Please Read & Help: Results of Compression Test on Rebuild!
 

Ok, all you Rotary Experts out there...I seriously need your opinion on this! I installed a fairly new Rebuilt Block in my car about 1 month AGO. I was sold this block by this Rotary Expert shop in my town, which they got out of a Wrecked Car. The shop told me this engine has been rebuilt recently, probably had 2000-3000km on it and is a Mazda Reman Block. It was a car that they had seen from time to time and worked on (but they didn't DO the rebuild themselves) and heard about the writeoff and bought the engine from it. Anyways, it was totally shinny silver (like a Mazda Reman Block looks like) and it had a new water pump on it and everything. So convinced it was a GOOD engine and gotten the word too that it must have like 120 or more compression readings, I bought it and got it installed.

Anyways, after installation and everything, it ran great...just had some shitty idle (a bit rough, misfires), which I'm currently trying to solve. This engine runs with GREAT power, my car is faster then EVER! Also starting the engine in the morning is a breeze, starts up 1st or 2nd crank easily and never had a flooding problem of any kind. Even hot shutoff and restart takes only 1 to 2 cranks!

Ok, so now...I saw my own mechanic today and got him to RUN a compression check on the engine to see HOW GOOD it REALLY IS! But to my surprise he got some crappy RESULTS!!!! Here is what I got:

Front ROTOR: 2 readings of 80-85 and 1 reading of 70!
Rear ROTOR: 3 even readings of 90

We did the TEST on the trailing spark plug holes. I have NEVER detonated with this engine yet and only run about 12psi on it tops. So why are the readings SO bad and what does it mean...will it blow in another couple weeks, was I sold a BUMD engine???

The readings sound low but that doesn't jive with what your saying about how well it runs. Was the test done with a Mazda tester or something else? If it was a Mazda tester, you should have a paper trace showing the compression cycles. Also, the test needs to be done with the throttle wide open and the engine warm, otherwise the readings will be low. Measuring at the trailing is correct.

Henrik
87TII

Thanks for the swift reply Henrik! Your right, that what bothers me the most about my car, it runs too GOOD to have these readings!.. I mean, I never knew I had this PROBLEM/WEAKNESS in my engine, until I did this compression test. My mechanic used a REGULAR compression gauge, not a Mazda one. The engine was sitting for 2 hours, so it would have been close to cold when we did the TEST. With this Engine, I just ran my BEST 1/4 mile @ the track yet, posting a 14.21 @ 99mph with a bogged launch and crappy 60ft time of 2.2, launching at 3500rpm. Everything seemed positive, until I did this compression TEST for kicks!

With the readings I got, should I be VERY cautious and be saving up for another new engine block in a month or 2 from NOW? I'm definitely NOT going back to that place that ripped me off!

1.If it is a recent Mazda rebuild it should have a blue and silver tag on it,just below where the crank angle sensor slots in.They have been using this tag for about a year I think.
2.Personally I think a compression test with any thing but a recording compression tester,recording pressure and rpm is only an indicator at best.I would have it tested properly.

Actually my engine HAS a spot for that tag and it has traces of it (the outline) being there, but its NOT there! The Rotary place told me it FELL OFF and they couldn't find it when they got the engine. WTF?! I dunno, yeah I guess I shouldn't worry too much until I can get a REAL compression check done by MAZDA. Thanks guys!