Thread: 51 Ford flathead.

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I have a 51 Ford flathead given to me for work done and had it magnaflux with no cracks. problem is the cylinders are worn and my buddy who's a machinist whats to bore it .125 over. I've worked with flathead before but since I don't want to sleeve the clyliders, I think I'm asking for trouble with that much overbore. I was thinking of a .060 over with a 53 merc crank but he says a .060 over wont clean up the cylinders and .125 over won't hurt. Not being what you would call a true machinic for flatheads, what's your opion. This enigne will be using Edelbrocks heads, 2 new style 97's and a 3/4 cam.

These engines start life with a 3-3/16 bore and a 3-3/4" stroke (239cid) and can easily go to 3-3/8(usually, and some can go even more) - but I wouldn't if it's the first rebore. My last flathead went to 3 and 5/16 +.030 with a 4" Merc crank for about 280+/- cid displacement. The optimum is a "3/8 x 3/8" which is about 296 cid. With all that said, I would probably do the 3-5/16 which is your .125 overbore. It's safe and proven. Of course with that said, there still is the old rusty corroded/eroded water passage internals problem which may lessen the ability to go that far unless you have had a sonic check -

Good advice above. 3-5/16 will still leave room for a clean up in the future if needed. Get the sonic test if you can. It's well worth the money and will detect any core shift which could cause problems. Flatheads aren't cheap to rebuild so the extra caution is well worth it. What kind of cam are you looking at for this rebuild?

I have a Isky's 400 jr. but I don't know if that's what I use.