I'm about to go check out 84 with a 79 motor in it. I'm going to check the compression . How many psi should i get on all three sides of each rotar ? Also , should i check it on the leading or trailing side ?

Thank U,
Paul

 

Anyone out there ?

 

Doesnt matter leading or trailing. Need more info. stock ports? streetport? bridgeport? stock apex seals? carbon?

 

No portting. stock 12a out of a 79 with 55k miles.

 

According to the 1984 Mazda Factory workshop manual, compression is to be checked at the trailing plugs. A conventional compression tester reads only the highest pressure of the three combustion chambers (each side of rotor) in the housing. Compression should be a minimum of 85 psi with a difference between max and min. pressure of 21 psi at a cranking speed of 240-250 rpm. Its the reading for both 12A's and 13B's so I can assume that these numbers will work for a '79 engine.

 

info here

 

Generally speaking, RB and Mazda say 105-150 hot compression is good. Thats at good cranking speed, make sure the batt is fully charged and hold the throttle wide open. 85 psi is really low, barely acceptable. They usually wont run at all below 75.

 

Looks like an item for the christmas list!

 

Ditto

~T.J.