Rotary 12A engine/casting numbers (Engine ID)

:
12A Rotary engine only
Purchased HP Books "Street Rotary" book, and have attempted searches on more than one Mazda forum--but no success.

I want to identify a 12A core engine (engine casting has 12A cast right into it); purchased out-of-the-vehicle from a Craigslist advertisement.

Owner claimed it's from an RX-7; but I suspect it's like every Chevy engine or engine part sold is from a Corvette.

1. This has a single distributor (1974-newer, but not so new as to be distributorless, which would be--what? 1986?)
2. Has electronic ignition (magnetic pickups) in the distributor. I don't know when Mazda dumped points in favor of electronic ignition.
3. Has two coil wires. I read that later engines used three coils.
4. Has thermal reactor, so it's older than catalytic-converter equipped vehicles.
5. Has carburetor. Older than FI-equipped vehicles.

I'm kinda guessing that it's from the second-half of the 1970s, but I'd like to narrow that down to year and model.

I'm sure there's engine ID numbers including partial VIN stampings somewhere on this engine...but I haven't found them. I wouldn't know where to decode them anyway. Tips?

I'd kinda like to hear this thing run (on an engine stand, I don't have a vehicle for it.) but since the starter motor bolts to the bellhousing instead of the engine block, AND I don't have the ignition amplifiers and wiring harness, that'll be near-impossible. I bought it as a non-running core with the intent of pulling it apart for inspection to satisfy my curiosity.
 
As far as I know there are no identifying numbers on the blocks to tie it to a particular car. I don't know as much about the 12A as I do about the 13B but I can tell you they all those sold in the U.S. had carburetors. A quick Wikipedia search suggests they were in a number of applications from 1970-1985 and the thermal reactor was ditched for a catalytic converter in 1980 in the U.S. So as you said you likely have a late '70's engine, which could have come out of an early RX7 but also possibly out of a RX2/3/4.
 
Purchased HP Books "Street Rotary" book, and have attempted searches on more than one Mazda forum--but no success.

I want to identify a 12A core engine (engine casting has 12A cast right into it); purchased out-of-the-vehicle from a Craigslist advertisement.

Owner claimed it's from an RX-7; but I suspect it's like every Chevy engine or engine part sold is from a Corvette.

1. This has a single distributor (1974-newer, but not so new as to be distributorless, which would be--what? 1986?)
2. Has electronic ignition (magnetic pickups) in the distributor. I don't know when Mazda dumped points in favor of electronic ignition.
3. Has two coil wires. I read that later engines used three coils.
4. Has thermal reactor, so it's older than catalytic-converter equipped vehicles.
5. Has carburetor. Older than FI-equipped vehicles.

I'm kinda guessing that it's from the second-half of the 1970s, but I'd like to narrow that down to year and model.

I'm sure there's engine ID numbers including partial VIN stampings somewhere on this engine...but I haven't found them. I wouldn't know where to decode them anyway. Tips?

I'd kinda like to hear this thing run (on an engine stand, I don't have a vehicle for it.) but since the starter motor bolts to the bellhousing instead of the engine block, AND I don't have the ignition amplifiers and wiring harness, that'll be near-impossible. I bought it as a non-running core with the intent of pulling it apart for inspection to satisfy my curiosity.

sounds like it is from a 1980-85 rx7...
79 rx7 12a had points
80 was first yr of electronic ignition
85 was last yr of carbureted 12a in US
86 was 13b motors only
I am not sure about the thermal reactor yrs.
 
Last edited:
If you have the "smooth side" 12a then it's a79-80 rx7 motor. The 81 up 12a motors have collars around the spark plugs and you need a thin walled spark plug socket. Thermal reactor is also a sign of a 79-80.aka SA rx-7 motor. You can switch over from the points ignition dizzy on any 12a so that's not a sign there are no serial #s on a 12a motor.
Older 12a motors also l have Mazda written in a different script.
 
If you have the "smooth side" 12a then it's a79-80 rx7 motor. The 81 up 12a motors have collars around the spark plugs and you need a thin walled spark plug socket. Thermal reactor is also a sign of a 79-80.aka SA rx-7 motor. You can switch over from the points ignition dizzy on any 12a so that's not a sign there are no serial #s on a 12a motor.
Older 12a motors also l have Mazda written in a different script.

yes , agree 100%
 
From my experience with 12As it sounds like an early 1980 RX7 engine. At least at my best guess. I have a few 12As laying around two from 84, and one from 79. The thermal reactor was ditched for cats after 1980 and points distributor set up was ditched after the 79 model year...I think. So an early 80 model sounds about right.
 
