I have spoken in the past to Autocycle engineering, he has taken over Alpha from Max Nightingale after his death. He said that the one piece crankpin are ok on the 350 engine, but not on the 500. He has never heard of one snapping on the 350 but has on the 500, the biggest problem that he highlighted was that they are now available in oversizes to compensate for worn flywheels and does them in oversizes, from experience I’d suggest if yours feels loose in the flywheel to send it to him to have a pin made to suit. They should really go in with a crack as they press in (yes, that tight!) from my experience the holes are not totally round and you may have an issue getting the pin to go in straight without peeling back some of the metal in the hole and causing problems trueing the crank. I do lots of cranks but these can be problematic if you get it wrong. So reluctantly I’d suggest getting them to fit it. I believe he does both types of pin, both one and two piece.
Rode my '52 G80 to Tuscany, keeping under 60. Back in UK at 73 the crankpin exploded out into the world, just missing my leg. Built up another bottom end & sold the bike. Apparently it did it again. Nearly 40 years on I'm amazed Alpha are still selling that part. It's not fit for purpose and dangerous. Unlike Bullets there's too much flex in the early AMC big end assembly. As far as I remember AMC beefed up the bottom end in '54 but I don't know if they changed the big end. I'd had that bike as sole transport for 12 years. I used to rebuild the engine once a year. Never had a part actually break until we ran out of OEM pins. I'd say AMC had the weakest engineered bottom end of all brit big singles, that is until they belatedly added a norton pump. That's a lovely engine.
My pals Matchless 500 inconveniently broke its crankpin just after leaving Skye during a 2,500 mile trip around the Scottish mainland and islands...It was a long ride back to Devon with the AA for him:frowning:..and my tour became a solo one on the B33...Ian
