Just bought a 94 with 102k miles. I tested the compression this weekend and found the front rotor had 85 psi, and the rear rotor had 75. I hooked up a boost gauge, and the boost shoots up to about 11, drops to about 8 around 4500 rpm, but doesn't rise much after that.
I have read that anything below 100 psi of compression is unacceptable. Should I be expecting the engine to quit any day, or should I be alright for a while?
Obviously I have never dealt with Rotaries, so it's new to me.

 

I ran with 90psi on both for about 1.5 years and went to the track many times and made great power. i would think that the biggest concern would be the fack that they are not the same.

~Luke

 

man that engine is dying! anything worse in compression might cause starting problems!

 

thats wut happend to mine i had low compression, now my rx wont start. im in the process of gettin it rebuilt now. dont feel bad it happends to the best of us. it also sounds like your second turbo isnt boostn either.

 

If you checked the compression using a conventional gauge, you might consider having a dealer or experinced rotary shop double check your numbers using Mazda's special compression tester. It will correct readings for the actual test RPM and etc. and give you numbers for each of the 3 faces for both rotors. It's the only way to know for sure.

 

Hindsight is always 20/20, but why didn't you get a comp. test before you bought the car? You could have knocked about $3k off what you bought it for.

Anyway, to help you out: do what FD Junkie suggested. Take it to the dealer, they'll charge you about 100 bucks but it's worth it. And reading under 6.5-7.0 are not a good sign...especially if one of the faces is noticealby low compared to the others, for example.... on Face #1 6.5 #2 6.8 #3 5.5. <----not good, shows a busted apex seal. It's "better" to have uniform numbers, but the bottom line is that no compression means no compression no matter how you shake it. Good luck, and start saving your pennies if you haven't already begun to.

-Dan in Phila.

 

I didn't have it tested because the dealer just told the previous owner (my neighbor) that the engine was fine and only needed a new rear main seal. In any case, they replaced the seals in November, so I assumed the engine checked out. That's what I get for assuming.

 

someone correct me if I am wrong but only needed a new rear main seal (very technical description) would require a rebuild!!!!!! to replace. buyer beware I guess, should cost about $2500 for a rebuild

 

Rear main seal is a $8 part and 3hr job to replace. It does not require a rebuild.

K

 

guess I was corrected, I thought they meant the rear rotors apex seal. sorry

 

The rear main seal is a large gasket type thing that is located on the rear of the engine. Drop the tranny, pop the flywheel & counter weight off, pry the leaking gasket off, replace with new, reassemble. Very common gasket to leak on our motors after a while. Probably second only to our well engineered oil pans...

K

 

Hehehe. A main seal is a main seal is a main seal.

Sorry................

Yes, not the apex seal.