13b flywheel in 12a motor/tranny
 

i know a guy selling lightend 13b flywheel for cheap.
i want to make them fit in my SA and i was told that i can use auto 12a counterweight to make 13b flywheel to work in my 12a motor and 5 speed.

Aftermarket flywheels are the same for all NA rotaries except the RX-8. He is correct, just get a 12A rear counterweight and you're good to go.

Note that your car came stock with a 215mm clutch setup. This will work on a flywheel designed for 225mm clutch parts, but if you're going to replace it anyway, I recommend upgrading to 225mm (215mm aftermarket stuff is getting hard to find, as well). When shopping, look for clutch parts for an '83+ non-turbo RX-7.

To be specific, a 215mm DISK will work on a 225 flywheel. The pressure plate will not fit, there is a register depth difference.

One of my friends bought two clutches on eBay that were supposed to be for a 225 but they were really 215. The pressure plate was all wrong. We ended up using one of my used 225 pressure plates with one of the new 215 disks and it worked fine.

....

Is it a LIGHTWEIGHT flywheel or a LIGHTENED flywheel? If it's an aftermarket flywheel, then yes just get the rear counterweight for your year engine (no need to mess with the front like some people parrot) but if it's a stock flywheel that has had metal machined off, it won't work.

Im thinking the same. The only problem is getting the counterweight. Where can you get just the counterweight?

gettting that counterweight(83-85) is pretty hard as it has been discontinued, but you could put a wanted to buy ad and maybe someone has one laying around that they will sell you. Don't expect it to be cheap as most people know what they got. I've been looking around a while now. good luck!

There are two 12A RX-7 counterweights, '79-82 (what an SA engine will have) and '83-85.

They are not interchangeable! This is why knowing what year rotating assembly you have is important.

that mean i cant use 13b flywheel in my 1980 SA since there not any 13b counterweight will fit in my motor?

Good point, I'd forgotten about that. In any case, boxerpicker, just get the 225mm setup assuming you're replacing it, which you should anyway.

Stock flywheels have the counterweight cast into the flywheel. Aftermarket flywheels do not. If it is a lightened stock flywheel, it's not going to work on a 12A. If it's an aftermarket lightweight flywheel, you use the rear counterweight appropriate to your rotating assembly. In your case the '79-82 12A auto counterweight is what you need.

as mentioned aftermarket light flywheel is a neutral weight and will swap 12a to 13b and bolt up to the correct auto counterweight for your engine series

you do have to concern yourself about the ring gear diameter
-- units for 13bt "R" boxes use a larger ring gear than earlier R and M boxes for all the NA rotors


if your engine has the "H" housing casting on top then it is the later counterweight
as pictured in this link
https://www.rx7club.com/1st-generation-specific-1979-1985-18/problem-fresh-rebuild-940802/
83-85 12A
-N226-11-751A
---------the flat edge measured at the rim of the weight thus
https://img515.imageshack.us/img515/...7110ez0aw9.jpg
( do not measure the rolled edge chamfer )
should be 6.07 to 7.01 mm

if you have housings with the solid lump instead of the H then the motor is pre 1983
( 12a 6p excluded )
these use the 79-82 12A weight
-1883-11-751A-------- 8.25 to 9.17mm on the rim measurement


there is another confirmation if you have a hybrid build engine
74-76 engines have MDR symmetrical rotor bath
( and use the 1883 weight )
77-82 engines use the LDR assym rotors,, viewed through exhaust port you will note front and rear rotors have F or R stamped into the rotor bath
( and also use the 1883 weight )
the 83-85 engine ( include the 1981 6p 12a and also the 83-87 12at engine )
will have F or R,, but also T or N ( turbo or NA )stamped into the rotor bath
( and use the N226 weight )

If the car is an SA, it has the early rotating assembly or it's had an engine swap. If the latter is the case, I would not use the rotor housings to identify the rotating assembly because there's a good chance that it's been rebuilt at some point, and who knows which rotors were used. I'm guessing there's probably a way to confirm which rotating assembly you have by looking at the stock flywheel, though I don't know what you'd look for. Otherwise, just visually check the rotors as bumpstart describes.

But if it still has the original engine, you don't have to worry about that.

It's very interesting that the N226 rotor weight class had such a long run from '81 to '87, but we only got it in the 83-85 motors.

I've seen N226 cast into some of the parts from a 6 port 12A, which I'm sure is something only a rotor geek like myself would find intersting. :)

the exceptions are for the japanese HB cosmo
,, avail in 1981 as a 6p in japan and its actually using the later rotors and housings
then extending as the HB cosmo with 12at to as late as 1987
until introduction of the rotary HC luce versions with 13bt s4/5 hybrid engine
( usually the update s5 plates and housings ,, with s4 rotors and s4 manifolds and s4 turbo )

i include the exceptions because its common to see these engines as imports in australia
- using the blanket 1974-82 and 83-85 advice will catch owners of these engines out

as mentioned ,, its prudent to check the actual rotor baths for the stampings as its very likely that engine swap and hybrid builds may have occurred over the 30 year lifespan of the vehicle till now

There are numbers stamped on the engine facing side of the flywheel. MazdaTrix website shows the matching years/weight. I'd use the corresponding counter weight.

http://www.mazdatrix.com/faq/flywheel.htm