Has anyone tried Metzeler Block C tyres on a B31?  My 59 B31 has a non standard 18inch back wheel, I can get matching Block C, 19 front and 18 rear. 

Other option is Dunlop K70 front and K82 rear, Dunlop have advised me that they are a suitable match.

Maybe I should bite the bullet and go back to standard with a 19inch rear rim?

For info:  I had been trying for 6 months to find a distributor cap for my alternator 1959 B31, Distributor 18D1, part number for cap 424151.
I must have tried every parts shop and was getting concerned that I would not be able to source one.  A tip off led me to the 'Distributor Doctor' tel:01984 629540 (the advertise on the front page of the Old Bike Mart), they had stock and it was delivered a few days later at half the cost that others had been selling them for in the past.  Highly recommended!     

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