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Bearings & Bearing Bores

March/April 2007

The plain (explanation follows) bearings used in our Flathead Fords require certain elements for long service life. This is plain as opposed to frictionless like ball and roller. Among these elements are lubrication, cooling, and proper clearances.

Proper clearances depend on the bearings being correct for the application, the correct undersize for the crankshaft journal, and, sometimes, the proper oversize on the outside diameter for housings machined to a larger than standard inside diameter.

So what are the standard housing IDs inside diameters? These dimensions are not always easy to find today, 53 to 75 years after they were manufactured. Here are some that I have found or developed from bearing thicknesses and journal sizes.

Connecting rod big end bores

1932 1946 for 1.998-1.999" standard rod journals these rods use 48-6211 or 81A-6211 rod bearings, depending on crankshaft.

1939 1948 for 2.138-2.139" standard rod journals, these rods use 99A-6211 rod bearings.

1948 1954 also for 2.138-2.139" standard rod journals, but with two oil holes per journal, these  rods use 0BA-6211 rod bearings.

1937 1939 V8-60 for 1.598-1.599" standard rod journals, these rods use 52-6211 rod bearings.

1940 V8-60 for 1.698-1.699" standard rod journals, the rods use 92-6211 rod bearings.

1936 1941 Lincoln V-12 for 2.125-2.1255" standard rod journals.

1942 1948 Lincoln V-12 for 2.250-2.2505" standard rod journals.

1947 1951 H series 6 cylinder for 2.2980-2.2988", rod journals.

1952 1953 OHV 215 CI 6 cylinder for 2.2980-2.2988", rod journals.

That is about it for rod bearing housings, also known as big end bores.

How about main bearing bores?  Yes, we need to know those dimensions also. If the machine shop needs to line bore or line hone your block, they will need to know.

1932 mid 1936 standard main journals.  These main bearings are poured in place and line bored after, to whatever the crankshaft main journals were reground to.

Mid 1936 1938 for standard main journals 2.398-2.399".

1939 1953 for standard main journals 2.498-2.499".

For the above, use the correct bearings for the year block in the correct undersize for the crank main journals.

1937 1939 V8-60 for main journals standard at 1.998-1.999".

1940 V8-60 for main journals standard at 2.098-2.099".

1936 1948 Lincoln V12 for main journals standard at 2.4000-2.4005".

1947 1951 H series 6 cyl for main journals standard at 2.8732-2.8740".

1952 1953 OHV 215 CI 6 cyl for main journals standard at 2.4980-2.4988".

Do camshaft bearing bores matter?  Yes they do, and Ford made them at Standard, +.015" and +.080", with bearings larger on the OD (outside diameter) to match.  Standard OD cam bearings are also available at +.010, .020, and .030" undersizes for cams that have had their journals reground.

1932 1954 21 and 24 head fastener engines have cam journals standard at 1.796-1.797", and standard bearing bores.

V8-60 I have only the cam journal size at 1.497"

Lincoln V-12

1941 1946 G series 6 cyl standard cam journal 1.796-1.797" standard bearing bores.

1947 1951 H series 6 cyl standard cam journal 1.9265-1.9270" standard bearing bores.

1952 1953 OHV 6 cyl standard cam journal 1.926-1.927", standard bearing bores.

Wow, that's a lot of numbers.  Some of them may help you or your machine shop. I have found mistakes in many of the bearing catalogs, and there may be mistakes here also. If you see any, please let me know so I can correct them.

Some points to remember the bearing housing bores must be correct to provide the proper bearing crush. This tight fit helps insure heat transfer from the bearing area to the block and the cooling system, in the case of main and cam bearings, and this is required for long life.

The correct bearing bore size also helps insure correct clearance between the bearing and the shaft that it rides in it. This is necessary for any bearing life (lack of correct clearance is sure death).

If you have an oversize housing, find and use an oversize OD bearing.  That way you keep having fun with your old Fords.

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