Model A & B

Ford Garage

Rear Main Bearing Caps

This page details the evolution of the Model A and Model B engine rear main bearing caps.

Part
Number
Material Usage Notes
A-6327-A Steel Forging Rear Main Bearing Cap
1928 Model A and AA engines
5/16" diameter A-6321-A drain pipe
3-5/8" length A-21214-A bearing bolt
A-6327-A Steel Forging Rear Main Bearing Cap
1928-29 Model A and AA engines
5/16" diameter A-6321-A drain pipe
3-5/8" length A-21214-A bearing bolt
A-6327 ? Rear Main Bearing Cap
March 1930-31 Model A and AA engines
3/8" diameter A-6321-B drain pipe
? bearing bolt
A-6327-B Malleable Iron Casting Rear Main Bearing Cap
April 1930-31 Model A and AA engines
3/8" diameter A-6321-B drain pipe
4-3/16" length A-21214-B bearing bolt
B-6327 Malleable Iron Casting Rear Main Bearing Cap
1932-34 Model B and BB engines
3/8" diameter B-6321 drain pipe
4-3/16" length B-6344 bearing bolt
A-6328-A Pipe and Ball 5/16" diameter drain pipe assembly
With ball check valve
Released for Service 1928-30
A-6328-B Pipe and Ball 3/8" diameter drain pipe assembly
With ball check valve
Released for Service 1930-31
B-6328 Pipe and Ball 3/8" diameter drain pipe assembly
With ball check valve
Released for Service 1932-34

Early and Late Forged Steel Bearing Caps

Early 1928 bearing cap on left courtesy of Rodney Gage

Typical 1928-29 forged steel rear main bearing caps are shown above and below. The early 1928 cap on the left has less material around the bolt holes as indicated.

Both forged caps use a 3-5/8" long bearing cap bolt. Early rear bolts had a square head similar to the front and center caps, whereas later rear bolts had the typical 'D' shaped bolt head used through 1934.

Early 1928 bearing cap on left courtesy of Rodney Gage

The pic above shows the reduced material and strength around the bolt hole of the early forged steel cap on the left versus that of the typical forged steel cap.


Model A Steel Forging versus Malleable Iron Casting

Above and below is a comparison of the Model A forged steel bearing cap on the left and the cast malleable iron cap on the right. Note the larger diameter pipe and the longer bolt used with the later malleable iron bearing cap.

Also note the differing shapes of the caps on the forward side.


Model A versus Model B

Above and below is a comparison of the 1930-31 Model A bearing cap on the left and the 1932-34 Model B cap on the right. Note the increase in bearing diameter and cap size and the decrease in the pipe length of the Model B cap.

The Model A main bearing size is 1-5/8 inches diameter, whereas the Model B size is 2 inches diameter.

Also note the two small oil supply notches cut into the Babbitt thrust face on the Model B cap.

Both caps use the 4-3/16" long bearing cap bolt.

The rear slinger of the cap is much larger and fits the crankshaft closer on the Model B design to better control oil loss out the back of the bearing.

The Model A cap on the left has only a single helical oil groove, whereas the Model B cap has X-shaped helical oil grooves. The Model B oil grooves extend forward into the thrust face notches, compared the the Model A groove which terminates in the oil well along the side of the journal.


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October 2017