photographic metal finish

[WIDSM]

I searched everywhere and didn't find anything on this, maybe there's a different name for it but, At work lately we've been machining photographic finishes on steam pipe flanges. I asked why we did this type of finish as it didn't seem as though it would seal as well as a clean machined surface. Well I was told that it's harder to blow out when there are all of these little riges, so the steam can't escape. So my question is, that these pipes go under extreme heat and pressure, so couldn't this application be used for engine surfaces? Can someone with machining experience help me out on this one.

 

[gsx951]

It is used! When you take a block or head in for work, you typically tell the machinist what "ra" or "roughness average" is desired on the finish. Smoother, low ra, finishes are required for engines that run MLS gaskets.

 

[WIDSM]

Couldn't a stock head gasket with this finish be comparable to a metal head gasket as far as how much boost it can handle though, because the gasket would have something to grab onto? Obviously running a metal hg wouldn't work with that finish.

 

[BoredDSM]

In a way yes and no. If the surface area is polished to a mirror finish it means the area would be flatter and allow the gasket to rest on it completely. If there are ridges in there yes there would be more surface area but the gasket cannot settle down into the block completely and there would be gaps between the block and the head. Those area's would be where you would leak or blow coolant and oil.