I want to know how to check compression on a rotary.
I have been told FI will kill the rotor seals faster, so I want a baseline now to compare to later.

 

1) buy compression tester gauge
2) unplug eccentric shaft sensor plug
3) take out one sparkplug, screw compression tester in.
4) crank engine 5-10 seconds while holding down the accelerator pedal fully.

 

Unfortunately, that procedure will only give you an overall reading for each rotor. A rotor could have a failed apex seal and still provide a good reading for just the one "sealed" face. To effectively determine engine health, you need some way to determine the absolute and relative compression for each face of each rotor. Something like this:

http://RotaryDiagnostics.com

 

Or you could save yourself a few hundred dollars, and just remove the pressure relief valve from the end of any regular compression tester, and watch the needle bounces.

 

curious - why this step?

 

“To cut the fuel injection and ignition, make sure the eccentric shaft position sensor connector is disconnected.” (RX-8 Service Manual)

 

Thanks!

 

Do you do this and at every crank look at the reading it is giving you making sure all readings are in the same thresh hold?

 

If you want one check this out.

Compression Tester

 

Yeah, any more info? Would the needle bounces work, don't you have to let it build up pressure for a few cranks before it gets a good reading? Also, when doing just a standard test, what's the number range that each plug hole should put out on a stock 8?

 

I have a 04 rx8 six speed. When I start it I see some grayish smoke come out the exhaust. This is my second engine. The first one smoked real bad and was replaced by the dealership for free. I am going to buy a regular compression tester form harbor freight to save some money. I just wanted to know 2 things. Am i being paranoid being it only smokes when the engine is cold and it's 55 degrees or colder outside. And what are the specs for a good compression test? Also, I checked the ignition system and replaced two of the ignition coils. This lessened the smoke but it's still there. And when the engine comes up to normal operating temp. it doesn't smoke at all.

 

The stock tune dumps oil through the Oil Metering Pump when cold.
Check your oil every fill up.
You should also consider a good pre-mix oil to add to the gas and make it smoke moar....

 

Good luck with that.
You need to find the compression for three rotor faces.
This might be possible with a standard compression tester if you recorded it and played it back in slow motion.
Then write down each "peak" readout X3.
But this won't tell you what RPM you're cranking at which is important to know.
I guess if you have an AP you could get the RPM logged through that.
Then once you figure out the numbers for each rotor face, on each rotor, and the RPM, you can calculate/normalize those to give you your results.

Now you see why there are rotary compression testers?
Mazda's spec is 120psi normal, 98.6psi minimum, at 250rpm.

 

Thanks for the info. I have an access cobb. Just wanted to know which compression tester is recommended and how much it would be. The dealership wants to charge me 170 for the test. I don't want to get it down if there is nothing wrong.

 

Also, is it possible that the seals expand when heated up and that is why I don't see smoke when the engine is up to temp. And what is normalizing?

 

I paid $400 for my rotary compression tester, so you won't find anything cheaper than the dealer.

Here is a couple screen shots from a test I did on an engine.
Maybe a visual will help you understand what I'm saying:

 

Okay that helps. Thanks again. Maybe the dealer is the way to go. I just don't want to think my engine is going bad with only 4500 miles on it. Is what I am describing sound normal at all?

 

I don't know if this makes a difference but I use royal purple 5w30. I check it once a week.

 

That's what I use

 

And I take it you don't have any smoke on a cold start?

 

Not grayish smoke... maybe white smoke for a few seconds, but that's normal.

 

If I use the dyno function on my ap, and it reads a decent pull, wouldn't that tell me I am just crazy.

 

The "dyno" feature on the AP isn't accurate... so its not going to help in troubleshooting in any way.

 

Ok. Well thanks again. Maybe I'll make a quick video and post it on youtube or something so you can see what I'm talking about.

 

If I had to take a guess... if the grayish smoke is only present during start-up for a few seconds, it may be due to fouled plugs not igniting, causing random misfires, and oil getting into the exhaust and burning off.
When was the last time you replaced the plugs?