T6 76mm Turbo Failure
03-31-2010, 11:17 AM
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T6 76mm Turbo Failure This is my RX7 with 5.3 install. I have a couple posts about it in the hybrid forum, but wanted a little insight from the forced induction croud. This is what I believe and what I found:
-- Oil supply fittings, lines, all looks good and clear to the turbo(AN -4 no restriction). Feed is from recommended location on LSx oil pan above oil filter. This is filtered oil that it headed to the mains. Pressure measures good.
-- Drain is 3/4 inch to oil pan location specified by banks install manual. Angle is not great on the drain line but is downhill, room for improvement here. I can blow into the drain tube and air comes out crank vents, but pressure builds in crankcase and when I let off some air comes back out drain tube. That doesn't seem right, the engine is going to have more blow by than I can blow into the crankcase, I would think??. I do not have a crank vent to intake so vacuum under light throttle will help evacuate, maybe I better do this. I have a valve cover vent on each valve cover.
-- Took apart turbo and see that brass bushings and main shaft at location of bushings look OK. No scrapes, no heat marks, shaft still spins freely in bushings. Thrust surface is scuffed and has heat marks. Front seal is shot and scraped. Compressor wheel wobbles and hits housing. No signs of damage to fins from foreign object.
-- Some Facts: Car never had a blow off valve. Car was driven about 10 times down driveway, less than 5 miles. Few hits of boost, about 8psi. Compressor always chopped/surged when throttle plate closed since no BOV.
What I get from all of this:
I am no turbo expert, but I don't see signs of oil starvation. I believe the first thing that happened was the compressor hit the housing and the shock bent the shaft. Once this happened and the compressor wheel started wobbling, then the thrust bearing made contact and heated up, the front seal wore out and that is how the turbo sets now. I think only two things would have caused the wheel to hit the housing at boost rpms, short loss of oiling (not sure how this would happen, even with crankcase pressure I should only see the seals fail and burn some oil) or compressor surge on letting off the throttle after boost run caused the wheel to shake and hit the housing. I believe the second occurred, but have no way to prove it. Remember, this is a T6 frame turbo with a 76mm compressor wheel. It was pushing some serious volume when I would let off the throttle and cause surge, I know a lot of people don't believe surge can hurt a turbo but I am convinced that compressor hit the housing because of it. I could be wrong, but I have to go with something and I don't see lack of oiling by looking at the bushings.
What I apply to the next turbo setup from this experience:
Try to angle the drain line better. Try to evacuate crank pressure better. Install a BOV from the beginning. Maybe run with the 1 quart overfill for the well known LSx sump issues, I was not doing this but I wasn't on the race track either.
Anyone have other insights before I install the next turbo? The turbo was a Detroit Reliabilt TV71, had never been installed before my install.
-- Oil supply fittings, lines, all looks good and clear to the turbo(AN -4 no restriction). Feed is from recommended location on LSx oil pan above oil filter. This is filtered oil that it headed to the mains. Pressure measures good.
-- Drain is 3/4 inch to oil pan location specified by banks install manual. Angle is not great on the drain line but is downhill, room for improvement here. I can blow into the drain tube and air comes out crank vents, but pressure builds in crankcase and when I let off some air comes back out drain tube. That doesn't seem right, the engine is going to have more blow by than I can blow into the crankcase, I would think??. I do not have a crank vent to intake so vacuum under light throttle will help evacuate, maybe I better do this. I have a valve cover vent on each valve cover.
-- Took apart turbo and see that brass bushings and main shaft at location of bushings look OK. No scrapes, no heat marks, shaft still spins freely in bushings. Thrust surface is scuffed and has heat marks. Front seal is shot and scraped. Compressor wheel wobbles and hits housing. No signs of damage to fins from foreign object.
-- Some Facts: Car never had a blow off valve. Car was driven about 10 times down driveway, less than 5 miles. Few hits of boost, about 8psi. Compressor always chopped/surged when throttle plate closed since no BOV.
What I get from all of this:
I am no turbo expert, but I don't see signs of oil starvation. I believe the first thing that happened was the compressor hit the housing and the shock bent the shaft. Once this happened and the compressor wheel started wobbling, then the thrust bearing made contact and heated up, the front seal wore out and that is how the turbo sets now. I think only two things would have caused the wheel to hit the housing at boost rpms, short loss of oiling (not sure how this would happen, even with crankcase pressure I should only see the seals fail and burn some oil) or compressor surge on letting off the throttle after boost run caused the wheel to shake and hit the housing. I believe the second occurred, but have no way to prove it. Remember, this is a T6 frame turbo with a 76mm compressor wheel. It was pushing some serious volume when I would let off the throttle and cause surge, I know a lot of people don't believe surge can hurt a turbo but I am convinced that compressor hit the housing because of it. I could be wrong, but I have to go with something and I don't see lack of oiling by looking at the bushings.
What I apply to the next turbo setup from this experience:
Try to angle the drain line better. Try to evacuate crank pressure better. Install a BOV from the beginning. Maybe run with the 1 quart overfill for the well known LSx sump issues, I was not doing this but I wasn't on the race track either.
Anyone have other insights before I install the next turbo? The turbo was a Detroit Reliabilt TV71, had never been installed before my install.
