The 13B is balanced all as one unit; rotors, eccentric shaft and flywheel all together. Putting a light flywheel on unbalances the motor so engine balancing must be done. Just a warning to anyone thinking of putting a light flywheel on.

I'v seen it mentioned in an archived thread that gives you a list of mods to make your FD run better, and it mentions a light flywheel. No offense intended to the thread starter but this is just a warning to any who didn't know about it.

 

The engine assembly is balanced by the counter weight(s), not necessarily the flywheel itself. It just so happens Mazda included the counter weight into the Manual flywheel.

 

Yes, you have to balance the counter weight when changing to a light flywheel, or any flywheel...

 

just curious, what are the symptoms if its not balanced ??

 

Thats why when you switch to a light weight flywheel you need the counterweight from a autotranny. You would notice some pretty harsh vibrations if your motor was unbalanced I would think.

 

Yes, but you have to balance that counter weight for your engine, its not a bolt on mod.

 

How would you balance it? I'm doing the swap soon and want to make sure it's all good when I'm done.

 

I've never experienced problems with vibrations or any other damage to the engine as a result of using a lightweight flywheel. I'm currently running one in my FD with no problems. Guitarjunkie rebuilt my engine and supplied the counterweight for my flywheel. My brother and friend also bolted up the flywheel/counterweight to their 13Bs with no problems.

 

So - did you just wake up this morning and decide: hey, I'm going to resurrect a long discredited myth and apply it to a car I know nothing about?

Is your next revelation going to be about cracking aluminum flywheels?

If you had spent more time searching you might have discovered that light flywheels are a very common FD mod and cause no problems.

 

+1 to that



i installed a 9.5lb flywheel with a mazda oem counter weight, and i have no problems. the motor idles great, no vibrations, etc.

all i did was bolt mine up and it's been running just fine.

 

no vibrations with my 9.5lb act prolite flywheel with counterweight.

 

How? You send your assembly to a shop (like Racing Beat, Mazdatrix, etc) to have them do it.

 

Exactly, this is not a myth(?)

 

Wrong. You absolutely do not have to balance the counterweight. There may be a few high level racers who have done this. However, for the other 99% of us with light flywheels, balancing is completely unnecessary. My current FD is the 3rd rotary I have owned, and raced. All have had light flywheels with stock counterweights. None of them were balanced.

 

Ok, i have talked to two different builders here in sweden, both balance the counter weights and says its necessary.. But i guess you can be lucky... Its only a few grams but i guess it can affect the longlivety of the motor?

Mazdamotorsports recommended it too. I had a link but its dead now

EDIT: Found it! http://www.mazdamotorsports.com/weba...counterweights

"The complete rotational component group (eccentric shaft, rotors, flywheel, counterweights must be rebalanced when changing any of the components."

 

Mazda manufactures thousands of rotary engines with OEM counterweights for their cars with automatic transmissions. How many of them do you think get balanced? The answer ................... NONE!!!

Like I said, perhaps the highest level racers do it, but "we" don't need to

 

They are talking about race or competition engines, which spend most of their life at high rpms.

 

Yeah and all piston engines have balanced and blueprinted rotating assemblies from the factory too(sarcasm).

 

Yeah, but where do you draw the line? I track my car all the time. Why use a light flywheel on a daily driver?

How do we know when balancing is needed?

 

Regardless of what everyone else here is saying, you are exactly right. The auto counter weights and even the manuel flywheel have holes drilled from the factory to balance the rotating assembly. When you install a light weight flywheel with a generic/new auto counter weight, that weight may not be balanced for your rotors. The factory counter weight is balanced more towards the heavy "A" rotors, however what do you think will happen if you install a new counter weight on a engine that's balanced with lighter "F" rotors? It will vibrate and not run as smooth as original. Remember rotor weights vary from "A" the heaviest thru "F" being the lightest.

Example and engine with all "A" rotors will have a completely different balance from an engine with all "F" rotors. My own personal experience: When I rebuilt my 91 NA 13b a year and a half ago, I swaped the "A" & "B" rotors from my original engine with 2 "C" weights. We were always told to keep the letter weights from within 2 letters of each other. I thought I was doing great by having a matching set of "C". I was wrong. From day one my engine has slightly vibrated more than it ever did. It took me while to figure it out. That's was when I learned of the factory drilling holes in the counter weights for balancing. There's a reason Mazda includes a flywheel on manuel re-mans and also a counter weight for the autos. Every engine's rotating assembly is individually balanced from the factory. My engine has 14k on it and still runs great however, I bet my bearings are begining to take a ****. We'll see when I pull it apart after I get my 20b up an running.

 

See my post your just one of the lucky few. All this means is you have an engine with "A" or "B" weight rotors. The counter weight you installed with your flywheel just happens to be balanced for the rotors you already have inside your engine. Not everyone is going to have that luck.

 

Completely wrong there are drill holes in the counter weight themselves. No two counter weights are the same.

 

Thats exactly what i was told, thanks. This must be a common cause of engine failure?

 

Not really. An unbalanced rotating assembly will mainly wear out the bearing sooner. The reason most don't notice it that much is because of the factory liquid filled engine mounts. Stiffer mounts is a whole different storey.


I'm really suprised how so many people over see this kind of thing. You can't expect a single counter weight to balance an engine with five different internal rotor weight combinations.

 

I guess I'm another lucky one. I'm running a ACT Prolite 9.5# flywheel with auto counter weight no problems and idles nice and smooth. I guess I'll find out what my bearings look like when rebuild times comes, hopefully another 60K miles at least. Knock on wood..!!