The crankcase stud at the front of my Comet engine just below the barrel (the one which also holds the tab to attach the top of the mag cowl) has damaged threads where it protrudes from the crankcase, and consequently the nut will not tighten. Looking at the parts diagram, there are 2 types of stud, the early one (ET109/3AS) appears to be a bolt which goes right through from the timing cover, the later one (ET109/13 is a plain stud into a blind hole. To avoid unnecessary dismantling of the timing cover, can anyone tell me if my '51 Comet would have the earlier or later one at engine number 66**? It has a slot in the end so I am guessing it is the later one. I have tried (gently) unscrewing it but it won't move. On confirmation that it's the shorter stud I will weld the nut on it and hopefully it will loosen with a spanner.