NoPistons -Mazda Rx7 & Rx8 Rotary Forum - Side seal failed 30 miles in

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I built a '90 6-port motor a few months ago. I was very careful to properly clearance the side seals to no less than .002". However, I believe I had a side seal go out today. I have been breaking it in pretty gently, nothing over 5,000 RPM but occasional full throttle, varying the revs a lot. It saw about 20 start-stop cycles.

Compression test with the needle depressed on a standard gauge yields two strong pulses and one dead pulse, so... side seal, right?

This is a stock port motor. FD oil pressure regulator and shimmed front bypass. Thoughts on why it might have failed? I'll be tearing it down tomorrow.

John

Was the motor ported? Improper closing angles and/or no bevel on the closing edge will cause this.

stock port will not damage a sideseal.

sounds like a sideseal is getting jammed. did u clearance side seal to the side of the rotor groove? i always give it a .0015 of clearance

Yes, stock port motor. I did not check the clearance between the side seal and the groove, only checked that the seals moved freely which they did. I wonder if there maybe was a stray piece of carbon in the side seal groove? I cleaned them very carefully so I wouldn't think so.

How do you adjust the clearance of the side seal to the rotor groove anyway? I don't see anything in the manual about this... so is it a "if it isn't right, replace the rotor" kind of thing?

I was more thinking maybe one seal was too tight to the corner seal and that's what caused the failure. I hope it is able to be diagnosed when I tear the motor down.

Thanks for the input.

Quote:

Originally Posted by John V (Post 839307)

I knew Ito couldn't stay away...........

If its apart in the AM, no need to speculate, but I have seen this: Poorly cleaned grooves and a trapped side seal. In fact the side seal may be fine. Or if this happened some great time after a fresh startup, perhaps the top oil is not an ash free oil. Or it is an ash free and too much is being added. It turns into chewing gum and hangs things up. A long soak with a cup of auto trans fluid will clean things up. For breakins an ash free dyno oil is best, just whatever the OMP puts in is enough.

After breakin, a synthetic top oil at 1/2 to 1 ounce per gallon. Lower for standard street use, the full ounce for long periods above the red line.

The other possibility would be a stray piece of something passed through the engine, and the rotor sheared it in half. A chunk of gasket, or a spur from a lock washer or similar.

But I could be completely wrong.

Lynn E. Hanover

from this point you should be ok..

Quote:

Originally Posted by John V (Post 839324)

Lynn,

It was running fine and then it lost compression on that one seal. Would it be possible for a seal to stick in that manner? In other words - should I try soaking it in the auto trans fluid before yanking the motor? The motor and trans are ready to come out right now, so if I'm going to make one last ditch effort to save it before pulling it, now's the time.

I used Castrol GTX 10W40 in the sump and I run the OMP. When I assembled the motor I used lucas engine oil stabilizer on everything.

I guess if you do the auto trans fluid trick, do you just pump it into one of the spark plug holes and spin the motor a couple revs?

Thanks,

John

Crank it around until the bad face is against the plugs. Then pump the trans fluid into the trailing plug hole, with the shop oiling can. Let it sit for a day. Drain the oil out through the leading plug hole. Spin the enginew for a second so you don't hydraulic it with the starter.

Replace the plugs and give it a try.

Lynn E. Hanover

I tried that and let it sit for a few hours, and when nothing happened I got impatient and yanked the motor.

As it turns out, the rear face of the rear rotor has half of a side seal. It cracked right in the middle. I guess the stray piece went out the exhaust manifold. I don't see any damage on the iron or the rotor housing. The oil control rings are fine. The top side of that rotor has a couple scars on it from the side seal making its exit. None of the other seals are damaged.

I'm puzzled how this happened. I was very careful to clearance all the seals to .002" or larger. I checked the groove that seal was in and I don't feel any carbon. The rotors were spotless when I assembled the motor and the rear one is spotless now.

Thoughts?

Quote:

Originally Posted by John V (Post 839333)

John according to all your data. the only thing left is the simplist, but sometimes the worst. When your building the engine and laying down the side housings, sometimes and in very rare occasions. if the side housing did NOT lay flat on top of the rotor housing, the side HOUSING(iron plate) will push the side seal out of the rotor groove a little and twisted the side seal. at this point it goes un-noticed and the rest of the build is done,(the damage happens when you torque the tension bolts). the engine will fire up. but the damage was already done.

for your next build, always make sure the plates come down even on the dowel pins, on both sides. and always make sure the side seals are tucked away in the rotor. side seals have a tendency to pop up out of the rotor groove while assembly. .. hope this helped a little.