Crankshaft end-float. Maybe the last word ? !

[BRIAN MARSHALL]

Hi
I have been given a letter from the factory dated 1935, which states that the correct crank end float is one sixtyfourth of an inch. Over the years many people have opined on this subject, and stated some very different figures for this rather critical clearance. Maybe this will put the subject finally to rest. Somehow I rather doubt it…..
That measurement is of course the MINIMUM amount of end float. It is quite OK to have rather more, perhaps up to 30 thou”, but not too much or the crankpin screws will try and mill their way out through the crankcase doors! –and other nasty events.
If you have less than the minimum, you may be able to save the day by finding a thinner pair of glands, but if that doesn’t do the trick it is time to think that the flywheel tapers are oversize/worn, and start looking for a fresh flywheel. Alternatively someone like Roger Moss can put a new centre into your flywheel, with tapers back to the correct size.
Brian

[Deleted User]

I have always set to 0.012″ with a tolerance of +/- 0.002 so between 0.010″ and 0.014″. In truth it does not matter if it is a bit more, but I prefer not less than 0.010″ as the case is not low expansion aluminium and as I know that the 2.625″ dia main bearing bore will grow 0.004″ then the span across the cup gland faces will be perhaps 0.007″
The last thing we want is the glands to be pushed hard against the cup faces, but if the end float were to be excessive, then the tendency for the rotating assembly to move axially can oblige the rods to stand at angles that are not ideal for the bearings.
As regards Brian’s comment about the flywheel tapers, then if the engine is running poorly, then before you dismantle it, check the runout of the flywheel in situ.
Best with a dial indicator. Outside diameter runout should be within 0.004″ TIR (Total indicator Reading) and side within 0.007″ TIR For my rebuilds I prefer less than this. If you do not have a dial indicator, fix a bit of stiff wire to just touch at the highest point and use feelers at position of greatest gap. If the flywheel is wobbling, then the cranks are also running out of true and this has a detrimental effect on bearings. Scotts will run in a pretty bad condition and I suppose the old maxim of “Leave it alone if it is running acceptably applies.
I apologize that I have not updated my website for a long while but as Richard no longer works here, it is a bit beyond me unless I spend some time to study the subject.
However, the bit about dismantling and assembling cranks to flywheels is highly recommended to anyone considering these operations for the first time
Roger

[Deleted User]

Further to Brian and Rogers info it may be of interest in a conversation I had with the late Matt Holder senior regarding crankshaft end float. He told me that under no conditions should it be less than .015″. The maximum can be .040″ but in this case ensure nothing is rubbing. All checks should be carried out with the top spacer in place and bolted tight if required.
It can take quite a bit of leverage between the flywheel and crankcase to move the c/shaft to its extremities.

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