Wrist pin surface finish.

RonA

RonA

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Feb 26, 2008
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I bought a fancy set of wrist pins a while back and I'm debating whether or not to use them. Between the heat treat and the finish grind there are a couple of spots that didn't quite clean up(just a few small spots on the outer surface)and the surface finish is substantially rougher than a stock pin. I was told you want the surface finish to be rougher to hold oil better, but I am not sure about the wearing of a heat treated wrist pin that is rough against a soft bronze bushing and aluminum piston. Any opinions?
 
You have a good point on wear. I always thought they were supposed to be ultra shiny and smooth.
 
What process are you using?

In a perfect world you would want a mirror like finish like a 4RA or lower, but it's more like 10-12.
 
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DLC coating. I'm not buying the rough surface, my pins are DLC coated and even after pummeling them at high speed and steel pistons, you can't even tell they were in an engine. I'm sold on that stuff. The finish is mirror like.
 
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The finish on this pins does not appear to be a ground finish. It has feed lines that look like they were generated by lathe turning. They were over $100 each.
 
damn, no wonder you were getting second thoughts about this build. has anything went your way???
 
While on the subject, does anyone have the pin diameter written down?

This thread makes me wonder about using a wire bush to clean them up though.
 
Is a wristpin that's an upgrade from the OE pieces lighter or are there other advantages? I've seen everything else fail in B series engines for one reason or another, but not a stock wrist pin.

The stock wrist pins are pretty nice pieces. I keep a few dozen by the mill to help with complex setups since they're pretty tight tolerance. Nice to have them for leveling machinery too.
 
I wouldn't use a wire brush unless your polishing them after, the coating is also a great add on.

Depending on who's pins you use they could be anywhere from 11RA and lower, Most are in the 11-12 range which is fine, the lower the better 4RA being a mirror finish, but most don't go that far.
 
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i wonder what the weight and strength is compared to a stock wrist pin. looks like the wall thickness is less than that of the stock wrist pins. i would suggest having them polished.
 
RonA said:
This is what i have. If you rub your fingernail over the surface from end to end, it sounds like rubbing over a phonograph record.

Enterprise Engine Performance - Wrist Pin (Tool Steel) 3.25" Misc.

RonA
Click to expand...

I can see it holding oil better, but it seems a surface that rough (the way you described it) would chew thru a wrist pin bushing in short order? I have no experience with those posted, maybe they are for competition use engines that get rebuilt every so many (20-40) passes?

Just out of curiousity, did you weigh one of them Ron?
 
I'll let Wade explain it. I bought them from him for my p-pumped 6.7 daily driver.
 
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