Unexplained noise - sounds like a bearing - R100 Mono Shock 1991

[Steve Boar]

A bit of additional information: My R100 has a sidecar and has Unit Leading Link forks, and the Brembo brake calipers are underslung on the active arm of the forks.
Hi
This one has me baffled.
I am getting a noise that sounds like a bearing whining very loudly, that stopped when I applied the front brake. It sounds like an external bearing and also sounds like I am riding towards that noise. And when I get the sound, I get a definite loss in power.
But here is the weird thing, it only occurs after approx 70 miles. And only after taking a fairly hard and sustained right-hand curve.
I thought it might be front wheel bearing ( they are 10 plus years old) but they appear to be perfect with no notching. It could be the brake pads being displaced, because with a sidecar the steering is turned, the bike does not lean over.

Has anyone got any ideas, of has anyone had a similar experience?

[Kurt in S.A.]

No experience but I'll mention that the 1991 bikes were within the range of years where a circlip was removed from the front of the output shaft in the transmission. The result was that the shaft tended to "walk" inside the transmission as it moved towards the rear of the case. I'm not saying that this is your problem...I don't see how an internal bearing would behave as you describe...but weird things do go on. At any rate, FYI!

Kurt

[Steve Boar]

Thanks Kurt, if all else fails I will check that out. Cheers

[Kurt in S.A.]

A thought...how long has this been happening? Any maintenance done previous to it starting that could have created the situation?

Kurt

[Steve Boar]

I did change the output shaft oil seal. But like you I don't see how an internal bearing would behave in that manner. I will check the condition of the gearbox oil. If the shaft was walking as you say, then there might be powdered alloy in the oil. It still seems to me as an external noise.
Thanks Kurt

[SteveD]

Unsure how the sidecar would affect this diagnosis method, but rolling the bike on a flat surface should not illicit any clicking sound from the trans. If you hear it, suspect that big front bearing.

[Steve Boar]

Thank you, I will try the roll test.

[Rob Frankham]

Sounds to me like a 'dragging' front brake. This would account for the apparent loss of power and the noise. The noise won't occur when the brak is applied because the pads are firmly pressed against the disc.

The fact that the issue doesn't occur for the first 70 miles might indicate that the problem is in the master cylinder with the relief port being blocked causing the brake to 'self apply' when the fluid heats up. A pad or piston may also be sticking.

Well worth servicing the complete brake system.

Rob