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Oversize pistons, what is "oversize"?

Old 03-Aug-2005, 11:09 AM
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Question Oversize pistons, what is "oversize"?

Been reading some tech here and there. Increase the stock bore from, say, 75mm to 75.5, 76, 77, and what not. Then they talk about using stock oversize/overbored pistons.

So my question is, is the actual piston bigger in diameter or what makes the piston bigger? Bigger piston rings to fill up the gaps of a bored cynliner?

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Old 03-Aug-2005, 12:25 PM
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The outer diameter(OD) of the piston must reflect the inner diameter(ID) of the bore size, minus some clearance.

Oversized pistions must be installed with rings manufactured for that specific pistion size and as always your ring endgaps have to be set.

Piston to bore clearance specifications differ from engine to engine but correct me if I'm wrong it is usually around .001"-.002"

There are experts on this board that will give a better answer than I, but I believe I'm in the ballpark with this one.
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Old 03-Aug-2005, 01:26 PM
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So basically, an oversize piston requires an oversize bore...right?
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Old 03-Aug-2005, 01:46 PM
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honda offers one stock oversize piston for rebuilds. the actual piston is larger than the stock bore, so the cylinder block needs to be machined (bored out) and then honed to accept the new larger ristons and rings.
this machining is critical if it's not done by a pro like Steve_Leitner then the cylinder walls may end up tapering, or not being parallel, or the bore centers being off center, or not being square to the crank journals, etc, etc...
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Old 03-Aug-2005, 03:31 PM
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So the actual piston is larger, I see. Thanks
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