117k mile renesis teardown
 

So when I bought my 04 rx8 it was an AT 4 port with 110k miles on it, one owner lady driven. I was told it was original engine, and I found nothing about the engine to suggest otherwise (I can usually recognize remans and rebuilds very easily).

The engine was tested to have 90-92psi, below the mazda lower limit for a running renesis engine, but it still started and ran great, idled normally, never stalled, didn't smoke after initial startup, and got 18mpg on the highway. I drove it this way until it had approx 117,800 miles and then did the AT to MT swap along with a fresh 6 port MT engine. Since then, the old AT core has sat in the corner, and I finally motivated myself to tear it down.

This thing was in surprisingly good condition and would have probably ran fine for a long time. IT had very little in the way of carbon buildup, it looks like an engine with 20-30k miles on it in terms of carbon. Now, I can't speak to how the first owner drove it for her 110k, but I know that I drove it fairly hard much of the time in the last 7k, using the paddle shifters to downshift and upshift manually and bouncing off the rev limiter unintentionally at times (the auto's sometimes get quirky near redline and won't shift when you tell it to, until you let off the throttle). I also did the "water injection treatment" to the car when I took possession of it, so this may have helped as well (note that I do not recommend it for rx-8 owners).

There is not much bearing wear, but I do not think that the previous owner used the dealership (or it's recommended 5-20 oil) for oil changes, so it is likely that 10-30 or higher was run in it. I know that I ran 20-50 in it during my ownership.

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Irons have very little wear on them.

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Rotor housings have mild to moderate wear, not really bad at all. It also startled me that this is one of the first sets of renny housings that DO NOT have any cracking whatsoever at the sparkplug holes. Such cracking is normally an indicator of local overheating at the plug hole. This means that this engine, high miles and all, must have run cooler than most others. My theory is that this is due to the talle gearing of the auto, keeping the engine lower in the rpm range at all times and helping the water pump stay in it's efficiency range and out of the mid/high rpm range where cavitation and poor efficiency occur.

So you may ask...since this engine looked really good all the way through, why was it making low compression? Simple...the apex seals are worn in the center, but not on the ends. This results in blowby and poor sealing, although there is no significant wear or damage to anything else. So why do they wear in the center?

My theory is that on the renesis, the 2 outside oil jets keep the ends of the apex seal from wearing, but that oil never makes it to the center of the seal. Thus you get more friction and wear there. This is why I highly recommend premix to all renesis owners, as this provides much more even and consistent lubrication to all areas of the chamber (and seals). Not to mention the superior lubrication and burnoff/anti-deposit characteristics of 2 cycle.

Here is a pic showing one of the apex seals from this engine, up against a straightedge, with a light source underneath. It is hard to see due to my poor photography skillz, but you can definitely see the gap in the center and the edges that are taller (sealing surface is facing down, against the straightedge).

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Class dismissed.

thanks for the pics RR. you gonna rebuild her and sell?

+1,000 on the center of the apex seal wearing out due to poor oil injection. I think mazda finally figured that out, hence the additional injector on the new engines.

What are your thoughts on cranking up the OMP settings instead of pre-mixing? Think it will serve the same function?

I have never liked the e-OMP used on 89+ rotary engines. They tend to fail a lot on the rx7s, not only throwing a code for the driver, but actually killing the driver section in the ECU at the same time, requiring BOTH a replacement OMP and ECU to fix the problem.

There is also no way to know if they are actually injecting what they should be. In theory even if you tell the programming side to inject more, the OMP can lose calibration and still not inject as much as you want, in theory anyway.

I like using premix because if the engine is running, it is getting the proper amount of fuel, and thus oil, for the given load and circumstances. It's a perfectly elegant solution. Not to mention that (in theory) you should never be able to flood a premixed rotary, because the oil film that prevents you from flooding is constantly being injected in appropriate volume to the gas being injected, thus the gas can never wash away the oil film.

