This is what destroys your turbo
 

Here is the crack which eats turbo's on our cars.

I have 2 S5 turbo's and both have this crack.
It is on the exhaust housing and when heated will expand and start eating the turbine fins.

One of the turbo's shows etching already while the other is salvagable.

These housings are useless though.

https://www.rx7club.com/attachment.p...postid=2759955

Do you know what causes that?

Not sure but I am guessing heat and age

yup definitely not good housing! sux that you got two of those!

Can you actually hear the turbine fins hitting the housing? If so what does it sound like?

I have never heard these when running.

One came off my Jspec and the other from a friend.

The Jspec Spun freely and you couldn't tell until you removed the housing.

The One above did make some scraping noises but you can see a half inch line/etching on the right side if the crack where the turbo actually hit while spinning.

Here is how you check it.
1. get a 12mm(I think) socket and undo the 6 bolts on the hotside.
Two will not go very high because the oil oinlet things are in the way.

Back it out as much as you can and grab a hammer.
If your lucky a few light blows will knock it loose.

Other wise get a big one and whack away at the sides in a downward motion(toward the exhaust).

Once free just undo the rest of the bolts and check it out. A few cracks are normal I guess but the one mentioned above is a bad thing.