Jeff20B

Hey Mike, I've got a quick question about '71-'73 rotor housings and '74-'85 rotors. They're compatible, right? I've got some '83-'85 rotors (the whole rotating assembly) and a '73 streetported 12A. If I were to use carbon apex seals in the FB rotors, the trochoid chamber would allow that, right? Or was it slightly changed like what people say about the change-over from '85 to '86 13Bs? I'm getting closer to rebuilding my 12A and it would be really cool if I could use newer lighter rotors in it.

thekid

I believe the tension bolt pattern was different on the real early 12A's so they would not be interchangeable with the later engines.

Jeff20B

Yeah, there's two that were moved in '74 to give greater freedom for exhaust port height and the L sparkplug position.

j9fd3s

yeah ive heard of people rebuilding 73 12a's with 74+ rotor housings so it should work fine. carbon seals would be good too, i dunno if you can trust the early rotor housings with steel ones



mike

Jeff20B

Yeah I'm going carbon seals for sure. In like 20k miles, it'll probably need a rebuild, but the rotor housings should still be fine. I think if I were to use iron seals, the chrome would be sorta missing in 20k miles.



I'll stack a '73 on a '78 housing and see if there's a difference in the chrome thickness. I'll be sure to use some dowel pins for this. I hope they're at least close. I'll also build the front of the engine to see if the rotor tips will clear the chrome all the way around.

JefeSpeed

The early 12a engines (1972) didn't have chrome plated housings did they?

Jeff20B

Yeah, but it was different (weak).

sevenracer

Sorry to thread jack, but has anyone tried to relocate the 2 tension bolt holes on an old style housing to match newer irons? I'm thinking you could maybe could use that 3M jb weld type stuff they use for P port engines, and then redrill. Possible?

I have a couple sets of nice early housings, but only later style irons, etc.

Lynn E. Hanover

I used to mix and match old and new styles to get a late engine into an RX-2. Just used an old (Small) rear iron so it fit the early (Small) bell housing.

Just tap the unused bolt holes in the rear iron for pipe plugs lest the water fall out. The missing bolts have no effect on performance.

Lynn E. Hanover

sevenracer

Wow, so for what I am trying (all new style irons, transmission, etc), I could just leave those two tension bolts out, plug the holes and have no ill effects?