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post #70 of (permalink) Old 06-15-2007, 09:41 PM
DennisW
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Quote:
I will also add the reason you want to vary your RPM's during break in, is to prevent the pistons "reaching" to the same spot in the cylinders, as this can create a small ridge in the cylinder that when the piston reaches past that point, the rings can chip.[/b]
Well in many years of building cars and engines I have to admit that's one I've never heard before.

If your pistons are reaching different points at TDC dependent on RPM you better find some connecting rods that aren't made out of rubber.
Sorry, but that's an absolute falsehood.

And eventually a ridge will form at the top of any cylinder bore, the top ring land on the piston isn't exactly at the top and in most engines the piston's TDC is slightly below the deck anyway. Add those tolerances together and you'll have a certain area at the top of the bore that the top compression ring will never reach to, thus forming a ridge as the rest of the bore below it wears from ring contact.

But trust me, they always travel the same distance in the bores.

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