Engine noise/rattle over 4k

[ty998]

Bike: '81 GS650G

When the engine revs over 4k it sounds terrible. I have done the complete cleaning of the carbs and adjusted the valves (6 of 8 were tight). Engine sounds great up to 4k.

What I plan on trying next:
To validate whether it is an engine issue or not I plan on pushing the tach up towards 7-8k. If the bike pulls well with no performance issues then i am going to assume the sound has to be from something rattling.

What I have also recently discovered from PO:
If you follow the exhaust pipes to bottom of bike there is a cross piece which connect the pipes laterally. Over this piece the PO used a screw-tightened cinch to hold an ad-hoc piece of metal over what I am presuming is probably a rust hole (awesome) . That should be fun to fix. That would make sense why the bike possibly sounds so terrible at 4k. I am guessing the hack job cannot hold the pressure and resulting in the noise.

As always, any feedback is appreciated.

The good news!:
I always like to provide some good news to in this effort. I found some matching airbox components on ebay with good-quality boots for a total of $80. I now have the stock air management system on the bike! Yay!

[Big T]

So, you're talking about an exhaust noise here, not a noise from the top end?

[ty998]

So, you're talking about an exhaust noise here, not a noise from the top end?

I will try to define that better tonight...

[tkent02]

Perhaps the cam chain tensioner is not quite cutting it?

[ty998]

Perhaps the cam chain tensioner is not quite cutting it?

As part of this rehaul. I removed, inspected and tested the tensioner.

By "validation" this is what I did:
1. Reinstalled after pushing plunger in and tightening lock nut
2. Loosed lock nut and turned outward less than half turn releasing the plunger/tensioner.
3. Turned tensioner nob out while turning engine backward slightly.
4. Then I rotated engine forward and watched the tensioner turn in and take up slack.

Based on that i would say it is working.? That is what Clymer says

[tkent02]

As part of this rehaul. I removed, inspected and tested the tensioner.

By "validation" this is what I did:
1. Reinstalled after pushing plunger in and tightening lock nut
2. Loosed lock nut and turned outward less than half turn releasing the plunger/tensioner.
3. Turned tensioner nob out while turning engine backward slightly.
4. Then I rotated engine forward and watched the tensioner turn in and take up slack.

Based on that i would say it is working.? That is what Clymer says

That sounds correct, were the springs in the tensioner supplying adequate pressure? Is the wound wire type spring on the outside wound the correct amount?
I was thinking maybe it's working but just not tight enough for the high RPMs.

That's probably not it.

[ty998]

The plunger was surprisingly hard to push in. I'm not saying it was getting stuck. I'm clarifying that the spring was in very good shape.

A short, related story for entertainment (hopefully):
I had a newer bike once and it needed to go in for warranty work. After I got the bike back it sounded terrible over 4k. I was getting kind of stressed out. I decided to take it apart to see if I could fix whatever happened. Turns out the tech had put the square electrical connecter between tank and frame on wrong side of frame and that is what was causing my misery. Something that simply can cause a lot of noise.

I'm posting my issue here cause I am trying validate whether it is an engine issue or not. I will try to provide better noise location details tomorrow.

[tom203]

As part of this rehaul. I removed, inspected and tested the tensioner.

By "validation" this is what I did:
1. Reinstalled after pushing plunger in and tightening lock nut
2. Loosed lock nut and turned outward less than half turn releasing the plunger/tensioner.
3. Turned tensioner nob out while turning engine backward slightly.
4. Then I rotated engine forward and watched the tensioner turn in and take up slack.

Based on that i would say it is working.? That is what Clymer says

JUst to clarify... step 1, you meant you tightened lock SCREW
then step 2, you backed out lock screw half turn, then tightened lock NUT to prevent lock screw from wiggling back in on plunger shaft.

[tkent02]

JUst to clarify... step 1, you meant you tightened lock SCREW
then step 2, you backed out lock screw half turn, then tightened lock NUT to prevent lock screw from wiggling back in on plunger shaft.

The key is leaving the screw loose and the locknut tight.
You did this I think?

[ty998]

The key is leaving the screw loose and the locknut tight.
You did this I think?

Yes. Based on the test and movement in the tensioner after rotating engine forwards, it appears to be working.
However, the screw is now definitely tight as it is secured by the locknut. I am not sure what you mean by "the key is leaving the screw loose..."?

[ty998]

One more update: I didn't get a chance to run the bike and listen to it cause the kids went to bed, but I did get some time to look at the weird exhaust cover under the bike. It wasn't covering a rust hole. It was covering two purposefully drilled half inch holes. What would have possibly been the intention of this "modification"? Blows my mind. I spend months restoring something while someone else drills holes in it.

Anyway, I will look at the tensioner tomorrow again, just to be sure.

[ty998]

JUst to clarify... step 1, you meant you tightened lock SCREW
then step 2, you backed out lock screw half turn, then tightened lock NUT to prevent lock screw from wiggling back in on plunger shaft.

Yes you are correct. I had mistated, but did do it in that correct order.

[ty998]

Found the issue. Thankfully it was not the engine. It was one of the muffler side covers.