counterweight issue
 

Looking at an aluminum flywheel for a 12a. RB was somewhat helpful but had no definitive answer.
I have a J-Spec 12a turbo. Looking to put aluminum flywheel on but need counterweight for that engine.
Any advice on counterweights for an unknown year 12a that was never sold in
USA?

Check the ausrotary forum, they got the 12AT.

I was going to say call RB and ask them in person, but T's idea is probably even better.

Looking at the Austalian Forum, it appears that all 1983-85 12a counterweights are the same.

would a TII flywheel work?

No, and it won't fit the tranny either.

So if you used a TII flywheel and a TII tranny on a 12AT would it work? :P

Mix matching flywheels and counterweights can be dangerous and destructive. Counterweights are matched to the rotors. Some of the counterweights even have balance indicators in the same year run meaning there were 3 different rotating assemblies.
I work as a firefighter / emt at Road Atlanta. Crank shafts and flywheels fail. A chunk of a flywheel nearly took a man's leg off 3 years ago. Racing Beat says not to use their flywheels over 8500 rpm.
Wrong counterweights may result in vibration up to failures as mentioned above. There were at least 5 different 12a counterweights. Do your research before changing out flywheels.

thanks for the info

Thanks for the info.


If I got the counterweight for the flywheel would it be alright, or would it still not work.

I know a guy who bought a lightened TII flywheel and put it in his 12AT with a TII tranny and he is making me ask these questions. it wasnt me :lol::blush:

The counterweight is matched to the rotors and eccentric shaft, not the flywheel

So, putting a lightweight flywheel on an engine that has all the counterweights is fine?

AFAIK the flywheel has no impact on the balance of the rotating assembly, unless the flywheel itself is out of balance for some reason, in which case it's not safe to install on any engine anyway. A lightweight flywheel will reduce the engine's rotational mass, allowing the engine to spin up and slow down quicker. It's pretty much the same as having lighter wheels.

FACTORY MANUAL rotary flywheels have the eccentric balance inbuilt
AUTO vehicles have a separate eccentric mass,, to which mounts the flex plate

this mass is to match the rotor weights

billet light flywheels have no eccentric weight , and so are designed to bolt to the AUTO mass instead


each generation of motor has evolved in rotor weights,, and so must run the correct specific mass

since 12aT didn't actually come as an auto in any production form
you are lucky that mazda maintained the rotor mass for each model to be the same,, irrespective of compression ratios

so,, since 12at is a series 3 rx7 12a,,, it will use the mass from other s3 rx7 engines,, 1983-85

this is the correct way to do it

dodgy shops will look at the total rotor mass,, and realise that some of the 12a rotor weights aren't dissimilar for the 13bt ones
and its then that you see mismatched flywheels on the wrong engine

not a great practice,, as the balance is certainly beyond mazda spec
and that why they dont give you 13b masses for 12a engines,, and have subtle differences that matter,, lots

Great :) I was starting to think I was going to be looking for a new flywheel.

Yeah, stock flywheels have counterweights on them. I figured he was talking purely about the aftermarket one, as he asked about the scenario where all the counterweights are already correct.

Damn, and I just sold a running 85 gsl automatic cheap. Knew I should have parted that car out or converted it to the 12at with 5speed that I have sitting in the garage.

/\ the OP still requires a 12a 1983-85 counterweight

the N304 1983-85 13b GSL-SE mass is infact suitable only for N304,, and for 1757 ( rx4 /rx5 13b )

What if you use an eccentric shaft from a GSL-SE and rotors from an 89 NA?