So about a year and a half ago I installed one of Rotary Aviation's OMP adapters so that it injects 2 cycle oil from a seperate tank instead of oil from the crankcase. About the same time I installed my twin Weber 36 DCD carburators. Not long after that I began to notice that my oil level was rising. It rises about 1/3 quart or a little more over 1500 to 2000 miles. Does not appear to be containimated with coolant or obviously smell of gasoling. My first suspicion was that the carbs were leaking/flooding somehow so I double checked the float levels and the fuel pressure, all appeared to be good. Just for good measure I backed the pressure down to not much more than 2psi. Problem continued. After thinking about it I determined the only possible causes could be:

Fuel (most likely even though I cant seem to smell it in the oil)

Coolant (Not very likely as coolant level does not drop, no sludge in oil)

OMP pump allowing injector oil to leak pass the omp drive mechanism. (Not sure if this is possible or how likely it may be).

The only other cause I could think of is my relocated oil cooler may be draining back to the crankcase? It sits in front of the radiator and is a little higher than the stock location.

I wanted to be sure so I sent a oil sample to a lab, they found no indication of fuel or coolant in the oil so they suspect th omp pump leaking back to the crankcase. The detective a slight loss of viscosity that would seem to support this idea.

I am considering temporarily removing the omp adapter and going premix for a while to confirm.


My question is has anyone else using the RA adapter experienced this problem?

 

i think all of us without the metering system show an increase in oil level, its partly just the nature of the beast.

there are two things you can try. first is building a good PCV system, the stock system works, but its a bit small, i understand (but haven't tried) that going to larger hoses helps, the competition manual might be a guiade here.

the second is to possibly lean out the mixture, it may be that there is a rich spot,

 

It's fuel. The OMP usually pumps oil faster than the fuel dilutes it so you never notice.

 

Thanks for the input!!!!


[QUOTE]i think all of us without the metering system show an increase in oil level, its partly just the nature of the beast. /QUOTE]

I guess its more common than I thought.

[QUOTE]first is building a good PCV system, the stock system works, but its a bit small, i understand (but haven't tried) that going to larger hoses helps, the competition manual might be a guiade here. /QUOTE]

I am in the middle of doing this now, using vacuum sources that pull from both carbs equally so they will still syncronize well, using a PCV valve from a chrysler.

[QUOTE]the second is to possibly lean out the mixture, it may be that there is a rich spot,/QUOTE]

[QUOTE]It's fuel. The OMP usually pumps oil faster than the fuel dilutes it so you never notice./QUOTE]

the fact that both of you suggest this means I will have to reconsider this as a possibility. I had decided it was not the case, going by the oil lab's results, their report says there is no indication of fuel dilution.

If it were enough to raise the oil level, would'nt it show up on their report?

Also my wideband o2 sensor shows about 13 @ wot, about 15 at cruise and about 11.5 @ idle,, Should I be reassured by this or should I will consider leaning it up a bit?

 

WOT and cruise are perfect (if it's never lean-misfiring under cruise) but idle could theoretically stand to be leaner. If it will cruise happily at 15:1 then it should idle happily a lot leaner than 11:1.

I only shoot for a certain mixture at WOT. Idle and cruise, I just try to run it as lean as possible before it starts to miss. On my bridge engines that is about 12-13:1 under light cruise, on stockports that has been as lean as 16:1.

 

I would also think that based on the lab results, especially with the amount of volume difference, that you rule out fuel...but that's just me. However, 11.5 is a suuuper rich idle. I'm not too familiar with carb tuning, but I'd lean that out a lot on an EFI car (generally above 15).

 

Once again, thanks for the input!!

The numbers I gave were from memory, and since I was mostly worried about wot and cruise I am less certain about the idle number, I didn't shoot for any certain number , just tuned to give the highest rpm at the lowest throttle position, I will see if I can lean it out some, (although I am pretty certain I will not get it to idle at anything as lean as 15-1). Also, these carbs have a starter circuit that I am also leaning out, There is no doubt that it has been adding too much fuel so I am in changing both the fuel and air correction jet for it. This is one possible opportunity for extra fuel to get in the engine.

Any tips for getting it to idle at a leaner mixture?

Its a 4 port 13 B with large streetports that idles well at 980 - 1000 rpm.

I pulled a front cover and an old metering pump out of storage to examine to see if its possible for the oil to leak past the shaft and get into the oil pan, looks like its possible but I don't have an extra adapter to look at so I will have to wait until I get mine off the engine for final examination.

Thanks again for the advice

 

The "best vacuum" method is not really the best way to set idle, I don't think. You wind up with a mixture that's too rich and can foul plugs, and the mixture quality can go nowhere but down. This also depends on various qualities of the carb that I can't go into here, but part of getting a rock steady idle is the ability to self-correct - if it sags down then the mixture changes such that the engine makes more power.

Retarding the timing helps you run it leaner at idle. More vacuum means more exhaust gases pulled up means you need to run it richer to get the mixture combustible, so making less vacuum allows you to run it leaner. This is much much more noticeable with big ports, you shouldn't have much of a problem with a street port. I used to idle at 22 degrees and never needed it as rich as you have it.

