Heating gearbox components - how much is OK?

[Jesus-Ninja]

Weird question, I know. I have to do a bit of a bodge on the centre diff, which involves machining out the diff flange and making a bush to go inside. It will be very much an interference fit, to the point where I intend to freeze the bush in a freezer and heat the diff flange in an oven before pressing in. I'll then finish machining of the bush in the flange.

I'm conscious of heating gearbox components too far, but I'm thinking that 250 degrees (which is the maximum temp of the oven in my workshop) isn't actually that much, and the piece I'm heating doesn't have any gear teeth in it.

[Kenneth]

I would be loathe to heat, though freezing the bushing should be OK. You might be able to get some liquid nitrogen (pretty sure you can get it from 3M) for the bushing which should be plenty sufficient in terms of reducing the size.

I also wouldn't be too worried about having an extremely tight fit, there shouldn't be any load on it , you just want to support the shaft.

Thinking about it more, there is probably no hydro-dynamics in there, the shaft should spend most of the time going at the same speed as the diff cover, changing speed when you turn corners (or get wheel spin).
The more I think about it, it might just be OK to put it all back together as it is, just making sure all surfaces are smooth. (could pay to change the shaft)

[Jesus-Ninja]

Yeah, I'm just worried about the thing migrating outward.

I've also been thinking about this (a lot! :D) and I think that bushing it is the right thing to do. I'm going to use brass, which should be easier to press in, is self lubricating, and being a softer will die before anything else does - ie if anything happens to it, it is less likely to lunch anything else. As said, there are no real lateral loads on it. It will be performing a similar job as a crank spigot.

What has occurred to me is that the bushing should have as thin a wall as possible, as I shouldn't remove any more material than is necessary from the part of the diff flange which is also taking loads transmitted through the tapered roller pressed in to it. So, I will machine out just enough of the flange to present flat, parallel sides. I'll rough bore the bush to nearly the right ID, then press it in, and finish it in situ.

I probably will heat the flange, but only to about 150degrees. This certainly won't affect the properties of the metal, and shouldn't warp anything either, especially as it'll be evenly heated in an oven.

Also hunting out a replacement flange and lay shaft as well, just in case...