GM forged rods

Does any one know how GM heat treated there rods?
What process they used or might have used?
I have stock GM forged rods for my 3.4L and was thinking about geting them plasma nitrided but that processes tempture is some what close to what the heat treating would be done at.

Does any one know how GM heat treated there rods?
What process they used or might have used?
I have stock GM forged rods for my 3.4L and was thinking about geting them plasma nitrided but that processes tempture is some what close to what the heat treating would be done at.

I'm curious as to why you want to case harden your connecting rods. Plasma or ion nitriding is one of a number of ways to increase the hardness of the surface of a part up to a maximum of about .8 mm (1/32 in.) deep. This hard "case" is most often used to resist wear in a rubbing application. The hard case is quite brittle and may not react well to the tension and compression loads seen by a rod. The "core" properties of the part would depend upon how the rod was cooled and subsequently tempered. The core is where the tensile strength comes from.

The only rubbing or sliding wear a rod sees is if the piston pin is floating, and most aftermarket rods have bronze bushings there. My guess is the production V6 had pressed pins. Most forged rods would have a thru hardening form of heat treating with moderate final hardness, perhaps like a grade 5 bolt. That would make them strong but not brittle like a case hardening would. Ion nitriding is done in the 450C to 750C range, I think. That's certainly enough to thermally distort a finished rod, so resizing and maybe "untwisting" would be necessary, IMO.

FWIW, GM says the stock 60 degree V6 forged rods (2.8 thru 3.4 engines) are good for mild competition up to 7000 rpm. If you need stronger rods, small journal SBC can be used. I think you have to bush the small end to the V6 pin size (.912) unless you order pistons with .927 SBC pin size. Isn't the V6 rod also 5.7 long? It's narrower in the big end than the SBC but that can be machined.

I'm being negative here not to pick on you, but to point out what's involved. By the time you had the rods heat treated, which might involve annealing prior to nitriding, and remachine them to eliminate the distortion, replace the 9mm bolts with stronger ones (if you can find them), you "could have had a V8" and used much stronger aftermarket SBC rods just narrowed to the V6 width and rebushed for the same or less money. They are probably available off the shelf, and MUCH stronger than used reworked, stockers.

My $.02

I was just bouncing around ideas.
These forged rods cost to me was very little about $30 with shiping.
Why I wanted to case harded the out side because that is where cracks start.
The process only involves temps as high as 975'F.
The only good small jornal forged rods that I can find are around $500-$600. Then I would have to get them machined and stuff.
If I can spend a few hundred dollors on these rods and make them a lot stronger that would be good.
I'm not sure about nitriding the rods, becasue there is a lot to them.
If not the rods I was thinking of nitriding the crank, becasue with the crank I have no options. Eather an untold amount of cash for a custom crank or make the tough little stock one stronger.
The nitrided nextel cup cranks don't break.
I was thinking just geting a little cryo treatment done to the rods at only 8.75 per rod plus shiping it sould be good.
I got them form a machine shop where they were used but checked out good, they have just been getting seasoned for me to cook them, while they were in the other car.
I wanted to push this engine to about 6500rpm+ to right at 7000rpm, the worked and floated pin rods should take it but don't quite need reworked SBC rods.
The rods were cheap and fit the appication but I would like a little bit of insurance.

I was just bouncing around ideas.
These forged rods cost to me was very little about $30 with shiping.
Why I wanted to case harded the out side because that is where cracks start.
The process only involves temps as high as 975'F.
The only good small jornal forged rods that I can find are around $500-$600. Then I would have to get them machined and stuff.
If I can spend a few hundred dollors on these rods and make them a lot stronger that would be good.
I'm not sure about nitriding the rods, becasue there is a lot to them.
If not the rods I was thinking of nitriding the crank, becasue with the crank I have no options. Eather an untold amount of cash for a custom crank or make the tough little stock one stronger.
The nitrided nextel cup cranks don't break.
I was thinking just geting a little cryo treatment done to the rods at only 8.75 per rod plus shiping it sould be good.
I got them form a machine shop where they were used but checked out good, they have just been getting seasoned for me to cook them, while they were in the other car.
I wanted to push this engine to about 6500rpm+ to right at 7000rpm, the worked and floated pin rods should take it but don't quite need reworked SBC rods.
The rods were cheap and fit the appication but I would like a little bit of insurance.

Thoughts:

Metals, like women, remember every stress they ever encounter. You can't tell by looking at them how close they are to a catastrophic failure. If these rods are from a production 3.4 that wasn't raced a lot, you might liken them to a middle-aged woman who didn't have a violent marriage; there is probably a lot of life left in them. Think "Desparate Housewives" :)

You should Magnaflux the rods to look for cracks which may already have developed. If I were going to use them I would do that, and not just take someone's word that they were ok. The Magnaflux inspection, by a competent shop, is your insurance. Upgraded bolts and converting them to bushed small ends for floatng pins for your new pistons is also good insurance. When GM says the rods are good to 7000 (Chevrolet Power, The Official Factory Performance Guide published by HP Books), I would have no concerns running them there, especially with the bolts and prep described. Of course you should have the big ends check/corrected for roundness after you install the new bolts.

There are very few "magic bullets". Even sub-zero treatment isn't something that makes parts last forever. It probably can't hurt, and it might make YOU feel better. I think I'd replace the rod bolts after the sub-zero treatment.You are not going to make these rods "a lot stronger" by anything you can do to them, but better bolts, or at least NEW stock bolts will probably be your best bet.

If you case harden the rods, that is where cracks WILL begin, because the case is brittle. Crank journals are nitrided because they take rubbing wear. I believe that the nitriding is quite thin also. Cup cranks rarely break for a number of reasons, but nitriding isn't the main reason.

Tension loads from the pistons trying to fly out the top of the block kills rods. Limiting rpm to 7000 or so and using pistons which are a bit lighter than stock should serve you well.

Be careful about trying the trick of the week (or year), or applying a treatment to the wrong parts. The more you know about metals (and women) the better chance you have of surviving a relationship with them.

My free advice...and worth what you paid for it.

Good luck.

BTW any small journal(2.00") 5.7" long SBC rod will work in your motor if they are narrowed on a surface grinder. To me that says a Eagle H beam with the right amount of work from a good machine shop would be more than what you need.

Bret

The chevy power manual is good, I got one.
I found ARP rod bolts for the connecting rods, there 9mm (as in bigger than an SBC 11/32'' bolt).
I didn't just buy the rods form some one, they came form an engine shop, they do have fresh hone marks in the big end, they were magnafluxed.
I do have a big gram scale so I can weight match the rods to like .1g of each other, it's winter over here and I don't have any thing else to do.
Does any one know where I can get the small ends bored for piston pin floating?
There arn't any good machine shops around here, I would have to send them to Tokyo and it would not be cheap to send them or have the pin floating done there.