B31 crankshaft endfloat

[Mike9]

I recently bought a 1959 B31 and I am having a few problems.  A bit of a tale I'm afraid.

Whilst at the National Rally this year the bike developed a rattle from the primary chain case area and at the same time an oil leak past the inner primary case felt seal, the oil level was also down in the tank. 

On investigation the alternator securing nut/tab/washer had come off the crankshaft.  I refitted the alternator nut and fired up the engine with the case removed; and there was oil leaking/misting from the crankcase.  A compression test, cold throttle open, produced 124psi and 150 with a little oil in the bore.  I had left the oil in the bore for 4-5 days and freed off a sticky breather valve in the meantime, on running again the oil leak had stopped.

I cannot carry out another compression test right now as I have loaned the tester out to another club member.  Thinking I might have had a lucky escape I went ahead and have ordered a primary chain engine sprocket and complete clutch (the clutch is heavy compared to other B31s I have tried and is a 6 spring, from what I can gather it should be a 4).

Today I discovered approximately 0.9mm end float on the crankshaft, drive side, I take it that is excessive?  Does anyone know what it should be please?
I am now wondering if the crankshaft oil leak into the primary case was due to the excessive crankshaft end float whilst the engine was running without the alternator secured.

A big Thank You to everyone who helped me with advice at the Rally, a great bunch of people.

Mike

[Derek996]

When the alternator nut is torqued up it should pull the crankshaft up against the drive side bearing, so there will be no end float. The alternator engine has no crankshaft shock absorber so should have the 4 strong clutch with built in rubber shock absorber.

[Mike9]

Thanks Derek, That's a relief.

Do you know the torque setting for the alternator nut, I cannot find it anywhere.  Also, how I go about  aligning the engine and clutch sprockets?

[neil1964]

I doubt BSA ever stated a torque setting for 50s machines but 30 to 35 ft/lb would be about right.

The usual way to get the chain aligned is shims behind the engine sprocket between the spacer that fits in the recess in the crankcase.  Of course it is possible that you need to reduce the spacer thickness to go the other way but not typical.

Assuming that your alternator inner sleeve is not loose on the main part of the rotor (I've had a couple come loose requiring machining conical washers to clamp up) once you are happy with your chain alignment then I would thoroughly clean the threads with brass wire brush and carb cleaner, add a drop or two of loctite as well as a new tab washer and torque up to 30 ft/lb (my alternator Triumph twins were approx there).

[Mike9]

Thanks Neil,

I will check the alternator inner sleeve.  I am having trouble with the alternator tab washer.  The parts book shows 29 2024 tab for a plain nut, two suppliers I have tried show a tab with that number (picture hopefully attached) which is the correct dia for the shaft but without a protruding tang to lock it onto the cut-out on the crank shaft.   

Mike