I don't know if I should have went to the Turbo Tech section or come straight to the Advanced crowd.

We have a diesel pulling tractor running the Detroit 14L series 60 with a compound setup. The turbos are all gt55's 88mm compressors (twin primaries, single secondary). All are just journal bearing setups.

A problem we have had about two years ago and again (apparently) at the end of last season is, the secondary charger spinning the compressor wheel off the shaft and shoving into the housing.

The side story behind this last failure is the engine siezed at the end of the pull. The engine failure was rod bearings and welding rods to the crankshaft.

The first time this happened, we had zero engine issues and actually just replaced the bad charger and continued to run.

I would like to try and understand what could be causing this to happen. I know that, most likely, I am not providing enough info and am braced to provide whatever I can to help identify this issue.

The datalog did not show that charger coming apart during or right up to the end of the run. Boost pressure was good, temps were good, and things did taper off at the end but I was losing engine RPM pretty quick and figured that boost would drop.

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Just at a race this past week. Guy was running a compound deal on a cummins. He has a s366 and s480 combo. His killed the small turbo. It broke the shaft.
He stated that what caused his failure is excessive exhaust pressure. It will push the compressor side so hard to move air that it kills the shaft.
It sounds like this is common when he pushes hard consistently. Usually for him when it happens the s366 turbine wheel gets carried down to the s480 and kills it.

 

Good point that I forgot to mention. I have a wastegate on both the Primaries and the Secondary. Exhaust pressuee has been about 10-15 psi less than intake pressure.

I am running the Primaries fairly hard at about 4:1 but the Secondary, once the Primaries come on, is only running about 2.5:1 which I thought it would live a long time.

I have heard Secondary chargers take massive abuse but I also hear those same people telling me to take the wastegates off which isn't gonna happen. Without a wastegate on the Secondary, it will, for sure, spin the snot out of it and break shafts.

Neither time has the shaft broke. It is intact with threads and all. The wheel obviously doesn't make it though.

 

I've seen it one time, and thought it possibly was from a sudden slowing or stop of the turbine, and the inertia of the compressor wheel loosens it.

 

That was my thinking before getting the turbo removed. I figured it oil starved right at the end of the run and locked the shaft and spinning the compressor wheel off. When I finally got it out, the exhaust wheel/shaft spin freely like there is nothing wrong with it. Didn't even see any damage on the turbine wheel.

Does the shaft just pop out of a GT-55 once the compressor wheel is off or do you have to dig deeper?

 

....nevermind...i need to learn to read....Mod please delete.

 

Dang, I didn't even get to see the original reply. Haha

 

High Boost, (compounding) while running a journal bearing Turbocharger set-up is at some point going to fail the thrust bearing in the turbocharger. Ball Bearing Turbochargers are designed for much higher thrust loads.

My theory is the thrust bearing wore to the point of now at high boost the compressor wheel fins touched the compressor cover.
Once they dug-in to the metal then the wheels began to wear very rapidly. At some point the wheel locked and the now the turbo was trash.

You mentioned the same thing here concerning a different time the turbo failed.
"A problem we have had about two years ago and again (apparently) at the end of last season is, the secondary charger spinning the compressor wheel off the shaft and shoving into the housing."

In both cases this is a Thrust Bearing issue. Ball Bearing Turbos can handle much higher boost pressures and shaft thrust loads.

Tom V.

 

We have been hearing that Tom.

Is it the overall pressure that turbo is running in that causes the thrust issue?

I was figuring the secondary charger running at about 3.81:1 PR which I thought it could handle well. It is also swallowing about 400°F air (we are injecting water just before the compressor so maybe that has something to do with side load.

Our primaries are running around 4.8 PR but they get fresh ambient temp air.

 

You are right on your assumption. The Pressure Ratio (force on the compressor wheel) is what damages the thrust surface on a journal bearing turbo.

A Ball-Bearing Turbo has a much higher capability to handle High Pressure Ratios and Large Compressor Wheels, especially in compound boosting applications. Tom V.