MontegoRX7

Here are the results of my compression test. How does it look?

Chaz

It's hard to tell from those pictures but it looks like your compression is low (near 5). The minumum you want is 6 kg/cm2.

Nathan Kwok

Looks like one rotor in the mid 4s and the other in the high 4s. Definitely very low, does the car still run? If it seems to run ok, the test may have been done incorrectly, because with compression that low it should run very poorly if at all. The good news is the pulses are very even and the difference between rotors is pretty small, so you may need a second opinion here.

MontegoRX7

yeah, they are around 5. What is the new compression level? Should I be looking to rebuild the engine soon?

MontegoRX7

Yeah, the car runs fine. Only time it struggles is once in a long time when It is started. It will start and then stall imediatly. That is only about once every 30 times though. Other than that, it runs well. The idle was a little rough when I got it, but after the computer and midpipe, it smoothed out a lot. Maybe I will take it to the mazda dealer for another test.

whitekingsnake

Squirt some oil into the bottom plug hole and then turn the pwr steering pulley to mix it in and then do it again.

Are you using the top plug hole, if not then do.

Later..Scott

pweizman

Assuming that the test was done at 250 RPM than they look a bit low.

New engines should be in the 8-9s...

Mazda minimum is 6 kg/cm^2 @ 250. If the test was done lower or higher...you have to compensate.

Later,
Patrick

Wargasm

I've tested several cars with my tester and I'd say that those readings are low.

Either the engine is just old and tired, or maybe your tester isn't reading right or you are losing pressure somewhere in your testing.

Key points:

- make sure you hold the throttle all the way down
- make sure you have decently peppy battery
- make sure the hose for the tester isn't leaking anywhere and it screwed in snugly (hand tight with a rubber O-ring is sufficient)
- for the "most valid" results, the engine should be warm. You can still get an idea on a cold engine, but that's not how Mazda likes you to do the test.
- does your tester's needly move smoothly?
- I know this sounds like a bitch, but if you have an air tank and a regulator, you could double check the calibration of it.


How many miles are on the engine? If it's up over the 100,000 range, I'd be more likely to just say "it's old". If it's like 50,000 miles, I'd suspect the tester or methods are flawed.

Brian

Wargasm

Just another note, I know that the Mazda book claims that a perfectly running [3] should be about 8+ on this test, but I've never seen one get that... The same car can vary by at least one whole point from day to day or as the exact conditions change.

I've tested my 87 TII a bunch of times, and sometimes the compression is higher or lower than others...

People also say that a ported motor will score a touch lower, but I don't have too much evidence one way or the other on this myself...

Brian

MontegoRX7

I was actually not the one who did the test. One of the local rotary shops around me did it. Where could I get a compression testor so that I can do the test myself? The car has 52,000 miles, so I want to double check it. Please let me know where to get a compression tester. Is there a special kind I will need to get or will the same one for a piston engine work on a rotary.

Chaz

I believe the testers are pretty expensive. I would just recommend taking it to another rotary specialist if that's at all possible. I know the tests are a little pricey but it's better than spending the money on a new engine if you don't need to. Since you indicated that the original test was done by a specialist I would hope that they knew how to run the test correctly. Maybe you could talk to them and see if they'll re-test it at no cost so you can compare the two. Good luck and let us know what you find out.

artguy

as far as your rebuild question....

you could drive it til it goes out...which it will eventually...or you could do the rebuild soon with a streetport as motivation and NOT have to replace the housings and the ROTORS especially...if you do it now rather than after you crap a seal out your exhaust you will save a couple grand in parts.

good luck

j

trust me..lol...I drove on low compression and fucked up a housing..cost me dough that could have paid for my radiator upgrade.

MontegoRX7

So i could do a partial rebuild? Like just have then replace the seals? How much would that cost, and would that bring the compression back up to 8 or 9?