Wondering what this process involves(polishing con rod beams) and why it is done. My best guess would be to say it removes casting flaws in a stock rod application. Even if that is the case how does that add to reliablity, and again, why would it be performed?

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Polishing the beams removes "stress risers". Stress risers are high points, such as a seam from casting. Stress concentrates on points, or pointed areas. This can lead to cracks at the stress point, or "stress riser".

Reliability is improved when the areas prone to developing stress cracks are removed. Polishing does this.

 

thank you.

 

Are you talking a casting or a forging?

That principle works for a forging. I question the use of cast rods for anything other than stock torque output. IOW, if you are going to the trouble, may as well go with forged.

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ARNIE-
I realize the benefits of forged pieces over stock cast and also relaize by the time you are done making a stock/cast piece stronger you might as well go out and get some forged rods. I was just unclear of what the polishing process did but am clear on it now. thanks.
-scott

 

Polishing the rods is only the first step. They should then be balanced, shot peened and resized. After all that, some good rod bolts and the rods will take more abuse than the factory originally designed them for.

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So what is shot peening then?

 

I've read about rods actually being weakened by polishing in certain cases but I don't remember the details.

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Think of shot peening as sand blasting with small ***** of lead. It has the same effect as using a ball peen hammer. By hitting the entire rod you create tiny dimples all over it. This relieves stress from the metal. The rod must be then resized because shot peening will distort the metal.

 

I wouldn't classify shot peening as a stress relieving process. As you described, it blasts the surface and creates dimples, but the idea of shot peening is to toughen the surface by compacting the grain, much like a forging process does, and make it less susceptable to crack formation and growth. Mike

 

actually it creates resudual "negative" stresses in the metal, so that when its loaded normally under stress insidee the motor is will actually see a "zero" net stress, and when unnder maximum stress it would still be less then normal since the negative residual stress keeps it lower.



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