The Western 0.090" wall compared to the CP 0.120" wall side by side. Notice the 45 degree I.D. chamfer on the CP wristpin. Now, look at the Western and if you look closely - you'll notice that the I.D. has been rolled with a radius instead of a single chamfer. Very nice feature. While your focus is there, take a look at the finish down each pin. Notice the smooth, reflective polish of the Sunnen machine honed Western Wristpin? Attention to detail is definitely a trademark of Manuel Maldonado, WW's owner. What good are pics without some data? Here's the best part:

Stock OEM wristpin: 90g

CP wristpin weight: 72g

Western Wristpin weight: 56g

-Ron

 

Sorry but it looks like a chamfer to me, and this is a machinist talking. Also, I don’t understand were a radius corner is better then a chafer in this particular application. I know radius corners are better for distributing stress but I can’t see how the I.D. edge is a high stress area on this pin. As long as there are no burs I don’t see an advantage in having a radius edge over a chamfer.

BTW, what’s the material and hardness specs on those pins??

 

The macro shots aren't doing the pin justice. Only the ID is rolled, but there is still a flat contact surface for the wire locks. The 0.090" wall isn't helping things either. I will take a shot of 0.180" wall western wristpin.

Since you're a machinist, try giving Manuel a call directly. He'll be more than happy to explain - craftsman to craftsman. I'm not fully qualified to give you the answer you seek.

The material is 52100 and I don't have the hardness spec handy.

-Ron

 

Hopefully with this 0.180" wall you can see the rolled I.D. better in these pics to illustrate the feature.

-Ron

 

stresses tend to align on edges. The wrist pin ENDS are what contact the piston directly. I think it's easy to understand why you'd want to combat the formation of stresses along a chamfer boundary bearing that in mind. The radiused inner edge makes the pin more durable at a critical area of the pin. It's probably a marginal gain in a piece that is typically much stronger than it needs to be, but those marginal gains are very critical when you're trying to shed mass. The radius might not make a difference on a thicker pin, but on one this thin, it's extra reassurance.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by MadtownSi &raquo;</TD></TR><TR><TD CLASS="quote">Sorry but it looks like a chamfer to me, and this is a machinist talking. Also, I don’t understand were a radius corner is better then a chafer in this particular application. I know radius corners are better for distributing stress but I can’t see how the I.D. edge is a high stress area on this pin. As long as there are no burs I don’t see an advantage in having a radius edge over a chamfer.

BTW, what’s the material and hardness specs on those pins??
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Rolling the edge cold works the metal and refines the grain structure. This makes it hard for a crack to propagate and greatly increses fatigue strength. Its not just the shape but the process that helps here.

 

Is that significantly thinner wall going to be strong enough. I would hope the material is much harder than the CP pin. Looks nice though. I'm sure you guys know what you're doing so i'll assume the thinner wall will be sufficient.