After having issues starting the bike and trouble shooting for about a week, it turns out the engine has really sad compression readings. Double checking the carbureter settings, valves clearances and camshaft positions wasn't a fun time, then I found the ignition leads were badly corroded and replaced those with a spare set (a positive in hindsight) but it was a leak down test that revealed there was more than 80% leakage through the intake valves, which suggests something along the lines of bent valves. Considering it was running (albiet roughly) a year ago I would put it down to my own error at some stage while doing the clearances and not prior damage from the crash. One thing that does come to mind was that the torque wrench used was 1/2 inch and exceeding it's accurate range for the low torque settings on the cam holders.
Head rebuilding for an MC22 engine is more complicated than larger motorcycle engines and fairly costly when compared to buying a second hand engine. Thankfully sourcing a second hand motor wasn't too difficult, picked it up one afternoon and had it in the frame within an hour. These motors are bulletproof and will happily run past the point where the odometer resets but they need a lot of care when touching internals, something that will definitely be kept in mind when it's time to do the valve clearances on this second motor.
Huge thanks to Riley Duddles for providing a second hand engine and Rob Fry for lending his time, knowledge and workshop for a leak down test on the original engine.
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