Thread: 59A Ford flathead

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From my recollection the early Mercury flatheads in '39-'48 were the 239 cu. in. 3 3/4" stroke x 3 3/16" bore with 24 studs while the 24 stud Ford V8s of '40-'41 were 3 3/4" stroke but only 3 1/16" bore. After WWII the '46-'48 Ford V8 and the Mercury V8 were the same 3 3/4" stroke x 3 3/16" bore. In 1949 through 1953 the Ford V8 remained 3 3/4" stroke x 3 3/16" bore but the distributor was moved to the top front and the water inlets to the heads were moved to the front upper corners, BUT (!) the 1949-1953 Mercury V8s got stroked to 4" with the same 3 3/16" bore. The hot rod bonanza was that the Mercury 4" crank, rods and pistons can be retrofitted without any grinding into the earlier 24 stud blocks whether from Ford or Mercury. Further boring to 3 5/16" or even 3 3/8" was often done along with the usual chance of thin cylinder walls and overheating. Therefore if you have a block with "59A" on the bell housing, it was originally a 3 3/4" stroke with 3 1/16" bore but if you can find a 4" Merc crank (I have one for sale, contact me) and rods you can upgrade to a stroker just with replacement of the crank and rods along with the pistons which have the proper pin placement. A warning should be that you really ought not to bore the cylinders any more than is necessary for a cleanup to roundness since the cores at the factory were not overly straight and you could over bore and end up with a motor that overheats easily. Another problem is that if/when the overheating occurs there is a strong possibility that block cracks will develop between the cylinder wall and a valve pocket. Often the engine will still run with such a crack but the coolant will mysteriously disappear as vapor through the crack but when the crack gets large enough, water will fill a cylinder and then real hydraulic damage can result. Some people say they can repair such cracks and maybe in some cases that can be done but it may be a matter of luck if such repairs can be made. One way to look at this is to recall the additional torque from a SBC 383 due to a 3 3/4" stroke so the 4" stroke of the flathead is pretty good although it will take some expensive porting and relieving to get over 200 HP, maybe 250 H.P is realistic with a 4" x 3 5/16" flathead and other speed parts.
One addendum is that the Merc 3 3/4" x 3 3/16" block probably goes back to 1939 but I am not sure whether the Ford 3 3/4" x 3 1/16" block goes back to 1938, but I am sure that is right for 1940-1941. Another consideration is that the block has only three bearing webs and that the two middle cylinders on each side share the same exhaust port through the block which tends to heat the middle of the block more than the ends and this can also lead to cracking. Still the engine was quite hardy in stock form and would really take a beating, but probably overboring ruined a lot of blocks over the years.

Don Shillady
Retired Scientist/teen rodder