Cracked crankcase.

In the big wide opens the moderns can pull longer to higher top speeds but in the con-testing conditions of judging and handling speed into and out of turns with running up to 100-ish in between, moderns feel like peddle bikes to me and they lose some ground on each shift while a geared up Cdo can stay in an 850's 2nd ratio from upper 30's mph to upper 80's or more. Its saves engine strain some but eats up lay shaft bushes for clutch wobbles. Geared high though does make starting off in 1st more of a control commitment if not on pavement. Less worry-need of slipper clutch though on let offs so rear don't tend to skip and hop off surface.

If was mine and not ruining like hard heated racers into 6000's for long periods, I'd grind out and JBW to seal crack then plate over the DS, fit the JMS piston/rod kit, rebalance crank [after its cryo tempered] and make some more extra windy memories for another decade+. If running like wasteful racers might consider just the DS Maney case and steel fly wheel.

When using stock pistons I was cracking cases & cranks when racing because I was reving the 850 until the valves floated. I went for the case reinforcement and added an outrigger bearing for the tranny because the shafts were flexing so much that the gears were wearing at an angle. Heavy cases won't keep the rest of the bike from cracking. I remember a DNF at a national race because the wires to the ignition cracked. Out of desperation I made my first lightweight pistons and the problem was solved - no cracks since.



the first lightweight pistons - approx year 1986



below see radius cut into PTO shaft to prevent cracking

In a different location, but also a cracked crankcase. Noticed this while swithing camshafts. Explains some of the oil leaks lately. The other leak was from a cracked oil tank - also not in the normal place as it was at the threaded area where the intake screen fits. Now need to find a good aluminum welder.

Good Luck on the weld.

Its a shame Matchless didn't develop their twin cylinder motor more and/or use a centre main bearing on Nortons. This would seem like a logical step. There again, from the sixties onwards the British industry was anything but logical.
The rad. cut into the drive side crank looks like a very good idea & maybe would have saved my previous crank from breakage. Wouldn't have saved my 650ss crank though. It snapped through one of the big end journals. Luckily the rod held it together & saved the shrapnel shower. It was over 30 years ago & I can still remember the noise it made!

Matchless had no end of troubles with that centre main bearing - and eventually scrapped that idea and went with Norton engines, they were way better !
Norton engines had a good record of winning, and Matchless (twin) engines well, um, ah......