Hello,

I have a 81-85 keg with a 79-80 flywheel. My understanding is that I will use the 215mm clutch to match the older flywheel. My question is, should I use the 79-80 counter weight or the 81-85 counter weight?

Based on this info from racing beat, it looks like I should use the 79-80 counter weight.
Thanks in advance

 

You really want the flywheel and counter weight to match the rotating assembly inside the engine.

So, you would need to identify which engine you have and get the flywheel for that year range I've indicated below.

https://mazdatrix.com/identifying-an...-of-flywheels/

79-80 12A - 215mm

81-82 12A - 215mm

83-85 12A - 225mm

 

Thanks for the link, that helps.


It looks like I have an 84-85 with the 4 dimples on the housings. However, the rotors I pulled out of this keg don't have the "N" markings. I wouldn't be surprised if this is a mix n match engine that has been rebuilt at some point, I got it from some old SCCA IT7 racers.

I'm trying my best to do this on a budget, I don't need this engine to be perfect and just want to get it back in the car and running. I'm thinking I should be fine to use my 79-80 flywheel and cw if these are the old style rotors? Even if its slightly out of balance, it shouldn't cause any long term damage right? Just some extra vibrations?

 

a couple things ...

1. it might help if you post photos of the rotors in question, if you have some. someone with more knowledge may be able to identify or narrow down what you've got.

2. it's not just vibrations. you'll probably be screwing your main bearings as well.

in my humble (and unsolicited) opinion, it would be worth trying to see what you've got and track down the correct flywheel if you're thinking long term.

 

This will be a good start on identifying your current counter weight.

https://mazdatrix.com/identifying-rear-counterweights/

The e-shaft isn't an issue for the flywheel, but the rotors and counter weights are.

This was posted by j9fd3s on another forum

77-82 combustion chamber is teardrop shaped, LEADING deep recess. they are different front to rear

83-85 Have a 2 letter stamp in the combustion recess instead of just f or r

 

Ok, now I will admit I am a little confused. I thought the rear counter weight was made into the flywheel? I'll outline everything I have here:

- Flywheel and front counter weight I pulled from my bone stock 79
- What looks to me to be 77-82 rotors from the engine I bought:


- Unknown front counter weight from the engine I bought:


If I have the 77-82 rotors, I should be ok to use the 79 flywheel and front counter weight, correct? Thanks in advance!

 

You are good to go.

 

The counterweight you have listed there as "79" looks like a 81-82 counterweight to me, and the unknown front counterweight looks like a 79-80.

I had an issue where I swapped from a 79 flywheel to a 81/82 flywheel to reduce rotating mass, which introduced a bunch of shaking in my engine. I had to replace the front counterweight to fix it. The one I pulled off (that shook with the 81/82 flywheel) was the one shown as ? in your picture, and the one I put on (off of the same1981/1982 engine I pulled the flywheel off of) that solved the shaking looked like the one you have labeled as "79".

Check out Mazdatrix's listing for front counterweights. It should give you a good idea on what year which is.

 

I agree, the "79" cw does look like 81/82. I assumed it was 79 because that is what I pulled out of the car. I double checked and the flywheel I have is a 79. When the car was running, there was never any vibration issues. Weird that the car had a 81/82 cw and 79 flywheel, but I guess thats what Ill put back in since that is what I took out. Worst case I can put in a 79 cw if I have to.

 

its simple but hard to type simply.
79-82 use the same rotors, they will just have an F or R stamped in the combustion recess. (83-85 are NF or NR)
79-80 use a heavy 215mm flywheel with the 180 degree counterweight.
81-82 use a lighter 215mm flywheel with the we will say 90 degree counterweight.

for 83-85 the clutch is 225mm, with a flywheel that is a little heavier than 81-82, but the rotors get lighter, so net/net the whole rotating mass is about the same
also most aftermarket flywheels can use either clutch size

 

you're right. it is. since automatics don't have a flywheel per se, they attached the ring gear to a removable counterweight.

never realized this before, but i guess it makes total sense.

at a time when i didn't necessarily go out of my way to collect data, i think i had an argument with someone about this very point. he swore up and down that the S3 12A rotating assembly was way lighter than the S2, and i said it wasn't that much.