compression test on 85 rx7 GSL-SE
 

Hello,
I am looking at buying a 1985 rx7 GSL-SE with the factory 13b fuel injected rotary engine I don`t know if the motor runs but I did A compression test and it showed 50 to 60 psi on all the spark plug holes. And when I pulled the spark plugs out they were not covered in oil and They were pretty clean. I need to know if the compression is good. I know the rx7 has 103,000 miles on the rotary engine.

Thanks

Im no expert but i know that on second gens 120-130 psi = brand new excellent engine. 110-120 psi = still good. 80-90 psi = a little wear still ok, anything under 70psi is an blown rotor waiting to happen.

that is pretty bad compression lol, buy the car swap in a new engine ;)

Compression results can vary widely depending on the tester used and the conditions in which the test was conducted. Don't let the above uninformed posters scare you off just yet. In the following link to the FSMs, read the section on compression testing.

http://foxed.ca/foxed/index.php?page=rx7manual

Compression testing starts on page 10 of Section 1. I will assume you used a standard piston compression tester and we'll go from there. You need to remove the Schrader valve from the tester to be able to see the compression pulse of each rotor face. If left in, all the reading will indicate is the maximum compression of the best face of that particular rotor. If that rotor had a bad side or apex seal, it wouldn't show up.

Piston testers are also notorious for under reporting rotary compression. On a piston engine, generally 4 compression strokes are needed per cylinder for accuracy. On a rotary you only get one quick pass per face. That's why rotarys have thier own specialized compression tester. If you can get your hands on one, retest and follow the proceedure to the letter. If not, retest following the proceedures in the FSM. You can get a general idea of the compression of each fach by simply holding down the Schrader release valve but your eyes need to be quick.

Go back and give it another try. Warm up the engine if possible, connect a dwell/tachometer to check cranking rpms and squirt a little oil into the lower spark plug holes to raise compression. Crank the engine over to spread out the oil. I suspect your results will be quite different under these conditions.

With such low mileage on that engine, it should have much higher compression than you're seeing. Is this the actual mileage on the car or has the engine been rebuilt? More details about the SE may help.

^^ now that is solid accurate information!

thanks for enlightening us. trochoid always is full of information.

you said that you don't know if it runs?

Not well if at all with that kind of compression =P

If it doesnt run and the engine was cold, thats bad.

If I recall doesn;t the compression go down when the engines warm... thus its probably even lower

The 13b's in SE's are strong engines. Mine has 100k more miles than the one you're looking at, on the ORIGINAL engine, no rebuild, regular oil changes, and never letting it overheat.

SE 13b's got 3mm apex seals, a larger (longer) oil pump in the front cover, and better overall cooling with the front mount oil cooler below the radiator. Additionally, the fuel injection and intake system helps to prevent hot start flooding, cold start flooding, and rich conditions which can deteriorate the inside of an engine. They're built stronger than 12a's, and that's why they put out 35% more power.

If the PO has taken care of that car, you're likely going to get a solid engine. Drive it, and you'll know right away. Good luck,

yeah. My SE has 135,XXX miles on it and it pulls really hard. I'm thinking i can hit 200,000 no problem

I agree with Trochoid. I also would like to ask how you performed the test.

Did you hold down the release valve? Did you leave the release alone and test like a piston engine? Was the engine warm? Did you hold the throttle to the floor while cranking? Was the battery stong and cranking the engine quickly?

I would do this:
- warm up engine
- disable spark/fuel
- start testing on rotor 1, hold throttle down, crank (don't touch release valve) for a few seconds. Record this value.
- now hold the release valve and have someone crank (pedal to the floor) and watch the bounces on the tester. It is more important that they be even than the actual value. You have already tested the max compression in the previous test. This test is to make sure that all faces are even
- repeat both tests for rotor 2.

If bounces are not even or if there is more than about 15 psi difference between the max compression on rotor 1 vs. rotor 2, then you may need to worry.

Good luck.

Kent

I redid the compression test like you said and I got between 75 and 80psi on a compression gauge for a piston motor. And that is the actual mileage on the motor and it has not been rebuilt. And when I did it the motor was cold, And I took the Schrader valve out of the compression gauge. And I pushed the gas petal to floor as I cranked the engine. And the needle bounces were even.

If the pulses are even then that's a good thing. To me it sounds like this engine is just carbon infested. If the car was sat up for any length of time, the carbon will make some of the seals stick with-in their grooves. All the internal seals need to move freely to get maximum compression.

have you been able to start the engine yet?

Is the 75/80 psi the peak measurements or the bounces?

If 75/80 psi is the peak, that is low. Might be able to free up the seals with Seafoam or similar.

Maybe i'm just being an ignorant 16 year old here...

But at only 100k with an NA 13b should you even be too worried about seals deteriorating to the point of compression loss? If anything, shouldn't carbon buildup be your number one concern? seafoam treatment and a few redlines are bound to increase compression by de-stickying the seal grooves.

1coolmazda, where in ohio are you located

That is the one one part of the test I forgot to mention, holding the gas pedal to the floor. You didn't mention cranking speed during the 2nd test. If the cranking speed is below 250 and the engine is cold, compression is most likely much higher. Did you add any oil to boost sealing for better compression?

At this point, I'd venture the engine is decent. Seafoaming and carbon removal would be the next step along with checking the that the aux ports are closed, not open. If open that can skew comp readings too. Finding an SE with that low of original miles is very rare, you might as well buy it.