I was supposed to meet my brother on his M21 combo at the Onslow park vehicle rally at the weekend but he rang me to say he'd broken down, so when he got back he stripped it down to reveal the following! He dropped the motor off with me on Tuesday evening and it was ready on Wednesday evening complete with redone crankshaft. The only thing I coudn't get done was his barrel as we had no piston, but I rebored it just undesize of the nominal size for +0.060 (as the broken conrod had been hitting on the bore) So basically we're just waiting on a piston.
What was interesting was that his M21 pulls a huge triple adult sidecar and is in daily use as his only means of transport and has covered in excess of 150000 miles and has been on the road pretty well non-stop since the 1980's. So it has served him well. A couple of years back I did the Harley big end roller conversion to it when it had a bit of play in the big end so it gave me an opportunity to check all was well with it and it showed absolutely no wear at all, so I guess the conversion does work fine!
email (option): davmax@ntlworld.com
A rare occurence with the M20/21..I would say your brother was lucky to get away without righting off the barrel. I have just taken delivery of a Carrillo rod for the M20 sprinter...I really didn't fancy trying to do over 100mph with the standard one in case the same thing occurred!. Years back I bought an M21 off an old boy who had owned it from new and it had never had the bottom end stripped in 106,000 miles...Tell that to kids today (or Norton owners) and they don't believe you....
...Ian
email (option): ian@wright52.plus.com