Strange noise at 5700+

[Shack]

Dear Forum,
My 1979 xs special is acting strange....I adjusted the cam chain tensioner as per xs files and recently turned 12000 miles so after the chain adjustment i have a wierd noise when I am at about 75 or 5500rpm, when I let off the throttle the valve make a weird noise I think it is the valves? It almost sounds like they are floating or somthing, I ran acompression check and the compression is 168,159,155,162, so I think it is within specs.. but a little lower than 1500 miles ago> I know the PO never did anything to the valves since new and at 9500 miles It did not need it , What should I try now... I have adjusted the cam tensioner and rode the bike 200 miles in two days as long as I stay below 5500 no weird noise?
SHACK

[strom]

Hmmm... I hope you remembered that the bikes crank turns backwards.
Or maybe you just need a carb sync.
Check the oil supply to the head.

LP

[TopCatGr58]

Hey there Shack,
Those are good compression values. Your valves are most definitely not floating at 5,500 rpm, they might try to above 8,500, hence one reason for the red line! They have double springs!!!

Can you duplicate the noise in a lower gear at the same RPM? You said it was when you let off of the throttle, not when you are maintaining engine speed?? Many folks have posted that a check of the exhaust system is probably warranted, those bolts/nuts get worked loose and you can get all sorts of harmonic vibrations from the engine with loose pipes and attachments.

When you let off the throttle, the butterflies close, but the engine is still spinning at a faster speed and trying to suck in air/gas, perhaps you're just hearing the normal engine noises more easily when you drop the throttle, less noise from the exhaust when not under throttle??? A better description of the noise would be helpful, ie. grinding, vibrating, tapping, etc.. Have you done the valve clearance check?? Just throwing out ideas!

[nwilley]

As mentioned, one good possibility is an intermittent exhaust leak. As the system gets heated up one of the headers could pull away slightly from the head. This makes for a metallic tapping sound...not a hard metal sound, but it does sound metallic. Let everything cool down and the sound disappears. Try tightening the header bolts, but use some caution, as these 20+ year old bolts are getting brittle and can snap with too much torque DAHIK!!!

[Shack]

Thank YOU,
I did check the exhaust and the header bolts are tight and the pipes do not move any. The noise is almost a ringing noise.. I checked to make sure I turned the indicator clockwise and I did... The noise is still there even with the bike on the center stand and in neutral...I will check the rest of the exhaust system when it cools down and see if it loose any place.
Thanx Shack

[MartyA]

On my 78E, I also have a ringing noise, mostly over 4000RPM. Tough to pin down because it is only when I am running. didn't try to duplicate it on the stand in the driveway, but I will. Tougher at speed since as soon as I turn my head the ringing changes with the rush of air. And it seems like it is most evident in 4th or 5th gear, when I hold a steady speed.

It almost sounds like you are dragging a chain, but the sound is somewhat muted.

One thing I noticed when I replaced the back brake pads this summer is the little rubber grommet that sorta insulates the back brake armature on the mounting pin on the swing arm was worn. This pin is on the wheel side of the swing arm, about where the rear peg is. While it was on the stand, I was tapping around to see if I could get the bike to ring and it seems if I tap the back wheel just so the back brake assembly rings. At speed, I can quiet the ringing by tapping the back brake. But it comes back.

I tried to pack some rubber around that bolt, but I still get a ringing. Not sure I got that rubber right.

The only other place I can think of a sound like that coming from is the drive shaft / final gear. When I had the back off this summer to re-grease I examined the gears, but no extraordinary wear was evident.

Nothing else seems out of order, I have 34k miles on it. So, I live with it, for now.

[strom]

Hmmm... maybe a worn top camchain guide? Stretched primary chain or a link half-broken off? (mine was 1cm stretched and a link in the middle missing)

take a small hammer and tap the engine till you find a part that could produce the same sound.

LP

[MartyA]

Strom, you strike a fading memory chip! Several years ago I took my bike to a dealer for their $99 tune-up. They do valve shims, carb tune and balance, etc. A comment by one of the mechanics - by the way, younger than my bike - was something about a chain something. maybe he said something about starting to wear, I don't recall. It was not said with much alarm, and I guess I didn't pay too much attention. It just registered! He must have meant the cam chain guide, since they were in there.

Well, it has been 4 years and 12K or so miles.

Durn it, now I am going to worry till I get in there.

[crunchbird]

I have an XS500 which has a chain-driven balancer. When the chain is adjusted to take up slack, it makes a high ringing at high rpm, and there seems to be no problem but no cure. It's a screamer for a thousand miles, then it quiets. Maybe you just need to wait it out.