takahashiRyosukeFC3S

Do all aftermarket flywheels for our FC series cars need a counterweight? What does the counterweight do? I thought this was a rotary and was perfectly balanced... Im in the market for a new lighter flywheel and street / race clutch for my '88 T2.

thank you for your input and not flaming because i did a search. flywheel, counterweight, clutch counterweight, flywheel counterweight, flywheel weight.

TR

kungfuroy

iTrader: (6)

The engine itself is balanced, but the need to connect a motor to a transmission to make it work calls for the need of the counter weight. Having the flywheel at one end of the engine makes it unbalanced until you put the counterweight on the opposite side.


I believe with a few of the lightened flywheels out there, you can use the rear counter weight from an auto tran. Please correct me if I am wrong

takahashiRyosukeFC3S

does the counterweight then replace the front CW on my engine now? or is it attached with the flywheel to the rear of the engine?

thank you,
TR

drago86

No, the engine is not inherintly balanced and require a front and rear counterweight to not vibrate, or cause bending of the e-shaft. The stock flywheel has the counterweight cast into it, hence the need for a counterweight from an automatic car when you upgrade to an aftermarket flywheel which does not have the counter weight bilt in because then it would be harder to manufacture and no longer universal.

RotaryResurrection

iTrader: (8)

I dont understand why this confuses people so much.

Here is the text from a writeup I have on my computer. I made it for the website which will be redesigned soon with more info. There are pics in the original writeup, but I dont know how to transfer and host both the text and the pics and have them show up properly after the transfer (it is a word document) so I will just post the text:

Stock flywheels/counterweights versus aftermarket flywheels


There seems to be a lot of confusion about the different counterweights and flywheels (stock and aftermarket) for the rotary engine, so I’ll attempt to clear some of that up here.



Rotary engines have a balanced rotating assembly just like any other engine. This involves the e-shaft (which doesn’t require any external balance in itself), both rotors, a front counterweight, and a rear counterweight. There were different weights of rotors through the years, so the balance is different for each of these different engines. The front counterweight is under the front cover, and should never be changed unless a custom engine is built using different rotors. The rear counterweight can take one of 2 forms; it can be a flywheel with the counterweight integrated into it (cast) or it can be an automatic counterweight with the 6 bolt pattern for the ringgear to bolt onto. All stock flywheels fit a specific year and model of engine, and are numbered, and all have the counterweight for that engine cast into them.



Note that for 1st generation cars and older rotary vehicles, 12a or 13b, only one DIAMETER of flywheel is used, the 205mm nonturbo version. Between various years of 12a and 13b the COUNTERWEIGHTING changed to reflect the weight of the rotors inside the engine, so there are several different flywheels for the different engines.



For 2nd generation cars, there are 2 DIAMETER flywheels used…the 205mm nonturbo, and the 225mm turbo. In addition, the weights of the rotors changed between 88 and 89 (series 4 and series 5) so for each of the 2 diameters, there are 2 different counterweights, for a total of 4 unique flywheels for 2nd gen engines.



For 3rd generation cars, there is only one stock flywheel, in the larger 225mm turbo diameter, since there was only one engine available stock.



Here is a pic of the back of a stock flywheel (this happens to be a 205mm from an 84-5 GSLSE 13b, but the mounting looks the same for all stockers) for reference as to how it attatches to the rotary. Note that it is a single hole with a keyway to hold it from spinning on the shaft, and a single large nut (indy car wheel style) to hold it in place…this is different from almost every other engine in the world, most of which use a 6 or 8 bolt pattern on the end of the crankshaft.



Also note the counterweighting, which is cast into the outside edge, favoring one side more than the other.






Let’s say you have a manual transmission car, and want to install an aftermarket flywheel, to save weight. Buying the flywheel is simple. Though there are many companies that offer flywheels, and several weights available from each company, there are only 2 diameters of flywheel, the small 205mm and the larger 225mm. Aftermarket flywheels DO NOT have the counterweight cast into them or attatched in any way. They are a flat unit with a 6 bolt pattern. Obviously this won’t bolt to your engine, you’re missing something.






All aftermarket flywheels are made this way. They REQUIRE use of the appropriate automatic counterweight for your year of engine. Any engine within the same series (86-88, 89-95, etc.) can use the same rear counterweight, regardless of whether it originally was an automatic or a manual, or whether it used a 205 or 225mm flywheel. So, if you have an 89 manual nonturbo, you can use an 89 nonturbo automatic counterweight. IF you had an 89 manual turbo, you could still use that 89 nonturbo automatic counterweight. You could not, however, use an 87 counterweight.



Here is a pic of the auto counterweight. These usually sell used for $25-60, and new for $100-120.






So you bolt this to your engine, and then install your flywheel to that (or you can bolt your flywheel to the counterweight, then bolt it all to the engine, doesn’t matter). It looks like this when installed together.









The reason flywheel manufacturers do this is threefold (in my estimation, anyway).



First, they can claim that their flywheel weighs less than half what the stock one does. Of course it does…it has no counterweight attatched, and the stock one does. The counterweight weighs 4lb or so…making a 9.5lb aluminum flywheel weigh 13.5lb. This is compared to a stock flywheel that, depending on year and model, weighed between 20 and 25lb.



Next, it’s MUCH cheaper to make a flat piece of metal, than it is to machine out the complex rotary mounting pad (the center section that’s fat), which is tapered inside with a keyway. To get around this unique issue, they just continue making the regular 6 bolt pattern flat flywheels that are similar to what they sell for every other car in the world, and let you and mazda handle the mounting issue.



Finally, it’s MUCH cheaper for them to manufacture 2 flywheels for the rotary (205 and 225mm) than 6 or 10 (the different stock variations from year to year). Since demand for old rotary parts is relatively low compared to a large market like a honda civic, it would be unrealistic to expect them to make a bolt on flywheel for every year and model specifically. Letting you use your respective automatic counterweight from mazda gets them around that issue.



