Weird sound after running at high RPMs

[freppa]

Hi!
My first post here on the forums. Hope i posted in the right place.

I have a honda CB750k 1981 (might be 1981) and after driving the bike at higher RPMs for a while i get a weird, soft but noticable rattling sound from the engine. The sound follows the RPMs so when i revv the engine it speeds up similarly. I'm pretty sure it's coming from the starter clutch down by the left crank case cover. It only appears after driving a good while at the higher RPMs, say 5000 rpms steadily for about 10 minutes. And once it has appeared  the sound stays (now even at lower RPMs) until i turn off the engine and let it cool. Once cool the sounds gone until i go for a run on the motorway again.

I recently rebuilt my starter clutch with new springs and rollers and my first guess was that one or more of three bolts that attach to the what i think is called "the freewheel" had gone loose, but this wasn't case.

Has anyone experienced this before?

[Johnnylevi]

did you adjust your cam chain tensioners?

[freppa]

Noes. Haven't touched the cam chain tensioners. I didn't have this problem last season and haven't changed anything but the starter clutch rebuild.

[Johnnylevi]

You might try adjusting them and see if that helps at all. couldn't hurt

[Butcherblock]

My first guess was the can chain as well. Easy fix. I just did myself. Look in the fsm for details, but I can paraphrase.

Remove alternator cover. Loosen the Cam chain tensioner in the front. Have friend turn over the bike with a 17mm wrench on the alternator. Tighten while it is turning. Loosen both Cam chain tensioner in the back (under the carbs, kinda a pain if you have large hands like me). Have friend turn over engine while tightening the nuts. Done!!

This procedure stopped a small rattle that was forming in the top end of my girl. Good luck!

[freppa]

I'll try and adjust the cam tensioners, will be back for results!

Another question. Under my alternator cover, under the points cover to be more specific i have a layer of white goo (oil mixed with water i guess). I've wiped it off and checked about 14 days later and it's back again.  Is this due to condensation or do i have a faulty seal somewhere? i'm pretty sure the cover itself seals good cuz i temporarily sealed it with silicone rubber in lack of better options.  I've ordered a new gasket just in case. The white watermixed oil, i think, is only on the points cover inside because the oil seems fine when i check it on the stick.

[seestheday]

Did it look this bad?



That is what mine looked like.  Yes it is oil mixing with water.  Do you ride it in the rain?  I was.  You are probably not letting it run long and hot enough to let the moisture evaporate out of the engine.

I also had some bad valve cover seals.  That is where the moisture was getting in.

The seal on that cover isn't necessarily bad, it's just that the cover there is the coolest part of the bike that gets oil so the gunk accumulates there.

[freppa]

Yes that looks about the same. I never ride in rain though. I checked my valves, both the bolt seals (i assume those were the ones you had a problem with seestheday) and the head gasket seems to be leaking. (You could see small traces of oil around it, not enough to drip but enough to notice) The seals on the bolts were in quite bad shape too. Time for a replace.

I've adjusted my cam tensioners now and the noise was reduced but not completely gone. I'll know more when i change head gasket, the chain might reveal something..

[seestheday]

I just saw that you used silicone to seal a gasket. Get that shit out of your engine right now. Hopefully you haven't done any damage.

Oil breaks down the silicone and it forms boogers that get stuck in many of the very small oil passageways within the engine.  It will first clog your oil pickup screen.

If you have run it for any amount of time since you used the silicone then you should probably do an oil change and pull the pan to clear out that oil pickup screen.

A plugged oil pickup screen/blocked oil passageways can mean a thrown rod or worse.