Machining your own rods..

silverpsd_06 · Nov 21, 2013

The more and more I learn about the new mill we have at work the more I am tempted to make my own connecting rods. The mill itself is capable of holding +/-.0001" of tolerance I have no doubt in the equipment or the ability of the programmer. My question is this, most rods are built with 4130/4340 chromoly steel, what if a guy was to use an abrasion resistant steel such as AR4/500? From what I have found on the properties of the steel 4340 beats out AR400 in ultimate tensile strength by 9000lbs, but in yield strength AR400 has 4340 beat by 20000lbs. Has anyone ever attempted this? I only ask cause the steel is free, the programmer requires payment in beer and running the program is up to me after work. Damn near free set of connecting rods!

ncollins64 · Nov 21, 2013

Sounds like a good idea. I'd like to see this done. Good luck

silverpsd_06 · Nov 21, 2013

Thanks, I'd like to get some insight if I'm missing something in the metallurgical properties that would make AR400 a bad choice. All I can really find is the yield/tensile strengths for the two. I know AR is abrasion/ impact resistant. 1/2" will stop a .50bmg a point blank so it's definitely some tough chit

lincolnlocker · Nov 21, 2013

silverpsd_06 said:
Thanks, I'd like to get some insight if I'm missing something in the metallurgical properties that would make AR400 a bad choice. All I can really find is the yield/tensile strengths for the two. I know AR is abrasion/ impact resistant. 1/2" will stop a .50bmg a point blank so it's definitely some tough chit

It will stop it cuz its more pliable and dens. Prolly blow through the chromolly.

live life full throttle

David N · Nov 21, 2013

Talk to Jason Hoffman aka HotrodTractor. Im sure he could help you.

dentexpowerstroke · Nov 21, 2013

Hell I'll be the guinea pig if you want. I have a spare motor that has pmrs that I wouldn't care if I blew up. If it works I have bad as rods, if not I have a block to match Davids pmr block.

backwoodsboy · Nov 21, 2013

I've machined rods before. Not for a 7.3 but the principle is the same.
AR400 would not be my first choice. Make sure you consider heat treatment of 4340.
-Heat treated 4340 UTS= 195ksi vs 180-200ksi for AR400
-Heat treated 4340 Yeild= 182ksi vs 140ksi for AR400
Basically you are going to achieve permanent deformation in AR400 at a lower pressure than 4340. Necking and failure are going to occur at roughly the same pressures.
Not much abrasion or impact occurring on con-rod (at least I hope not anyways), so the advantage AR400 gains in Brinell hardness is moot.

Apologize if this post is brief, studying for a exam tomorrow morning.

sootie · Nov 21, 2013

AR 400 is a poor choice as it is quite brittle. its carbon content is high which makes it more prone to cracking.

4340HT is much better suited to handling torque of sorts and the heat treat factor is a major component.

TyCorr · Nov 21, 2013

Interesting thread, to say the least.

Jbenso127 · Nov 21, 2013

Interested to see what comes of this. OP, please follow thru with it!

powerlifter405 · Nov 21, 2013

opcorn:

ToMang07 · Nov 21, 2013

TyCorr said:
Interesting thread, to say the least.

powerlifter405 said:
opcorn:

^WTS...

silverpsd_06 · Nov 21, 2013

Sootie the carbon content is actually higher in 4340 than AR400 the only thing that stands out to me between the two is the chromium content which AR has none. I don't think it is so hard that it is brittle it will flex and I have seen it bent on a press brake. Takes allot of effort but it does bend with 150+ tons of pressure

silverpsd_06 · Nov 21, 2013

And if I do this it will be underneath 400/400s and compounds. It's going to take a beating...

sootie · Nov 21, 2013

silverpsd_06 said:
Sootie the carbon content is actually higher in 4340 than AR400 the only thing that stands out to me between the two is the chromium content which AR has none. I don't think it is so hard that it is brittle it will flex and I have seen it bent on a press brake. Takes allot of effort but it does bend with 150+ tons of pressure

i'm not into all the technicalities but i frequently break AR400 on the press brake.

we make wear components out of AR400/450/500 and and we make machined parts like axles, stub shafts etc out of 4140HT/4340HT

i have applied enough torque to twist 4340HT like butter,

what i have found is with 4140 and 4340, the metal is very consistent which is quite condusive to machining.

the wear plate goes through a different process and is quite inconsistent.

i'm just cautioning you-wear plate in a machined part like a con rod is not that cool.

silverpsd_06 · Nov 21, 2013

So is there a process one can apply to AR or look for a different process to make it more consistent?

Rideracelivemx7 · Nov 21, 2013

if you slap some big power to a set or two and find out they hold up ill purchase a set.

silverpsd_06 · Nov 21, 2013

I'm reluctant to throw unproven rods into a built motor.. I think I'll buy a cheap running motor and have someone build a tune specifically to try to break them and see how long they hold out..