I was able to cut a 3/8 by 24 thread in the crank end but I'm afraid it wasn't strong enough and I'm having to re-tap to the next larger 7/16 by 20, as the factory did on later engines. I'm having trouble getting the tap started even after drilling the hole out with my 3/8ths bit. I hesitate to use anything larger, because it'd be a 7/16ths and that won't work if I want to thread a bolt in, that size. Is there a secret to getting a tap started? Crank steel is anything but mild!