razorback

ok, i just got a 12a in a trade and wondering what year it came out of. it doesnt have the beehive oil cooler, but it looks like it has a hookup for a front mount oil cooler, what years came with these?

diabolical1

iTrader: (3)

assuming that it's an Rx-7 12A, you're possibly looking at 79 to 82 based on the oil cooler setup - and assuming the PO did not convert.

do you have any pics? the flywheel and rotor housings might help narrow it down some.

razorback

mazda is really big on the housings, ill get some photos tomorrow. the plates have 3b stamped on them. (well the rear and mid one do anyway)

MosesX605

3b sounds an awful lot like 13B to me. Perhaps you have an old 4 port motor and not a 12A at all.

razorback

it says 12a on the housings.

diabolical1

iTrader: (3)

is it mazDa ... or ... MAZDA?

Jeff20B

iTrader: (13)

You have a '74-'75 12A. The rotors should have a symetrical compression dish. The intake ports may have the cool 13B '74 spec later closing port timing. The oil pump should have a 15mm gear set.

Things to watch out for: The thrust bearings and thrust plate tend to wear out on these engines faster than the later R5 and Y engines. The stationary gear teeth are shorter which can lead to cracking and failure at high RPM/load (like if you're boosted and trying to extract a lot of power) which was fixed by '76 with lengthened teeth extending toward the base of the gear. The apex seals were 2-piece 3mm and had a full-length contact to the rotor housing chrome surface, with the little triangular piece under the long piece. Read here for some details. (scroll to bottom) http://www.mazdatrix.com/b3.htm If you use the later apex seals, they can wear the chrome faster.

I can't think of anything else. Oh yeah, the exhaust port sleeves look smaller than later engines. They still flow pretty well though. Infact, I think the velocity is increased and therefore louder than '76 and later engines. Or something like that. Let's see some pictures.

Rogue_Wulff

Is this one that came from Adam?

razorback

yes, the assembled one.

and its MAZDA (pretty much how it says its on there)

i borrowed a former boss's impact wrench, has a 1100ft lbs removal and it took the nut off in 4 seconds its a nitro cat for thos of you wondering. i got sick of pounding on the damn flywheel nut.

Rogue_Wulff

I am thinking that was a mid 70's 12a. It had a different type of carb, with the OMP lines at the bottom. I *think* it was a hitachi. It also had a darker blue air cleaner.....
I don't have them, but I know where they are, along with the factory intake.......
I believe it also had a 4 speed behind it when he aquired it.
Doesn't it have a single point dizzy?

razorback

i didnt get a chance to look at the dizzy, just took it off and laid it beside it. ill get a photo of that tomorrow too. he said he also had a 4spd, so im assuming it came off that motor. the front rotor is gone, i see some cracked apex seals when i look in it.

Jeff20B

iTrader: (13)

If it's a 12A, it'll be a Nikki.

razorback

pictures:














i will disassemble it tonight and get photos of the rotors and such.

razorback

ok, another oddity, well actually 2. there are 19 bolts, 17 that go into the housings, then the normal 2 at the bottom. and there was a looks like a chain tensioner in the front oil pump.

85rotarypower

There should be a code on the back of the flywheel. it across from the "counterweight", a thicker piece of metal on the engine side of the flywheel. What is that code?

Going by the distributor, its 79 or older. Its the old points style. Also, the way MAZDA is embossed without 12A directly above it on the rotor housings suggest its not from an RX-7. Beyond that, your pictures don't say much.

EDIT: Hmmm, I just realized that there are no dowel pin holes on the flywheel. A little strange IMO.

razorback

no flywheel code.




also has that type of corner seal.

since it looks like it isnt a fb motor i guess this should be moved to "general rotary" tech?

85rotarypower

Put a link to general rotary tech to this thread. Might get more help from them, but at least you won't have to type out much. Some of the 1st gen guys are well informed in pre RX-7 motors.

Those corner seals are more or less an aftermarket part. I'm not completely sure if any rotary came with solid corner seals from the factory though.

razorback

mazdatrix has the 74-75 motors with solid corner seals. only years listed for that style thats stock.

Jeff20B

iTrader: (13)

Keep the pics coming. This is entertaining.

MosesX605

Did the earlier motors have EGR? Strange that the '79-80 didn't if that's the case.

Rotaryhaven

iTrader: (17)

This look like a pre 74 engine. I bet you it won't bolt up to a newer tranny. Back in the old days Mazda used solid corner seals.

Jeff20B

iTrader: (13)

I bet you it will bolt up to a newer tranny.

Rotaryhaven

iTrader: (17)

I know I had an old engine and it didn't bolt up, unless this is a trick question you are trying to impose, LOL!

razorback

i have an 84gsl trans i can see if it matches up to. and there is something in the mid plate that looks like it was an egr, but its blocked off.

Jeff20B

iTrader: (13)

That would be a '73 or older engine. I have one too. I also have a '74 '3B' engine which bolts up to any '74-'92 (non turbo) tranny.

That hole at the top of the intermediate plate is for a water temp sender. It's left over from the earlier engines which did not have a temp sender under the oil pedestal. Depending on the model, some got dual temp senders. The 3B engines are the only engines with dual temp senders.