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MG MGB Technical - Standard or oversize

I have just removed the pistons from my 76 B and it looks as if they are standards (big end shells as well) As the car has 96000 on the clock and was running reasonably but loosing a lot of oil I took the engine out to try to stop the leaks.

Where are the oversize markings on the pistons and shells???

My pistons have a number"53480"(or so)under that
" Front " and in the middle
"A" or
"B"

The shells have the makers name and some other numbers

Thanks in advance

Jim
Jim

Jim. The pistons I have seen were marked on the crown if they were oversized. The markings A and B were, as I understand it, only found on the factory pistons. At 96K miles, with modern oils and frequent changes, the engines I have examined showed very little cylinder bore wear and the crankshafts were often not in need of turning. I suspect everything is probably original on your engine. Whether it should remain that way needs to be checked out by a machinist with the proper tools to measure the crankshaft journals and cylinder bores. Les
Les Bengtson

Definitely get the block and crank checked by
a machinist. My car with only
50K miles had significant bore wear. I think the
previous owners just left it out on the street
in the Los Angeles area and never changed the oil.
The crank was in perfect shape (consistent with
the assumed 50K miles.)

Lack of oil changes causes the rings to harden,
bore wear, and resulting heavy oil consumption.
Your excessive oil leakage could be due to
"blow-by" past the rings, causing crankcase
pressure to build up.
Ronald

I would go for the smallest over bore possible but I would get High compression pistons
Ross

Hi Jim The oversize marks can be found on the top surface of the pistons eg +.020 meaning that the pistons are +.020 oversize. The A. B. C stand for the grade of piston fitted. Stock pistons at the factory came as a stock size, but due to the factory limits and fits (where things manufactured in mass pruduction can vary a little) each piston was matched to a bore to make it as close to the correct running clearance as possible. Chose the smallest increase in bore size that you can get pistons for. Or as a alternative go for some performance increase and increase the engine size to 1950cc for example, the amount of work undertaken to do this is the same in both instances, the cost increase is also negligable if at all different, if you shop around for the pistons some good deals can be found. Beware with the large bore conversions these can be problematic if you do not take care.
John

This thread was discussed between 04/05/2002 and 05/05/2002

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