From my experience with 12As it sounds like an early 1980 RX7 engine. At least at my best guess. I have a few 12As laying around two from 84, and one from 79. The thermal reactor was ditched for cats after 1980 and points distributor set up was ditched after the 79 model year...I think. So an early 80 model sounds about right.
"Early" 1980, or just "1980 model year"?

Are you saying there's differences between early 1980 and late 1980 model year engines?




Thanks, guys. I guess I have the answer I was looking for. This engine is apparently from a "1980 RX-7", so it's a year or three newer than I expected. I'll check eBay for a Mazda service manual. It may be that I can find ignition amplifiers and coils. Rebuilding the carb doesn't scare me too much. I'd have to find out why the air pump and the water pump are both seized--but that can't be too difficult. The big deal is that I've got no idea how to hang a starter on this thing except to buy a bellhousing. Starting the engine--or even doing a compression test--doesn't seem likely at this point.

I'm surprised that there aren't ID numbers including a partial VIN number stamped or etched into the engine somewhere. I thought that was part of Federal law, as an emission-control and anti-theft regulation.
 
Last edited:
The starter hangs off of the trans, so there isn't really any way to crank the motor with out a trans. you can remove the points ignition and install a later dizzy and swap over to an msd ignition for the leading coils and use one coil for the trailing.
 
"Early" 1980, or just "1980 model year"?

Are you saying there's differences between early 1980 and late 1980 model year engines?




Thanks, guys. I guess I have the answer I was looking for. This engine is apparently from a "1980 RX-7", so it's a year or three newer than I expected. I'll check eBay for a Mazda service manual. It may be that I can find ignition amplifiers and coils. Rebuilding the carb doesn't scare me too much. I'd have to find out why the air pump and the water pump are both seized--but that can't be too difficult. The big deal is that I've got no idea how to hang a starter on this thing except to buy a bellhousing. Starting the engine--or even doing a compression test--doesn't seem likely at this point.

I'm surprised that there aren't ID numbers including a partial VIN number stamped or etched into the engine somewhere. I thought that was part of Federal law, as an emission-control and anti-theft regulation.

There aren't any huge differences It was just to my understanding that the thermal reactor was phased out later in 1980 and the points phased out early on in 1980 models. That was why I said that. Otherwise it doesn't really matter much. The engine may have been made in 79 as well as actual 1979 model RX7s were made in 1978. My 84 RX7 was built in 1983.
 
Banzai racing has a page on their website about starting an old rotary engine. It had some good tips. Idk If the page is still there. May be worth a look. I agree with switching to an electronic ignition though. The MSD boxes hooked to the leading plugs usually performs really well. Its actually something I'm working on doing to my car.
 
2. Has electronic ignition (magnetic pickups) in the distributor. I don't know when Mazda dumped points in favor of electronic ignition.
3. Has two coil wires.

you can remove the points ignition and install a later dizzy and swap over to an msd ignition for the leading coils and use one coil for the trailing.

I agree with switching to an electronic ignition though. The MSD boxes hooked to the leading plugs usually performs really well. Its actually something I'm working on doing to my car.
Engine already has two magnetic pickups in the distributor. Seems I'd need two MSD boxes, one for each pickup. Not a problem, I've got a small stack of them. I'd have to come up with a pair of coils and fabricate some wire harness, though.

As said, the starter is the real problem. I don't have a bellhousing to bolt it to; and I don't like the idea of pull-starting the thing like an outboard!
 
Engine already has two magnetic pickups in the distributor. Seems I'd need two MSD boxes, one for each pickup. Not a problem, I've got a small stack of them. I'd have to come up with a pair of coils and fabricate some wire harness, though.

As said, the starter is the real problem. I don't have a bellhousing to bolt it to; and I don't like the idea of pull-starting the thing like an outboard!

I wouldn't want to attempt a pull start either! I have two spare transmissions I got cheap a few years ago. Maybe check eBay or local junk yards. That's great that you have some MSDs laying around. The distributor does indeed have two pick ups. One for bottom two plugs (leading) and one for top two (trailing). A lot of people use two MSDs and three coils. They usually wire one MSD and one coil to each leading plug. Then wire the two trailing plugs to the third coil and the distributor. Wiring the MSDs to the trailing plugs doesn't offer much in the way of any improvement in how the engine runs. Most rotary engines will run on only the two leading plugs firing. Mine will. Google MSD ignition swap RX7 and a nice how to page from mazspeed should come up. It may help.
 
Back