dori

Solved! Problem was a little washer wore off and slipped through the speedometer cable and left the square/tapered end of the cable vibrate as it spun and making the whole display casing make that horrible noise. I put the same washer back, and covered the square end with a bit of paper tape to make it thicker and amortize buzzing if it should arise.

I got the impression it comes from the front so I took the front wheel off... bearings seem to be nice and well lubed, but the tachometer gear seemed really dirty and actually noisy when I turned it manually... I cleaned it and lubed it and will test soon... It might have been the mechanical tachometer cable inside not being properly lubed. Stay tuned. Thanks all for the suggestions (it might be true that the tachometer gears contract in cold making the noise nastier or maybe the bad leftover lube in the cable becomes hard and facilitates noise). Does synth oil do permanent damage? If so I will switch of course. Thanks It is speed dependent, but not rev dependent... I realized the noise frequency varies slightly with speed, and I can't do the stethoscope because it only happens at over 40km/h ... it would be a little dangerous Right now I am suspecting the internals of the spedometer/tachometer. Weird problem I would say, but I think I will have to somehow open that up and lube it.

no, I had the noise before changing the oil too... I do know what you are talking about (it being very slippy), but I find it makes the gear changes smoother and quicker... the only time it is bad is when I rev it up too quickly while releasing clutch too slowly... it slips as in it revs up quicker then it should without making the bike move much (not enough rezistence). It is a small power bike, so even doing hard acceleration, the clutch grips fine. I went on a 500km trip last weekend and tried everything and ran fine. The noise comes on only some days, when it is cold... for all I know I could start it up right now and it might be fine.

My bike cries! :'( The bike in question is a 1982 XS400 Seca in an apparent great condition. I want to bump up the cond even more. It runs fine, yet, it produces a bad sounding noise. Let me describe: 1. Seems like it is dependent on ambient temperature as it is more likely to happen if it is cold (and it started happening all the time now). The speed at which it starts seems to be lower the lower the temperature. First few times it happened it rained heavily so I assumed it might be dependent on water, but last few times it was just cold. 2. It is not directly rev dependent. It starts around 40-60km/h (depends on air temp) and keeps at it even when I pull the clutch in or stop the bike... It stops with a dying sort of fluctuating pattern after a few seconds after I stopped (about 20 secs after I pull the clutch in.. total). 3. If I was to describe it, it would be either a wet rubber belt rubbing on metal squeaking somehow, OR a blown up balloon letting air out while holding the lips apart (and having the inside slightly humid) I try to describe as accurately as I can. 4. I cannot make the sound start while stopped (neutral/clutch) and reving the engine. Please diagnose or suggest something. Make my baby stop crying (I wanna ride it through the winter, so it is very important). Thanks! Darie PS. Main issue is that it seems to run fine ... no impairment of performance while making that sound (could it be some filter, tube, wet thing, transmission?) EDIT: I should mention that I recently (500km .. last weekend) changed the oil to recommended for under 15 degrees Celsius usage. It was a synthetic one Pennzoil 10W40 or 10w30 ... the proper one. And the bearings do not make noise, I don't seem to find any vibrating loose screws either. I eliminated the possibility that the chain might be making the noise as noise persists when the cycle is stopped. It really seems to be something to do with the internals.