I have been buying/selling/running RX7 for a while and just picked up a rough 3rd Gen. The seller stated he bought it about 16 months before and had to replace the motor. He had a local Mazda shop install a Mazda remanufactured motor. He drove it for the following 15 months (He only had the car for about 17 months) and had issues again (Absolutely no real detail the failure). So I decided to run a compression check. The front rotor registered between 90 and 100 PSI, but the rear only looks like 15 - 30 PSI. So I placed a mirror down by the plugs hole (Looking in) until I saw the first apex seal face (What I could see). It looked good, and I rotated the other two around and they looked good as well. Is there anything outside the motor that could cause a compression check to be low on the rear rotor? I have seen apex seal failures and they typically cause damage to the Apex seals.

Let me know………….

Downloading the Factory service manual now and looking for anything that could cause it there as well

Thanks in advance
David

 

My guess is the apex seal springs could be shot, not allowing the rotor to hold compression. Also a side seals could be gone. Overheating can also cause you to lose compression if the housing becomes warp.

 

Looks like a pretty nice car, what size wheels are those.

 

Wheels are 17" Konigs, but I only have three of the four. Looks as if I will be pulling the motor and looking @ the rear assembly.

 

Wow the wheels looked a lot bigger than what I thought.

That's what I would do, really with low compression that is the only thing you can do. Even your front housing is out of spec I believe the minimum is 100 psi on each face, probably just worn out motor needs refreshening. The good thing is the motor only has about 17 months since remanufactured, so there is a good chance most of the internals are reusable. Sounds like the previous owner ran the $hit out of it, any idea on how many miles the reman has.

There is so many things that can cause low compression in the rotory's it's rediculous.
Carbon build up, worn housings, basically anything that deals with apex seals could be worn and needs replacement, warped housings, out of spec rotors, out of spec housings.

 

The guy had the car for less than 9000 miles and had two motor failures (First was bad when he bought it).

Any ideas where I might find a single Konig rim (Looked but could not find the model on the rim)

 

i just pulled an engine with low compression on the front rotor, all apex seals were incact, but it appeared that something had been injested into the engine, because there was MAJOR scarring of the rotor housing. all seals seemed to be in great shape.