so a friend of mine put m52b28 pistons in a m50b25 block with the full m52b28 guts. after 1500 miles while driving hard the pistons got stuck in the engine. i did the same thing my engine ran about 3-4000 miles with no problem. my friend told me that there are 2 different piston sizes for the m52b28 and that he got the bigger ones, i asked him if the piston was a repair piston +1 and he did not know to tell me. im asking you if there really are different piston sizes, could the same thing happen to me? in europe m52 have alu blocks and m50 iron. i thought that all 2.5 2.8 pistons are 83,980mm. what tolerance should there be between the block and piston?
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well there is an aluminum block m52 here in the US but that was was a rare case, i believe the 2.8 z3 came with aluminum block also there is also the m52b28TU or TUB which also had an aluminum block and was used on e46 and e39 2.8l engine i believe. do some more research and im sure some other guys will have some input in a bit, but if you can read the top of the piston it will normally tell you the bore. also if he used oversized piston rings that can also be an issue i believe.Originally posted by evandael -
I find it hard to believe that you would be able to run normally with too big of a piston for 1500 miles. Sounds like an oil problem if your piston is stuck or something is broken
Did you check the end gap on the rings? Did you use new, correct piston rings? Were the cylinders machined to each piston?
83.98mm sounds correct for the 84mm bore.
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totally possible. Almost lost one building mine. i suppose if a main bearing was in the wrong way it would do just about the same thing, blocking oil from getting to the squirter at all.
my point though is that if the piston was the wrong size i dont think it would have run for 1500 miles, it wouldnt have even broken in properly. For a piston to seize like that it would most likley be an oil problem. OP, i would have a long talk with whoever built this engine for you or your friend.
also, unless your block was bored, you would not be able to fit the repair piston in. the smallest +1 piston is 84.23mm.Comment
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do all european m50 have oil squirters like us?Comment
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There are 2 different piston sizes - I recently put together a 2.8L with M52B28 rotating assembly in a M50 Iron block. My M50 pistons were 83.98mm and the M52 pistons were 83.99mm.
I doubt that you would have been able to assemble it with the bigger pistons in an M50 block - when I went to put it together, i sat a piston on the top of the bore and there was no way in hell it was going to work - ended up boring block to match the 83.99mm pistons.90 318i M62B44 OBD1
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