T-25 compressor free spin

[Andyrock78]

I have an odd question that I could not find an answer for by searching. I have a stock 95 tsi awd with 74,000 original miles. The T-25 turbo has zero shaft play, barely any side to side (less than .030). I tried spinning the wheel the last time I had the intake off. It spins just fine when I move it, but slows down right away. Is this normal? I have little experience with turbos, but assumed it would free spin longer than 1 sec or so. The car was off so there was no oil being fed through the turbo. There is a very slight grating noise under acceleration between 2000-3000 RPM - any advice would be appreciated

 

[crash89]

A journal bearing turbo wont really free spin like that for long at all. Its nothing to worry about. Even when I first bought my holset Id spin it and it wouldnt turn for long.

 

[TSITurbo95]

That is normal. As for the noise, could you please elaborate?

 

[Andyrock78]

thanks for the quick replies every one The grating noise I'm hear is hard to pinpoint - very intermittent. Sounds like very faint metallic grinding under partial throttle while boost is starting to build around 2000-3000RPM. I'll have to rule out engine knock somehow - I don't have a logger yet

 

[JusMX141]

Any turbo as small as a T25 with zero rotating mass will pretty much stop as soon as you let go of the wheel.

 

[T is for TURBO]

Is the sound vehicle speed dependent? Engine speed dependent? Consistent between 2000-3000 rpm?
I would check for loose bolts, or maybe a cracked timing cover. If it were something grinding you would most likely hear it all the time. My guess is, at part load at those RPM's you're hitting a natural frequency for something at isn't completely snug.

For my car, with my old exhaust, I would get a TERRIBLE metallic vibration at 2300-2700 rpm. I switched exhaust systems and the noise is no longer there.