Engine tear down: uneven seal wear, scored housings *pic*
 

I tore down my engine yesterday and found some things I expected and some that I didn't.

Background: rebuild engine and turbos 1500 miles ago. Engine made 125 psi compression on both rotors. Used Atkins master rebuild kit + a few extra parts and JHB Cermet B resurfaced rotor housings.

The problem: I didn't loctite the turbocharger nuts and my primary compressor wheel came off the shaft and shot metal down the intake.

The results: 110 psi on the rear rotor and 90 psi on the front rotor after the incident. The front eventually ended up at 75 psi and the car was impossible to start or keep running.

Tear down: I observed normal wear on the rear rotor except for medium scoring on the rotor housing from the compressor wheel parts. The rear rotor had unevenly worn apex seals and deep scoring on the rotor housing. I can't believe the engine still ran at all...

http://i34.photobucket.com/albums/d1...n/DSC00648.jpg

I don't have an explanation as to how the seals would wear like this. There were no lips or gouges that weren't in the same direction that the seal travels. Maybe the cermet coating acts like a file when it's damaged?

I'll take rotor housing pics later. I didn't have my camera with me when I tore it down and just brought the seals home with me to post up on here.

Wow. Were the apex seals still free to move in the groove? At an angle that severe I wonder if it could bind up.

Dave

The first thing i did was take off the turbos and feel the seals through the exhaust. The bad seals you see were free to move, but had no spring pressure at all on the worn side.

I think the less worn side kept it in the groove. Thanks to that, my rotors came out unscathed. I'll be spec'ing out the grooves again, though.

The wear on the seals and spring makes it looks to me like the small spring was not inserted all the way during the last rebuild. Look on the bottom of the apex seal for wear, you should see four polished spots, one at each step.

Dan

how did you install the apex seals / springs? pre-assembly on-rotor or the way the fsm does it

I don't think it would have made 125 psi to start off with if that were the case. Here is a pic of the back of the seal:

http://i34.photobucket.com/albums/d1...n/DSC00649.jpg

I can see polish marks from the springs in the right areas.

http://i34.photobucket.com/albums/d1...n/DSC00572.jpg

FSM procedure. It's pretty much fool-proof, since you can see the springs sitting correctly before you push the seal all the way down.

I'm 99.9% sure the springs were in properly. All three apex seals on the front rotor are worn the same way. If I improperly installed a spring, I'd expect just that one to be worn unevenly.

i'm with chadwick and sevensix.

i personally pre-assemble the rotors, drop them in, and just put the corners in. come to think of it, everyone i've known who's done a rebuild has done it the pre-assembly on-rotor way (like in the atkins video)

well mazda way should be fine if he could visually see they are in. maybe the cermet is to blame, were all 3 rear apex's worn the same way?

Yes, they are all worn identically.

Also, all 3 have the polished marks from the springs being in correctly. 2 marks on the ends from the long spring and 2 in the middle step from the short one.

To add to the background:

The turbo compressor wheel came off only 300 miles into break-in. After the turbo went, i rebuilt the turbos only and continued to drive until the ~1500 mile mark when the car began to have starting problems and eventually wouldn't start or run.