GS750 engine noise at high rpm

[longranger44]

So unfortunately my 82 gs750 has started making a scary noise when it's revved past ~4k rpm. I took a couple videos of it that I'll post below. The tach cable had just broken so I replaced it and then noticed it making this noise. Thinking it had something to do with the new cable I took it off as well as unbolted and pulled the entire bottom end of the tach cable - the piece that has the gear that goes into the cam cover. It looked fine and with it removed I still have the noise. Oil level is fine.
Has anyone heard this type of noise before? It sounds really bad to me so I won't be running it again until I figure out what it is :/
Thanks in advance.

[longranger44]

[Rijko]

i do not recognize the sound unfortunately.
Ear to a big screwdriver can help determine where the sound comes from, like a stethoscope.

If you are positive that sound started only after changing the cable, you could remove the wormwheel in the cam cover.
Plug the hole with something and see if that helps.

How is the machine maintained ... valve lash set, cam chain not worn, camchain tensioner functioning well ?

[unfocused]

That doesn't sound like an internal issue.

[Rijko]

That doesn't sound like an internal issue.

agreed, could be some part loose and resonating

[Rich82GS750TZ]

I have the same engine. While I'm not an expert on all the noise this engine can make, I've heard my share. It also sounds me like something near the outside of the engine that is loose enough to rattle when you rev it. Sounds "plasticky", if that makes sense.

Message edited after I re-read the first post.

[rphillips]

To me sounds like a rotating mass is rubbing against a cover when XXX rpm is met... Just for simple kicks, that don't cost anything, try it with clutch pulled in, just to see if any change.

[longranger44]

i do not recognize the sound unfortunately.
Ear to a big screwdriver can help determine where the sound comes from, like a stethoscope.

If you are positive that sound started only after changing the cable, you could remove the wormwheel in the cam cover.
Plug the hole with something and see if that helps.

How is the machine maintained ... valve lash set, cam chain not worn, camchain tensioner functioning well ?

I removed the worm gear and the sound was still present. One of the videos was taken with it removed

I checked the valve lash a couple months ago and everything was good. The cam chain looked normal, I didn't pull the tensioner. I've had the bike for just over a year and put about 500 miles on it. Never heard this sound before. I had carb trouble and gas leaked into the crankcase unbeknownst to me and I let it idle for probably 30 minutes with diluted oil and was worried that could've done some damage. But it seemed fine for about 100 miles in the past couple weeks until Wednesday when I put on the new cable.

[longranger44]

I have the same engine. While I'm not an expert on all the noise this engine can make, I've heard my share. It also sounds me like something near the outside of the engine that is loose enough to rattle when you rev it. Sounds "plasticky", if that makes sense.

Message edited after I re-read the first post.

I looked for anything loose but couldn't find anything. I have an automotive stethoscope I'll have to try and pinpoint where it's coming from

[longranger44]

To me sounds like a rotating mass is rubbing against a cover when XXX rpm is met... Just for simple kicks, that don't cost anything, try it with clutch pulled in, just to see if any change.

I'll try that and use my stethoscope and report back

[oldGSfan]

My bike's levers rattle when I rev past about 5K, make a similar sound but a bit more jingly-jangly.

[longranger44]

Well I used my stethoscope and figured out where the rattle is coming from. Not a loose timing chain, or a catastrophic engine failure, but a...wait for it...loose exhaust heat shield lol. I psyched myself out for nothing. It sounded like it was coming from the top of the engine and then with the coincidence of the tach cable replacement and the sound reverberating up through the cable I was sure it was coming from the engine. So I guess I won't be needing a new motor, just a 10 cent bolt haha. But thanks for the replies, next time I post I'll make sure it's actually something serious lol.

[rphillips]

Great to hear, you're kind'f double lucky. When my heat shields came off the little tabs broke, not just a bolt came out. I don't want to hear your next post, I never like serious problems... Congrats.

[Rich82GS750TZ]

Don’t beat yourself up. Important part is you found the issue, and it cost you nothing. If the people that replied were truly bothered by what you might think was a silly question, they wouldn’t have bothered to reply. Sometimes we all need a reminder to KISS, and check the easy, cheap stuff first. And thanks for reporting back. It’s always nice to have a mystery solved.

[Rob S.]

Now that's a happy ending. When I heard your recording of the sound, I thought, "I wouldn't ride that." Best of all outcomes!