I was reading GRM the other day and they describe how they lightened a stock MG ( I think ) flywheel by about 3 or 4 pounds to give the engine a bit more zing but still keep it streetable. I was thinking of doing this when I changed the clutch on my 12a.

Now I've read most of the posts and I understand that the counter balance is all on the backside of the flywheel and that it can't be touched because it will throw off the balance with the rotors and the front counter weight. I have an 80 12a and the flywheel is 30 fricking lbs! I gotta believe that can be lightenend some without buying a new flywheel and for a fraction of the cost. Its just a matter of getting the machinist to understand what I want.

My question is can this stock flywheel be lightened by say 5 lbs. by taking material off the front ?

One idea I had was to shave down the clutch friction surface and the mounting surface for the PP some fixed amount to achieve a lighter flywheel but preserve the gap for mating the PP with the clutch to the fly wheel. Another issue is will doing this cause problems mounting the PP, like not enough thread depth or need to cut the length of bolts for the mounting? Will the flywheel be too thin or risk heat fractures ?

Ideas ?

 

I inquired about this when getting my flywheel machined last clutch change, and the guy said that because the flywheel has a counterweight built into it it makes it more difficult to get the exact same balance after lightening, they basically drill out holes from the back of the plate, to remove material and weight. He told me he'd be able to safely remove 4-6 pounds, for $350. he said hed have to run it first on a balancing machine to get the stock ballance specs, and then remove as much as he can in keeping with the original balancing. for $350 i think its a much better idea to just buy a tried and tested light weight flywheel, that will save you more like 15-18 pounds instead of 5 or 6. Tweakit the austrailian company has super cheep flywheels.

Good luck, Matt

 

Thanks for that idea, Matt!

http://www.tweakit.net/shop/product_...products_id=98

$143.22 USD is NOT a bad price for a lightened steel flywheel. I will remember this. Probably one of the cheapest ways to gain back those ponies lost through the drivetrain.

 

I agree with purchasing a new flywheel. The ones i looked at are around 450$ for what i want. its all aluminum and has the removable friction surface so i never have to throw it away when it gets machined beyond spec. REPLAcement inserts were only 50 bucks which is 20 bucks more than the cost to resurface where i live.

Also i dont have to worry about the machinist being hung over or haveing a bad day and fubar 'in my wheel when he resurfaces it. I've lost a few nice things to other mechanics before. anymore i only trust my own work.http://www.racingbeat.com/FRmazda1.htm

 

Add the nitriding and ring gear, the flywheel goes to 322 aud. I wonder how much shipping is?

 

Good point, if the machine shop comes back with a number thats close to a new lightened flywheel its not worth it. But I really only want to shave 4 or 5 pounds, not 12! Thanbks for info.

 

3-5lbs would hardly be worth the effort/cost,considering the stock flywheel is a healthy 30lbs, and most of that is near the outer edge.In case your wondering,there is NOTHING un-streetable about a 14lb aftermarket steel flywheel.

Yes,you will have to slightly alter your driving/clutching style.....but its so minute a change that youll forget about even making the adjustment after a couple days.Now....the improvement in acceleration and fun factor....that is something that you wont soon be jaded with!Its a big mod,my personal favorite of all rotary mods.In 1st-2nd-3rd,the change is impressive and idle quality is still perfect,so long as your tuned up.Ive had light steel flywheels in all my engines,from stock 12As to my current turbo engine.Its WELL WORTH the money spent.

 

dont forget you will need a Auto counter weight for the flywheel to bolt to.
here's my new Clutch and fly package i just bought for my 12at and series 4/5 box. cost me $545 au



Paul

 

It all depends on cost, if I take it too the machine shop to have it resurfaced and then ask for them to lighten it a bit then the cost has to be low or I would just buy the steel lightened flywheel. No brainer. But if the cost is minimal, like say 100 bucks for the surfacing and taking a bit of weight off then to me its worth it. Anything over 200 is a deal breaker because I can get a new one from RB or MT for 372 brand new and if I shop around I might find it a bit cheaper.

Also, won't need any extra counter balance because I'd have them take it off the transmission side as I described above.

I'll update the thread on the outcome. I think at the right price its a good mod.

 

I've been doing some investigation and it looks like if I get an 81-82 12A flywheel it is 23 lbs versus the 79-80 flywheel thats 30 lbs and it should work for what I need. The rotors weigh the same for 79-82 so there shouldn't be any counter weight imbalances that I can tell.

I'm basing most of this on the info at the mazdatrix site:

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

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

Any problems with this flywheel swap ? It looks pretty straight forward to me to do. I just have to find an 81-82 flywheel to swap in that has enough surface left to use.

 

DOnt forget about balancing.

 

Not sure I understand what your referring to ?

I am considering the balance. From looking at the numbers on the mtrix site it appears that the rotors weight the same from 76-82 and the flywheel from 81-82 is 7 lbs lighter than the one on my 80 12a but both should have the same counter weights because the rotors still weight the same.

Maybe I'm missing something, but this seems like an easy way to get a 24% lighter flywheel for the cost of an old flywheel and resurfacing.

 

I believe you are correct that the 81/82 flywheel is a direct swap for the 79/80. Rotor weight is the same, therefore, the counterweight *should* be the same amount.
Where problems can arise, is trying to use either a flywheel from 83-85 on an earlier engine, or vice versa.

 

Yes the 81-82 flywheel should be a direct swap.

 

Thanks for the info, I think this might be a better way to get a slightly lighter flywheel than trying to lighten my exitsing 30 lb. one or springing for a steel light flywheel. Now off to find that flywheel ...

 

Doesn't the front counterweight have to be replaced with the lighter flywheel, even though the rotor weights are the same? Mazdatrix lists a different front counterweight for the 81-82 vs. the 76 to 80. The later front counterweights are considerably smaller.

RXDad

 

Good question.

I know the rotors are the exact same weight for 76-82 and based on that I'm assuming that the counter weights should be equivalent and the lighter flywheel shoudl work with my current counter weights.

Maybe this assumption is wrong. Hopefully someone who's built a few hipo 12a engines can drop by and let us know.

I think it would be a nifty upgrade from the junkyard if it balances out ok.

 

I asked Mazdatrix and RB if I could use the lighter 81/82 flywheel with a stock 1980 12a. Heres the reply from Mazdatrix ( haven't seen the RB reply yet)

"Each engine CAN be different. I specifically screwed a "race" motor together
with "matched" parts - meaning all parts were of correct years and it shook
pretty bad above 9000 rpm. So it can happen.

With that slight warning, you are correct - the lighter 81-82 flywheel
should bolt onto your '80 engine fine."

So looks like I'm off to find an 81-82 flywheel

 

you don't change the front counterweight with the rb flywheel. The counterweight they give you bolts onto the light one

 

I'm referring to the stock 81/82 flywheel not the RB light flywheels.

The 81/82 flywheel from a 12a is ~23 pounds versus the 31 pounds of the stock 1980 12a flywheel. So you get a flywheel thats 7 punds lighter but works without changing anything else on the engine, theoretically.

Its a lot cheaper upgarde than buying a steel or AL light flywheel from RB or Mazdatrix which does require a rear counter weight to be bolted on to balance the engines rotating assembly.

 

And RB says:

"All 1974 through 1982 12A engines utilize the same
rear automatic transmission counterweights when
installing our lightweight steel and aluminum flywheels.

Assuming you can accurately identify the stock flywheels
in question you should be ok."

At first I didn't get what was being said and had to stop and think about it. I see now why rbf41182gt was talking about the light weight RB flywheel and counter weights.

So there it is from Mtrx and RB, the 81-82 flywheel is a cheap way to get a lighter flywheel for a lot less than buying a lightweight steel or AL flywheel with counter weight. It may not be 14 lbs but its a lot less than 30.

 

Ok, I think this turned out good. I was able to buy an 81 flywheel type "21" stamped on the back for $60.00 (+s/h) on ebay and have it resurfaced for $40.00. So for ~$100.00 I have a 7 lb. lighter flywheel. I think this is a good compromise versus the new price for a light steel or AL flywheel and counter weight.

I bought this from this ebay store (http://stores.ebay.com/ROTARY-RESTORATIONS) and I highly recommend this guy. He treated me well even though I bugged him a lot about the details. If you need something pm him on ebay. He may actually have the item but just not have a listing up for it. My flywheel was not listed but I pmed him on ebay and he said he had some and quoted a price. One week later I had the flywheel and its ready to go on.

Once I put it on I'll update the thread on how I like it.

 

Thats the main reason why Im holding on to those 81-82 flywheels. Just in case.

 

Yeah, this guy referred to this as the "rare lighter stock flywheel". He said the reason he didn't have a listing was that he didn't have many good ones left. So apparently folks have been using this swap for awhile and these are getting harder to come by. May be a good investment for you