Work Hardening

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Mar 26, 2008
How long does it take for internals to work harden? I know its going to be different for different metals etc, but I'm mainly curious about valvetrain. Is it a heating and cooling cycle thing or just friction? Is it something that happens during the 20 min break-in or does it take years?
I thought the same thing, what ever needed harding was hardened by that part mfg. If it wasn't, then the part either didn't need hardening or was defective.
All engine parts are heat treated, tempered, and (artificially)aged prior to installation.

Camshafts and cam follower or lifter faces are also rockwell tested to ensure of proper surface hardness.

The cam face and lifter face are machine honed to a specific finish(not quite mirror smooth) during the 20 minute break in period allows these two surfaces to polish one another to a mirror finish under adequate lubrication(a cam is splash lubricated).
I build knives in my spare time. Alot of the steels I work with have applications other than knife blades.
One of the better steels out there that is relatively inexpensive that has been around awhile is 440C.

Not to get mixed up with Chinese or Pakisani 400 or 440A. When properly heat treated it is very hard and very corrosion resistant.

They use it for valves in alot of cars.

The VAST majority of cars can get well past 100k miles. Im pretty sure if they have work hardened parts it is on low wear parts that are not in critical applications. Door locks and some springs could be Case hardened.
But that is different entirely. Hard on the outside, springy in the center is what case hardening is.
Some items will be purposely work hardened as a part of their manufacturing process, particularly things like stamped rockers and the like...nothing will be designed to work harden in service, as service is too unpredictable.
Pablo and tom slick, among others, are correct. I've studied worn surfaces at high magnification, especially valvetrain materials. If there is work hardening going on, you can expect premature wear. There should be nothing more than burnishing of the part surfaces.
Just been reading a lot about pre-mature cam failure's and the many speculations revolving around them. A couple people seem to think over time the cam & lifter face's harden over time and, even with SM, that's the reason many stock flat tappets are still in service because of this.

Thanxs for clarifiyng!
The reason flat tappets have excellent wear resistance is because they are made of chill cast gray iron. The cast matrix at the wear surface has around 50% carbide, and carbide is a superior wear surface when compared with traditional hardened steel.
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