engage clutch and revs drop

[haynes]

Running in my new engine and when you dip the clutch the engine revs drop. Its a lightweight non verto flywheel with orange plate, adjusted as per previous instructions. Anyone had this problem, or know why?

[Plotloss]

Its not some sort of vacuum issue?

Disclaimer: This is a very hazy memory, that could in fact be related to brakes and not clutches...

[pdV6]

[pedant]
Title should read "Disengage clutch..."
[/pedant]

Sounds fine I think; low mass flywheel will lose speed very quickly down to idle once the roadwheels aren't turning the engine via the clutch. Will also spin back up more quickly. Which is the whole point, I think.

[haynes]

ok so i ment engage the clutch disengage pedal, i knew what i was trying to say. The flywheel is of the ultralight steel variety with steel backplate, crank is wedged as well so pick up is responsive to say the least, especially compared to that old verto lump.

[Mr2Mike]

My brother had this problem, but read no further unless you are feeling brave.

After driving home about 60 miles from the place where he'd put the engine in, he took out the engine and box and stripped it to find his freshly reground crank was now scrap metal.

Basicaly the crank thrust bearings had been put in back to front, so the crank was pressing against the steel backing rather than the phosphor bronze bearing surface.

If you suspect this could be the case, then don't even start the engine again before you strip it down.

[Cooperman]

I have had to rebuild a 1275 engine for someone who had an 'engine expert' build his engine and put the thrusts in the wrong way round. Yes, it did scrap the crank, Lucky I had a good spare I let him have for £25 plus the re-grind cost.
However, with an 'orange' diaphragm and a light flywheel you could expect the revs to drop by up to about 150 to 200 rpm when the clutch pedel is pushed right down. It's the diaphragn causing the crank thrust face to push into the thrust washers. My 1293 Cooper 'S' always does this and I advise anyone with a heavy clutch to change the thrust bearings regularly to avoid crank wear. You should do this when the end float on the crank exceeds about 0.009" maximum. If you don't, you can wreck the crank in the worst case.
Check your crank float and as it's a new unit it should be no more than about 0.004" maximum. To do that, remove the starter motor, put a dial gauge against the flywheel or starter ring through the aperture, with a long screwdriver push the crank fully forward by levering against the front pully. Set the dial gauge to zero then push with a screwdriver backwards against the starter ring and read off the deflection on the dial gauge. That's your end float.
Email me on my personal contact if you want any more help with this. I think it's probably OK, just a heavy clutch, but you may just need to set the tickover up a bit.

[haynes]

thanks for the advice chaps, its good to have a better understanding of whats going on so that i can discuss it with the engine builders. I always used to stall a mates full on competition car and i realise now that it had the same characteristic.

[haynes]

after a few hundred miles drop in revs has pretty much disappeared. Oh yeah, bloody oil pressure gauges, left me with a rather large puddle in the car as it leaked and oil oozed down the dash, shouldn't have tried repositioning it last night.

[Cooperman]

Sounds all OK then. Great.