Whining noise like a bad fan bearing

[Windmill John]

Here's a weird one. 1988 Dommie
Riding a long at speed; over 40MPH at least, I suddenly hear a whining.
If I pull the clutch in to make things quieter, the whine continues for a few seconds then stops.
This whining is very easy to describe. It's as if the cooling fan has a dry bearing.
What cooling fan?
Exactly!
It's as if the fuel pump in the tank is running out of fuel.
What fuel pump?
Exactly!
Any ideas?
It stops when you slow down or pull the clutch in.
I hear it from above, not necessarily leaning over listening.
It doesn't strictly sound internal, but who knows.
It sounds like something revving quickly then stopping, but if I've pulled the clutch in to drop the revs and they do drop, what's still whirring away!!!
Curiouser and curiouser said Alice

[catteeclan]

Sounds like a dry bearing maybe?
Think I'd start with the rear sprocket carrier and wheel bearings. Could be a good place to start if you think they feel a bit dry or noisey.

[MadWelshBiker]

Could it be the front disk brake?

The Dommie is the the first bike I have owned with disk brakes (but not the first bike I have ridden with disks) and so I notice a noise when I brake. I think it is the air escaping between the drillings in the rotor. I have noticed this on other bikes as well. Some days it is more noticable than others and more so when I wear an open faced helmet.

Mike

[Windmill John]

Thanks for the responses guys.
The strange thing is, if it was the drive sprocket, how come it suddenly stops a few seconds after I'v e pulled the clutch in? The bike is still moving at speed.
I haven't touched the brake, so unsure about that.
I've taken the bike off the road this week, so I'll check all fittings and lubrication.
We'll see.

[catteeclan]

Thanks for the responses guys.
The strange thing is, if it was the drive sprocket, how come it suddenly stops a few seconds after I'v e pulled the clutch in? The bike is still moving at speed.
I haven't touched the brake, so unsure about that.
I've taken the bike off the road this week, so I'll check all fittings and lubrication.
We'll see.

Not the sprocket, the sprocket carrier bearing. They can get pretty bad before you notice anything.
Could well be wrong but def worth checking.

[datsun fan]

Long shot, but I get alot of similar noise, comes from my tyres!! - MT21's on an xl250 on tarmac. anything above 35, - worth investigating????

[fatowl]

Could be the primary drive gears?

[Windmill John]

Catteeclan, you mention the sprocket carrier bearing.
I was not psyched up for an engine strip!
I assume we're talking about the bearing output from the gearbox?

[catteeclan]

Catteeclan, you mention the sprocket carrier bearing.
I was not psyched up for an engine strip!
I assume we're talking about the bearing output from the gearbox?

No, rear sprocket on the back wheel. In the carrier is a bearing, know for causing all sorts of noises and vibrations.
Got to check the easy first. Into the engine last.

[Windmill John]

Thanks for that, I'll keep you informed.