A Christmas Conundeum – to Case Harden or not to Case Harden?

[ChrisHParticipant @chrish]

I am just making a cam ring for a model three cylinder radial aero engine. This is a new experience for me – first cam I've made! There are just two cams, an exhaust and an inlet, mounted closely together on a cam ring, diameter a tad over 2.5" diameter. The ring is a snug fit on a support piece. As it was a first attempt I made it out of EN1A, not ideal material maybe but given my record of making scrap parts and the likelihood of having to make it again probably a wise move.

In an ideal world the cam would be case hardened, and I would like to do that out of completeness, but again that would be a first for me, so a number of questions arise:

1. If the engine is not going to be used other than once or twice to prove it runs then is it worth it?

2. Will there be any growth in the cam rings as a result of case hardening, and is so, by how much?

3. Will the ring as a whole grow – I want it to still fit on it's support ring after?

4. Is there a way to case harden only the cams and not the rest of the ring? I did read somewhere recently about using fireclay or similar to protect tapped holes, would applying that to the whole of the area to be protected work?

5. Is it normal to case harden cam rings for model IC engines? That should have probably been the first question.

All things for me to ponder over the festive season, but if anyone has been there, done that and can offer thoughts and/or advice then it would be gratefully received.

In the meantime, Merry Christmas to one and all, keep safe

Chris

PS – a final question, how easy is the case hardeneing process?

Edited By ChrisH on 24/12/2020 12:42:23

[ChrisHParticipant @chrish]

[BazParticipant @baz89810]

Chris I can answer your last question, how easy is case hardening, very easy indeed, plenty of info on here in other posts on how it’s done.

[SillyOldDufferModerator @sillyoldduffer]

My view:

1. Is it worth case hardening for an engine only run once or twice? No, but it's a valuable learning opportunity, and it would allow the engine to be more than a display item.
2. Growth? Almost none. Case hardening isn't an outer skin like paint. Rather carbon (or nitrogen), diffuse into the base metal. Raising the percentage of carbon slightly near the surface creates a thin layer of hardenable steel. Case hardening doesn't alter dimensions though stress-relief due to the heat might cause bending. (If so, stress relieve before cutting the cam.)
3. Only the cams? Apply case hardening compound only where it's wanted, or protect with fireclay as suggested.
4. See 3
5. Is case hardening normal? I don't know! Essential if the engine is to be run I would think. Cams have a hard life.

Dave

[ChrisHParticipant @chrish]

Thanks Dave – sound advice from you as always

Chris

[Dave HalfordParticipant @davehalford22513]

What about the followers? Or is that the cam ring

Edited By Dave Halford on 25/12/2020 16:26:54

[Clive HartlandParticipant @clivehartland94829]

Case hardening can be done just on the wear points, The cam followers should also be hardened. For occasional use you will not need deep hardening.

[ChrisHParticipant @chrish]

Dave , Clive – The followers are not a problem as they are very straightforward, but point noted – obvious really!

The major worry is the cam ring which is literally a ring with the cams cut on top and a short flange on one end with M3 tapped holes for securing. The inside diameter of the ring is a sliding fit over the cam support piece, which is an aluminium piece running on ball races on the crankshaft (it rotates in the opposite way to the crankshaft) and also carries an internal gear.

I think I will get some case hardening powder in ready, but see if the finished cams work first before hardening. Then at least I will know if it needs a redesign or not, and if it does deform whilst case hardening I can approach the making of a replacement in a slightly different way.

Chris

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