Is a 12A engine a 12A engine???
 

I have an '85 GSL and an engine from a '79. The emissions and all of that are different but I plan on removing all of that anyway. I pulled a spark plug out of the "new" motor (the '79) and it is completely flush at the end. The '85's spark plug has the four prong electrode. Is there something different with the internals?

I'm waiting for a clutch to come in. Should be here in a couple of hours. Am I going to catch hell trying to put this '79 engine mated to an '85 tranny/engine bay?

The 79 used a smaller Clutch, But it sounds like you caught that.

The plugs in the 79 were just the wrong ones. The 79 and 80 call for a Denso 3 prong, but run the NGK just fine. There should not be any other differences, Just use your 85 stuff on the 79 "block" You will want to change to the 85 Dizzy, the 79 would have points as stock.

Well, the '79 came with a tranny but no clutch. I'm putting in an '85 clutch. Any problems with that?

'85 dizzy'= distributor? There aren't any "points" in the '85 or the '79. Not points in the way the old piston engines anyway. I looked at the distributor on the '79 and it "looks the same" to me. I didn't measure anything but it's the same setup as the '85.

79's came with a point and condenser distributor, but the conversion to a newer electronic style ignition is SO common that it is likely that there are very few that are still running with the original distributor.

The engine itslf shouldn't really give you much trouble as long as you have the right combinations of things attached to it. As long as you are using a later model transmission in a later model car, you won't have a problem with the shifter hole in your tunnel being in the wrong place as it would with a 79' transmission.

Yes. Clutch too big. Need a 215mm clutch ('82-earlier). No, you can't swap the flywheel, different imbalance.

Somebody changed it to an electronic unit then. The '79 had points, the '80 was electronic but *different* from '81-85.

The engine is a bolt in, as long as you don't need to pass emissions. Use a header, not the thermal reactor.

Everything is staying stock. I don't trust the knuckleheads at DMY. I SHOULDN'T have to worry about emmisions but getting the DMV to apply common sense isn't always easy.

What do you mean about the clutch? I need the '79 clutch? I noticed the flywheel is much bigger and heavier than the one on the engine. Keep the flywheel or swap it? If the internals of the engine are the same and the tranny is the '85 then there shouldn't be a problem using the heavier flywheel.

Again, I'm using the '85 tranny. The clutch I bought is an '85. I'm going to go compare the pieces now.

The clutch plate fits but is tighter than in the '85 flywheel. The big difference is in the pressure plate. It doesn't look like the pressure plate is deep enough for the clutch plate material.

The '85 also has guide pins in it to align the pressure plate.

If the e shaft is the same as the '85 and the tranny is an '85, why not swap the flywheels?

Can I change the counter balance on the front of the engine?

Bob, I don't think the engine is a '79, I want to say '83 or so. The electronic distributor was the give away for me and the exhaust manifold. I hope this info helps out.

Well, the flywheel definitely isn't the same as an '85.

Is there a way to decode the engine serial number? IS the VIN # somewhere on the engine?

Flywheel is dependent on the rotors used. (So is the counterweight! Don't switch counterweights around, keep it matched to the rotors in the engine) '79-82 had heavy rotors, '83-85 had lightweight rotors. Incidentally, '81-82 had really light flywheels and they work just fine on a '79-80 engine because the imbalance is the same.

It is easy to tell a '79-80 engine from a '81-85 engine. '79-80 have passages just below/to the center of the exhaust ports (one per rotor housing) for air injection, which was done through the exhaust manifold ("thermal reactor"). On the '81-85 engines this area is blank, just a couple casting indentations.

'83-85 engines originally had the water/oil cooler (the "beehive"). Swappable item so this is not a good judge of year.

Mazdatrix's website has a FAQ section that details the numbers on the backsides of the flywheels, so you can see what flywheel you have on it, which is a fairly good way of determining engine year. Assuming some dipshit didn't put the wrong flywheel on the engine, of course.

Well, I slapped the hevier flywheel on just to see if it would fit. Appears the same on diam. I "chucked" the engine back into the engine bay. I'll mess with it when I find an extra $200 laying around for my own hoist. It may be spring before we get a decent break in the weather and I have time to mess with it. I really want to get it running but right now, we are spending more each month than we make. I've got to get the house refinanced and the credit cards killed but that is a whole nother story.

It is even easier than that. the 79 and 80 do not have the "eye Brow" over the Spark plug hole like the later engines do.

The eyebrow can be ground off... ;)

Bob, you *must* use the flywheel that came with the engine. I cannot stress it enough. There is only one flywheel for the lightweight rotors, which is '83-85. If your "new" engine came with a different flywheel, then it *has* to have the heavy rotors. Suck it up and buy a clutch, it's cheaper than killing the bearings in your engine because you used the wrong flywheel.

All N/A flywheels (except for REPU) will physically bolt on and are the same outside diameter. They are not interchangeable due to the imbalance difference.

I've only taken one 12A apart and that was the one in the '85. There is NOTHING light weight about those rotors!!

As for the flywheel, I'll check for the eyebrows. Nothing was ground off unless it was done a very long time ago and on a machine. I've already bolted the intake manifold with the carb back on so I don't want to take that apart and look for the ports. I believe they were there but then I also believe the eyebrows were there too. I may be thinking of the '85 tho.

By the way, the intake from the '85 looked better than the '79 so I used it. Am I going to have to change it to the older one?


Damn, so much for a 12A being a 12A!!!

Here's a couple of pics of the '79's intake.

They are the second lightest rotors ever put in an RX-7. They are only a few grams heavier than the vaunted Seres 5 and FD rotors.

The other rotors weigh on the order of 1 to 2 pounds more.

Got it mixed up. You check the *rotor housings* for eyebrows around the spark plugs, '81-85 engines have these beefy eyebrows over the spark plug areas, earlier have these weeny little eyebrows. The upshot is that you cannot use short-body 13/16ths hex spark plugs (which is what pre-81 plugs were) in an '81-up engine without having a special thinwall socket, or grinding the eyebrow out.

The ports you want to look for are under the *exhaust* ports, not the intake. You cannot tell SA from FB just by looking at the intake ports.

You can use either intake on an SA engine, but you can't use an SA intake on an FB engine. The FB intakes are junk but they work well enough. SA intakes do not have the shutter valve paraphernalia, but they do not cover the port under the center intake ports, so of you put it on an FB engine you get a big exhaust leak.

Well, it's not that bad. There's two kinds of emissions systems (SA, FB) and two weights of rotors ('82-down, '83-up). That's only three different total variations, and only two things you have to worry about for any given operation.

That's not a '79 intake. Shutter valve is dead giveaway.

Either it's an FB engine, or someone put that intake on it for whatever godforsaken reason.

Sorry should have thrown in a paragraph break there. I know the eyebrows are over the plugs. Didn't have any. It did have a funky plug in it. It was flush at the bottom, no electrode. Since an NGK plug tho. Don't remember the number off the top of my head. "S" something.

What the hell is a '79 then? I thought all the first gens had the 12A motor with the exception of the GSL-SE.

I went and looked up the SA. Didn't know that...

Anyway, Charles said the engine might be an '83. How do I go about decoding the serial number of the engine?

Did any of the paper work I gave you mention the year?

I have an 81 block in my 84. it has all the 84 externals on it though. carb and clutch and everything. pulls strong

I'll check it again but I don't think so. Sometime this weekend I'll take the other clutch back and try something else.