Alright all you know it alls. What is the average compression I should have in a 12a? Because I am going to my dad's and we are going to test the engine to see what shape it is really in. Also anything else I might need to know? or check for?

 

Mazda specs for my 80 12A are:
85# with no more than a 21# variance between chambers (readings)
or
6kg/cm2 with no more than 1.5kg/cm2 between readings
hanman

 

80-120 psi is what I was told, but it varies depending on cranking speed, elevation, etc. With maximum variance between rotors - 20 psi

 

Thanx guys. Well hopefully everything will go ok this weekend and she meets specs, or I may be looking for a place to send it for rebuild or new engine.

 

In case you don't have a Mazda compression tester, and aren't familiar with compression testing with a conventional tester:

If you want a relatively accurate compression test you can use a conventional compression tester. Heres the process.
Disable the fuel system, pull the fusible link, plug the fuel lines whatever. You don't want fuel into the chambers when you are turning the engine over.

Pull all of the plug wires.
Pull the trailing (top) plugs from both rotors.
Screw in the compression tester in the top hole of the front rotor. Hold the release "pin" in on the tester, this will allow the pressure to immediately release on each compression "stroke".
Have someone hold the gas pedal to the floor and turn the car over while you watch the gauge. You should see the needle on the gauge start "bumping" up and down. After watching you can see the three compression cycles. They should all be fairly consistent and not too low.
Repeat the process with the rear rotor.
Also, the car needs a fully charged battery and good starter. It needs to rotate around 250 rpm to get a decent reading.
hanman

 

Agreed to your compression test, thats the way to do it. Except when I do I add one step, when watching the needle bounce I use my digital camera on MPEG That was I can play it back in slo mo and see every bounce perfectly

 

Hey Mike,
What a cool idea. I will have to try that.
hanman

 

mine is right around 8.5kg/cm^2.

 

You guys are making me want to pick up a compression tester and try out this shiznit... or not lol

 

Thx guys. Well hopefully all goes well when I do it on Sat. I feel everything will be fine, but no better way to find out then test.

 

mine was at 9.5 per rotar when I had mine rebuilt with now housings

 

If it starts easily when it's hot, it has good enough compression.

The first engine in my '80 had 25psi compression cold. Fired right up every time. (The second engine had 125psi compression with a street port and old seals! )