SA or FB
Joined: Mar 2001
Posts: 31,833
Likes: 3,232
From: https://www2.mazda.com/en/100th/
there are several ways to ID an engine.
the Rx7 engines are the first with nitrided side irons, so these should be grey in color, the earlier engines were just iron painted black.
the 79 model year engines had cream colored pulleys, 19 tension bolts, a screw in heater hose adaptor. the rotor housings have ribs front to back on them. the rotors are LDR type, with an F or R cast in the combustion recess (front or rear)
the 80 model year engines have 18 tension bolts. late in the run the pulleys are black. California has an oddball center iron and rotor housings for an EGR system.
in 1981 the engines got revised for the catalyst, the rotor housings are smooth on top with a thing that kind of looks like an H on top. the air injection passages are different. apex seals were redesigned as well. the flywheel goes from 30# to 22#
1982 is the same, although at some point the heater hose adaptor goes from a screw in fitting to a pressed in fitting.
in 1983-85 things change again, the rotors get redesigned, they will now say N F or N R, presumably the turbo rotors have a TF and TR. the heater hose fitting becomes a T for the oil to water oil cooler (beehive). flywheel gets heavier to about 24#, the rotors are lighter, so the net rotating weight is the same.
the Rx7 engines are the first with nitrided side irons, so these should be grey in color, the earlier engines were just iron painted black.
the 79 model year engines had cream colored pulleys, 19 tension bolts, a screw in heater hose adaptor. the rotor housings have ribs front to back on them. the rotors are LDR type, with an F or R cast in the combustion recess (front or rear)
the 80 model year engines have 18 tension bolts. late in the run the pulleys are black. California has an oddball center iron and rotor housings for an EGR system.
in 1981 the engines got revised for the catalyst, the rotor housings are smooth on top with a thing that kind of looks like an H on top. the air injection passages are different. apex seals were redesigned as well. the flywheel goes from 30# to 22#
1982 is the same, although at some point the heater hose adaptor goes from a screw in fitting to a pressed in fitting.
in 1983-85 things change again, the rotors get redesigned, they will now say N F or N R, presumably the turbo rotors have a TF and TR. the heater hose fitting becomes a T for the oil to water oil cooler (beehive). flywheel gets heavier to about 24#, the rotors are lighter, so the net rotating weight is the same.
Joined: Mar 2001
Posts: 31,833
Likes: 3,232
From: https://www2.mazda.com/en/100th/
LDR = Leading Deep Recess. the 12A rotors have a tear drop shape to the combustion recess, with the deeper part of the recess toward the leading side, LDR.
the 74-75 12A and all the 13B's have an MDR, which means its just "square"
the shape of the combustion recess has an influence on the gas flow and speed of combustion. like with everything, there is a trade off, so the LDR is better at some things than others. if there is a new rotary, the combustion recess will probably be special, like the SKY Aktiv pistons
