I recently came across another M20 cylinder that has cracked. Like the two previous examples I have had the cracks were near the exhaust valve, one running from the liner to the valve seat.
Has anyone else had similar cracked cylinders?
These are just 'hairline' cracks...not easy to see...so if you are working on an M20 currently, or buying parts, it may be worth taking a close look....Ian

email (option): julie@wright52.plus.com

I have only had that with a 1933 side valve Sloper BSA, I had it welded and had a valve seat placed. The bike has done quite a few miles after this fix, This might be still to expensive to have done with an M20 cylinder.

Henk

email (option): ahum@quicknet.nl

Hi Ian, had the same problem with my M20. A local engineer fitted a seat insert. The cracks are still there, but the insert has never come loose or moved. This was at least fifteen years ago now.
Cheers. Mick.

email (option): mick@motorbikemike.org.uk

mick was the original seat cracked

email (option): roger.back@node6.com

Hi Mick...I have also found that fitting a valve seat insert provides a long term fix...Ian

email (option): julie@wright52.plus.com

Hi Roger, yes, one crack ran from the cylinder wall, the other from the corner head bolt hole.
Cheers, Mick.

email (option): mick@motorbikemike.org.uk