young olds

I run an annealing oven at work, as well as two smaller curing ovens, and I've been curious if tossing some engine parts, crank, rods, etc. in during a burn would do me any good or be a waist of time. I commonly do 1150* stress relive burns as well as 1550 "full anneal" burns. The idea is reduce hardness and increase ductility, making it more likely to flex then crack or break? Thoughts?

76olds

I'm not sure what the hardness is on a stock crank nor the material used, however I have been having much better luck with "Form Blocks" being heat treated to 54-56 for both A2-D2 material. Less cracking and breakage.
The days of heat treating to 58-60 and 60-62 are gone. Depending on the hardness of a stock crank, I would think you could draw it back to 54 if not more if breakage and cracking is an issue. It certainly wouldn't flex at 54rc
I'm sure your seeing tool steels coming out with less hardness in the past few years as well since your in the business.

joe_padavano

There are two different issues here. One is stress relieving, where you heat and slowly cool the part to release residual stresses. This is useful on complex castings like engine blocks, but frankly, a used block is already stress relieved from numerous heat-cool cycles over it's lifetime.

The second is annealing, which as you point out reduces hardening and improves ductility. This is usually used for complex weldments where thermal stresses can be induced during welding.

The thing you DON'T want to do is to anneal a heat treated part. Yes, it will improve ductility, but at the loss of yield and ultimate strength. This is like the people who think it's better to use a Grade 5 bolt instead of a Grade 8 bolt because the Grade 8 is more "brittle". While that is true, it ignores the fact that the Grade 5 bolt will have totally failed before the Grade 8 bolt even starts to yield. In that case, a poor choice.

young olds

So it would be a Waste of time on the block and no good on a crank? I won't brother bringing anything to work

76olds

On an engine block I wouldn't even think about it, as Joe mentioned the heat/cool cycles have already done its job.
As for a crank, you could check the hardness prior to drawing in back, I'm sure you know when you anneal something it throws it out of tolerance so regrinding is a must.
I would be interested in knowing what the hardness of a factory crank would be if someone here has the numbers.

young olds

What if you welded the mains to build them up to accept 4 bolt caps. You'd want to anneal it after wouldn't you?

joe_padavano

Yes, to stress relieve it. That would, naturally, need to be followed by complete remachining of every critical surface on the block.

76olds

This is off topic a little, but... Has anyone ever coated bearing surfaces, or any other internal engine parts for wear longevity.
Just because, we have been coating die sections for several years now, especially on high volume stampings.
Even something like inexpensive Tialn coating used on carbide endmills... say on valves, rings, bearings, pistons. ?
Anyone doing this ?
Thanks
Eric

young olds

There are friction reducing coatings as well as thermal coatings already in use on engines they just aren't main stream for the everyday builder. What do you guys think about welding a block with invar? It's a nickel-iron allow with a low thermal expansion/contraction coefficient, and we do a lot of invar tooling where I work. Always wanted to try building up a big block for 4 bolt caps

74sprint

Olds nodular iron cranks already have a nitride hardening process applied to the bearing surfaces so annealing it would destroy this. Also some say if a crank is cut more than 0.010" then the nitride process should be redone and I agree because the process is usually only 0.015" deep. I know Byrant and other crank makers apply nitriding to their cast & billet cranks.

Yes and I am an absolute believer in coatings especially for bearings and that's for street or strip.

Ray

Fred Kiehl

It would probably be a lot cheaper to just buy a 4 bolt block.


If you want to pay for the technology, there are coated bearings available.