jarrett2k

the turbo that came on my miata was blown, big time. the shaft that holds the compressor wheels was actually broken off on the end. no biggie, it's only a TD04-H so i just replaced the turbo.

well, i've been thinking about putting it back together just for shits and giggles, and i can do it for free (in machining classes). however, i have no clue as to what type of metal it is. all i can tell is that it is some type of hardenable steel.

my main question is, would 4140 steel suffice? would it require heat treating?( can do that too)

any input is greatly appreciated.

Fabrik8

The shaft is friction welded to the turbine wheel, so I wouldn't bother making a new shaft. You can get new parts to rebuild the one you have though, including the shaft, turbine wheel, and compressor impeller. Or you can get a complete new CHRA that will replace everything in the middle, bearings included.

If you want to do this just to play with bearing tolerances and surface finishes, that's cool, but I think you'll have to stop with just making the shaft itself and not actually making a fully functional turbo with it. Unless, of course, you have an inertial friction welding setup and a whole bunch of turbo parts to experiment with until you find the right recipe. Or, you could braze it I guess, if you have an induction furnace that can melt a high temp brazing filler. I don't think there's any easy answer to this..

You'll probably have to either post-machine or grind anything you do after heat treating, because heat treating will leave a decarburized layer that won't have held your pre-treated tolerances. So keep the bearing surfaces oversized and plan to finish them after. Not a lot of fun to post machine heat treated parts, let me tell ya. Hard as shit usually and they care too much for being machined. Your mileage may vary.

I don't know if heat treating is really necessary though, now that I think about it. The shafts don't need to be very hard if it's a floating bearing system, and there shouldn't be much of a moment on the shaft end.. Hmm. I have no idea if that's actually done or not by Garrett, etc.

I'm skipping the high speed balancing part because you can't balance what you can't assemble.

That was fun, it's 1:30 and I'm going to bed.

jarrett2k

woah, thanks.

honestly, i have no desire to make the turbo function anymore, seeing as i have another one. but it would be kinda cool to have a spare. i was thinking more along the lines of making it turnable by hand, polish it up and using it as a show piece in my shop/office.

Fabrik8

Cool, go for it. You could probably (torch) braze or tack weld the wheel to the shaft well enough for a show piece. I wouldn't worry about heat treating or anything else like that obviously.

t3focus

keep ot for parts ull regret it if you get a cracked housing trust me

jarrett2k

over a 175 dollar turbo? i doubt that.