Hey all, Noticed that the flywheel and counterwight on the later s1 12As is lighter than the SA22. Has anyone made the switch? Is there a noticable difference?

Same questions regarding the rotors.

What years came with the lighter versions.

Thanks, Herb

 

The counterweights need to match the rotors in the engine or it'll be outta balance and SHAKEEEEE.

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

 

Does that mean that if I change the flywheel and the front counterweight that I also have to use the lighter rotors? Or are there other counterweights that I am not aware of?

Herb

 

for an Rx7 12A there are three cases.

79-80, uses the "heavy" F or R stamped rotors, with a normal counterweight and heavy flywheel.

the 81-82 uses the same rotors with a smaller front CW and lighter flywheel.

so in these two cases parts can be swapped.

for 83-85 they went to the "lighter" rotors FN or RN stamped, with a normal, but different from 79-80 counterweight and different flywheel.

 

Switching to lighter rotors or counterweights(flywheel in the case of the rear) doesnt really amount to much gain if your keeping all the stock parts.Some years have higher compression rotors,but that only applies to 13B's.

All rotaries have heavy flywheels,its their nature from the factory to have them to help out with lowend smoothness and compensate for a lack of torque.No matter your year engine or any other specifics,a light flywheel with the appropriate stock rear A/T counterweight is the best way to get some more zing from a rotary for little work.Youll have to adjust your driving style depending on how light you go and your gearing,but its a very noticable pickup in responsiveness and you dont have to tear your engine down to get it.

 

Just want to make certain I have this right.

1) I can change the flywheel and counter weight on my SA22 to a matched set of flywheel and counterweight from a later model 12a without changing the rotors. This will give me a quicker revving car that I will have to rev a bit more off the line.

2) Since I already have the engine apart. I can also change the rotors to a later set which will do more of the same.

Is that correct?

Thanks for the input.

Herb

 

1. the rotor is the same from 76-82, but for 81-82 they ran a lighter flywheel with a small counterweight, so the 81-82 flywheel and counterweight will work with no problems. it is a factory combination.

2. if you switch to the 83-85 rotor set, you need to run the 83-85 counterweight and flywheel, which are not lighter. to run the light rotors, with the light counterweight and stock 81-82 flywheel, you need to rebalance the whole assembly as its not a factory combination

 

I have the 82 flywheel on my stock port 80 12A and it works great. No other changes,
never even cracked the keg yet, so its all stock, just using the lighter flywheel.
Theoretically its out of balance but its an old rotary racer trick to get a lighter flywheel
past tech inspection You can really tell the difference between the 31# and the 23#
flywheel. Revs much easier, of course there is no power change, but might
be useful in an autox situation.

 

Thanks.

 

we need a pictures and weights for the front counterweights to make it simple.

 

Agreed, some photos and data on counterweights would be a gold mine.

So Tim, when you put that 82 flywheel in your SA, did you also change out the counterweight to an 82 counterweight?

 

He probably didn't Ray. It's technically not necessary. I'm just telling YOU to do it because your engine is apart and the access is easy.

 

Didn't change anything other than the clutch and flywheel. Never looked back.

 

I'm still scratching my head on this one.

I need to double check this and will tomorrow, but when I first weighed my 79-80 counterweight it was about 3 lbs and the 81-82 counterweight came in at about 2 lbs.

So how can these two be equivalent?

 

Jeez Ray, can't you just accept it and move on? lol

But I see you're not convinced yet so I'll see if I can explain. The 80 and older is a half circle. So you have 180 degrees of iron to balance the adjacent rotor. Does that make sense?

The 81-82 concentrates the iron into a narrower lump, thus saving weight while still balancing the rotor the same once things are spinning. In this way you can lighten your rotating assembly while still balancing it out properly. I don't know if that explanation made sense but it's the best I can do. Just know that it works. Many rotorheads before you have done it and it always works. I hope this helps.

 

Sorry Jeff, we scientists are like that, always asking questions. Drives fundamentalists nuts.

That angle explanation is exactly what I was thinking. But I thought I better get independent verification, having never been there, done that.

Whew. Now I can move on.

 

Oh and Ray if it makes you feel better (less in the head, more in the heart), do you remember the half bridge R5 12A I built last year? I simply swapped in an 81-82 front CW and a good used 81-82 flywheel I had saved for just such an occasion. Worked perfectly. First time for me for this kind of swap. If I can do it, you can do it.

 

I like the 81-82 flywheel idea, but I still can't figure something out.

Why is it you can't combine the later, lighter FB rotors with the lighter 81-82 flywheel and front counterweight?

The front counterweight balances the flywheel, right?

And the weights of the rotors need to closely match to avoid harmonic imbalance between the rotor housings, right?

But if these two are independent of each other, why can't you use any year rotors with any year flywheel and counterweight?