And since the gas is injected in a fine mist that coats almost the entire chamber, so then does the oil. It is so simple that it is slap-in-the-face obvious, hiding in plain sight.

Doing it this way, I am in control of the engine's health. Also, 2 cycle burns cleaner than crankcase oil. So, even if you could adjust the OMP ratio, and even if you did trust it implicitly, the premix solution is STILL a better alternative. It also allows you to run full synthetic in the crankcase, IF you block the OMP feed off altogether.

IN fact, here are some excerpts of an email conversation I recently had with a curious owner:

the biggest purpose is that you are still relying on the metering ability of
the stock metering pump which is always suspect on rotaries. Whether it be
to original programming or learned programming changes to the computer, or
some deterioration or failure of the OMP itself, or deterioration of the oil
injectors, there is always the question of whether the OMP is actually
delivering as much oil as it should, during the proper conditions. This is
where premix shines...it leaves little room for doubt. IF the engine is
running smoothly, fuel is being injected in the proper volume, and thus you
are guaranteed that oil is also being injected as well.

The ultimate solution would be some aftermarket OMP, or a means to directly
control the existing OMP with certainty (maybe integrating a realtime volume
display or warning system for low flow), in addition to the external
reservoir and adaptor. But by the time you factor in the cost of the parts,
time spent engineering the reservoir and plumbing, I would just question why
the proven, simple but bulletproof premix method needs to be re-engineered.

FWIW, I premix in my rx7 and rx-8. In the rx7 I run no OMP, in the rx-8 I
have obviously left the OMP due to the stock PCM requirements, and have left
it to inject whatever minute amount it sees fit in addition to my premix. I
have never noticed that the car burns any oil whatsoever, with the original
AT engine/OMP/PCM, or with my rebuilt swapped MT engine/OMP/PCM. I could
have believed that the tired old AT engine was producing weak compression
and probably fuel diluting the oil supply to make it look like I was not
injecting much oil; I have a much harder time beliving that my tight, fresh
rebuilt MT engine is fuel diluting at all. That combined with the higher rpm
and harder driving I give the MT, should be producing a drop in oil levels
over time, but it is not, thus I believe that for whatever reason the OMP is
not doing it's job. An external reservoir of dedicated 2 cycle oil does no
better than using crankcase oil supply, if the OMP does not inject it in the
proper volume.

[regarding adjusting the OMP flow rate via an accessport]:

that's great if you can verify increased oil usage after the adjustment.
But in my mind you are still relying on a device that is known to fail and
be inaccurate, and you have very little way of actually verifying what it is
doing on a per-line or per-chamber basis at a given load. At least a fuel or
ignition deficiency will show up in performance or driveability issues, but
OMP deficiencies are a silent killer. Even if you do notice increased oil
usage, how do you know that both chambers are being fed equally? Or that
both lines to a given chamber are? Or perhaps it is delivering enough at
cruise but not enough at WOT?

The beauty of premix in the fuel is that your metering is guaranteed to be
even, accurate and appropriate to the conditions. Fuel is shot into the
chamber and coats the walls (both rotorhousing and iron side walls) much
more evenly than the flow out of the 2 oil injection ports. On older
rotaries with the single injector in the center, you can actually see a
shiny stripe in the center of the housing and dull/worn areas out near the
sides as a result of the poor distribution from the oil injection ports. Not
many rennies have enough mileage to make this determination yet, but I would
expect to see the same effect on them...not much wear on the sides, and more
wear in the center. In fact, I have already observed an inverse warpage
effect on some apex seals from medium mileage low compression renesis'. IN
other words, the center seems to be worn slightly more than the edges,
resulting in lower compression due to blowby.