IF you have an automatic engine, you don’t have to do anything…just buy the flywheel, and bolt it to your existing automatic counterweight.

Bigretardhead

nice write up. very informative. but... uh....
aftermarket flywheel for automatic car?

RotaryResurrection

iTrader: (8)

those doing an auto to 5sp swap, with a previously existing auto engine, do not need to buy a counterweight, or remove the existing one. just bolt on their lightweight flywheel.

Damn, I guess every little morsel of information has to be spoon fed. No wonder people say that the FSM and haynes manuals suck, and don't contain much useful information.

Carzy Driver

nice write up Kevin, but I have a question that goes against your wirte up. I bought a Fidanza lightweight, and in their mounting instructions, they say to use N351-11-521, which is the CW for the s5 and above. I actually called their tech number and explained that I was planning on installing on my 86 N/A and the guy said that the s5 CW must be used either way. is it by some planetary alignment that you may not be correct, althrough sounds correct, or did this guy just not know what he's talking about. if by a slight chance he is right and I use the s5 CW I bought from you, will there be noticable or very bad side effects when using on an s4 motor?

jacobcartmill

iTrader: (6)

stock 5speed flywheels have the counterweight included into the mass of the flywheel.


automatic stock flywheels and aftermarket flywheels dont have the counterweight build in. its attached onto the back of it, so you can use one off of an automatic flywheel or buy one to bolt onto your aftermarket flywheel.
its not too complicated.

jacobcartmill

iTrader: (6)

the tech didnt know what he was talking about. you have to have the counterweight that matches the series of the rotors.

drago86

Tech was a retard, using the s5 counterweight will most likely eat the rear bearing and kill the motor.

rotaryracer1

iTrader: (1)

so when you buy an aftermarket flywheel you have to also buy a counterweight from an auto? why dont they include one with the flywheel?

RotaryResurrection

iTrader: (8)

ACT does offer to sell you a counterweight at extra cost. It keeps cost down, making the flywheel purchase look more attractive.

RotaryResurrection

iTrader: (8)

You always use the exact counterweight for the year of engine you are running. However, I will say that in my experience of testing and measuring s4 vs s5 automatic rear ctwts, I can note no difference in them physically or on the scale. Usually the s5 version will have one more balance hole drilled in it, but not always (2 or 3 holes vs 1 or 2 on the s4). The counterweights weigh in at right at 4.02lb, either s4 or s5/6. I dont see any problem with running either one on either engine, but if you're ordering the part, order the right one for your series.

RotaryEvolution

iTrader: (30)

i wish the counterweights were selling for 25-60 used. people are jacking the prices up to near new for used ones, greedy bastards.

RotaryResurrection

iTrader: (8)

well hell, I would too. people are always beating down the damn door trying to get a friggen counterweight. I guess everybody and their mother is running a light flywheel these days. It's the law of supply and demand. High demand, low supply, price high. It's not like auto ctwt's are really common.

Back a few years ago I had a box full, and I knew what they were used for but I didnt know why people didnt just buy a new one. I used to sell 'em for 15, 20 bucks to get them o ut of the way. Then I started getting a LOT of requests, and selling a LOT of them. Finally I asked a dude why, and he told me, new ones were over $110! Then I got smart and started getting 50-60 each. I still sold out really quick, and I rarely have one laying around these days.

RotaryEvolution

iTrader: (30)

ahh well, i would rather pay 110 for a new one than 85-90 for a used one, screw the greedy bastards.

RotaryResurrection

iTrader: (8)

I agree, but when you think about it, it's a chunk of metal that doesnt really wear out so a new one is not advantageous to a used one, and 25 bucks will buy a lot of big macs.

RotaryEvolution

iTrader: (30)

i don't like old grooved seal surfaces, it just causes oil seeping/leaks to form quicker so there is a slight advantage from used to new but not much that most anyone would worry about.

Whizbang

bringing this back a little. The RB one for the GSLSE comes with the counterweight...did anyone notice that?

my main question i cant seem to find a real answer for is for everyday driving in an NA. How does the lightened flywheel affect things?

that and im selling that counterweight from my bad auto tranny now! lol.

Tournapart

iTrader: (4)

Well, you were talking to a Tech that just makes/troubleshoots flywheels for all makes and models. Kevin, builds rotaries for a living, do the math. damn, its always a contest of whos right, we all know that his information is correct, its been proven a million times and i cant even remember how many threads ive seen on this, SEARCH BUTTON!

oakback

I just recently installed an aluminum flywheel from racing beat, with the heavy duty street/strip clutch, and the street/strip pressure plate. It is not bad at all, I was expecting much worse. I never stalled out, I can start on a hill just the same as before (I use my hand brake for that), and clutch engagement is simple; I can creep forward in traffic without revving the engine above 2k rpm or lurching the car forward.

Everything just seems more responsive is all.

Whizbang

might be worth it then. the clutch might be up for replacement soon so...might as well.

rotoman2

Thanks Kevin for clearing up the difference between s4 and s5 rear counter weights. I just changed out my S4 for the s5 and couldn't tell the difference between the two. Is there a code number or anything to tell one from the other?

Incidentally, even if the two weights are the same, the moments of inertia could be slightly different, which is what really matters.

RotaryResurrection

iTrader: (8)

The physical aspects are identical with no markings or numbers at all. They are the same thickness, diameter, and 'timed" the same with relation to the eshaft. Checking the exact weight and drilled holes are the only hope of figuring out which engine it came from, but there is so little difference between them that I think a man would be okay if he accidentially swapped them around.

Once removed from the box/engine, there is no real way to discern between them.