So I got a head scratcher here. Need some other brains to think of possibilities here.
Backstory : 04 Forester XT. Unknown history, but overall in good shape, 145k miles, ran well except for a large amount of black smoke and lacking full boost. Removed Turbocharger, it had lots of obvious shaft play, bearing and seal failure.
Took the turbo to a local, reputable turbo repair shop. All they do is reman turbos, mostly for diesel trucks and semis, but they do smaller gas turbos too. They rebuilt our turbo using a pre-assembled and balanced shaft assembly supposedly from a reputable european company.
We installed the turbo on the car. Ran good for about 1/4 mile then started making bad sounds and boost was intermitent. Turbo sounded awful, so we remove it again.....heres where it gets weird. THE SHAFT NUT WAS MISSING! it had spun loose and then gotten sucked through the turbine and was found in the intercooler. damaging the turbine.
So we take it back to the turbo shop. They are confused, first saying that it must be an issue with the engine. Insisting it must be backfiring. Well, it wasn't....ran smooth as butter, no CEL. We verified oil feed to turbo while engine running, and engine was not backfiring.
Anyhow, they get us another shaft assembly and housing and reman it again. We install it. This time there was alot of smoke on start up......we figured some coolant/oil fell down the uppipe upon the last removal. So we warm it up, take it for a test drive. This time it did well for about 2 miles.....then same issues again.....noise, loss of boost. Remove turbo again......SAME ISSUE!!! the nut has spun off....this time it got kicked forward into the plastic intake tube that runs under the IM and stayed there in a groove in the tube.
So we go back to the shop......Shop owner is apologetic and confused. His lackey was more rude, insisting that "well that engines eaten three turbos, somethings wrong". While in a sense that's true, I point out the the first turbo indeed had failed bearings, but its shaft nut stayed in place. Asked if he's ever seen a turbo fail and the shaft nut come off?.....He scratches his head and then admits "No". So even if there had been an oil failure, that doesn't explain why the nut came off.
Additionally, the lackey said "I checked the torque on that before it went out" This made me alarmed, because when I brought the second failed unit in, he had begun trying to fit the nut back on the shaft by threading it right hand......except this is a left hand threaded unit....specifically to keep the natural rotation forces from loosening the nut! He seemed to not know this! But then pretended that "oh yeah, I knew that" when I called him on it. In fairness, their shop is filled with literally hundreds of turbos for service of all sizes and types, and they do have a stellar reputation in the area. Hard to tell what's BS and what's not.
They are going to order parts for one more, and this time the shop will disassemble and reassemble and re-balance the unit themselves to verify.
They have asked me to verify oil pressure. And any other possible engine issue.
we are about ready to demand our money back, take to small claims etc....and just buy a genuine Subaru reman for a few hundred more.
My question here is
a) has anyone seen this type of failure, nut coming off?
Is there any possible way that the VVT system is taking oil feed away from turbo when it activates? They do share the same banjo fitting feed off the passenger head. (BTW, I checked the screen it's a-okay)
c) Is there any way a fault in the tumble generator system could cause back pressure in the intake similar to a backfire (but this engine is not actually back fireing, and there are no CEL codes)
turbo experts rack yer noggins!