Rotary Car Club - View Single Post - Oil pump O-Ring Mod

rx4ur7 · 04-07-2009, 12:09 PM

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.

04-07-2009, 12:09 PM	#3
rx4ur7 Rotary since 1972 Join Date: Nov 2008 Location: Tucson Posts: 231 Rep Power: 17	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.