When to rebuild?

[CorvallisBMW]

I have a K27 from the 745i m106 motor. The seller included a rebuild kit, but how do I know when it needs to be rebuilt? There is some radial shaft play (I'd estimate about .015") and zero axial. I've been searching but haven't found any good info yet. I have no qualms about rebuilding it myself, but from what I'm reading it's not a good idea unless you can get it balanced (which very quickly gets expensive!). Any info is appreciated. Thanks!

[Jaxx_]

Concerning rebuilding the turbo: Some radial shaft play is okay, but axial is a big no-no. If the compressor and turbine don't rub and the assembly moves freely, it's probably fine. Some will tell you that a turbo that is used and has been sitting on a shelf for a while should be rebuilt, but I don't subscribe to that theory. If the turbo is supposed to be in good working condition, I would leave it. If the seller says it needs to be rebuilt(oil smoke, oil coking, etc) OR if the turbo is going to be a pain to remove and reinstall(rear of the engine bay with heatsheilds and IC piping galore), I would rebuild it.

Concerning balancing:
It has been my understanding from rebuilding MHI TD04 turbos that if the compressor and turbine wheel have been balanced separately that the assembled turbo does not require balancing. If you remove the compressor housing of the turbo and see balancing cuts in on the compressor wheel you should be fine. If the nut holding the CHRA together is ground down, it means that it was balanced as a single assembly, requiring it to be balanced professionally again.

You can also mark the shaft and compressor wheel before disassembly in order to not lose the original balanced configuration from the factory. Make sure you don't lose the marks when you are cleaning the turbo components... Something like a sharpie will be gone in an instant.

I have been told that "flutters" when in boost (quick spiking/shaking of your boost gauge) your turbo is out of balance, even if it does not make noise or rub against the turbo housing.

[CorvallisBMW]

Awesome, I will look closely for any balancing marks on the turbines and retaining nuts. I've been doing some reading/researching and it seems critical to mark the position of all components before disassembly so that it all goes back together right and balances out. I don't know yet how hard the turbo will be to access once it's in the car, so better safe than sorry :)