Do we have a DIY compression test?
#1
Registered
Thread Starter
Do we have a DIY compression test?
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.
I have been told FI will kill the rotor seals faster, so I want a baseline now to compare to later.
#2
The Professor
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.
#3
Registered
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
http://RotaryDiagnostics.com
#4
Rotary Superstar
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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.
#8
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?
#10
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?
#11
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.
#12
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#13
Grasshopper
iTrader: (1)
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.
Last edited by Jon316G; 03-22-2010 at 10:05 PM.
#14
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.
#17
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?