Thanks for this. As I have removed the barrel, what is the best way to tighten down the one difficult nut that holds the barrel to the crank cases. I cannot seem to get a socket on it or a spanner. Do I grind/flat a good spanner?
A good quality ring spanner has always worked for me.
Do you have the correct nuts?
The correct nuts are reduced hex and slightly taller, "normal" nuts won't permit the use of a ring spanner.
There are many old bike situations where the use of sockets is impossible, when these things were first conceived, the socket had not been invented, let alone in widespread use.
Yes I always manage it with a combination spanner, by little nips and sometimes by tipping the spanner up to the widest gap further up the mag to get enough turn to get the spanner on for the next bite. BSA actually made a special cranked spanner for the job. Ron
The M20 collets do look odd when fitted if you are used to OHV engines. In the past the exhaust valve and seat in particular needed fairly regular attention and with the barrel in place on the cases there wasn't the benefit of gravity when it came to replacing the collets...So it was all to aid replacement in that particular circumstance..I have to admit when in short supply for OHV motors I have removed the M20 'extensions' and converted them for use in those types....Ian