PDA

View Full Version : Shot peened Rods....


Loozen_it
02-28-2007, 01:31 AM
I've heard of people having their conrods "shot peened". What does this mean? What is the process? Is this something worthwhile doing if I am using a eta bottom-end and i head to create a 2.7l boosted engine?

peerless
02-28-2007, 01:47 AM
Shot peening the rods is typically something you do after polishing the sidebeams.

Bascially you are spraying the rod with high speed metal shot. This serves to work harden the steel to add additional strengh. It is generally said that you can double the strengh of a stock forged rod by polishing and shot peening the rods.

I charge about $150 to recondition a set of M20 rods, not including new bolts.
$215 with new rod bolts. This includes magnafluxing the rods, rebushing the small end and resizing to your supplied piston pin, resizing the big end, polishing the sidebeams and having them shot peened. Keep in mind you will need to have them balanced afterward.

Here is a pic of a set I did recently for a customer.

http://img.photobucket.com/albums/v176/peerless/Rod1.jpg

http://img.photobucket.com/albums/v176/peerless/Rod2.jpg

digger
02-28-2007, 04:09 AM
shot peening is used to create reidual compressive stresses to improve the fatigue life. It does not increase strength as the load to ultimate failure is still the same, what it does is increase fatigue life since cracks will not initiate and grow under compressive stresses.

dmoffitt
02-28-2007, 09:19 AM
why does it look like someone ran 80-grit sandpaper inside of the big-end?

colin86325
02-28-2007, 11:06 AM
I think the big end was honed/burnished. That's not the bearing BTW.

Auto-X Fil
02-28-2007, 11:41 AM
shot peening is used to create residual compressive stresses to improve the fatigue life. It does not increase strength as the load to ultimate failure is still the same, what it does is increase fatigue life since cracks will not initiate and grow under compressive stresses.

That's exactly right. Since fatigue is really all we care about in engine parts I often see that mis-stated, but it's worth keeping straight.

bearing01
02-28-2007, 11:54 AM
And what they mean by fatigue is this..... say you got a piece of steel that is rated to hold say 1000 lbs without breaking. If you apply / remove a force (say 200 lbs) that makes the steel bend a little (like a spring, not deforming or permanently bending it) and you cycle this force then over time little surface cracks can form. These cracks can grow and cause the metal to fail not at it's rated 1000lbs but rather at some low force like say 600lbs. shot-peening hardens the surface to prevent crack formation and failure at forces below the steels rated strength.

peerless
02-28-2007, 12:46 PM
shot peening is used to create reidual compressive stresses to improve the fatigue life. It does not increase strength as the load to ultimate failure is still the same, what it does is increase fatigue life since cracks will not initiate and grow under compressive stresses.

Thank you digger and bearing01 for putting it into the proper technical terms. You are very correct on the shot peening process. The benefit to polishing the side beam is that you remove the source of potential stress fractures. This in itself improves the durability and strength of the rod itself. So polishing the sidebeams and shotpeening combined improve the overall strength and durability of the connecting rod.

Here is a excellent explanation and even a video concerning the shot peening process:
http://www.metalimprovement.com/shot_peening.php

Stock forged steel rods are an economical choice that should be able to handle one horsepower per cubic inch with quality fasteners, and as much as twice the factory-rated output if the beams are polished.

http://www.hotrod.com/techarticles/choosing_the_right_connecting_rods/

bottlecape30
02-28-2007, 11:15 PM
Thanks for those links i learned a lot. So how much does a shop charge to shot peen?