I've been doing a lot of searching and asking around on the question but everyone I've spoken to about it has either had an older Rotary car (Early FC, RX3/4) or an FD so I haven't been able to get a clear answer on the subject as their OMPs seem to work fine.

I've been told the FC's Electronic OMP is fairly crappy compared to the FDs electronic system and the old mechanical systems used in older Rotary-powered engines in the sense they just don't get anywhere near enough oil in to keep the engine lubricated, thus killing seals and such prematurely, so premixing is an absolute must...But rather than having to premix each fill-up, is there any way I'd just be able to replace the standard OMP with a more capable one, or even an older mechanical one from the older FCs or install some sort of external oil tank to slowly feed into the fuel?

Can it be done? Is there any solution that'll prevent me needing to premix? If not, then that's understandable but I figured with how old the engine is there'd surely be some sort of a miracle system to solve my worries. I don't trust myself premixing the right amounts each time, and the last thing I want to do is grenade my engine.

Feel free to point and laugh, I've only got a vague idea of what I'm talking about, which is exactly why I'm here! Thanks in advance for any replies.

 

you wont grenade an engine by failing to mix the proper ratios, in fact it's pretty forgiving with these engines. i have even run without any rotor seal lubrication for a few tanks with no noticable side effects, i wouldn't suggest it long term though but it gives you an idea that the lubrication requirements are actually very little.

IMO you either go one way or the other, premix or rely on the OMP, anything else is just a duct tape job.

why? because the oil metering system doesn't replace premixing, even if you use an external 2 stroke oil source. the Rtek chips will disable the OMP limp mode so you can premix without needing the OMP any longer. the S5 cars are just a pain because the OMP is a failure waiting to happen, simply because it will fail eventually no matter how well you take care of it. switching to a mechanical system would be as much work as it would be just pouring oil into your tank for several years.

 

By whom and what evidence backs the assertion?

Others here have far more experience than I and I've long lamented the crappy implementation of the OMP (specifically, the exposed and vulnerable external lines) but teardown of my old 300k NA engine was a revelation.
It was practically spotless, with very little carbon buildup and no sign of underlubrication.
IMO, the OMP had worked perfectly despite my reservations and in the years I ran that motor, never once acted up.

I've seen several attempts at "mechanizing" the pre-mix process but I don't believe any actually got finished completely. Rotary Aviation makes a system that introduces pre-mix oil instead of engine oil but that doesn't address objections to squirter placement.

You face a dilemma that is inescapable with the rotary engine...you have to guess.
With a piston engine, it's a relatively trivial matter to pull the head and examine the combustion chamber to see how things are going. Doing the same on a rotary means a full teardown, it's all or nothing. Your OMP could be working fine (as mine apparently was) but you can't really confirm (or deny) that fact without a fairly substantial commitment.

I struggled with this same problem when I swapped in the replacement engine this summer and two things swayed my decision:
-Unless you go standalone (or otherwise bandaid your stock ECU), you must keep the S5 OMP plugged in to avoid limp mode, even if it no longer is attached to the block and functional. This seemed clunky and inelegant.
-The RA system solves the issue of using crankcase oil but leaves the stock system otherwise intact and adds the same extra steps that pure pre-mixing does (you must monitor oil level in your new reservoir instead of just dumping straight into the gas).

I figured the stock system which had kept my old motor alive for so long was worth gambling on again, all my experience (again, VERY limited) says it works fine.

 

I'll add that the RA system allows a higher quality of oil to be used instead of dirty crankcase oil.

This is an advantage because you can run a really good 50:1 synthetic two stroke instead of whatever you want to dump in the crankcase and it's always clean.

 

i have a box of dead S5 OMPs, even the ones i thought were ok wound up DOA when i put them on after sitting in a box. i keep them in order to investigate possibly repairing them, but that may be more time than it's worth.

all the higher mile engines i tore apart had wear lines leading from the oil metering nozzle in the rotor housing, so the carbon laden oil theory isn't so much just a theory.

 

Thanks for the replies guys, I guess premixing really is unavoidable. But at least it doesn't seem to be an exact science. and there is actually a little bit of give and guess in the whole process of it all.

I guess my best bet here will be to premix and run the stock S5 OMP until it decides it's no longer with me any more, replacing it with an RA system, or simply deleting it altogether, and by that time I should probably have premixing down easily anyway so it's really just whatever is less of a hassle at the time. I'll always be doing some daily research on the matter but making this thread has really put my mind at ease for now, I know to just deal with it for now, thanks!

 

it's not unavoidable, but i still say it is preferrable.

 

You also have the problem with s5's that when it OMP goes bad, it takes the ECU with it

 

the RA adaptor doesnt replace the omp...the adaptor just bypasses using engine oil for 2 stroke oil in a separate tank....I assume the S5 and FD share the same omp except for the fd being 2port and S5 4port correct?

 

there has to be some additional internal changes, because the FD OMP rarely fails, however it only has to do half the work.

 

that sucks...anyway of piecing the two together to get a 4port version of the FD one?

 

maybe, but the EOMP isn't friendly to dissecting as it is.

 

Is it difficult to create a makeshift RA adapter? It'd be neat to see someone reuse the sub zero tank for such a purpose.

 

I think several people have done that...or at least, tried.
I vaguely recall that maybe there was an incompatibility between 2-stroke oil and that particular plastic, but could be wrong.
Any old two stroke street bike (Yam RDs and RZs) will have an oil reservoir tank that could work.

 

Interesting. Have there been any write-ups on how to adapt a DIY two-stroke reservoir to the OMP? Seems like a great reliability mod, I'd just prefer not to have to shell out a bunch of money on the RA system if there's an alternative.

 

all you need to do is drill and tap into the oil feed hole and thread a brass barbed fitting into it then plug the hole in the front cover that used to feed engine oil into the OMP.

the hardest part is getting that at an angle that you can still run the line to it unobstructed.

 

Ethylene glycol and two stroke oil are completely different animals, I would be very careful about the type of plastic tank that would be used.

 

i doubt there is any compatibility issue with the sub zero reservoir tank, but the seals for the pump most likely are not oil friendly.

 

Im not too familiar with how the OMP looks/operates,but to clarify, you'd block off the hole to the crankcase oil, tap a new line for your reservoir, and that's more or less it? Does the S4 OMP work by gravity/vacuum alone?

 

there is a small amount of pressure feeding and pushing through the OMP system but it is just about non pressurized.

if you have the reservoir higher than the engine then that should suffice.

 

RA recommends the tank should be no less then 6 inchs above the pump inlet to get enough head pressure...IIRC i think someone used the zero assist tank but after a period of time the oil softened the plastic.

 

The sub zero tank is probably a poor choice indeed. There's still a novelty in trying to find a use for it, though.

 

polypropylene should work for holding oil, which is what i figured the sub zero tank was.

 

It comes in different flavors though. give it a try and find out. I'll be honest and admit that I don't really know.

 

Inspiration pictures how modified my car. 2stroke oil bottle from a KTM Motocross bike.