Back to the point about fuel injection. When you are cruising, fuel is
trimmed back, and thus premix oil with it, because you don't need much in
times of low/mid rpm and relatively low chamber temps. When you go WOT, you
get a ton of fuel, and thus a ton of oil. And since the fuel is required to
be evenly distributed between chambers, you are guaranteed of proper oiling
as well. To me, this is what makes it such an elegant solution.

believe it or not, I use the basic wal mart premix in both my cars. TC-3
is the standard quality rating for 2 cycle oils, so as long as you see it,
it is acceptable. Given the low volume we are using in this application, it
is my opinion that unless you are running a dedicated race car, there is no
need for concern as to specific brand or quality. Otherwise I would say that
the pettit Protek or the idemitsu are the top of the line choices that
should also work fine, but I see no need for the added cost or difficulty in
obtaining them.

As for volume. The accepted standard for those running with no OMP at all is
1oz to 1 gallon of gas. For those running known working OMP's that just want
additional insurance/protection for their driving style, or perhaps a track
day or dyno session, or those with heavy mods and no way to increase the OMP
injection rate, 1/2oz per 1 gallon is the standard. I choose to run 1oz/gal
in my rx-7 with no OMP, and in my rx-8 with stock OMP and pcm. I choose this
because I feel that the OMP is doing next to nothing. Rather than spend
$600+ on the device that you have I choose to just throw in additional
premix which is far cheaper.

In a non turbo rotary, too much premix can never hurt you, up to the point
that you see visible smoke at idle or possible plug fouling/buildup issues.
Too little can hurt you, though, so again I err on the side of caution.

Running a thick film of premix or oil injection also promotes slightly
better compression, as the oil film takes up air gap between seals and
sealing walls. This is a trick sometimes used to overcome flooding that is a
result of weak compression in a high mileage older rotary, or in a fresh
rebuild with marginal/worn used rotorhousings that is not broken in yet and
sealing too poorly to restart reliably. Running a fat premix ratio can give
you an additional 2-5psi compression.

with 2 cycle burning almost completely compared to regular
dino oil, you'd have to be running WAY over the proper ratio to get any
significant buildup or actual fouling of the plugs (or buildup on the rotors
for that matter). In fact that is another big upside to premix only without
OMP injection...fewer engine deposits from OMP injection/dino oil
combustion.

Note that you can actually block off the OMP feed ports on the pump while
leaving the pump plugged in and keeping the computer happy. At least you can
on 7's with the electric OMP. I have not tried it on an 8 yet, but I do not
know of any way that it has to actually see what is flowing through the
lines...it simply opens the metering valve inside and expects that the oil
will flow out into the lines. You can simply remove the banjo bolts holding
the lines to the pump, and put in solid bolts instead to stop the flow. I
have been meaning to do this myself, since I run enough premix that I do not
care if the OMP works whatsoever.

ON the premix, for each car I bought a 16oz bottle of premix and also keep a
gallon jug at home. I keep the bottle in the pocket of my driver door. Run
the tank as far down near E as I am willing, then dump in the entire bottle
and fill up, which facilitates automatic mixing while the fuel is sloshing
around. Then when I get back home I refill the little bottle from the jug
for the next fillup. You can also keep the jug in the car with you, but
there is a chance it could make a mess during spirited driving. In the rx-8
my fillups are usually 14.5-15 gallons which puts me just a hair rich on my
intended premix ratio, but I have seen no significant smoke except the
normal 1 minute puff at cold startup and no other issues.

If you don't keep premix in the car with you, the 16 ounces they sell for
boats at the gas station will probably cost as much or more, as the entire
gallon from the auto part store bought in advance.

another thing...rotaries can be flooded if shut down during the cold start
cycle due to chamber wall wash of the oil film. The film maintains
compression, and if the engine is stopped before it is restored, there may
not be enough compression to restart later, thus a flood. In my mind, premix
prevents the possibility of a flood, because oil is metered with fuel, so it
should be impossible to wash the oil film away.

I have never been able to flood a rotary that I have premixed. But, my rx-8
would never flood even before I started running premix (old engine, before I
did the MT engine build/swap) so I am not sure if my rx-8's anti flood
properties are a result of premix or simply of my climate or other factors.

With the OMP blocked off/removed, what ratio oil to gasoline do you think would be adequate for lubrication?

