I found someone at Cal Poly willing to help me with annealing and rehardening 901 internals so I can machine them. He said it would be helpful to know what alloy the steel is. He also asked if they were case hardened.

unobtainium is what I have heard..............

Dang! You beat me to it!

I'm sure they're made of some rare earth something or other!

Shannon

Case hardening is a coating that hardens only the outer skin of metal. I doubt the metal is all that unusual, but I do know that Porsche uses or used a cyanide bath of sorts to harden crankshafts. Gearbox internals, who knows. All this is just FYI, and it probably doesn't help much. Mismatched heat rehardening of gears can lead to accelerated wear of the softer gear. I don't know exactly what you want to machine, but perhaps using carbide tooling and leaving things hard is your best bet.

Hmm, I tried carbide.. it wore bits dull and barely made a scratch... it's hard stuff! It's good to know about the mismatch tho, I'll do whatever I do to both gears so they match. (what I'm trying to do is cut second off the main shaft and machine the inside to be able to use the second gear set as 5th) This is an extreme longshot, and if it works it'll be a miracle... but I have to try

I'm missing something here. Can you cut off second gear without destroying it? I'm assuming you want to end up with a 904 mainshaft. You want two second gears in the same transmission, for racing purposes, correct? Anyway if the shaft and gear is heat hardened (or case hardened), you need to get a Rockwell hardness before annealing it so you can come back to it, so it will match the gear it meshes with. I don't know if they case harden gears. If yes, the metal should be soft a few thousandths under the skin.
I know they aren't cheap, but Ottos sells new 904 mainshafts, and you might be ahead of the game buying one.

you might also have the option of grinding the gear off....it's a slow process and can be a PITA depending on the profile needed.

Two second gears? Nope. I want a taller ratio for 5th, for a v8 conversion. I want to reverse the positions of the second gear gears and put them in place of 5th. I am trying to sacrifice a mainshaft to get the gear off. The remachined gear will go on a stock mainshaft. I don't think it's case hardened, I did some grinding on the pinion shaft I plan to use as a broach, and it's hard well past a few thousanths deep.

Case hardening is more than a few thousandths deep. What is done is the steel part is hardened on the outer surface (maybe ~ 1mm deep) to give a hard wear layer. The main body is still ductile so the part will not shatter under load. All transmission gears are case hardened AFAIK.

Crankshafts can be nitrided - a chemical surface treatment, but that is not a process used on tranmission gears.

Why not change the ring and pinion? There was a thread abit ago about using a 901 sporto R&P....effectively does what you wanna do to ALL the gears across the board for a lot cheaper.

The PorChev board has a guy named Felix that has done it and Bradholio claims to be able to do it....he alos sasy the R&Ps are CHEAP.

Gears are typically made of 8620 steel, then carborized (sp).

Shafts can be made of lots of different things depending on the application. Could be 4140 heat treated or even something as exotic as Jethete.

If you are trying to match steel components you could always send a scrap piece to a testing lab and for about $200.00 they can tell you what grade of steel it is.

Good Luck

I don't want to change the ring and pinion because I want to be able to use 2nd as my first gear, since 1st is too weak. I'm afraid an R&P change would make 2nd gear starts difficult and/or hard on the clutch.

It looks like I'm gonna have to test the hardness.. Fortunately the guy I talked to siad he had a hardness tester. I'll post results of course.

A hardness test will not tell what "kind" of material it is.

The only way to do this is with destructive testing. You have to isolate key elements in the steel to determine what grade it is.

Well he said it would be nice to know what kind it is to know what temperatures to anneal and reharden at... but he said a hardness test would give him a good enough idea that he could probably get close enough. The real destructive testing will happen when I put it together and bolt it to a V8

Ahhh, I see.
I figured case hardening to be about 1mm. That's about 40 thou, "few" is subjective. If Cal Poly has a machine shop, they may very well have a Rockwell tester. As stated a hardness test doesn't indicate the type of material, but it will give you an idea of how hard the gears need to be.