Flathead V8 Crankshaft Stroking and Block Boring

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This information is from an old Badger Manufacturing Company catalog. This data has not been proofed for errors or inconsistencies so it is recommended that the reader verify the information with his rebuilder for accuracy on the build of the motor. The crankshafts listed below are for Ford & Mercury flathead V8's

Application Factory Part Number Standard Stroke
Ford V8 - 1932-38 68-6303A 3.75"  (3")
Ford V8 - 1939-42 91A-6303B 3.75"  (3")
Ford V8 - 1946-48 29A-6303B 3.75"  (3")
Ford V8 - 1949-50 8BA-6303 3.75"  (3")
Ford V8 - 1951-53 1BA-6303A  * 3.75"  (3")
Mercury V8 - 1939-41 99A-6303B 3.75"  (3")
Mercury V8 - 1942-48 29A-6303B 3.75"  (3")
Mercury V8 - 1949-50 8CM-6303 4.00"  (4")
Mercury V8 - 1951-53 1CM-6303  * 4.00"  (4")
* For the Fordomatic or Mercomatic transmissions. These crankshafts will also fit regular standard and overdrive transmissions. Has the larger pilot bore in the crankshaft flange. The 8BA crankshafts have the smaller pilot bore - used with manual transmissions only.

Stroking Information:

Mercury 1939-48 (99A-6303B and 29A-6303B) crankshafts can be stroked 1/8" (to 3-7/8") by offsetting the rod throws 1/16" when grinding. Throws should be ground to Ford Standard diameter (1.998/1.999"). These shafts when stroked can be used in 1939-53 Ford V8 and 1939-48 Mercury engines when installed with the Ford early type 81A full-floating rod bearings, and the Ford 21A or 91A connecting rods. The early Ford type (18-6200 and 48-6200) rods will also fit but are not recommended.

Mercury 1949-53 (8CM-6303 and 1CM-6303) crankshafts can be stroked 1/8"  (to 4-1/8") by offsetting 1/16" when grinding. The crankshaft throws should be ground to Ford Standard diameter (1.998/1.999"). These shafts when stroked can be used in 1939-53 Ford and 1939-53 Mercury engines when installed with the Ford early type 81A full-floating rod bearings and the Ford 21A connecting rods. These crankshafts can also be used (without stroking) in 1939-53 Ford and 1939-48 Mercury engines when a 4" stroke is wanted. In this case, it is preferred to use 29A-6200 Mercury connecting rods with early type Mercury full-floating rod bearings. You can also use 8BA, 8CM, and 0BA connecting rods and the insert type rod bearings.

The 8CM-6303 crankshaft was original equipment in 1949-50 models and the 1CM-6303 crankshaft in 1951-53 models. The 8CM crank can be used with conventional (standard) transmissions only. The 1CM crank can be used with both conventional and automatic transmissions from 1949-53.

The 8CM-6303 and 1CM-6303 crankshafts can be built up on the rod throws by welding so as to deposit sufficient metal to allow the throws to clean up when offset 1/8" while being reground. This will make the 4-1/4" stroke crankshaft.

Engine Block Boring Information:

The 1941 and earlier Ford V8 blocks are usually bored to 3-3/16" (3.1875") only.

The following can be bored to 3-5/16" (3.3125") * and even 3-3/8" * (3.375"):

1942-48 Ford (including 59-59A-59Z)

1949-53 Ford (including 8BA and 1BA)

1939-48 Mercury (including 99A-59-59A-59Z)

1949-53 Mercury (including 8CM and 1CM)

* Special Notation: Due to the age of these blocks, and the significant possibility of corrosion in the water jackets, it is strongly recommended that your block be checked for thin areas in the cylinder walls before any boring is done. This is normally done by sonic testing the wall thickness and even pressure testing the block for pinholes. The block should be totally cleaned and magnafluxed prior to testing for wall thickness.


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