I never knew that. I would suppose that many blocks that could have been bored to make a 425 were made 401 instead at the factory. Perhaps by knowing the code cast in the rear of the block, you could overbore one to a 425 without having to worry about thin cylinder walls. I can't see how a balancer could be different from a 401 to a 425 when they both have the same stroke. But I guess anything's possible. I learn something new every day here on this website.
Well the blocks are different so you dont have extra thin walls. the balancers were supposely difference due to the difference in weight of the pistons(but this is just one story) some swear they have personally seen the problems caused by a 401 balancer in a 425. others say they never had ..... I am going thru all this right now. Cause I have a MT with a rectangle so I think its a 425. And I am buying harmonic balancers that came off an unknown engine (401/425). So if it vibrates then I will be in a pickle.
Mine cost $200. It has never ran so smooth. Harmonic vibrations can literally shake a motor apart. If you want it to last a while, do it.:bglasses:
