I just recently picked up a parts car, and had to swap engines with my daily driver. While swapping engines, I had to change the ring gear on the new motor, so I swapped it with my old one. My question is..... Did mazda make 12a's with different sized flywheels? The flywheel out of the "new" engine is almost 2 times as heavy as the one out of my blown engine..... I used the lighter of the two, naturaly. Kinda makes me wonder thats all.

 

did they look the same just one was lighter?

 

well this is just a thought, but i know that there is a difference between the flywheels in a s4 13b, and a s5 13b, the rotors were different weights so the flywheels had to be balanced differently. Kinda makes me think that maybe they did the same things with fb's, what are the years of the two cars?

 

and by the way, swapping an s4 and s5 flywheel is bad for the engine, so maybe you shouldn't have switched flywheels, maybe...im really not sure

 

Whoa there, you have to have the proper front counterweight or your motor will be unbalanced.

 

Yup, I think it was the 81-83 12a's had the heavier rotors and lighter flywheel and then the 84-85 12a's had the lighter rotors and heavier flywheel. Not to mention there was a change in the size of the friction surface too IIRC.

 

They are both 82's. One is just a base model, the one I drive with the swapped engine, and the other is a higher end model, has leather seats, power everything rear disc, where mine has drum in the rear. Also the car I recently got, has a posi or lsd rear end, when you turn the tires both tires turn the same way, rather than opposite. I thought the heavier flywheel maybe had something to do with the difference in rearends....

They basically do look the same, but on the heavier one, there are two large pieces of steel on the inner side, weight for balancing I guess. I really hope that its not a serious problem having a lighter flywheel, I figured they were both 12a's.... I am hoping.

 

Here is pictures of all the stock Rx-7 flywheels.

LINK


John

 

I am not 100% on what they look like to be honest..... I will have to take a look at one, and that will be the heavier one, the other of course is in the bell housing.... I will see it this weekend...

 

WHOA! You MUST have the correct flywheel for that engine or it wont last. Just cause the car was an 82, doesnt mean the engine hadnt been swapped sometime in its life. Follow the link Rhino posted. Also there a bit of info on Felix's site regarding this. The FAQ thread will point you there. Its vitally important. Safest thing would be to put the FW back on the engine it came from. Of course thats assuming that it has the right one to start with.

 

where both tranis standard, automatics sumtimes have a heavier fly wheels

 

Automatic cars do not have flywheels, they are called a flex plate with a rear counter weight.

John

 

Ah man.... well at least I will get better at pulling the tranny for the 3rd time in a few months......

 

Thnx by the way... Hopefully there has been no, or little damage done....

 

Well I have changed the flywheel back to the one that should be on that engine, and now I have vibrations... what do I do now???....... The vibration is there weither or not I have the clutch engaged or not, starts at approximatly 1500 rpms, and is noticable as you rev it up thru 6000 rpm.... .............


expecting the worst.....

 

So did it have a vibration before you put the "correct" flywheel back on?

 

no vibrations prior to putting this on. I changed the ring gear as well. By heating it as it showed in a manual I have....I am wondering if that is the problem? I now know which flywheels that are on the two engines. the current and "correct" flywheel that I have on my car is a 83-85 12a flywheel, and the other one is a 81 - 82 12a flywheel. Both cars are 82's, my parts car had an engine swap, or at least a flywheel swap......?

 

Nah, the ring gear wouldnt throw it off balance. Maybe someone put the wrong FW on it to start with? Which sis messing you up?

 

can the fly wheel be put on at the wrong degree angle from the rotation of the motor perhaps weight is partialy out of sink with the motor don't know just a guess

 

No it can't.

I would change the flywheel again right quick. The '81-82 has a fairly lightweight flywheel, if a different flywheel was heavier, and you now have hellacious engine vibration, it's a good bet the heavier flywheel is from an '83-85. The '83-85 rotors are lighter so the flywheel imbalance is different.

FWIW '79-80 have the same weight rotors as '81-82 so the flywheels interchange, although the weights are a lot different. Also, starting in '83 the clutch diameter changed from 215mm to 225mm.

 

is there a way to tell the year of a 12a? Or is there other differences between an 82 12a and an 85 12a? That way I will be able to tell if this is the correct flywheel or not...

 

Externally there's not much to differentiate. Internally you have to look at the rotors, which of course requires engine disassembly.

 

The drivers side of the engine, has a hot water outlet nipple on the pre-83 and the 83-85 had a T' (dual outlet) because of the water to oil cooler.

John

 

well the engine is an 83 +, I converted the top mounted oil cooler to a front mount durign the swap..... I just read that the rotors on an 82 are 10.15lbs, and the 83+ are 9.6lbs. I spoke with a local rx7 guru, and he said that either way, it shouldn't really matter.... he was leaning more towards carbon buildup, and apex seal chatter...... I am not so sure about that tho, a little more than coincedence (sp) that it should start vibrating after the heavier flywheel was installed..... This car is my daily driver, and I dont' know if its safe to drive with a vibration like this....??? Also what do I do? put in the lighter flywheel again? I can't be pulling the tranny weekly... I am worried about this...

 

It does matter which flywheel you are running, cause there is a 3# difference between a 81-82 and a '83-'85 flywheel.

A '83 and later engine needs this flywheel...



You didn't pull the front main pulley off did you?

John