainly replace the cam chain, the tensioners and other needed parts.
So there you go -- a primer on the ins and outs of cam chains and how cam chains can skip the teeth on sprockets and ruin your day.
Good luck with your rebuild.
There are lots of parts to check, measure and replace as you go through the process, so be prepared.
This is not a job for the squeamish.
Best wishes,
Trwhouse