The 12a engine in my rx3 was missing when I purchased the car. I do have a older 13b that came with the car and it does seem to have the right engine mount on the front cover.

A couple of questions concerning this swap:

A flywheel from an automatic is currently mounted. I do have a 13bt flywheel that I can use. Would this be overkill or should I find an NA flywheel instead?

Will the 13b bolt up to the 12a tranny bellhousing?

Will the 13b clutch splines mate up with the original 12a tranny spline shaft?

Is there anything else I need to know for this swap?

If there is, please let me know. TIA

 

A couple of questions concerning this swap:

A flywheel from an automatic is currently mounted. I do have a 13bt flywheel that I can use. Would this be overkill or should I find an NA flywheel instead?
turbo flywheels are bigger than N/A.


Will the 13b bolt up to the 12a tranny bellhousing?
yes

Will the 13b clutch splines mate up with the original 12a tranny spline shaft?
yes

Is there anything else I need to know for this swap?
Notch the front engine mount

 

You got a '74-'75 13B there. Good find! I'm going to be building one of those later this summer for my '74 REPU. I'm sure you're going to use DLIDFIS with it, right? Sure you will.

Automatics don't use flywheels. You're like huh, what?

Which tranny do you have? The flywheel, clutch and pressure plate need to match each other obviously. Since that engine is from an auto, it already has a counterweight. Just get an aftermarket light flywheel that bolts to a counterweight like the Racing Beat light steel or aluminum.

"Will the 13b clutch splines mate up with the original 12a tranny spline shaft?"
Only if the clutch/flywheel/pressure plate matches the tranny. Turbo splines are different from '74-'92 NA.

There is probably more to it, but I Wacky already mentioned notching the motor mount. Hmm, maybe you could remove the rubber motor mount things and slot the holes on the crossmember. It's worth a look.

 

Ah okay... Thanks Wackyracer and Jeff20b for the replies!

So this setup, an NA flywheel with clutch and pressure plate, will mate up to the 12a tranny then - correct?

My bad... I meant to say flex plate. I had flywheel in the brain this morning...

I recently purchased a '73 rx3 so whatever manual tranny that came with it is the one I have. LINK

 

Is there a way to tell or know for sure exactly what model year this engine is from? Casting numbers, somewhere maybe, if there is one?

 

I recently got the same motor. Jeff20b is right about the year of the motor. I took mine apart to see if anything needed to be replaced and I was suprised to see that those 13b come with solid corner seals simular to atkins solid seals and the Apex seals are BIG! I quess I just wasnt used to seeing 13b 3mm seals. lol

 

Okay I'm stuck right now concerning the clutch...

The car has a 4 speed tranny. I was given a 13b na clutch just to see if it fits the tranny splines. The clutch splines was a tad bigger than the tranny shaft.

soooo....

what oem flywheel clutch setup do I need to make this swap happen?

Do I need a 12a flywheel clutch combo and will this flywheel fit the 13b eccentric shaft?

or would this work- a 12a clutch to 13b pressure plate...

I would really like to keep this tranny on the car...

Someone please help me out here

 

The most important question I must ask you is:

Does the tranny have a top mount starter or bottom mount starter?

 

I'll do one better! Here is a picture:

 

Interesting. It still looks like a '71-'73, but with a bottom mount starter.

Ok, I know the ultimate way to tell. Take a picture of the inside of the bellhousing. I want to see the 8 nuts. Please don't zoom in too closely as I want to see part of the engine bay for reference.

By the way, I installed a 13B in a GLC which happens to have a very similar engine bay. You just need the right tranny, which is what we're trying to determine.

 

Okay after several tries, here is the best shot of it... Click on image to enlarge:

 

I've never seen a tranny that looks quite like that before. I want to say that it will work with your 13B but I'm just not sure. I know there were some twin dizzy engines that had a bottom mount starter, but the early bellhousing bolt pattern and diameter, which is incompatible with '74 and later 12A and 13B.

For example, this is a twin dizzy tranny '71-'73.


This is a '74-'75 tranny out of my REPU.


A closeup. Sorry I didn't get the top in this pic.


You can kind of see the rubber cap in this picture.


And in this picture. These bellhousings are the same.


A good shot of the backside while masked for painting.


And back on. Notice how close the hole is? Yours is like way off to the side.

 

Ok, after comparing the pictures, I'd say your tranny is as I suspected: It is a bottom mount starter twin dizzy tranny and is NOT compatible with any '74+ engine.

Just compare the bolt holes around the edge of the bellhousing. Notice how my twin dizzy tranny maches your tranny? Interesting, isn't it.

You need to get a '74 or later tranny for that 13B to work. Plus you'll need to shorten your driveshaft and mess with the tranny mount because twin dizzy trannies are shorter. Plus the 13B is 20mm longer than a 12A so you'll need to absorb the engine's extra length somewhere too. I'd say shove it rearward.

There is a mod you can do to the shifter of an '81-'85 tranny to move it forward about 4 inches. That's a good thing to do in a situation like this, since early trannies are kinda hard to come by, and it will come closer to fitting the stock hole in your tranny tunnel.

Well, whatever you do, this should get you looking in the right direction at least. Good luck.

 

Thanks for all the great info! Its very much appreciated!

Do you think this would work... Replace just the bellhousing with one that will work with my 13b? Seems like the bolt pattern that mounts the bellhousing to the tranny itself are all the same but I have no clue...

 

That might work. It would be worth looking into. Now you just need to ask around to see if anyone has a spare '74-'78 bellhousing you could try.

 

I'm picking up a 12a motor from an '83 rx7 this weekend to drop in the rx3. Does it matter which clutch set I use for this? The only thing I see different is the clutch diameter and of course the price. Here is the info from Autozones website.

1973 12A
_____
Duralast / Clutch Set-Matched
About this product:
Part Number: NU1181B-1
Weight: 15.2 lbs.
Price: 108.99

Note: Disc outside diameter 8 1/2", spline inside diameter 15/16", spline count 22 kit includes: Clutch, disc, release bearing, alignment tool, pilot bearing, spline lube



1983 12A
_____
Duralast / Clutch Set-Matched
About this product:
Part Number: NU31084
Weight: 16.05 lbs.
Price: 143.99

Note: Disc outside diameter 8 7/8", spline inside diameter 15/16", spline count 22; Contains Premium friction, O.E. manufactured clutch components Kit includes: Clutch, disc, release bearing, alignment tool, pilot bearing, spline lube

 

Anyone with an answer for me on the above question?