Rebuilt Race engine Problem
 

I rebuilt a S4 engine for a road racing car. The Housing were professionaly honned. The platte have been lapped, Goopy apex and coolant seal, new bearing/sleeve rotor and stationnary gear.
New oring in oïl seal but using the same oïl seal.

I did a breaking of around 700km before starting to rev more the engine. After these 700km a increase the rpm by 500rpm every track session of 25 minutes. Until I reach 7500rpm

The engine start to drink oïl by the rear rotor (seperate exhaust) a lot of oïl.
At the end of the race week end, the engine take 1.5 liter for a race of 30 minutes.

Front excentric shaft seal start to leak somewhere when i atart to rev more the engine.
Front rotor where running very lean and rear rotor very rich. (one wideband by rotor)
Probably an injector problem.

When i opened the engine the rear plate has big grove done by the side seal. about 3-5mil deep.

No oder damage anywere, all part were in place.
The engine was still running great in the last race.

Question what cause thes damage on the rear plate, does the different in ratio between rotor could have cause that?

When you had the plates lapped, did you also get them re-nitrated?

And what clearance were the side seals set up with?

^ You think side seal to corner seal clearance would cause premature wear in the plates?? :scratch:


Probably a better/follow-on question would be if he had double stacked side seal springs.

I have found that if you set-up the side-seal clearance tighter than .003" the side seal will bind and become a cutting tool. (first attachment)

But since there are only two main leaks in a Rotary (apex seal and side to corner interface)
the next logical step for me was zero clearance side seals. (second attachment)

Barry

Somehow I knew you were going to try plugging that... :lol:

If you experience binding at .003 then you're doing something else wrong. Many people run less than that with no problems. Let's try to keep mis-information to a minimum...

http://www.racingbeat.com/mazda/performance/rotary-tech-tips/engine-seals.html

could be that iron had been lapped twice or too deep? in that event it's likely all the nitrite was gone which would expedite wear.

Typically a lapping will remove the hardened (nitrated) surface, so they need to be retreated to avoid quickened wear.

Side housings weren't hardened until 1978 or so and it wasn't a massive problem to where engines would fail in the first few hours.

Any time I see wear like that it is due to dirty air. Usually a vacuum leak somewhere or an uncovered port in an air filter. The dust gets between the rotor and side housing, in the area between the side seal and oil seals, and has no way out so it goes around and around grinding the side housing. The step wear in the combusion chamber area then destroys the oil seal holders and the engine starts burning oil rapidly.

If this was the cause, you will also see the side seal will be worn significantly shorter on the leading edge, and the apex seals will be worn thinner. (I had one 2mm seal engine where the apex seals were only 1.6mm thick)

i think a better question in that case would be, what type of racing does this car do and is it in a dusty environment? but dust wouldn't explain why it occurred on the rear plate only, if it was affecting the rear rotor it would affect both of those iron surfaces.

i think Barry's idea of it being a side seal binding might be the most plausable, disregarding the whole gap argument thingy.

I noted severe wear on the rear end housing on one of my engines that was traced to a vacuum leak at the intake manifold gasket. The sealing surface on the iron had a small nick and there was oily fuzz on the outside. Leaks work in both directions after all, if it's drooling oil out then it is sucking air and dust in.

Racetracks are very dusty places. There's a lot of rubber and brake pad/rotor dust in the air, and when it settles to the ground it just gets disturbed again.

then i'd suggest checking everything associated with that secondary port, if it's non turbo that brake booster hose to the firewall is very prone to cracking and causing a vacuum leak.

Thanks guys for all your answer.

After analysing everything, and looking again and again to the rear plate and the side seal. I think that one of the side seal(or two or all of them) didn't had the clearance they need and they wear excessively the rear plate.
Meaby a peace of dirt could had stay Under the side seal during the build and push the side seal hard on the plate causing the wear.

My next step, I will order part I need to "redo" the engine put it back in the car and go to race.

I will check the brake booster hose and look for any vaccum leak too.

Hope for the best. I will be back after the race to give you guys how goes the engine.
Thanks all.

I just had a very similar failure mode on my rear plate side seals on a low hours 13B race engine.

I would have 1+ quarts of oil blowby in my oil catch can in 10 minutes of track time.

When I tore it apart, 2 of the rear rotor side seals were broken/missing and the springs under the side seals were partially missing and extremely brittle. One of the adjacent corner seals was cracked in half at the apex seal slot. I had always had a really rich rear rotor. The all of the other side seals were in excellent shape, even those on the opposite side of the rear rotor. A difference to your engine was that my side housing was still in excellent shape, no wear or grooves. I have no idea how the side seal fragments managed to escape without causing harm unless maybe it occurred during starting or at very low rpm or something.

I thought about the following:

1) street port shape/chamfer issues; I saw no issues

2) dirty air; plausible, I had a poorly fitting airbox for a while

3) side seal clearance issues; maybe but all of the other side seals worked great

4) mixture issues; I had extremely lean and extremely rich running conditions under all loads while troubleshooting carb issues. Maybe it ran extremely lean = no oil for the seals leading to really high seal/spring temperatures? Additionally, the engine naturally tilts backwards. I had extremely rich conditions where a solid stream/drip of fuel out of the boosters would occur on the rear rotor = maybe hydraulic locking in the chamber during starting?

I replaced the failed side seals, did the clearances to 0.002" and everything is back to running great.

Just for some anecdote that isn't necessarily data: I exclusively premix, and I only have injectors in the center intake ports. ITB style intake. I don't see what I would subjectively call excessive side seal wear on the engines I'd have apart, that didn't die from dirt ingestion.

Current engine is almost five years old and many tens of thousands of miles. No problems.