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Old 04-19-2017, 10:15 AM   #13
JohnMc
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Join Date: May 2004
Location: St. Louis
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To the best of my knowledge, the internal castings are different on a B18, they didn't have an extra 3mm of metal there just hanging around through a decade of production waiting for the B20.

I've done a B20 piston rebuild on a B18 before, there was nothing to note in terms of issues. No overheating, no ballooned cylinder walls, only thing was convincing the machine shop it was OK to take that much metal out of a block.

I've done 2 B20 blocks up to B21 piston sizes. Same results as with the B18: no drama of any sort. The 2.1L B20 keeps cool with no issues in my PV with its small B16 radiator. Only issue was the same - reassuring the machine shop it was OK to take that much metal out of a block.

I have heard of rare cases where the internal voids were slightly out of position (core shift) and it caused problems in a large overbore like this. Might want to have the wall thickness checked sonically before boring it, if they're not fairly even you might not want to do it.
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