The Volumex engine I built for the Stratos replica had Vernier cam wheels. The scrapyard that removed the engine had hooked one of the originals to lift it out and, unsurprisingly, it broke... It was cheaper to buy the vernier wheels than pay a dealer price for a single cam wheel at the time!
So, I'm sat there one evening with the Stratos built up fully and, after an hour of thinking if there was anything I'd forgotten and looking around it I finally built up the courage to see if it would start. Well, it did but with one hell of a racket on the first turn of the key - not just the exhaust in a confined space but a metallic clicking I'd never heard from a twink. I turned it off pretty quickly and had a long hard look around it and found it pretty quickly - the timing pointers were being contacted by the cam wheels. Sorted with a ring spanner slid over the ends to bend the points away a few mm and it restarted perfectly!