Adam

will adding premix to gas make apex seals last longer

rs_1101

yes.

trainwreck517

iTrader: (1)

No, they will last just as long with a properly running OMP.

Adam

nah i dont trust or do i know if it even works. there should be an alarm for the omp and other ways to check to see if it works..

White_FC

Havn't torn appart many engines that've run on premix?

CompuBob

no, but why dont you share it with us?

White_FC

Because it's all been said before...
Many many times....

Having torn down a few engines with perfectly running MOPs and one running straight premix, there is a very noticeable wear mark extending about ~15mm from the oil injector bung hole with the ones running on their MOPs.

This same wear mark was not present on the engine running premix.

One might conclude this wear mark would also correspond to a similar wear situation on the actual seals themselves.

Other people on here have had this same experience.

WAYNE88N/A

The question you should be asking is "Does running premix make the rotor housings last longer"...

When I tore my 186,000 mile engine down, the OEM apex seals still had .3mm of wear to go (approx 20,000 more miles until they hit wear limits), but the housings were shot, and everything (seals, springs, rotor faces, etc...) was gunked up from carbon from the MOP...

gnome311

So really the best investment that could be made, would be to invest into ceramic coated housings?
Because wear would be to a minimal?

WAYNE88N/A

Never heard of such an animal (though it wouldn't surprise me if it existed). Don't know if I would like bits of ceramic rumbling around in my engine, though...

"Something" always has to take the brunt of the wear in mechanical systems with moving parts. If it's designed correctly, that "something" will always be the easiest/cheapest part to replace. For instance, on aircraft, it's always the bolt or bushings that wear, never the fittings or flight control rods, etc...The metal alloys used are designed to be harder than the hardware, so we change the bolt/ bushings (cheap, easy), and she's back to 100%...On the rotaries, I think they (attempted) to design it so the apex seals would wear, but due to some funky "rocking" motion of the seals on the spring pivot points (my theory), or the uneven hardness of the OEM apex seals (RotaryAviation's theory), or the lack of universal OMP coverage in the housings (another popular theory), the rotor housings wind up taking a lot of wear...

It's just one of those things that have to be changed on a high mileage overhaul, we don't like it, they're expensive as hell, but that's life

RylAssassin

When one runs premix, does one disable the OMP? Cuz it seems it would be useless at that point.

WAYNE88N/A

Yes, that's the whole point behind premixing- to get the oil that's not designed to burn out of your engine, and put the oil that is in there...

locketine

the oil gets injected straight into the engine? I always assumed it got injected into the fuel stream. why hasn't someone made a mod where it does that?

also i'd like to hear some mileage differences between premix and not.

rs_1101

premixing will inject oil into the fuel stream.

problem with premixing is that you have to do it on EVERY tank if you block off your MOP. and you have to measure pretty well.

good things are that it apparently oils better, and prevents oil burnoff by blocking off the main oil squirters.

the theory is that injectors atomize oil better, providing more even lubrication whereas the oil squirters only cover a small area.

Atkins Mama

Premixing is good for higher RPM's.. OMP are ok but the cleaner the oil the better. The oil metering was designed to meter in a small amount of oil to lubercate the 2 metal surfaces. When we premix in the race car (8,000+ rpms) we use the amsoil synthitic 2 cycle oil as it burns cleaner and stays suspended and does not fowl out the plugs. the OMP is gear driven and in the many years of working at the shop very seldom is the oil metering pump a problem, 89 -92 has an electrical device on the side of the oil metering pump that was an issue but that is a whole nother issue.

Atkins Mama

BTW in our rotary engine airplane that hubbie built, we use the oil metering system as it does us far less oil than the 2 cycle oil.

WAYNE88N/A

To the poster that asked about the gas mileage-

The answer is yes and no...

If you use the "standard" 100:1 ratio, you won't notice much if any mileage increases.

If you take her down to something below 90:1, however, you will begin to see the increases, and at 80:1 it really becomes apparent (about .2 gal's less every fillup, which for me is every 200 miles exactly).

But, with every good thing must come the bad- your lubrication system will magically "add" some of the premix to itself, at 85:1 ratios I was "adding" about a quart every 2,000 miles, and the oil was rather dark and "smelly" at that point...So, if you don't mind the early oil changes, you can get better mileage with premix, do the costs outweigh the benefits? You be the judge...

The "happy medium" for me is at the 96:1 point, give or take

rxseven

As mentioned correctly, it is not as much to do with apex seal wear as rotor housing wear. The omp injects thru a pin-hole so the distribution of oil may not be uniform. Have you ever noticed chatter marks on the intake side of the rotor housings? Using premix can greatly reduce those chatter marks.

scathcart

From the very moment you start your engine after you do an oil change, you engine oil starts become contaminated with deposits such as carbon. Is this really the best fluid to be using to lubricate against friction? Even if you change your oil every 500 miles, premix is always going to be cleaner.

This is just one argument, but here's a better one: As an engine builder, all of my engines run strictly on premix.
I can give a huge long list of advantages of premixes, but it ahs all been said before, so to simply summarize: Premix is better.

trainwreck517

iTrader: (1)

Premix should be done on high reving engine, or engine that just stay in the power band 90% of the time. Or people with a bad OMP.

For a daily driven rotary that nomally stays below 3k the oil injection system does a good job.

Apex seals don't wear out like people make them out to seem; what does wear out are the housing.. but then again this leads to whether it sees high rpms or stays in the low range.

So if Its daily driven OMP will get the job done, just use quialty dino oil that has very little ash deposit.

casio

i don't think too many people are posting on an rx7 forum because they drive under 3K RPM. i rarely redlined my car, but thats not to say i didn't do it. i drove fairly regularly most of the time, shifting around 3 or so, but sometimes i'd get on it. if you have more input for people that sometimes redline or drive hard, that may be more useful. i plan to run premix for the simple fact that i have high mileage parts and would hate my electrical MOP to fail. premixing seems to be a cheap alternative and well praised, even for daily drivers.

(everything is in past tense because my car is waiting rebuild so temporarily i'm minus one rx7 )

RylAssassin

What would happen if someone premixed and ran there OMP anyway?

inflatablepets

I was thinking the same. Maybe I should've stuck with the S4 MOP instead of putting the S5 one on the car.

WAYNE88N/A

Nothing, really, maybe a little "excess" lubrication, and the fact you'll be cleaning your engine for three days to remove all the carbon & gunk when you do the rebuild

Some people consider mixing both "security".