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Ok two questions in one sort of. When u buy pistons for a rebuild, (at least the ones i got) the casting is rough in the combustion area. Would it take away from the compression if i were to polish them smooth? Or should they be left the way they are.

Secondly, knuck / pan oil pumps. Are original pumps any good or is S&S the way to go. I only ask because in most of the catalogs it says to install an S&S pump on 36 - 72 cases, the cases require drilling for newer style pump.
 

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polishing a piston will help it reflect some heat back into the chamber.
so long as you do not remove 0.010" of material from the top I would not worry about the compression loss.
A quick sand and buff will help cut down on carbon building up and might lower the oil temps slightly.
polishing the chamber and exhaust port will also help keep an engine running cleaner with less carbon building up and slightly cooler

if you have an iron pump that is in good shape, there is no reason to not run it on a pan or knuck.
the S&S pump can flood the top end of a knuck pretty easy, pans are not as bad about it.
 

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dan r said:
polishing a piston will help it reflect some heat back into the chamber.
so long as you do not remove 0.010" of material from the top I would not worry about the compression loss.
A quick sand and buff will help cut down on carbon building up and might lower the oil temps slightly.
polishing the chamber and exhaust port will also help keep an engine running cleaner with less carbon building up and slightly cooler

if you have an iron pump that is in good shape, there is no reason to not run it on a pan or knuck.
the S&S pump can flood the top end of a knuck pretty easy, pans are not as bad about it.
I agree with Dan, most people feel the need to have high oil pressure but Harley at least on the early ones specifically used roller bearings in the crank and cases because they (roller bearings) will take extremly high loads and require only a film of oil to prevent galling. The stock oil pump is fine as long as it's to spec.
 
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