 

I understand how tuning to the lowest throttle position results in the "high vacuum" situation that you describe above , but (and please be patient as I am a novice compared to someone with your experience,) but what I am trying to figure out is how to get the leaner idle I need without opening the throttle up so that it begins to adversely affect the idle transition circuit and also how to retard the timing without hurting top end power because of not having enough advance?

once again, thanks!!

 

Without knowing your carb setup, I can't help you there.

But the fact that you are running progressive carbs means you can use a technique that I've had lots of success with on Holleys - you can use the secondary throttle's opening to adjust where the primary throttle sits in relation to the transition slots. That is assuming that you are running into this as a problem, of course.

Take notes with every change you make. On one heavily-cammed engine I was making adjustments in the 1/16th of a turn range on the secondary throttle stop.

 

good tips, the note book is the most important thing, it has a longer memory...

 

OK, So even tough the oil analysis showed no fuel or coolant contamination I wanted to eliminate any potential problems so I have re-engineered my pcv system. I was worried about pulling vacuum from just one carb so I put a nipple on each primary runner, ran hoses to a Y to a PCV valve to the nipple on the oil filler tube, then ran a hose from the middle iron to a fitting on the air cleaner.

I also knew that my starting circuit was richer than it needed to be so I wanted to lean it out. The starting jets I had are the only ones available so I removed them, checked them with a jet gauge and reduced them from a 100 down to a 50 with some fuel proof jb weld and a set of miniature drill bits. This was too lean to give reliable starting so I took them out and enlarged them to a 75 size and that gives me what seems to be the perfect starting mixture.

During all this I retuned and synchronized the carbs and now have a much leaner idle mixture. Its idling at just under 1000 rpm. The mixture varies from about 14 to about 15.3 or so.

The only other source of oil contamination is the injection oil. I thought about removing it temporarily to see if the oil rise went away, but I decided I would try adding some fluorescent dye to the injection oil tank and see if it makes its way to the crankcase. I'm hoping that the new PCV system and the leaner mixtures will diminish the problem to acceptable levels. We will see.

Since this seems to be something that may be unavoidable, how much oil rise should I consider acceptable?

Oh, and I also started a notebook to record and track changes, thanks for the input!!!!

 

The Webber 36 DCDs dont have an adjustment that allow you to change the secondary throttle, but they do have a small hole in the secondary throttle plate. Im thinking that you could experiment with the size of that hole to accomplish the same thing.

But since I got it to idle well at the leaner setting and I am not having any transition issues I will leave them alone for now. (these carbs are very responsive, I cannot make them stumble no matter how sudden I jab the throttle).

 

I confused how the Aviation's OMP adapter can allow oil back into the system. It's just a pump that is driven off the factory front cover shaft. The shaft on the Aviation's OMP adapter is sealed. On top of that, the oil would have to make it past two gaskets and a faulty shaft seal on the Aviation's OMP adapter. I say it's gas.

 

I havent taken my adapter off to check how the shaft is sealed, but I have an old omp, which is situated similarly and there is no seal between the body of the pump and the shaft, Im not certain that it could be getting in that way, but Im not sure yet. I was suspicious that it was fuel too, till the oil analysis gave no indication of fuel dilution. The dye test will eliminate the omp as a source. Hopefully the changes I made so far will address it.

 

The dye will get into the engine oil. It'll get in through the engine, since you're injecting it into the engine.

 

My thinking is the injection oil is leaking into the crankcase through the injection pump while the car is sitting, not while it is running. I dont think it would do it while it was running because the path that it would seep through is exposed to oil pressure. My idea is to put the dye in the injection oil tank, bleed the oil supply line and then let it set for a week or two, and then check it.

 

The injected oil will get into the crankcase by the same mechanism that fuel dilution gets into the crankcase - it sits on the surface of the side housings and gets exposed to the oil after the oil control rings pass over it, helped along with a little positive pressure from combustion blow-by past the side/corner seals.

This does not mean the engine is worn out. All sliding seals are imperfect and have to be imperfect in order to have any longevity. There are also gaps between the seals, gaps between the seal and its slot, the surface of the housing is porous. One of the Achilles Heels of the engine design is that there is a LOT of seal area compared to a piston engine of the same displacement, and it is also very inconveniently shaped.

You just never notice the oil level going up in a stock engine, because the OMP uses the oil faster than gasoline dilutes it.

Hmm... now you have me thinking. The RX-8s have a reputation for rapid oil consumption, more rapid than RX-7s ever had, and they supposedly inject far less oil than previous engines. I wonder if the extra scraper ring between the oil control rings and side seals is reducing the amount of dilution.

 

I get that the injection oil will get into the crankcase through the process you describe above, thats why I am doing my test without running the engine.

Putting the dye in the tank
Bleeding the oil supply line
waiting for a week or so (without running the engine).

This will tell me if it is leaking past the pump shaft while the car sits.

 

That scraper ring doesn't help my RX-8. The engine only had about 24k on it when I bought the car, and the oil still has a slight fuel odor, even though I change it every 2,5000-3,000 miles. I also have a slightly rising oil level with the OMP adapter, but I'm not really concerned about it. I have read about a few other 8's that have experienced the same thing.