does anyone have a good link on how to do a compression check, also what numbers should i be looking for in my twin dizzy 12a?
thanks Matt22

 

You should have roughly 9:1 compression. A fresh rebuild will register about 105 psi per face if you have a short line. If you're doing a test without the Mazda tape-conveying setup, then make sure you get an extra cheap gauge that doesn't have a check valve, or defeat the valve you've got. You have to be able to compare the readings you get by pulling both the High-Tension leads from the coils, then turn the engine over with the compression gauge in one plug hole and a spark plug in the other. As you watch the needle bounce, find the rhythm and watch for several cycles until you get an idea of where the needle stops for each face. It bounces pretty fast, but if you concentrate you can sort it out.

 

My twin dizzy 12a gives 125psi in front, and 115psi in the rear... Dono when it was rebuilt or if it ever was.. but from the numbers.. I would say something recent..

Anything over 80psi will get you by

 

hmm mine has a check valve, what do you mean by defeating the valve? what are the high tension leads? so i would need two people to do this then?

 

I think he means pull the cable from the coils to the distrubters so that the engine doesn't try to run. As for the check vavle, mine has a the release by pushing down on the little button, so I held it down while some cranked the engine at WOT.

 

ok so you jsut need to hold it down and crank it at WOP so foot on the gas.
do you have to watch for every third spike or is it an average of all three faces?

 

Hold the check vavle to disable it, and watch for all three faces, should be about the same psi for each face is nothing is wrong, You can also have the cheack vavle enabled so you can get peak compression, Should be what you seen on the faces.

And yes keep it at WOT, and make sure you unplug your coils going to the distrebuter.

 

Without the check valve you will see all three compressions. With the check valve you will see only the highest. The other two can be very bad, but seeing only the highest will give you an inaccurate overall picture.

With the check valve removed, try using a video camera to record the readings of the gauge. If possible record in a fast F-stop setting. Play back the recording in slow motion to see the three pulses with greater accuracy.

I don't understand the wide open throttle recommendation. Just make sure the coils are disconnected.

 

Mr. Matt22 I could do this for you all we need to do is find a way to hook up, PS, I need some LSD plates

 

LSD plates?

ya let m eknow i have sunday off this week, well and saturday too but i am gonna be really busy. let me know Matt22

 

LSD plates?

ya let m eknow i have sunday off this week, well and saturday too but i am gonna be really busy. let me know Matt22

 

OK going to make plans with the wife for this sunday, so all I realy need to know is how to, and when to get to your place

 

Well thanks Gambone for stopping by. We checked the compression, and is in the 80-85 range on each rotor. with out a video camera we couldnt get the exact numbers. but both were very consistant.but I am hoping that these number will improve with alot of cleaning. mainly basic components, and with more driving. once agian thanks to gambone.

 

pushing the check valve is BS, you are simply bleeding part of the air charge prior to it hitting the diaphram in the tester.

You need to remove the schrader valve that is in the tip of the tester (the part that screws in to the spark plug hole) this will allow the pressure to go back into the chamber (allows it to reset for next compresion cycle) without bypassing the diaphram inside the tester.

kenn

 

thats what we did.

 

Sorry for not bring the rite tester, One thing to keep in mind when useing a comperssion tester with a long hose that this will inpair the max reading, more space to fill befor the perssuer can build, so if you add 10 to 15 lb more you will be in the ball park, my tester has no more space than a spark plug, so bang it's rite there, all it is is a perssuer sensor from a AC system on a late madel car, just go to pick a part find the three wire sensor unscew it and the connector with as much of the wire hasnes that you can put in you pocket and from there it's most easy to wire it to gather,and you just need a O scope 1000 dollars or so to bring ot all to gather, just yesterday did it for spider on a 20B

 

If your dealer is cool they can use the WDS..

Use a "doner" RX-8 to power the WDS and run the pressure transducer to the engine on the Rx-7.

 

So Snap-on I read you reply and realy need some help, what is WDS and run it from a 8 to a 7 all about

 

The WDS is the diagnostic machine at the dealership.

One of the tests it can perform is a compression test on a rotary engine.

I fool it by hooking up to the DLC (OBD-II connector) on the RX-8 and going to the compression test function. Then I unplug the crankshaft position sensor.

Then pull a Rx-7 along side and remove the plugs and unplug the coils. Install the pressure transducer in the plug hole and crank the car.

This test will give you compression in percent or PSI, along with rpms and difference in chambers/rotors.

 

when I get home I send you a scaned print out of a 20b comperssion check, here at work I hasve no way of down loading it from the scope to the internet