Thread: crack in flathead engine

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Well the best thing about the '51 Merc is the crankshaft and the rods that go with it. Have that cleaned up and make sure you use the right pistons for the longer throw and you will have one very torquey flathead. I guess you know not to overbore too much because of the possibility of core shifts and thin spots which lead to overheating or worse. If the block is the standard bore of 3 3/16" and only needs a cleanup by 0.030", do that and don't tempt fate by going to 3 5/16"; the added stroke will really give the torque a boost and maybe you won't have to worry so much about overheating. I envy your project, you can end up with a nice closed car for year round driving and still enjoy the fat-fender era. I had a '47 Ford convertible in High school and dechromed it, painted it Aztec Red with wide whitewalls and had a mildly rebuilt flathead. It was fantastic for cruising but beware the standard translmission is fragile. Sadly I sold mine when I broke the tranmission for the third time but I should have kept it and saved it until I could get a stronger trans like a packard floor shift, but then of course the SBC era began and flatheads went into decline. Well have fun!

Don Shillady
Retired Scientist/teen rodder