Edit: never mind, you just answered it in your last post.

Great write up RR . I'm tempted to disconnect my OMP and go 100% premix .
Do you think different ratios for different uses is appropriate - ie street vs track .

Thanks for this, Kevin!

Yes...fat ratio for hard driving, lean ratio for cruise/road trips. I usually run a bit more than 1oz/gal for dyno days etc. and less for road trips.

EDIT: however, upon further reflection, most road trips in this car still result in an engine turning 4000rpm or more the entire time (for the MT models), so it would probably be wise to run the standard ratio anyway. When we took the auto to florida last year, I didnt run quite so much because it was cruising around 3000rpm which is not nearly so stressful IMO. In an rx7 you are also running around 3000rpm at interstate speed, so less premix for road trips is acceptable for those as well.

There has been discussion on using TC-3 premix that lends me to believe it isn't optimal for the situation in the rotary. I would stick to something that wasn't designed for cool running outboard applications...and go with something deigned for higher heats...like 2 stroke air cooled bikes or smowmobiles.

Or hell ...get the Rotary premix from Idemitsu.......

Well said, RR.

S

Subscribed

Very Nice, I want to do this with my engine someday.

That's great if you can afford it, or if you can wait days or weeks for it to be shipped to you. This is still far and away better than doing nothing, though.

I really need to start pre-mixing; engine is at 50k already

For sure....any pre-mix is better than no pre-mix......

I went through this with 2 stroke bikes though....and they don't use TC-3 stuff at all

To me this is why continued use of the OMP is compelling. If you trust that it actually works, then it correctly adjusts the amount of oil based on engine load and RPM. That being said, I think a small amount of premix is also good to help with the center of the apex seal which as your pictures show seems to be a problem.

What year did they add the new injectors?

As RR explained above - premix does the same . More fuel = more lubrication

2009 with the refresh is when they put in the extra center oil injectors

Supposedly...in theory, not in practice, obviously.

Using fuel to deliver the oil is a perfect metering method...since fuel delivery is a very accurate AND IMMEDIATE indicator of throttle position and rpm.

Then there would be no reason to use less premix for cruising/road trips. The relationships between amount of fuel injected, load, and optimal amount of oil are not necessarily linear.

/\ you have a good point there- perhaps there is a perfect premix% that would cover all conditions.
Remember the omp calibrations are only Mazdas best guess and they got it wrong to start with by their own admission.

Oh I agree that the OMP in it's OE form is far from optimal, especially with the coverage issue (which should be fixed on the '09). I'm just saying that I don't necessarily think it should be abandoned in favor of all premix for a daily driven car. If it's a track car I could definitely see going 100% premix.

I do not feel that the additional center injector in the 09 will be sufficient protection either.

See above where the apex seal is NOT worn? IT's only on the extreme edges...about 5% on each side. So basically the oil is ONLY getting spread right where it is injected, and is not being spread anywhere further inward.

So, even if you add another injector in the exact center. What about the area of the seal in between the center and sides? The oil only spreads in a 2-4mm wide area away from the injector port, as has been shown with wear patterns on rotaries since the beginning.

I feel you'd need 5 or 6 injectors across the entire width of the apex seal to provide enough oil to lubricate the entire width of the seal without significant gaps.

BUT...more injectors won't mean much without more oil flowing through them. IF we currently inject X amount of oil per injector and we add 2 more injectors per rotor, you are spreading X out further and thus injecting X/2 oil at each injector now. And we know that mazda cant inject the proper amount of oil to lube the seal for long life and good compression, while still meeting emissions and cat life requirements. Thus we have what is one of THE 2 MAIN issues holding the rotary engine development back. Since emissions requirements will never relax to the point that we are allowed to burn as much oil as we need to for the longevity of the seals, we must conclude that better materials must be used for the seals and surfaces.

