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Message: [QUOTE="RM_guy, post: 430789, member: 20652"] I’m just going to ramble on with some thoughts. This is usually a misunderstood topic and I’m glad to see it being discussed. Just because the plating and base material of the inner tubes are hard materials doesn’t mean that the surface finish is smooth. And you don’t have to be able to see or feel the roughness for it to be there. The fact is, there has to be some surface roughness that retains oil to lubricate the seals. As the seal slides along the inner tube it wipes oil from it. The nooks and crannies of a rougher finish will trap oil to allow the seal to slide and extend it’s life. There will be stiction if there isn’t any oil. The best surface finish for a dynamic seal is 10 to 20 micro-inches. Of course too rough of a finish and you’ll tear the seals apart. If you want I can email you some information on seal life vs. surface finish. As far as the piston is concerned, not all pistons have machining marks on them. If you look at a cast piston you won’t see as many machining marks as on a forged piston. Since the process for making a cast piston leaves small voids, they are enough to trap some oil, plus a cast piston usually has some friction reducing materials that are added to the aluminum. A forged piston doesn’t have the voids so there are small machined grooves that help with oil retention. The piston and the rings both wear against the cylinder wall so they both need lubrication. If a forged piston was smooth it would wear faster than one that had machining marks on it but the cross hatching on the cylinder wall has some oil so that helps. When ever two materials wear against one another there must be some form of lubrication or galling will take place and the softer of the two materials will be the looser. The lubricity can be from the material itself as in Teflon or from constituents in the material like silicates in a cast piston but the most effective lubricant is oil. The oil forms a boundary layer that separates the two materials so there is never any metal to metal contact. Since a fresh batch of clean oil is brought in with every cycle, there is always good lubrication. The oil can only do it’s job if it can “stick” to the moving components long enough to protect them. That’s why the cross hatching is needed. I’m not sure if ring seating has much to do with surface finish. Honestly, I’m not sure what even happens when a rings “seats”. There was an earlier post about engine break in with a new top end and if I remember, Rich said that tolerance’s were more important than anything. That’s why the pros can race an engine with little or no break in. The mechanics make sure that all the clearances and fits are perfect when the engine is assembled. [/QUOTE]

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