Entire bike shakes at 4500+, very loud.

[Kylll]

Hey all.

I've had this problem for some while with my project '89 GS500. From 1k-4k rpm the engine is fine, very smooth but a tiny bit of valve noise at 4k. As soon as the engine hits 4500+, the whole bike shakes (not violently, but noticeably more than at 4k) it also makes a completely different sound - i think most of it is coming from the frame's vibration. Imagine a loose bolt. I've double and triple checked that the counterbalance shaft in the engine is in the correct position. Does anyone know what could be causing this? Cheers.

Here's a YouTube clip of it, though it doesn't do it justice.
https://youtu.be/7uOE_z1oKNs

Thanks a lot.

[Bluesmudge]

Have you checked that all the engine mount bolts are tightened to spec? One loose bolt can really let the engine vibrate.

[The Buddha]

I had this happen when the alternator rotor started to disintegrate.
Cool.
Buddha.

[Kylll]

Hey. Finally took the bike for a ride today. Quite shaky, especially in high gear at low rpm. Quite violent, really. Feels like a single cylinder bike without a counterbalance.

Perhaps I've got a bent crankshaft? I bought the bike with a broken piston which ended up seizing.

[The Buddha]

Hey. Finally took the bike for a ride today. Quite shaky, especially in high gear at low rpm. Quite violent, really. Feels like a single cylinder bike without a counterbalance.

Perhaps I've got a bent crankshaft? I bought the bike with a broken piston which ended up seizing.

Oh didn't you check run out and true the crank shaft when you rebuilt it ?
You just replaced a piston ? What was the reason it seized ? and how did you fix it ?
Cool.
Buddha.

[Kylll]

^^ too poor for that. Bought bike with a broken piston and after my first rebuild i must've not torqued one of the conrod clamping bolts, conrod clamp bent open and came off crankshaft, jammed the piston in the cylinder barrel. Ordered pistons and new barrel, crankshaft spun very smoothly in the case though. Attached pistons etc and spun it with an electric drill (with oil in) to make sure it wasn't shaking terribly, which it wasn't.

The shake is more pronounced with higher load on the engine.

[mr72]

...after my first rebuild i must've not torqued one of the conrod clamping bolts, conrod clamp bent open and came off crankshaft, ...

I wonder if your diagnosis of why the rod cap bent was wrong to begin with. Maybe the new piston etc. has now a bent/not-right rod cap, and root cause is not improper assembly but instead something else like a bent valve or some other thing that is causing excess stress on the rod cap making it bend.

I think it's time to pull the bottom end apart again and see what's gone wrong. But something has gone wrong.

[The Buddha]

Replacing bits and pieces of the engine isn't a way to get a reliable smooth motor.
Better off getting a motor from someone who claims it "runs"

Drills don't spin 10,000, or even 4500 rpm. Does it run better past 4500 rpm ?
You've got balance issues or ... well is it losing 1 cyl. let me watch your video clip.
Cool.
Buddha.

[The Buddha]

I cant tell from your video.
Cool.
Buddha.