Hi.
Having rebuilt the engine gearbox and diff on my 850, I was feeling pretty stoked and having great fun zooming around for the last 500ks. Then after a 30 minute cruise on a beautiful Friday afternoon, when pulling into my driveway I hear a strange whirring supercharger type noise coming from the engine bay. https://youtu.be/e1Dx2iiMJWs
It seems to be from the water pump end. Only when the car is warm. When the car is turned off and restarted it goes away. No apparent noise or tone change with revs.

Nothing seems to be rubbing.
I have checked the fan belt deflection 12 mm.
Removed the generator, spins freely no noises and no slop.
The water pump spins freely no noise and no slop.
Here's the YouTube link, https://youtu.be/e1Dx2iiMJWs

Fan touching the radiator shroud?

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Yes, that's the simplest way.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Thanks winabbey.

Here's the Youtube link: https://youtu.be/e1Dx2iiMJWs

TK. Fan isn't touching anywhere, shroud and radiator have clearance, thanks.

Try the screwdriver stethoscope trick on the generator before and after the noise starts. Sounds like a bearing.

Wow, that's an obvious sound and just as you described.

Seems to be from the water pump or generator. Get a long screwdriver and very carefully rest it on your ear while touching the pointy end on various components in that area. That often helps to pinpoint the offending part.

gtogreen beat me to it.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Possibly water pump. Check by removing fan belt and turn water pump pulley by hand, checking for any lateral movement. Replace water pump (rather than changing bearing).

Subsequently, the bearing could have allowed excess movement of the shaft to throw it out of alignment and off axis, thereby allowing impeller blades to scrape.

In the video you have it making the noise then turn off and immediately restart and the noise goes away, it makes me think it's less about it being warm as outs not going to have lost much heat over that short a period imo.
The sound almost sounds like an electronic buzz, I'm wondering if it has something to do with load on the generator, and after a fair while of driving there's more voltage being asked of the generator because the battery is getting more full, as you turn off and start back up the battery has taken a hit with starting and the voltage required had lowered?
Anyone know if you could safely disconnect the battery on generator mini whilst running and see if it changes things?

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Roads need more corners
A Deluxe(CG13DE), 2 Clubbies(998 and 1275) and 2 Morris 1100Ss

Even just remove the fan belt so water pump and generator are disconnected, start the engine and see if the noise remains or disappears. That will either eliminate or confirm the problem is with one of those two components.

P.S. No water will be circulating so keep and eye on the temperature.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Thanks everyone, will try the screw driver trick and check the charging when I get the generator back on. I have it on the bench at the moment. I'll see what checks I can do on the bench first. Maybe the regulator? Was stumped about the sound going away when car is restarted.
Water pump feels solid with no side play at all and spins freely.
Thanks for all your responses.
Truly hope it's nothing inside the motor. Built it to specs and was very careful.

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Good opportunity to do what I mentioned above - run the engine (briefly) without the generator to confirm the noise has gone.

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ex-NSW Police 1970 MK II Cooper S
VMCI #43

Problem is that when I turn off the car and restart the noise is gone. I think I'll have to start with the generator tests and see if I can find any thing there. The noise doesn't change with revs... weird... would point to a electrical load issue?
Thanks for the help everyone.

Anyone know how to check a generator?

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Not the worst! Hard to spot exactly where, but its either the water pump bearing, generator bearing or the fan touching the shroud. All the same, not an engine out!

I would loosen off the fan belt first and poke around at the big three things, and go from there. Pumps are cheap, so are bearings or adjustment.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Fuzzy-Hair-Man the generator load theory makes a lot of sense. Gunna have to study up on generators and charging systems.
Thanks for you help.

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Difficult at the moment but if you can get it to a auto electrician they can spin up alternators (not sure about generators) at least to see if they are behaving themselves, they could probably vary load on it as well, might be a good opportunity while it's off.

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Roads need more corners
A Deluxe(CG13DE), 2 Clubbies(998 and 1275) and 2 Morris 1100Ss