Bad Vibrations at 5000RPM+

[Guest]

I have a 1981 GS650GL that is suspiciously vibration prone. This is my first bike so I am a little unsure as to what would be considered normal vibrations, but starting at about 5000 rpm the vibration gets so bad I can’t see out of the mirrors and makes my hands tingle. Basically I can’t rev it past 5200 rpm without it being unrideable which limits me to about 60 mph.

If anyone has experienced this or can point me in the right direction that’d be great. Thanks!

[Big T]

What maintenance have you Done?

[allojohn]

Start with checking all your engine mount bolts are there and tight!
Do not ride this bike until you have a better idea of what the issue is.

[embrnick]

I have changed fluids, lubed cables, and replaced tires and wheel bearings. The vibration is still present even when the bike is reved in neutral while stationary so I figured the source wasn’t the wheel assemblies.

[Rijko]

That rules out everything but the engine.

If you're lucky the engine is loose like John said to check.
The clutch hub may be loose.

Other than that, you're in for engine check.
Compression, valve timing, ignition, carb cleaning and sync, etc.

Now the mirrors will shake, that does not sound bad.
But not much is able to create a vibration that limits you to 5200 RPM but serious trouble usually. If you can, post a Youtube movie of the shaker, we may be able to comment.

[embrnick]

I’ll check the mount bolts today and edit this post. The bike has 7400 miles on it so it’s basically time to do a valve check (7500m), I’ll start there if the bolts don’t solve the issue. What does it take to check out the clutch hub and tighten it? The bike has a whine that is only present when increasing the throttle. (If I throttle down or coast, it disappears) It increases in pitch with RPM regardless of gear. Could this be a engine/clutch related issue as well?

[allojohn]

The bike has a whine that is only present when increasing the throttle. (If I throttle down or coast, it disappears) It increases in pitch with RPM regardless of gear. Could this be a engine/clutch related issue as well?

Probably normal cam chain singing. You should post a video of both issues to give us idea of what you're talking about.

[tom203]

Get to 60+ mph ,then pull in clutch and let engine revs fall and coast....is vibration still present? If yes, does in sound different?

[Grimly]

5000rpm is right in the band of secondary vibes from the four cylinder engines of the day. Once you get the ignition, carbs set up properly (and make sure you're getting proper voltage to both coils), the vibes will reduce.
More modern engines don't have the same level of secondary vibes that these older ones do - better design internally and a lot of attention was paid to make sure they didn't do it, or if they did, it was minimal.
If everything is set up properly, the GS engines can run very smoothly but you will never totally get rid of the slight secondary vibe patch - otoh, it's a useful diagnostic tool when you get more acquainted with your bike. Any change in its characteristics will alert you to something going slightly off-tune.

[embrnick]

UPDATE

So upon going through the motor mounts I noticed that one refused to stop spinning. I linked a picture of the nut and bolt below.

https://imgur.com/a8mKxVZ

My bike has highway bars on it, which I have come to the conclusion were a post-factory addition based on two reasons. First, google shows no bars in the old ads. Two, if you can't tell from the picture, the jabroni that added these cranked a fine threaded bolt through the coarse threaded nut until it stripped. Looks like the same bolts are on the other side as well, although those aren't stripped out yet. Tomorrow I will try to re-thread the jam nut and find the correct bolt. Hopefully this lessens the buzz. If anyone knows the recommended torque spec for the mounts it would be greatly appreciated.

Thanks a ton everybody that has replied so far; I'll update again after I get it back together.

[Grimly]

Yep, that's been well and truly stripped. A mounting like that will amplify the effect of the secondary vibes to make them feel as if there's something seriously wrong. The oval nut can be replaced by a simple ordinary nut with a tab welded on to it - I had to do it with one of mine.
Be very careful of the length of bolt you use in that location - a few mm too long and you punch a hole in the side of the crankcase. Just long enough to get it tight and only just protrude through the nut.

A common blooper is to remove the crash bars and re-use the bolts that held them on - they're now too long... cracked crankcase.

[embrnick]

My plan is to pull them all and replace them, even those that have yet to strip out. I wonder if the other mounts are tight enough; maybe after the previous owner stripped one they took it easy on the rest.

Another question: Should there be threads in the hole that goes through the actual motor mount? (Bolt --> HBar --> Frame -->Block --> Nut) I can't tell if there were threads and they're just stripped completely off, or if it was originally just a non-threaded hole that has some wear from the bolt. If its supposed to be threaded it's looking like helicoil time...

Apologies if that's too poor of a description.

[BigD_83]

My plan is to pull them all and replace them, even those that have yet to strip out. I wonder if the other mounts are tight enough; maybe after the previous owner stripped one they took it easy on the rest.

Another question: Should there be threads in the hole that goes through the actual motor mount? (Bolt --> HBar --> Frame -->Block --> Nut) I can't tell if there were threads and they're just stripped completely off, or if it was originally just a non-threaded hole that has some wear from the bolt. If its supposed to be threaded it's looking like helicoil time...

Apologies if that's too poor of a description.

if it is the mount I think you are talking about, no, there are no threads until you get to the nut on the other side. This applies to either of 30 or 31 in this fiche:

https://www.partzilla.com/catalog/suzuki/motorcycle/1983/gs650g/crankcase

Or are you talking about something in the frame?

https://www.partzilla.com/catalog/suzuki/motorcycle/1983/gs650g/frame

Another picture would help.

[embrnick]

This applies to either of 30 or 31 in this fiche:

https://www.partzilla.com/catalog/su...650g/crankcase

The bolt I pulled out was #33. Should there be no threads where that bolt passes through until the oblong nut, or should the hole be threaded through the crankcase? I’ll try and upload more pictures later.

[Big T]

The oblong part is the nut
Be very careful on the bolt length there, too long and it punches a hole in your crankcase