Rear wheel thump driving me nuts

[baz666]

Howdy all,
It's about my 1983 GS750ES with approx. 33,000 miles on it.
I've had a rear wheel rotational thumping ever since I got this bike about 18 months ago. At first it was very faint and I thought it was the crapped out rear brake pads. Changed those, no diff.
Then I thought it was the cheap Kenda rear tire. Changed that to a Bridgestone F11 130/90/17 Spitfire. Great tire, great grip but still that thumping. It seems to be worst at low speed, 2nd gear or so. Every revolution there's a detectable thump, sometimes very noticeable through the right footpeg and less through the left footpeg.
Sometimes I feel it through the saddle in my butt.
It does seem to be getting worse with time.
The thing is, the thumping lessens quite a lot at high speed.
A mechanic checked the rear wheel bearings and said they were fine but maybe not.
I took off the chain guard and took out the rear brake pads and rode it like that.
Still the same issue.
It's not rubbing or touching anywhere, no marks on the tire or rim but the same thumping remains every rotation.
Could it be something to do with the sprockets or a bent rim?
I put it on a rear stand and used one of those laser lights on the edge. It didn't cross the red light line at any time, a gap of less than 2mm.
Any advice would be much appreciated.
thanks,
baz

[derwood]

look for a tight chain link, one that doesn't quite straighten out after it goes around the front sprocket. It may be the master link, especially if it is the pressed togeather type.
i had that issue once , thump thump thump,

[baz666]

Thanks Derwood, I'll check that out and report.
baz

[smokydog]

same thing

Hi, My 80 750E does exactly the same thing and I too have been unable to figure it out. Please let me know if you figure it out. I have put 300 miles on mine since I first heard it and it doesnt seem to be getting worse but it concerns me. I just checked and its not the chain on mine, and I checked out the wheel bearings and its not them either.

Jerry

[OldVet66]

Check the chain all the way around for proper adjustment. A worn chain can also get loose and tight spots that will do the same thing. You would be quite surprised at the racket, vibration and power loss you will get if you just happen to properly adjust a worn chain in it's loose spot. Ask me how I know , 530 chain conversion will be ordered tomorrow.

[Clone]

After you confirm it is or is not the chain, revisit those rear bearings, go buy a full set you can get them at any bearing shop for about $14 each.

[TheCafeKid]

If you've not done it yourself, replace the sprockets and chain. And the wheels bearings. These things seldom get done by "fair weather riders" (guys that domt work on their own bikes) because a shop charges so much to do them. So they'll ride them with crapped out wheel bearings and sprockets that look like saw blades or a chain that looks like it was used for logging until something gives or they sell the bike to someone else.

Just because the chain doesn't look bad doesn't mean its ok. Also the countershaft (front) sprocket will often get a high, twisted or hooked tooth or teeth than can cause the thump thump racket. Riding around on a chain/sprocket set of unknown repair is simply asking for pain, whether it be one in the arse when the bike throws it in the middle of nowhere, or a pain somewhere worse when the bike throws YOU after the chain fails and wraps up in the rear wheel or countershaft.
Not to sound like the grim reaper, but that exact thing happened to my dads best friend when he was younger. He didn't live through it.

Best quote ever, from one Mr Brian Wringer, I believe it went sometime like:
"motorcycles are a lot like airplanes. When something breaks, it's usually painful," or maybe it was fatal. Either way, I saw that early on after joining up here and it's stuck with me ever since.

[baz666]

Well, CafeKid, you're scaring the sh** out of me with all that talk of chains wrapping around various moving parts so I think I'll take your advice and change the sprockets/chain.
A good mechanic I know checked the rear bearings and says they seem fine so I'll do the chain/spockets thing first.

I've been through too much with this bike and she rides so nice and so quick and sounds so good when things are sweet, I can't give up now.

Any tips on a good quality set that ain't through the roof?
thanks in advance,
baz

Actually, one other thing - I want to re-paint the bike - still original from factory - but I hate to lose that nice red and black pin striping and decals. Can that stuff be recreated and does it cost big?