what compression reading means its ok

[DJTenuto]

(1990 gxl-non turbo)what compression reading would indicate the need of a rebuild? what would a normal reading on a good non turbo engine be?

[GringoEJS]

Mazda has there own special rotary tester for this car, but I have always been able to use a cheap AutoZone tester to get an idea on compression. Basically you look for 3 even bounces on each rotor, while bleeding the pressure from the tester.

[DJTenuto]

Originally Posted by GringoEJS

Mazda has there own special rotary tester for this car, but I have always been able to use a cheap AutoZone tester to get an idea on compression. Basically you look for 3 even bounces on each rotor, while bleeding the pressure from the tester.

so if each rotor has 3 even jumps in compression its good? what are typical readings for these three highs in compression?

[GringoEJS]

Well, on my cheap tester, getting into the 60-70 range per rotor has shown to be fine (with MY tester). Others will tell you 90+ using a more accurate tester. More than likely, if both rotors have near the same compression numbers with even bounces, the engine is still good, providing your coolant and oil seals aren't blown.

[GringoEJS]

Oh...definitely 0 compression on either rotor or very low compression on 2 bounces and higher compression on the third bounce would immediatly point to a needed overhaul.

[fcdriver]

Ok this is straight from the book, 85 psi at 250rpm with a max permissible difference between chambers 21psi.