Got a 1990 RX 7 GTU normally aspirated. Oil consumption is about a quart every 200 miles. I figure I most likely have bad concentric oil control rings on the rotors. Someone tried to tell me that is just the OMP but I think the oil consumption is too high for the OMP. Any thoughts?

 

Sounds like oil O rings are shot and you need a rebuild

 

Any noticeable smoke?? 1qt/200miles is excessive, but normal consumption for a tired motor, leaks, and functioning omp can make the problem seem worse than it is

 

Unfortunately yes. Mostly on start up but noticeable at idle. Most likely I will have to bite the bullet and go for the rebuild, but my one concern is the possibility of spinning a bearing if I continue to drive the car. I was told that this was a possibility by an individual when I was discussing the oil consumption issue. I know that when you a spin a bearing on a piston engine the engine knocks and oil pressure drops off but I am not having any of these problems. Engine is quiet and smooth at idle and oil pressure is steady at 50 psi at 1000 RPM. Engine is also smooth with no hesitation at 3000 RPM and oil pressure is about 60 psi, so from these perspectives I can see no incipient indications of bearing failure.

 

Hi, I experienced a spun bearing, speed about 35 mph going uphill at a minor grade. It caused the rotor to tilt and take out the rear stationary gear! Complete lockup, pushed in the clutch and pulled to the side of the road.



My oil was topped up, what do you think caused this? The front rotor bearing was fine.

Look closely at the picture and you can see where the locking lug has been worn away or snapped off the bearing!

No indication of any problems until there was one.

 

Wow, that’s an eye opener. Were you having any oil consumption issues or did this come out of the blue with no warning?

 

This was not expected! The only way for this bearing to fail was for the hole in the bearing to not align with the oil feed hole on the E-shaft.

This leads me to believe that something caused the alignment lug on the bearing to break or be worn away allowing the bearing to rotate.

Again, my oil level was at the full line and I was just cruising along with the traffic. So, something was wearing away the bearing lug.

Any ideas what would cause this to happen. Such a small little bit that failed took out my engine!

What do you think?

 

>> Any ideas what would cause this to happen?
Lack of lubrication and excessive heat build-up.

 

lack of lubrication would also be a cause, a pickup tube sucking air after coming loose or simply not checking your oil can also very easily cause this. the front thrust bearing on the engine usually suffers from loss of lubrication first so there would be signs of bluing or complete failure on it before this.


what generally causes oil consumption issues though? OEM factory oil seal o-rings. usually noted by their green coloring for the inner seal, they can flatten out and cause major oil burning issues in as little as 5 years, i run vitons in all my engines. after countless engine teardowns almost half of the time those oil seals could literally fall out of the rotors because they lost their seal a long time ago.

adding half a quart of ATF for a few warmup cycles(then an oil change) might help to swell them up to get you by for a little while longer.

 

any signs of the motor being rebuilt prior to your ownership? Could’ve just been built with a tired bearing or perhaps someone pressed a bearing into a rotor/gear that had previously spun one, resulting in the bore not being tight enough on the bearing.

The alignment tab is simply that. It serves no structural purpose. Same as fd and rx8. Their main bearings use a locking screw, but if a bearing is going to spin, the tab and screws won’t prevent it. They’ll spin with enough force to rip the bearing through the screws or spin them right out of their alignment tab.

At my shop, any part (rotor or gear) that spins a bearing gets binned.

 

Thanks Brian,
This failed engine was an Atkins, in their warranty they explicably mention any bearing failure is NOT covered! It had about 75k miles on it.
I did not request new bearings on this engine, so I assume they were original. That would total about 150k on all these bearings. The front rotor bearing had just a bit of copper showing.
Perhaps this rotor did spin a bearing, and they just reused an old one that looked good.

 

Unlikely, in over 500 engines torn apart i have never seen a bearing spun, some engines having over 200k miles on them. I still believe you ran into an oil starvation issue. One engine did break a rear stationary gear and decide to turn a rear rotor into a donut instead of a dorito though. it's even possible you had a stationary gear failure that then made it appear the bearing had spun first, once you lose rotor clocking there no bets on what the engine will try to do to itself.

A jammed oiling jet in the e-shaft can also kill a rotor bearing there's actually a number of causes that could net your result, none of them are common though. the fact it made it 75k miles tells me it was unlikely a build quality issue.

Stationary gear failures are like unicorns, nearly impossibly rare but they do happen, generally no load high revs. The example i gave the customer was redlining his engine in neutral and then heard some not so nice noises and this was the result. wasn't my engine build but i did build him a new engine with what was still usable that made over 500whp, this was about 15 years ago though.

Still to date the most gruesome teardown and rebuild i've done.

 

Adding to the spun bearing stories, I also had a sudden spun bearing on my first rebuild back in 2013. I was cruising to work at 70mph when suddenly it started making a knocking sound.
It was a Weber carbed S4 6 port 13B, I think it already had over 100k miles on it, and my rebuild put about another 70k on it. The stationary gears were from an RX-8 and most likely had fewer miles on them.

There were no oil consumption issues prior to failure. Though the stock pressure gauge isn't highly accurate it read in the normal range the whole time.

Luckily it didn't lock up. I was able to drive home, a couple more miles for diagnosis, and its last trip to the shop where I swapped it.