Engine howl at 3500 rpm and above

[Crash09]

Had the bike (80 650 special) for years, just recently i started to get a howl (about a 300Hz tone) at 3500 rpms and above.., engine runs fine at idle and all the way up to that point. Howl seems to dissipate in a right hand bank.. I have checked in different gears and the howl always starts at about 3500 so that discounts any wheel bearings etc... I am perplexed.. any ideas...

 

[TwoManyXS1Bs]

Welcome to the forum, Crash09.

To get you started, and give you an idea of what you're getting yourself into, have a slow read through this thread:

http://www.xs650.com/threads/high-pitched-mystery-sound.23162/

 

[xjwmx]

The dissipating in a right-hand bank -- when my front chain guide went it made a distinctly different sound depending on if it was on the side stand or being held up straight. I guess the difference was the chain's position in that trough. Had another sound in a bank, but that was not engine speed; fixed itself, probably lightly rubbing rear tire.

 

[Crash09]

Thanks TooMany...
Had a look at this thread and it had a few things to try but I still have the tone (howl). My case is a bit different in that it only occurs once the rpms reach about 3300, below this either the problem does not exist or I cannot hear it above the engine noise. It gets louder as I move toward 3800 and then seem to drop off after 4000 (this could be just that the engine is louder at this point so the tone seem less but it certainly levels off). The tone frequency rises with the engine speed. I recently had the clutch apart to fix the starter benix gear, and so I went back in there to ensure I have all the washers etc. in the correct places. I reviewed the diagrams from the post and shop manual (Cylmer) and everything seems to be in good order ... It could be a worn bearing (bike has 67,000 km on it) but I would think that this would be apparent at lower rpms as well (at least this has been my experience). Rotating the clutch shaft, when I had the side panel off, I couldn't feel any roughness, but I know sometimes you need to have the bearing out to detect anything ...
As for dissipating in a right bank I can't be sure if this is actually happening or it just the way the sound is reflecting back to me...

 

[TwoManyXS1Bs]

While standing still, in neutral, you could try holding it at 3500 rpm, then lean the bike to the left, then right. The crank's lateral position is maintained only by the right ball bearing. If worn, the crank could shift, and the sound could change.

Is the sound different during acceleration versus engine braking?

Otherwise, this is probably a mechanics stethoscope thing, as noted in that other thread...

 

[Bob Kelly III]

Sounds just like the problem I had..... which hasn't been fixed yet but it steadily got worse and I discovered ...I think...it's the back lash between the Primary drive gear and the clutch basket. caused by the crank being slightly bent. ( the pin slipped in the pressed crank)
I don't know if that is the problem for a fact yet as I haven't repaired all the things that need to be repaired yet.
....what clued me in was I pulled the sideplate to see if I could find a reason for the Howl or Wrrrrr noise.... I think it was 2M that said check the crank end to see if it wiggled back and forth when the engine was turned over... I did and I could see a small wiggle... that translates into back lash of the clutch /primary drive gear interface......and a square gear sound from the right side plate.
I do hope that is not your problem My bike is a 1982 XS650 HS.
Bob......