Re: [ST] Shot-peen and others

[Robert Smith <robert@xxxxxxxxxxx>]

At 08:25 AM 17/05/02 -0400, Doug Bailey wrote:
>I haven't talked to Triumph or my dealer, but coming from a small aircraft
>engine manufacturer...

I hesitate to get into this because, as I said before, I'm no metallurgist, 
and I don't play one on TV, but this is my understanding. I got this 
information from Triumph and the John Wilcox Engineering website.

1. Cast vs. forged. Most Triumph pistons are cast. Daytona pistons are forged.

2. Daytona rods are shot peened, the rest not. My understanding is that 
shot peening modifies the crystalline structure of the metal at the surface 
reducing any tendency for crack propagation. I'm pretty sure Triumph 
wouldn't go to the extra expense of this process if it wasn't worthwhile.

3. The cranks are plasma nitrided. This is a low temperature process unlike 
traditional nitriding, which requires heat. The cranks are placed in a 
low-pressure chamber containing an atmosphere of pure N2. There's a voltage 
potential between the cranks and the inside of the chamber that ionizes the 
nitrogen allowing it to penetrate the surface of the steel. I used to know 
a bit about the chemistry of this process, but it was too long ago and I've 
fried too many brain cells since then.

Whether it's BS or not that Triumph is one of only three mfrs doing this I 
couldn't say. I was so impressed with the cool purple glow of the 
crankshafts in the nitrding chambers that my BS meter was set to "off."

Sheep Dawg & Old Shep
Vancouver, BC
www.smith.bc.ca


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