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MG MGB Technical - 5 bearing pistons in a 3 bearing engine?

I have just bought a 3 bearing engine to fit to my 54 Magnette. This engine appears not to have been reconditioned before (pistons have MOWOG stamped on them and no ovesize number). 3 bearing pistons are quite expensive. I was wondering if cheaper, later pistons would fit. Can anyone help?
phil may

I think there are issues with the small end wrist pins. Press fit vs. fully floating. So then the rods wouldn't fit.
Paul Hanley

Hi Phil

The 3 bearing engines (18G, 18GA)have a 0.75" diameter gudgeon clamped in the conrod.

18GB engines have a fully floating gudgeon 0.8125" diam.

18GD onwards have a 0.8125" gudgeon with press fit in conrod.

3 bearing and 5 bearing conrods are not interchangeable because of different big end offsets.

If push came to shove, you could have later pistons fitted with bronze bushes, but you will still need to get servicable gudgeon pins. This may not be economical though.

Ian F

Ian Fraser

3 bearing pistons - 5 ring design (County brand) at 120 the set.
Chris at Octarine Services

Use the 3 bearing pistons, its the cheapest way.

mga twin cam conrods allow five bearing pistons to be fitted to a three bearing engine BUT they are rare and expensive.

John Prewer

This thread was discussed between 13/04/2005 and 15/04/2005

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