Oil pump O-Ring Mod - Testers NEEDED

[TitaniumTT]

So here's the backstory, my last engine was a 13B-RE Cosmo motor with the stock oil pump, stock OPR, stock bypass valve and stock casting under the pump itself. At idle I would see about 15ish psi and on decel the low psi warning light would come on @ 15 psi I believe. I've seen as low as 7psi and the most I ever saw with that motor, I checked the logs, was 67 psi @ 6k+rpm. Not great but "acceptable." I use that term loosely. The pump, when I broke the motor apart was visibly scored.

The engine needed a rebuild and I wanted to really address the oil system for a myriad of reasons. I decided to go with
1) FD OPR
2) Shim the bypass with 2 washers
3) Clean up the casting under the pump
4) MAKE A POSITIVE SEAL BETWEEN THE ALUMINUM PUMP AND THE IRON MOUNTING SURFACE.

A friend of mine has a CNC mill and when I approached him about the idea, he kinda scoffed at it saying that no-one has ever done it to his knowledge and people don't seem to have problems so why bother? It didn't take long for me to convince him to try it and I sent him a stripped down and cleaned up pump. It was actually the one that was visibly scarred. There was no scaring on the pump body, just the troicoids and the pieces between them. I had a second pump on it's way to me anyway. This is what we have.

I cleaned up the casting, nothing crazy, about 20 minutes of work



And here is the pump body



And here is the o-ring installed with a smear of hylomar on the seam between the o-ring and the outside sealing surface to keep the o-ring in place and on the mating surface itself. THe hylomar cannot get into the pump.



Also of worthy note is my dual mocal oil coolers run in series with -10 line. Theres close to 15' of -10 line which should also reduce the pressure some.


bulkhead fittings


T-Stat


The results, well the are RIDICULOUS. At a fast cold idle I'm seeing close to SEVENTY psi. (I'm going to type out the numbers so you know it's not a typo) At a normal hot idle I'm seeing thirty-five psi and by Two-thousand eight hundred rpm's I'm seeing over a hundred and nine psi. I have the standard 0-100psi 0-5v sender and it's pegged at 109. I don't know what my max psi is yet becuase I just don't have a sender that reads that high. One is on order. Right now my dash is throwing a "code" and readin 0.0psi which obviously causes me concern. Upon first start-up when the rpms climbed high enough the dash read 0, it's default error. I quickly shut the motor off. It took me a minute to realize what was going on. I had to open up the Motec and bring up a dial gauge that read the voltage from the sensor. With the voltage pegged I realized what was going on.

I called my aluminum chip eating friend to tell him and he was pretty surprised. However, we are not sure how much of it is the o-ring, and how much of it is the motor itself, the builder, the tolerances I used, the FD OPR, etc etc etc. It's all me, the builder

Anywho, what we are looking for are people that are rebuilding motors that aren't going to change ANYTHING else in thier oiling system. We can't use my experience as an example becuase I did so much at once we cannot be sure what mod effected the pressure. For all we know the o-ring did nothing and it was the change in pump internals and the FD OPR. I doubt it. My gut is telling me that the o-ring made a significant difference but with so many variables, we cannot be sure. I have however done some research in both the FSM and with other peoples experience and it looks like my pressures are MUCH higher than other peoples with similar mods. I should also mention that the pump was actually worn PAST the FSM specs as measured with the feeler gauge. I didn't have a third pump on hand so I played musical internals until I got the closet tolerances I could. They were still out of spec though. In otherwords, the pump should've been thrown out but instead, it's making more pressure that the FSM states as minimums. In most instances, 2x the amount.

Is there anyone that wants to actually test this mod? The o-rings came in packs of 10 so you'll be getting a free o-ring. The machining we are not sure of the cost. He seems to think there won't be any interest. I told him I thought he could make a decent coin offering this service if we can prove that it significantly raises oil pressure. The first testers would pay very little if anything for the machining. It's up to him, not me. But if we could get a group of people that wanted it, I'm sure the cost would be insignificant.

So, if there's anyone who wants to try this - post up, or PM me. I'll be putting this thread in every relevant section just so it can get attention. However, if all responses can be placed in the "General Rotary Engine Related Tech Section," that would be great. Thanks guys

[David Jerome]

Did you replace the woodruff keys in the oil pump while you had it all apart?

[rx4ur7]

What I see is a pair of good elastic band pants with a belt and suspenders added when the body now has a 4 in smaller waist.

Mazda hasn’t changed the setup on the front cover and oil pumps since the 60’s. Other than bigger pumps and the double oring setup.

Lack of low rpm oil pressure is mainly due to worn out bearings. Scored oil pumps will also add to that symptom.

Believe the main reason you have higher pressures is the installation of two shims in the valve.

The front housing comes with a machined surface where there is no gasket or oring required. I think I see some frisky cleaning. I would imagine if you measured the surface it might not meet Mazda’s machine surface specifications. There really is no reason to use any abrasives on any of the machined sealing surfaces in the Rotary. To due so usually induces problems. When I went to school it was “Never use sandpaper to clean these surfaces!” If it is damaged or beyond spec, replaced it.

A new oil pump in a motor with new bearings and good eccentric shaft will produce plenty of idle oil pressure. Motors built here produce 120 psi at speed and ~35 psi at idle, depending on weight of oil. New pump, new bearings, and 1 shim. Never had any oil issues in any motor built, even in those that were built with used pumps, non-scored.

For you all with older pumps 72-82 you can install the impeller sets from the 83-85 pump. As long as the body is not damaged or scored you can go that route otherwise go new or if you have to get the comp pump.

You could possibly have problems with your oil cans. Mazda filters never failed in any of the race or street cars stock or with modified oil systems. The 792P used factory oil filters same the one used on street rotaries, never had an oil issue.

I commend you for your time and effort though. If this was the first run of the motor and there were oil pressure leak issues at the pump I believe it would have been in the testing stage.

I would put money and effort into a new oil pump and chain. And/or a good set of stainless lines, very nice work there. New bearings when you do the motor.

Just my opinion and thoughts after nearly 40 years building these puppies.

[jkstill]

I,m not sure how unusual your oil PSI numbers are, maybe some more folks will chime in here.

The motor in my car was built 3 years ago by Pineapple Racing.

Among other things it has mods to open up the oil galleys in the motor, and a few other goodies to help with oil circulation.

Nothing done to the oil pump AFAIK.

Running dual Mocal 19 Row oil coolers in series.

Fast cold idle is about 65 PSI oil pressure.

When the motor warm, it pegs the stock gauge when driven hard, which is about the only way it gets driven (autox and track car)

Planning to get a digital pressure/temp gauge to better keep an eye on it ,but right now I don't know what the max oil pressure is.