Flywheel Runout

Hi all.

I don't know if I'm going blind or just getting retarded due to lack of sleep, but I can't for the life of me find any specs in any of my manuals about acceptable flywheel runout or harmonic balancer runout.

I bolted and torqued up the flywheel and checked runout with a dial indicator right near the outer edge of the clutch face and got a difference of about 0.1mm ( 4 thou ) over 360 deg. This ok? I had previously surface ground it so its as flat as.
I got a figure of more like .2mm (8 thou) for the harmonic balancer.

do I have to mark the high spots and re-surface grind the flywheel? or is it within spec.

don't want the thing wobbling itself to destruction.

cheers
Adam

The first thing to do is establish where the runout is coming from. So as a first step take the flywheel and balancer off again and check the crankshaft for straightness. If the crank itself is reasonably straight then the next thing to do is check the runout of the flywheel flange and the balancer snout. Remembering that any runout at the flywheel face will be greatly magnified out at the edge of the flywheel, so even a couple of tenths of a thou at the crank flange could be a few thou at the edge.

How true is true enough? Some people get really picky about crank straightness, but considering that a crank has about as much radial stiffness as a piece of string I don't worry too much about it. If the total indicator runout is less than a few thou, and I can spin the crank easily by hand in oiled bearings then that's fine with me. As for the flywheel runout, .004" TIR is only .002" "tilt" and if the mating surfaces were in good condition and everything else looked good I could easily live with that. It'll wobble more than that due to crank flex when the engine is running anyway.

I would however be concerned about the .008" runout of the balancer, that's a fair bit for a small diameter. I'd be wanting to find out where it is coming from, crank snout, balancer itself or is it just that the rim is a little wonky on the hub? Lots of balancers have the rim a little cockeyed, and if this is all it is then it may be ok if there is no sign of movement. But I'd be watching it closely, and any other causes need to be addressed.

Edited by oldjohnno, 07 October 2011 - 06:44 AM.

Thanks John.

I put the dial back on the Balancer and checked the inner ring, it was sitting out a little on the key-way. I bit of a love tap with the copper hammer and it was running 0-0. The outer ring still has 0.1mm wobble but I put this down to the rubber being not perfect.

The took the flywheel off again to put the second dowel in (only had 1 before) and its still got the same runout of smack on 0.1mm so I'm gonna run with that.

cheers again.

Adam

pic of how I dial up Flywheel.
Yes the rust spots have been dealt with.