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There are three principal blocks to consider. LEFT, Austn and early Bantam. Middle. Bantam 2Main. Right. Bantam three main. Norm Booth was kind in setting out the differences for us.

1. LEFT. The American Austin, and very early 1938 Bantam cylinder block is part number D-1347. This casting number is visible in raised letter and numbers on the left (driver's side) of the block. The American Austin series A (1930 to1932) and the series 275 (1933) cars had the L type engine with the gear driven generator. The D-1347 block for these engines had 45 degree valves and seats.The 1934 series 375 and 1935 series 475 American Austin D-1347 cylinder block had 30 degree valves and seats and used a V belt drive generator.

2. Early 1938 Bantams used the D-1347 block with 30 degree valve seats.

3. MIDDLE. Most 1938 Bantams used the D-6853 cylinder block with 30 degree valve seats. The D-6853 casting number is in raised numbers on the left side of the block. You have to closely inspect the numbers since a casting flaw makes the numeral 6 look almost like a 8.

4. Some 1938 Bantams, and most 1939 Bantams used the D-7888 cylinder block with 45 degree valve seats.

5. It is not clear when the various 2 main Bantam cylinder blocks were phased in and out.

6. According to the Bantam Factory Material List Book (this is a 363 page 11 inch by 17 inch book that I obtained several years ago from the late Roy and Betty Beagle) the D-1347 cylinder block was used as a "service replacement" for all American Austins and 2 main Bantams. The major difference between the D-1347 and the other 2 main blocks has to do with the number of studs that hold the cylinder block to the aluminum crankcase. They are interchangeable, but the added hold down studs on the later 2 main blocks were added for a reason--- apparently to make the block more secure to the aluminum crankcase. D-1347 blocks are still around in numbers, so it would not be prudent to put a Bantam 2 main block on a American Austin. The Bantam blocks are getting few and far between.

7. All American Austins and 2 main Bantams had a nominal 2.2 inch bore and 3 inch stroke. The height of the cylinder block 4.810 to 4.812 inches. The intake and exhaust valves were all the same size with an opening of .890 to .900 inches.

8. RIGHT. The Bantam 3 main block (starting with engine number 65500) has a part and block casting number on the left side of the block and is D-8831. The nominal bore was 2.260 inches and 3.125 inch stroke. The height of the block was 4.875 to 4.883 inches. The number of holes for crankcase retaining studs was increased from 8 to 10 from the prior 2 main Bantam block. The valve seats are 45 degrees. The intake valves are larger than the exhaust valves. Intake valve opening .995 to 1.005 inches. The exhaust valve opening is the same as the 2 main engine at .890 to .990 inches.

9. The D-7888 two main block, as well as the other earlier blocks, can be fitted to the 3 main crankcase providing a spacer is used between the cylinder block and the aluminum crankcase. Not authentic, but perhaps another Bantam back on the road.

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