what is shot peening?

[00 scrub]

I have heard many people talk about shot peeing engine internals like cranks, rods, pistons etc. How is the shot peening process done?

[phaqgm]

Shot peening is a process where a metal shot is blasted at the metal. Doing so compresses the metal tighter and elimanates any weak spots from the factory casting. When ever you have a casted piece of metal it will always have microsopic irregularities and weak spots. The theory behind shot peening is to help eliminate these weak spots and making the metal nearly as strong as it's forged counter part.

[coOOlcelica]

is it a good idea to get shot peening before installing new internals?

[scapamouche]

It also releives stresses in the metal that have built up due to the forging process. By relieving the stress, you make the margin to the part breaking under load firther away.

If you are building a MEGA power engine, then yes, shot peening should be done. For a street engine making 'near stock' levels of power, it's not required, but still a good idea if the budget can support it.The only parts that would need it are the Rods, and maybe the crank. It won't do anything really to peen the pistons or block, too.

Essentially, you sandblast the parts with specially designed metal balls. It's pretty neat....

[Jesse IL]

Technically what shot peening does is increase the dislocation density near the surface of the metal. Shot peening increases fatigue strength of parts by helping to prevent crack formation at the surface. Metal has a lattice structure. Dislocations are imperfections in the lattice. Dislocations prevent cracks by blocking dislocation glide on a microspopic level. Case hardening (or case carburization) does the same basic thing, but without the stress relief properties of shot peening.

[00 scrub]

Thanks. wow, thats an interesting process. I have a follow-up question, if you shot peen something, don't you have to shot peen the piece of metal after it has been molded to the proper shape? If you shot peen it then woudln't you deform the piece of metal (crank, rod or whatever) or at least cause some irregularities?

[scapamouche]

After peening, the part will be polished, but the process won't deform the part to any great extent. The process doesn't involve big beads, but very small ones and won't destroy the part being peened.

[00 scrub]

ah ok then. Thanks scapmouche.