M30 throwing alternator and PAS belts

[gareth]

I did a track day at castle combe yesterday and early on my car threw off both alternator and PAS belts. I think the alternator belt must have one first as i nearly span on my own coolant, quickly followed within 30 secs by the PAS failing. The engine managed to get VERY hot indeed but being a M30, there were no facks given!

I managed to find a local motor factors, picked up come coolant and and a pair of new Gates belts, fitted them up, all ok.

I got another 20 or so laps in before it threw the PAS belt of again. I called it a day at this stage as I had a 170 mile home journey and I could live without PAS but not without a water pump! After this it made the home journey without any problems apart from tired arms (M30 + no PAS + Z3 quickrack = hard work!).The belts were correctly fitted and tensioned, so what's causing it? I've not lost one before in 8+ years of M30 ownership.


Suspected causes...
Water pump: - slight play, about 0.5mm at the lip of the pulley, this is only a couple of years old. Spins freely with no bearing noise.
PAS pump: - old, unknown age. No detectable play, also spins freely.
Alternator: - again old but no sign of problems here.
Bottom pulley - these are massive things on the M30 and I believe rubber isolated. I didn't try prying it about as if it's on the way out, breaking it completely would not be a good plan when many miles from home. There was no play to be felt by hand though.

When running all pulleys spin without any visible wobbling or misalignment.

All suggestions welcomed, silly or otherwise!

[wellard]

Might be worth checking the end float on the crankshaft,run the engine at idle and get someone to press the clutch in and out while you watch to see if the crank pulley moves in and out.
During normal driving it may be ok but on a track day it might be enough to cause the belts to come off if there is excess endfloat.

[gareth]

Good shout, will check that

[capnmchl]

Sounds stupid but are the pulleys on the right way?

I had a 106 I did the cambelt on and stupidly put the bottom pulley on the wrong way (in my defense, every other 106 apart from the 1.1's has it facing the way I put it on from what I've seen). Anyway, it went for miles absolutely fine, until I overtook someone on the A303 back from Yeovil. I hit the limiter (no rev counter) and off came the alternator belt.

On M10 engines, the alternator and PAS pump are mounted on rubber bushings, probably to stop noise/vibration. Seeming as M30's are just M10's with some extra cylinders, are they the same? It could be that if the rubber bushings are gone then it'll make the pulleys sit slightly pissed?

[gareth]

They all seem to line up pretty well, and it's been like that for around 8 years

Mountings are worth a look i guess. just need to find the time

in the meantime, my arms are getting much more toned!