Ben 84 RX-7

I bought a used lightweight flywheel and there is a counterweight on it. I have the stock flywheel in my car now and would like to put the lightweight one in. My question is how do I know the counterweight on it is the one I need for my 12a? Will the stock one work? I don't think so...anyone know how I determine what counterweight to use?

Kill No Cone

iTrader: (6)

Ben,
This is a tricky issue. The seires 1 and 2 12A engines have differnt weight couter weights. Put the wrong one and you have a vibration that can damage your engine. The probelm is that the damn thinks all look alike. I think I have both an early and later 12A counter weights. I will try to get them weighted this week and post the numbers. Then you can figure out what you have and go from there.

Good luck ~ JEB

re10

I think that the Mazdatrix web site has some info re counter weights - there are numbers stamped on some that you can use to determine which is which... or you could strip the motor and get the rotating assembly balanced!!!!!!!!!!!!

Ben 84 RX-7

So you are saying that I should put the one that is already in there on the lighter flywheel? Maybe I am misunderstanding what you are saying.

SPiN Racing

I think things may be getting misconstrued..

There are up to 2 counterweoights on a rotary.

Front counterweight that is inside the front cover..
Rear counterweight... Also known as with the Flywheel in a Manual application.. or as (Duh) the rear counterweight.

When you convert the engine to a light flywheel you need to purchase a rear Automatic counterweight for your specific engine. This is what the light flywheel usually attaches to if it is one of the lighter ones. (Yes some of them do not require one.. and are only sa little lighter than stock etc.. but that isnt where I believe you are going with this)

So basically you can do one of THREE things when putting on a light flywheel.

1. Go to Mazdatrix's website.. or your favorite Mazda parts spot.. and buy a rear counterweight for the flywheel you just bought... and slap them together on the rear of your existing motor and call it good.

2. Go to someplace like SR Motorsports..(Shane Racing) and talk to Ray... and order a ACT clutch and flywheel package.. that COMES with the rear counterweight... you just specify the year of the motor and they order it for you. And slap it on and call it good.

3. DO the above mentioned stuff.. BUT BUT BUT.... totally disassemble the engine.. and take the rotating assy to a machine shop that has a clue.. and have them balance the front and rear counterweight, Rotors, Eccentric... then neutral balance the flywheel.. then neutral balance the cover.
That way if you replace the flywheel you just get it neutral balanced.. and there is no need to re-balance everything else.

NOW... If you are talking about CHANGING the rotors in the engine.. say a 13B 86-88 with a 13B 84-85... you will need to change the front and rear counterweights as well.
ALSO... keep in mind there are several weights of rotors within a specific year range.. listed as A, B, C, D, E, and F (I think it goes to F) Anyhow... You are only allowed to combine certain combinations of rotors with each other.. the F are the heaviest.. the A the lightest.. all within the parameters of that specific year.. For example.. just for giggles.. a 10 Pound rotor may weigh 10.5 pounds and be a F.. and the same year A rotor may weigh 9.5 pounds.. NOW LISTEN... I am making the numbers up.. I cant remember the variance.. but it isnt that large if I remember correctly.. but it only becomes a issue at higher stock RPM. THe life will be much shorter using mismatched rotors of the same year.
Whenever making a new motor with different rotors try to keep the counterweights and rotors together so you dont have that problem. OR just get it all balanced and dont worry about it.

Hope I didnt cloud the issue more LOL

Kill No Cone

iTrader: (6)

Ben,
Your car is an 84 right? So you need a 12A counter weight for an 84 or 85 engine. The first question is what year engine did your light flywheel (with a counter weight) come off of? Do you know the guy you bought it from? Are you sure he got the right counter weight for his engine?

If you cannot get this info then you need to find the right couter weight and they have almost no markings on them. I have a stack of them here and you can barely tell them apart.

If you can find the Mazdatrix page, well please post it. I have not been able to find it again, and when I contacted them they simply did not reply.

Keep looking, there were a fair about of 84-85 autos shipped here.

Good luck ~ JEB

Ben 84 RX-7

Here is the Mazdatrix web site...

http://www.mazdatrix.com/INDEX2.HTM

Let me try to find out what engine this one came out of. If I need the counterweight from an 84...can't I just use the one that is on the stock flywheel and put it on my new one?

DriveFast7

iTrader: (1)

stock flywheels have flywheels that are sized to include and integrate the rear counterweight. in other words, the stock flywheels do not in fact have a removable rear counterweight. the stock flywheel is both a flywheel and a rear counterweight.

the rear counterweights were used to bolt the flex plate to on automatic transmission cars and aftermarket go fast flywheels.

Kill No Cone

iTrader: (6)

Well said DriveFast,
Ben I have the regular Mazdatrix site. They used to have a photo gallery of couter weights with the few that had casting numbers. It was very useful, but I have not been able to find it again.