Possible causes for engine rattle?

[Peter]

I just bought a project GS--a '79 1000L with 9400 apparent miles. I got it running last week but the engine makes a very loud and sharp rattling noise. It decreases somewhat when I kick the engine up to ~2300-2500 rpm. I have no idea if it would disappear under load because all I've been willing to do is let it idle briefly. On the bright side, the oil and filter came out with no metal specks. I can't detect any sort of a knock so it seems as though the bottom end's okay and the cams aren't slapping around.

As far as I can tell it's not the clutch basket (engaging & disengaging it makes no difference) nor does it sound like a loose cam chain. It definitely sounds like it's coming from the bottom end and it seems a little more pronounced near the left side. Could it have something to do with the starter?

Also, the petcock leaks through the vacuum line. Is it possible to fit a newer one (similar to what my '81 750L has) to the tank? I like having the option to switch to reserve. Thanks in advance!

[chef1366]

The top ends of these bikes tend to be on the noisey side. Just check your valve clearances and synchronize your carbs.

[Dave8338]

Could be the cam chain/tensioner...valve lash. Have you checked the valve clearance yet? Ont thing that might have me a bit concerned...if the PO ran the bike with the bad petcock and fuel leaked into the crankcase, there is a chance, however small, that you could be looking at cam bushings going bad. I'd start with the tensoiner and see that it is working correctly, then move on to the valves and check them...also check comprecion (warm with the throttle wide open) and see what you come up with.

[Peter]

Thank you for the advice! I haven't had a chance to tear into it yet but will have some time this weekend. I'll check the tensioner and top end first. Timing and compression (142-154 PSI) are good so at least it hasn't jumped a tooth or burnt a valve or anything.

I was worried about gas dilution soon as I spotted the bad petcock. The oil smelled and felt about right and the level wasn't high so I'm hoping against any cam problems. Perhaps someday I'll learn to temper my optimism with pragmatism.

[chiphead]

Just a thought-stator rotor loose?

[Peter]

Thanks! Since the rattling seems to be coming from the bottom left side I'll check it out. This one only has a sidestand so do you think I should drain the oil first? I did another search for rattles on the forum and apparently the starter clutch can do the same thing too. Think that's likely?