compression testing.
 

okay, so i'm gonna go compression test my potential 2nd gen rx7,
what compression should it read at?

At least 85 psi for each face of each rotor.

thanks dood

85 PSI is the bare minimum. 100+ PSI is what you will see on a strong, low mileage motor.

Along these lines, what does it mean if you hook up the compression tester (which i don't know if it is acturate BTW) and get these results:

60psi - 65psi puffs on each face witht eh check valve off

90psi - 95psi with the check valve on

and overall the engine runs perfect, good power, start everytime. overall very good running engine.

What do you make of that?

As said my gauge could be off, i don't know one way or the other.

Ace,

I think you're supposed to take the valve out of the bottom (the "spark plug" part) and when you test don't touch the relief valve near the gauge itself.

at least they are even

Not realy sure why your wanting to test your compression if its a stronge running motor. Unless your just curious =]

Don't quite understand what you are saying? I am supposed to remove the other spark plugs? Then it will make zero compression.

There is only 1 check valve on the tester, it is connected to the gauge.

Yeah that is what i said too but i still want ot know what is going on lol.

Well I am curious thats for sure, and even more so now.

The reason i did it at first was because i started feeling a LOT of sudden power loss. Ended up being that my CAS hnd spun some and retarted the timing.

But i had already seen the compression numbers and now i want ot know what is going on.

I have been/still am seriously considering selling the car and then getting a TII. If teh compression is real low then i think i might do that while i can still get something out of the car.

If it is fine then i will keep it for awhile.

So did you figured out your compression?

http://rotaryresurrection.com/2ndgen...ion_check.html

Check that section out.

nope gonna go do that today at 3.
:icon_tup:

the service manual has their own special rotary compression tester but you don't need to break bank to buy that, a regular piston engine compression tester will do but I'm drawing a blank on what are acceptable numbers.

110+psi = Brand new engine in perfect condition.
100psi = great condition
90psi = avg
80psi = on it's last leg
70psi = you ain't getting anything out of this one.

You have to remove the schrader-- or check valve, then put it in the spark plug hole. Make sure you have the egi fuse removed.

With a helper, have one person crank the engine about 10 times while the other person watches the compression gauge, in a good engine the needle will hopefully bounce even bounces, at 85psi or higher. In general 85 psi is the lowest your engine should be at to operate correctly.

Heres an article about compression testing http://www.aaroncake.net/RX-7/blown.htm

Sorry, Ace. Been away for a while.

I thought my compression gauge also had only one valve and it was near the gauge as well. When I took it out the needle would barely move.

But I found another valve and the end of the hose in the piece of metal that screws into the rotor housing, hence my reference to the spark plug end. That's the one I took out. Then I got nice readings.

Interesting, i will have to look at mine, i don't think mine has anything like that. I think it is just a hose until the valve/gauge. But i will check.

it also says to unplug the CAS in the FSM.

cant you just hold the relief/schrader valve button in? or does it have to be removed?

that and do you really have to warm the engine up to get a proper reading? I know many people will comp test junkyard engines by turning the motor over so....

Not sure about the CAS and holding the button in but as for it being warm.

The rotary engine actually give HIGHER compression when cold then hot as strange as it sounds. So yes, to get an acturate reading the engine does need to be warm.

But in a pinch when you can't start the engine you can test it cold, it just won't be 100% acturate

okay.
so i'm unsure of it.

weak battery, turned over a little then huge voltage drop and wouldn't turn over.
but i was getting about 50psi.
as i said though the battery was very low.
what can you guys say?

Pull both lower plugs.

Put a little engine oil in the spark plug holes and hand turn the engine a couple of revolutions. This will help in getting a good compression reading. I've seen engines that sat for two years and have horrible compression, come back to normal or good compression with just a little added oil in the rotor housing.

sick. :)
thanks man.

Dumping oil into the housing will likely give you a false reading, so don't bother. Unless you just want to feel good.:)

The compression readings will vary greatly with the engine cranking speed during the test. That's why Mazda cites the compression specification at a specific number--250 rpm. A slow cranking speed will result in low readings. Warm the engine up a bit if possible first and redo the test with a fully charged, healthy battery.

Remove the leading plug from one housing and leave all other plugs in place. [EGI fuse removed, of course.] Run the test, reinstall the plug you removed, remove the leading plug from the other housing and run the test on that rotor. [The other 3 plugs are in place.] Experience has shown that in doing the test that way, the engine cranking speed, with a healthy fully-charged battery, will be very close to 250 rpm, thereby not requiring any normalization of the recorded data for engine cranking speed.

lol.
okay.
learnin somethin new everyday.
and i'd much rather be happy in the long run with a strong running engine.
not just feel good for a second.