Visibly Distinguishing Among Mazda Rotary Engine Models
| All Mazda production rotaries use two spark plugs per rotor housing. Engines prior to 1974 models fired the top spark plugs from one distributor, and the bottom spark plugs from another entirely separate distributor. For 1974 models Mazda consolidated the functions of the separate distributors into one distributor housing. For 1986 models Mazda switched to electronically controlled spark, so the unconventional distributor was replaced by a crank angle sensor, with no cap for plug wires, which go directly from the coils to the spark plugs. | ||||
|
The MAZDA logo you see on the housing at left was the one
Mazda was using for literature and nameplates when it began, as Toyo Kogyo, exporting Mazda automobiles
to North America in 1970. This logo's first appearance on a rotor housing was
on the new for 1974 models, which debuted the 13B and incorporated substantial engineering
improvements over previous models.
On engines in new 1974 vehicles, the logo was painted
a dark medium blue. Cleaning for rebuild
usually stripped the blue paint, and paint was left off 1975 and replacement housings as well.
Note near the top of the rotor housing, just above the left of the two bolt bosses in the picture, are embossed the characters 13B, indicating the engine model. All production Mazda rotor housings have the engine model embossed in this location. On installed engines this embossing is usually visible, but sometimes obscured by various paraphernalia. You can measure the width of the housing to tell what the engine is as well. 10A rotor housings are 60 mm, 12A housings 70 mm, and 13B & 20B housings 80 mm wide. |
|||
|
In 1976, Mazda switched the automobile engine housing logo to the one that remains in use today.
The 1976 REPU engines continued with the earlier logo, and the larger intake ports. |
||||
| Until 1984 models, all Mazda production rotaries used 4 barrel downdraft carburetors. 10A and 13B carbs were manufactured by Hitachi. 12A carbs were manufactured by Nikki. Beginning with 1984 models, all 13B rotaries were equipped with electronic fuel injection, using two injectors mounted to the center engine housing in 1984-5, and four since 1986, two in center engine housing and two in intake manifold. | ||||
Felix's Home