Twin dizzy build
 

I been sitting on my 72 twin dizzy 12a for a while now. I was going to sell it, I had an offer and decided to keep it. I'm looking to build it now.

The only thing I am worried about is the second (inner, closer to the center) side seals. If they are out of spec or worn beyond use, Will I need to find a new set? Or could I just leave them out and rely on the outer side seal to do the job?

If i do in fact need the inner side seal, anyone know where to locate a set? never seen them for sale anywhere...

I wouldn't worry too much about those side seals ; the only critical thing is the clearance to the corner seal and of course that they spring nicely in their groove. Mazda obviously found them to be redundant and thus dropped them beginning with the 1974 engines. I have on occasion had to cut / make one from a larger seal when the original broke in the groove ; but again watch your clearance.

^Cool, I guess I'll just try using newer 12a/13b side seals and just make sure they seat properly.

Here's something different I am not use to seeing...

A tensioner on the chain and to brass colored bolts on the bottom of the rotor housings. Anyone know why these bolts are there? havnt cracked the motor open to see what there purpose is yet.

http://i282.photobucket.com/albums/k...P/SAM_0427.jpg

http://i282.photobucket.com/albums/k...P/SAM_0426.jpg




Here's two random shots of the motor with the twin dizzy front cover and oil pan already pulled off. It's ready to be cracked open.




http://i282.photobucket.com/albums/k...P/SAM_0428.jpg

http://i282.photobucket.com/albums/k...P/SAM_0429.jpg

Change the rotors to modern 12A ones so you dont have to worry about finding apex seals and stuff, also the modern seals are better than the old carbon seals. something else you should know is that theres a Mod you need to do to the front iron plate because it has a defect, there is a oil vain that doesn't pass through the oil filter so it caries unfiltered oil to the stationary gear which i believe goes to the eccentric shaft.

At first glance, all the seals look close to new. Everything moves freely and has no noticeable defects. We'll see if that's still the case after a good cleaning. I plan on re-using everything that is in spec, which I hope is everything. So hopefully I'll just be replacing the water jackets and o-rings.

The housings are the most amazing part. There is absolutely no flaking, chatter, wear marks or anything. Not even the brown heat marks around the spark plug area. The iron faces look equally nice. Considering this motor has been sitting for a VERY long time without being ran or even turned over and there is no pitting in these irons. I'm guessing this motor had been rebuilt back in the day and not ran very long at all if ran at all.

I might Switch the front and rear plates to resolve two problems. The front iron, to resolve the oiling problem. And the rear iron so I can use a newer trans. This is a 1972 motor, and and 74+ motors have the newer style bell housing that we are still using today.


By the way, This motor will be getting a decent sized PP with a set of 51 IDA Webers.

Two more random pics during tear down.




http://i282.photobucket.com/albums/k...P/SAM_0431.jpg

http://i282.photobucket.com/albums/k...P/SAM_0430.jpg

Damn you lucked out big time, when we tore mine appart the only usable things were the back plate, the E-shaft, and the housings were ok but I ended up changing them for a better set. If your interested in selling the front and back plate or anything else from the motor let me know.

are you going to keep the stock rotors in the motor?

If you use a later end plate, a couple of the thru-bolts won't line up.

re10 is correct, My last block was a TD with a s1 rear plate and used a s1 gearbox, Was a mint little motor, reliable as. Good luck with build, A nice pp should be sweet ! All the twin dizzy motor's ive seen all have mint internal's.

holy moly! this is quite a treat. this is one of only a handful of "old school" engines i've seen in pictures, and i have yet to see one up close, in person. you've really made my day with this thread.

i may be wrong, but i think they are related to whatever emissions system these engines had. i vaguely remember reading about them from my trusty old Racing Beat manual.

I knew the twin dizzy had more bolts than all the newer motors. But it's actually only by one tension bolt. Which is fine since it's right about where I would put my PP anyways. So It would become obsolete anyways.

But one thing I wasnt ready for, two of the tension bolt holes do NOT line up properly. One just below the spark plug area, and one just below the exhaust port. If I look through, only about half of each hole is visible.





Here's a pic to point out the areas:



http://i282.photobucket.com/albums/k.../SAM_0431b.jpg






On a side not, the twin dizzy tension bolts are much thinner also. The twin dizzy tension bolts are just under 7mm, and the 13b tension bolt I measured was around 9.4mm. But the thread and pitch at the end is the same. Obviously much less thread, but none the less the same.





http://i282.photobucket.com/albums/k...P/SAM_0432.jpg

Re: Twin dizzy 12A...
 

Yeah re10 and diabolical have got it right. All the early twin dizzy motors 10A & 12A with the 6mm carbon seals had 19 tension bolts and only mate up to early trannies. From 1974 on (12A & 13B) some of the tension bolt locations changed thus you can't update- backdate housings between them. Also later trans won't line up unless you use the early bellhousing (either top start or bottom start). As far as the "brass" bolts in the rotor housings , they are actually stainless steel air injection nozzles used for emissions. They probably appear brass looking because of old oil residue. You will need to carefully remove these and weld them closed or buy Racing Beat blocking nozzles. As far as the condition of the rotor housings , this was fairly typical of the old motors where the chrome is in great condition. That because of the softer carbon apex seal ; the 1974 on engines with metal seals tend to chew things up a lot more. You will likely want to run a one piece carbon seal with the PP anyways . After a thorough cleaning of those rotor housings , really check well for distortion and overeating damage as those cooling passages look gross!

I have a twin dizzy that was sitting in my R100...

It has electronic ignition!

turns freely, smoothly...

never heard if it ran or had problems...

IF YOU NEED ANYTHING?

let me know.
GLW PROJECT

10a or a 12a?

So it still has the twin distributors but its electric ignition? how was this done?

Just use a later front - common conversion - done this to my 10a

i guess you pull the pickup out of a chrysler distributor and put it in the mazda. you have to fab the mountings, but its what the racers here did in the early 80's

Nope its stock distributers and has special caps and internal pick-ups

I'LL try to take some pictures

and its a 12a

Subscribed!

If you need any harder to find parts, I know a guy in Sanford that has a lot of pre-74 12a and 10a stuff.

I can give you his number if you want to ask him some questions about the engine.

Are they for sale? How much for the dizzies?

sure

I have no Idea of value, just sent a pic to a man in the know...

Oops, forgot the pix, then the edit timed out, I add the coils next to the box that says Allison, the box pwoers the distributor...

I added the coils as I am useing a later model single distributor set-up

hear you go

here is a pic with the rotor off

and a couple pix off the flywheel

seems like a race fly wheel, very thin

and a straight on pic...

Sen2two did you ever finish work on the front end of rx2?

Nope, I was all ready to weld in my new frame rails, and bend all the tubing to finish it off. But the fire wall/floor area there seems real weak. I didnt feel right welding in nice new metal to a point that might fail. I am trying to source replacement metal. but as all of us know...it's hard to come by these original pieces. Especially when you have to have someone cut it out from there car.

Dang sorry to hear keep us posted. Keep at it!