Shot peening

[Blueboy]

I just received a price for Shot peening a set
of 24v rods. $500 does this sound right.

[f6jbob]

They must be supplying the rods at that price.

[j-rod]

They must be supplying the rods at that price.

Yeah $500 is high.

[theonlyz]

Are they polishing them to?

[9724VF350]

Depends, If that's shot peening, magnifluxing, putting new bushings in and resizingyour rods, it's about right. If that's simply the shot peening process it's way too high. I get rods shot peened, stess relieved, and heat treated for about $150 a set, then I have to do the rest of the work.

[Blueboy]

I didn't think there was any reason to polish
if Im going to shot peen. I took grinder to ridges.
This was for shot peen only.

[9724VF350]

Just using a grinder is worse than doing nothing. the grinder marks are also stress risers, and now you have way more. take a sanding drum in a die grinder and polish the beams while you're at it.

[Blueboy]

I should been a little more clear, I used die grinder
with fine stone on ridges. Where did you have your
rods done at. Even with shipping it would be cheaper.

[9724VF350]

The Bowdil Company - Heat Treating (http://www.bowdil.com/heattrt.htm)

They've done many sets of rods for me. They don't know a thing about engines, they just work on steel. You have to be able to tell them what you want done. Also need to have bushings removed, no bolts, and caps wired to rods before you send them.
There's also alot of circle track engine shops around here that shot peen rods.

[Blueboy]

Thank you, I will call them.
I was going to have them cryoed.
I think now I will just have them
shot peened, stress relieved, heat treated.

[rcfreak24]

I got mine does for 40 bucks.... 24v rods

[RJM06590]

I think I saw somewhere that Hypermax does it for really cheap.

[morkable]

so, do you get them peened, polished and cryo'd in that order?

[RJM06590]

Polished first.

[DIESEL_POWER]

Sometimes cryo can weaken the metal being treated, depends on the material and the prior heat treat....

Peened or polished offer the same results, polished would accually be better because it sheds oil while peening would hold oil.

[morkable]

so if you polished them you might not need to peen them?

[9724VF350]

While peening and polishing processes do somewhat "overlap" I wouldn't subsitute one for the other. peening does help eliminate stress risers, and it gets into alot of places that you really can't polish. As far as I'm concerned, not polishing rods in a performance engine is just crazy. It doesn't take long, it's easy, and it's cheap. Alot of billet rod manufacturers peen their rods, and you could almost call them "fully polished" being they are fully machined and don't have near the stress risers as a forged rod.

[DIESEL_POWER]

so if you polished them you might not need to peen them?

No, no need to peen them at all, the stress risers are on the beam ends(sides), where it is easy to get at, thats the only area of concern.


Folks get all twisted in what the polishing or peening really does. I'll tell you what it does.

It takes away the possibility of a crack forming on or around a forging ridge(stress riser) By simply polishing the beam you remove the possible issue and aid in oil sheding, which is another ballanceing trick. This allows for a closer opperating ballance within the engine.

Peening accually pushes metal together, making a rounder more uniform look, kinda like stabing a ball of plato with a pencil...yet oil will hold and stay in the peen marks and weight down the ballanced assy some,(when running) which will throw it off to a small degree.

Does eather one increase strength....NO! it just eliminates a possible problem area that is crack prone.

[j-rod]

No, no need to peen them at all, the stress risers are on the beam ends(sides), where it is easy to get at, thats the only area of concern.

Folks get all twisted in what the polishing or peening really does. I'll tell you what it does.

It takes away the possibility of a crack forming on or around a forging ridge(stress riser) By simply polishing the beam you remove the possible issue and aid in oil sheding, which is another ballanceing trick. This allows for a closer opperating ballance within the engine.


What about fatigue life?

[RJM06590]

Could you do a rough polish, then have them peened, then do a final polish afterwards?

[TMONEYDIESEL]

Hmmmm polishing and shot peening are completely different, the process's are different and so is the end result.

Polishing/lightening helps reduce weight and mostly helps take down stress risers and cracks that might already be there from the casting from the factory but when you polish you take away the surface hardening that's why you need to shot peen as well.

Shot peening is a process of small steel shot being hurdled at your rods that is like being struck with a ball peen hammer only smaller causes the surface to stretch and the dimple compresses the metal underneath, remember that metal fatigue cracks start where the surface is in tension, NEVER where it's in compression.

I'll touch on some key points of peening:

The maximum compressive residual stress produced just below the surface of a part by shot peening is AT LEAST as great as one-half the yield strength of the material being shot peened.

The peening compressive process is beneficial in increasing resistance to fatigue failures, corrosion fatigue, stress corrosion cracking, and erosion caused by cavitaton.

To create the dimple the surface of the material must yield in tension below the surface, the material tries to restore it's original shape thereby producing below the dimple a hemisphere of cold worked material highly stressed in compression.

Nearly all fatigue and stress corrosion failures originate at the surface of a part but cracks will not initiate in a compressively stressed zone, now because the overlapping dimples from shot peening create a uniform layer of compressively stress at the parts metal surface, shot peening provides considerable increases in part life.

Let's not get into Laser Peening that goes 4 times deeper than normal shot peening.

So as you can see Peening and Polishing are completely different and you should ALWAYS shot peen after you polish.

[morkable]

Thanks Taylor. That explains alot! What is the best method for polishing?

[theonlyz]

Awsome advise thank you.

[LReiff]

Very well explained Taylor!

[TMONEYDIESEL]

Gonna make me bust out my notes again huh Kevin? I can't take all the credit I do alot of research before I do something nowadays and with lots of help from different companys and notes and sending rods off that's what I've come up with, there was a company online that I got alot of tech from I'll try and dig up the name. Are you wanting to do them yourself or send them off? They are a pain and time consuming but will save a little money. Weren't you going billet? Most billet rods will come shot peened as well.

[rawdog]

dont the bolts need to be in the rod to properly heat treat and resize?

[morkable]

I want to go billet. But circumstances have changed and I dont think I can afford it this year. With the state of this "awesome running" engine that I bought it is costing way more than what I can afford.

[9724VF350]

dont the bolts need to be in the rod to properly heat treat and resize?

To resize, yes. To heat treat no. the metal needs to be able to move and do whatever it wants to, then the parting lines may need touched up if they do move. sometimes they do, sometimes they don't.

[morkable]

Cryo or heat treat? Which is better? I am imagining that you would do the shot peen before you would either heat treat or cryo?

[9724VF350]

Heat Treat. Not sure which order honestly. Bowdil does it and I never asked what order they do it in.

[morkable]

Why is heat treating better than cryo?

[12vriviera]

Heat treating relaxes the metal to a natural state, doing away with stress, cryoing will align metal within itself, but keep it in a stressed state.
That is what i have gathered.. if i am wrong please say so!

[TMONEYDIESEL]

You heat treat then cryo

[morkable]

ahh,,, how hot do they take them too? I will have to find someone that can do that for me,,, not likely something you could do in your oven I imagine

[TMONEYDIESEL]

No Kevin you won't be able to heat treat at home, I'll try and dig up a site that had some good tech on heat treating and cryo.

[TMONEYDIESEL]

Ok here's the first link for anyone who wants a little idea on metallurgy.

Tech: Basic Metallurgy For The Hot Rodder - Introduction - THE H.A.M.B. (http://www.jalopyjournal.com/forum/showthread.php?t=124334)

Next is a link for some good info on heat treating and cryo, happy reading.

Hot Rod Metallurgy - Lesson 2: Heat Treating - THE H.A.M.B. (http://jalopyjournal.com/forum/showthread.php?t=148497)