We are engaged in a battle between reducing oil consumption for emissions requirements and a better reputation for the engine, and providing enough lubrication for long life and a better reputation for the engine. Moving in one direction negates the other. I feel that mazda crossed the line away from reliability and towards emissions in 1989 with the e-OMP. Those engines, although the housing coating was superior to the older style engines, actually do not last as many miles on average as the older ones. And with each successive generation, mazda has removed more oil via the e-OMP, and each generation the engine life has gotten shorter.

That is of course how I see it...the armchair engineers likely have alternate theories that may blow mine out of the water.

Proof that the rotary can last a long time with out premix.

...and probably much longer with it. :)

Had this engine been in warranty it would have been replaced by mazda due to the compression test numbers, although it still ran fine. Most people would call this an "engine failure" and so technically, this engine did not "last" without premix, per mazda's own definition (minimum compression of 96psi).

Razz doesn't always read the text.

lol..

RR great summary and write up.
Some of us do have issues with dirty filters and fuel starvation/cut/low pressure on the track---mostly. i am working on a fix for this--i
part of my fix is an external filter--that way --it will not be a concern.
OD

Great write up ! :)

I did a compression test on my motor about 2 months ago.

numbers were

Rotor #1 @ 288 RPM - Warm engine

Face I - 7.1 x 100 KPa (102.98 psi)
Face II - 7.3 x 100 KPa (105.88 psi)
Face III - 7.1 x 100 KPa (102.98 psi)

Rotor #2 @ 286 RPM - Warm engine

Face I - 7.5 x 100 KPa (108.78 psi)
Face II - 7.6 x 100 KPa (110.23 psi)
Face III - 7.8 x 100 KPa (113.13 psi)

I know Rotor #2 looks ok. Rotor #1 to me it looks so-so. What ya think RR ?

and notice, I've been using Premix on this motor for maybe 20K+ miles, but I "stop" my premixing for 2-3 tanks of gas before I do this test.

I have temp gauge installed. and for some reason, when my water gauge reads something like 100 Celsius or over and I stop my car, restart it maybe a minute later. and in some rare cases right after the motor started it just dies right off. and I need to crank it again. somewhere not working right ?

I wonder what a 166,878 mile engine would like inside.

I often wonder that....hmmmm?????

come back when you become the first member of the 200,000 mile Renesis club :D

Wealth of info, thanks RR.

Only 17,000 miles in 8 and a half months? You're slowing down.

First, thanks for the EXCELLENT thread, RR! Great illustration and rationale for premix.

But I'm very curious why you don't recommend the 'water injection treatment'.

1. Dannobre said TC-3 may not be optimal for the rotary. What is the likely negative consequence?

2. If premix is as effective as RR (and others) suggest, then high mileage engines on premix from day one should show a very even apex seal edge. Are there any cases out there that have been observed? If not, this should be a priority for the RX8club.

3. When Mazmart tore apart expo's engine at 111,000 miles, the engine had a lot of carbon deposits on the rotors. Expo's response was that he would cut down on the premix with his replacement rebuild. In contrast, RR said a 2-stroke should burn very cleanly and not cause carbon buildup. Can someone explain please. Did expo not use 2-stroke?

4. Why can't a set of oil jets be used on the apex seals much like the jets on an inkjet printer, which can have hundreds or thousands? Is this technology not ready yet for some reason? Seems like it would be the goal for the future for perfectly even oil injection and distribution while minimizing the amount of oil used.

the oil is not injected--it is a weeping type of lubrication--it does have a very slight pressure to it from what I understand--but not enough to "spray" like a true injector.
its more of a drop and the seals spread it ---supposedly. i think i have that right.
OD

If you have a nozzle that sprays... it will clog.

Remember we are using oil here, so we need a good technology that will not cause clogging nozzles.

I never really gave it much thought about premixing.... even if you have the cobb MM tuned to inject more oil would this still be a issue?
Wouldt premixing clog the fuel pump?

GREAT THREAD!!

i am currently at 51K miles

compression test was

1st rotor: 110 PSI
2nd rotor: 105 PSI

they said it was still a good motor.

