>>>*Beats me on that, Kevin. Interesting, tell us more. It's not something I know a he** of a lot about, it was THE process in the 70's and 80's. Heating the rods was to be done slowly and for a long 8 hour period at 450?. We just left the oven door shut until they were cooled off enough to handle, and when done a file would slide on them unless we used a lot of pressure. Most rods are steel of course. Now we just repeen them after grinding, that is lots faster, all it does is stiffen them some.

The process was from an article written by Smokey Unick way back in one of the hot rod magazines. When I was a kid that man was THE word on racing tricks and I never really questioned that since it seemed to work. We never broke any, but now that I think about it, we weren't breaking any anyway...*LOL**....

But I am interested on serious cooling, I was poking around on Google and there are lots of claims but not a lot of real info....*EB

This is only kind of related, but I just read about it and it seemed interesting.
New Steel Heat Treatment

I thought about it a bit... And some more came back. 450?F is low enough to not anneal a set of rods, but hot enough to do some stress relief. I think we both read the same article in Hot Rod or Circle track in the 70's.

"The World's Greatest Mechanic," was his writing byline in (was it?) Mechanics Illustrated, which I had a subscription to in grade school. Then again, I also had subscriptions to Popular Mechanics and Popular Science, so maybe it was one of those. Yeah, go ahead and say it: "Nerd."

Smokey had a great article about making a vehicle engine last much longer than it usually does. That was the first time I'd ever heard of an engine pre-oiler and how it could be packaged, produced and used. Good stuff.

John B.

Am I thinking of a different story, or wasn't the lack of a proper cryo treatment on the early Toyota FJ Cruiser's ring gear blamed for several differential failures?

John B.

I did a really spiffy reply that just damnit disappeared somewhere...

What I read says that cryo extends the heat treating process past room temp into colder regimes, allowing more of the austenite to convert to martensite, and by precipitating eta carbides (very hard substances - diamond is a carbide) into favorable places in the iron crystalline matrix which greatly increases wear resistance. Internal stresses are removed. The piece becomes more dimensionally stable, effectively harder, and tougher.

I talked to one of my brake suppliers about this. He's got a good relationship with the engineers in the company. They did some testing on our brake rotors that were cryo'ed and non-cryo'ed. Mainly on the cop car applications and never had any consistently positive results. They had a couple that were markedly better, but the overwhelming majority was significantly worse than the non-cryo'ed rotors. They did cross cuts after the cryo treatment and then on some more after the abuse tests. The majority of those looked to have reverted back to the pre-cryo state after the abuse tests. Take that FWIW... <img src="/forums/images/graemlins/cyclops.gif" alt="" />

However, CV parts in the front axle wouldn't be subject to the level of heat (and heat cycles) a brake rotor would endure.

I'd say that if, at this stage of understanding of metallurgy present in man's progress, there isn't a proven reason that it works, then it may not be worth paying for.

Frankly, I've heard the term used extensively in regard to high stress auto parts, and just assumed it was a proven and reliable thing to do for certain applications. I haven't ever checked into the process any more than to understand what the basic idea was. I had no idea there was any controversy surrounding it. Good thread.

John B.

Perhaps it's just become fashionable to cryo your parts. In most cases, the end user would never know if it did any good or not...