Choice between 2, 239's
Cargo Master
Joined: Aug 2010
Posts: 2,927
Likes: 135
From: Houston
Tell us more about those two weeks of running before you decide to put the engine out to pasture. Did you run the motor many times for short periods, say less than ten minutes each time? Did you change oil at the start of the two weeks? Did you check oil during those two weeks?
Definitely check piston stroke. Get a piston at the bottom of its stroke and drop a ruler down the bore. 3 3/4 inches is 239 Ford crank, 4 inches is 255 Mercury crank. If the camshaft appears to be in decent condition you may want to go through the pain of getting it out of the engine.
Something else that is a red flag to me is the outside of that "51 Merc" engine. The exhaust manifolds, crank pulley, water pumps, and oil pickup all look to me like Ford truck, not Mercury.
Definitely check piston stroke. Get a piston at the bottom of its stroke and drop a ruler down the bore. 3 3/4 inches is 239 Ford crank, 4 inches is 255 Mercury crank. If the camshaft appears to be in decent condition you may want to go through the pain of getting it out of the engine.
Something else that is a red flag to me is the outside of that "51 Merc" engine. The exhaust manifolds, crank pulley, water pumps, and oil pickup all look to me like Ford truck, not Mercury.
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Tuned
Joined: Dec 2017
Posts: 353
Likes: 6
From: Arkansas
It still rotates and according to the book of you can put your pinky in the hole of the crank it is a mercury and if only a pencil will fit it is a ford. Pinky fits in just fine,L
If you know someone looking for this crank it would be appricated if you forwarded the info
If you know someone looking for this crank it would be appricated if you forwarded the info
Cargo Master
Joined: Aug 2010
Posts: 2,927
Likes: 135
From: Houston
I know lots of people who would like a 4" Merc crankshaft, including myself. However, if you are building a flathead you should consider it for your needs. There is no replacement for displacement, as the saying goes, and the Merc crank equipped flathead adds a bit of pep that is quite nice for most driving.
Fleet Owner
Joined: Jul 2004
Posts: 27,299
Likes: 1,059
From: NM
No substitute for measuring the stroke, there are lots of shortcut ways to ID Merc cranks but too many exceptions for it to be reliable. For the crank to be worth anything it has to be in good shape and able to be ground another time.
Cargo Master
Joined: Aug 2010
Posts: 2,927
Likes: 135
From: Houston
Turn the crankshaft until one of the pistons is at the bottom of its stroke, all the way down. Use a ruler to measure the distance from the top of the piston to the deck of the engine. About 4" is Merc, about 3 3/4 is Ford, anything else is questionable in an engine that looks unmodified.
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Tuned
Joined: Dec 2017
Posts: 353
Likes: 6
From: Arkansas
My eyeballs are not calibrated but put a tape measure to it and it comes out a shade under 4" probably closer to 3 3/4"
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