I will now begint to read up on premixing as im still a novice! so 2 stroke cycle oil... for gallon????

I have always liked the idea of premixing---but at the concentration needed-- to amount to anything. With Georgia's dirty gas and with us that track a good bit, there are certain things we have to address in order to do this.
Our fuel filter and pump assembly/delivery system is not made for the track. people will probably never have a problem on the street with it--but the track+r compound tires+mods and you start having fuel delivery issues. We believe pre mix compounds the problem by (over time) increasing fuel filter resistance through sediment/oil accumulation. There are other factors involved also. This is the best theory we have to date. We know for a fact that a symptomatic pump is down by capacity by approx 30%, we know that replacing the fuel pump assembly temorarily fixes the prob.
I am implementing a system that utilizes the oem pump/wiring and regulator/keeping it a returnless system but with an external fuel filter, a fuel can window and increased venturi action(shhhh---secret:)).
The reason I mention this on this thread is i too believe in pre mix---but due to these side effects i have been unable to do so with consistency. I still think that anything under 1/2 oz per gallon does nothing.
proper temp control will be just as important--if you get the sparkplug cracks you can pre mix all you want and you still will not get a long life engine. I believe it is going to end up being both.
Keep it cool (under 225F-230F) and keep it lubricated and you will continue to twirl the magic spinning triangles.
thoughts ????
Olddragger
Again good job man

man i wish i had a rotary motor just laying around to tear down.....would b someting fun to do while drinking some beers hahah

OD, I know heavier weight oil is popular here, but I have not yet gone above 5w-30 because thinner oil is also said to be better at cooling. Not sure if this is merely a theoretical difference or something that makes an actual difference in practice, but do you think going to 10w-40 or heavier makes an appreciable difference in engine temperature? Others?

the most important Thing about heavier oil is that it protects better, cuz it it has greater film strength. cooling is just a "side-effect"

if u want to cool better, then you might wanna improve your coolant cooling system's efficiency, like better Water Pump(Mazmart), Better Water hose, and Radiator(Like BHR, Mazmart, and some others)

speaking of Radiator ... now I think Im done testing Mazmart's radiator. Next one would be ... *hehehehe* ... but kinda too cold to change any new rad now. so hehehe ....

Better cooling is not a side effect of heavier oil but of lighter oil. I'm not currently trying to improve my cooling system (maybe if I used havier oil I would be). I'm just wondering how much increased heat might be produced by heavier weight oil, wether it would be noticable in the long term, eg, with reference to sparkplug hole cracks, or perhaps in the short term in looking for better water pumps or radiators.

heavier wgt oil has not increased my oil temps in any noticeable way. 20w/50 and 10w/40 here. true that oil does help cool this engine but the cooling of the engine comes primarily from the coolant not the oil. If you get the coolant temps under control--the oil falls right in line(as long as you have 2 coolers.:)
my on track temps on a cool day --mid 70's never got over 185:) street temps with a/c on on a 95 f day(i do have forced induction) never over 195 even while sitting still.
RR dont mean to get off topic here--i guess this is discussing what it takes to get long life out of our engine.
OD

Sorry I didnt explain my post clearly

What I mean was the primary cooling comes from Coolant, not Engine oil. The oil will carry heat away thats for sure, but its just one of the oil's "side" effect. the main point of the oil is to "lube parts" :)

off topic for a bit -

Now Im wondering is there any small leaks inside my engine or something.

Cuz during summer days ~ after car fully warm up my coolant temp is always around 200-225 f ~~ (something like 95-105 Celsius)

Im running about 50/50.

and when going thru Tunnel (like Holland or Lincoln), my water temp might "shoot up" to around 230~f ~ (I've seen 110 Celsius), might have something to do with the higher pressure inside tunnel ? dunno

I got the temp reading from water gauge, I installed the sensor after the thermostat. maybe thats why? I dunno :(

OK, now I understand what you meant. I presume your cooling issues did not develop as you started using heavier oil? Sounds a little more perplexing.