University Motors Limited, Ada, Michigan

University Motors Limited

Goldstar Products

Technical Assistance

6490 East Fulton
Ada, Michigan 49301
616.682.0800

MGB 3 Main Engine

I decided to put a 3 main MGB engine into my 1960 MGA. The MGA's 1600 engine is bored 0.40 over and has liners, and I was scared to eyebrow the block to enable use of a modern flowed cylinder head on the engine to get more power.

I've never worked on a 3 main MGB engine before. I bought a used shortblock for $100. When I got home with it and cleaned up the tops of the pistons, they look eerily like factory pistons! They are stamped MOWOG in the middle, with "Front" on the front side. They have a "3" stamped on the far side. Does this mean that these are 0.30 oversize? Does this mean that they are the original pistons and the block hasn't been bored out yet (which I find hard to believe)?

The pistons were originally sized at 3.160 inches. That number, stamped on the top (and stamped on the top of the block sometimes -- if you look carefully) is the number of ten thousandths oversize. The number is sometimes inside a rhombus. The blocks were bored and hone then measured. The pistons were spun and measured. The bores were not all the same size -- nor were the pistons. This marking allowed the factory to get the best fit. It is meaningless today.

The MGB block will work just fine for you. Consider using Pete Alberta's rear main seal -- it's very expensive, to be sure, but it is a positive seal. Otherwise, ensure that your machine shop align bores the main caps.

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