Can old school 12A housing be used to build a 79-85 style motor? I have a few of these hosuings but want to use the irons, front cover, water pump hosuing, oil pan and other parts from a more modern 12A. The old school housing do not have the water seal groove for the intake manifold. I guess it could be milled pretty easy. Does anyone know of any other restrictions to using these?

 

maybe, i think they might have a different tension bolt pattern? the other way is to just use the pre74 irons/housings with a 79-85 rotating assembly.

 

I'll do some checking tonight. I'll take some modern irons and front cover along with the old school housings and see if everything lines up. Then I'll see if the waterpump housing and oil pan will bolt up.

If the irons dont work I have a bunch of old school irons also. I just hate to see these old housing go to waste.

 

yeah i know! you could build a pretty nice vintage style engine, its too bad the Rx2/3/4/5's are so hard to find, i'd like to do a vintage race style car, and go hurt porsches

 

I believe REC does this. They also mill 13b housing down 10mm so they work as 12a housings and I think this is where they groove it as well.

rotaryengine.com | Rotary Engine Specialists | Mazda Performance | RX7 Specialties

They have a page on milling the groove but it is empty. Email them and ask for Adam Heyman.

 

those housings wont work at all, ill give u $50 for both...




















.... but seriously, theyll work fine. IIRC the tension bolt pattern never really changed, asides from as the years went on the irons were cast, machined and tapped for less tension bolts. Later engines omitted the extra tension bolt right on top of the intake runners. pre-rx-7 irons had 17 tension bolts around the perimeter + the 2 outer bolts, while later engines only had 16 + 2. The early Rx-7 irons ("R5"'s i think) still has the casting on the front and rear iron, but werent machined or tapped, then the later 12A's ("Y"s) had the cast completely changed to eliminate the spot altogether. But if u look at pretty much any 12a housing there will always be 17 holes (even some FC 13b housings will have the 17th hole, even tho by that era, all the irons were completely lacking the casting for it and mazda never intended to use it ever again)

 

I don't think they will work,difference in the tension bolt placing.i know for sure 74-85 12a housings are good.

 

Easy solution: Get a long drill bit that is the same ID as the tension bolt holes. I think like 25/64" maybe? Next bolt a couple of junk plates to your old school rotor housing. Now use the plate as your drill guide and drill down through the two offset tension bolt holes in each rotor housing. Do the housings one at a time, obviously, for best results. There is one by the exhaust port and one by the leading spark plug.

Does the above make sense?

Also be sure to use carbon 3mm apex seals on your old school chrome. But then I suppose Atkins seals won't destroy the chrome too soon.

As for the coolant ports in the housings, note they lack a machined o-ring land. I'd see if the ID is the same diameter as later housings, then get some 20mm freeze plugs and use a little RTV. Tap them in. Or better yet cut some NPT threads and use a pipe plug. You have to block coolant flow here. Reason is due to the port locations on old school engines are different from later engines. Therefore the old school gasket probably should not be used as I don't know how compatible it is with R5 and Y plates. It's unfortunate too because the old school gasket lacks the o-ring land as well and is less likely to leak. So I'd recommend blocking coolant flow here and using a 74-85 gasket without o-rings.

Now does that make any sense?

One other tidbit of information. The exhaust port location and exhaust stud locations are different. You will need an RB flange meant for 71-73 12As, and build your own header. Have fun!!

 

Thanks Jeff. This sounds very doable.

I have complete, unused, old school gasket kits also. I have what I beleive are 6mm carbon seals but not 3mm.

 

KC, so if you built a 12A using Old School rotor housings with New School parts, would you use New School metal apex seals or Old School carbon apex seals?

I ask because I read someplace and have been told by a reputable source that the chrome lining on the newer housings is harder and built to withstand the metal apex seals, whereas the Old School housings can only handle the carbon seals and metal seals will chew them up.

 

I would use the carbon seals. I would hate to shorten the life of such nice housings. I've been doing some testing with more modern irons and so far it doesn't look good. All but one of the tension bolts is lining up. I'm going to do some more "fitting" this weekend with a modern front cover and irons.

I do have the old school irons and rotors also so if the modern stuff doesn't work I can still build an "All Old School" engine. My only concern is if I have to use a dual dizzy front cover.

 

^lol, Ive heard the same. The chroming has evolved and been much improved in terms of durability, technique, and even overall surface friction. In terms of chroming in general... Old School < SA/FB < S4 FC < S5 FC < FD. But honestly, even for my next build with my beloved pair of flake free Rx-7-era 12A housings, Im only gonna run carbons for the chrome surfaces sake, as the 3mm iron seals devour them under normal circumstances (plus carbons are a **** ton cheaper and like high RPMs, such as in say... a full bridgey )