Lightweight Flywheels - Be VERY cautious
Next time you get a chance, go out raise your hood, and start reving the engine from the TB. Note the vibration at the alternator. Now find another rotary with original rotating assembly and do the same. You will find that a complete factory engine is damn near vibration free.
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Joined: Jul 2005
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From: Sweden
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'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.
Yes, it seemed a little wierd not to balance a such vital part. I thought balancing was standard when changing flywheel...
How do the builders do when they balance? Does anyone have a picture of a rig?
Balancing requires complete disassembly of the engine. People aren't willing to do such for a simple flywheel swap. Like I said earlier, most FD guys don't notice the vibrations as much with the factory liguid filled engine mounts. Mine is odvious with my stiffer rubber turbo II mounts! When I pull mine apart again, I'm going to send if out for re-balancing.
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From: Sweden
One of the builders i talked to also balance the pressure plate. He said that ACT has the worst balanced plates. He did a rebuild for a friend of mine, and the factory balancing (drilled) on his ACT pressure plate was on the opposite side of the builders balancing. Thats very strange. I have a OEM engine with stock flywheel, but i have changed the clutch recently. It will be interesting to see if i can feel any vibrations with the new clutch. The engine was totaly vibration free before the change. But im months away from starting it 
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Joined: Jul 2005
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From: Sweden
Balancing requires complete disassembly of the engine. People aren't willing to do such for a simple flywheel swap. Like I said earlier, most FD guys don't notice the vibrations as much with the factory liguid filled engine mounts. Mine is odvious with my stiffer rubber turbo II mounts! When I pull mine apart again, I'm going to send if out for re-balancing.
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.
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.
1. 79 RX7 with stock 12a. Full competition CSP autocross race car, with all the legal bolt ons.
2. 82 GSL with street ported 13B, intake & exhaust. Street car with stiff suspension that I owned for 20 years.
3. My current 94 FD. Mods in sig.
I have never had any balance problems (or premature bearing wear) with any of these cars in nearly 25 years of continuously owning a rotary powered car.
My friend Greg has owned 4 rotary powered cars with light flywheels. One of them was a full race RX3 (ITA??) with all the legal bolt ons. He never balanced a counterweight, and never had a problem either.
Relax guys...no need to take this personal.
Both sides are right; balancing the complete rotating assembly - including the clutch and flywheel if you wanna do it right - is vital to maximal engine performance and longevity, especially at high rpms (ie an engine that is constantly and continually stressed). That's why balancing the rotating assembly is routinely done by the professional Mazda rotary racers I know.
Having said that, how necessary is balancing the rotating assembly (with or without the clutch & flywheel) on a weekend warrior? Not very. Sure, there will be stories like the one Rich just mentioned, but those will be very far and few in between. The vast majority of us won't see any noticeable changes to warrant doing it even when we swap out stock flywheels for lightened flywheels. Ppl on the forum have been running lightened flywheels for over a decade now without any ill effects - myself included.
The argument about wearing out bearings faster...while it may be true, it reminds me of the natural vs. synthetic or Group IV vs Group V motor oil arguments. Is there a difference? Of course. But has anyone (from us weekend warrior drivers) ever lost a motor due to the difference in such tolerances/properties? Never. So is it worth all the worry? Na... Your engine will prob blow from poor tuning, bad fuel, or a fuel system failure YEARS before any premature wear from a lack of balancing/using the sub-optimal motor oil will make a *noticeable* difference in engine longevity
Worry about the tried and true causes of engine failure rather than losing sleep over the least likely scenarios...
~Ramy
Both sides are right; balancing the complete rotating assembly - including the clutch and flywheel if you wanna do it right - is vital to maximal engine performance and longevity, especially at high rpms (ie an engine that is constantly and continually stressed). That's why balancing the rotating assembly is routinely done by the professional Mazda rotary racers I know.
Having said that, how necessary is balancing the rotating assembly (with or without the clutch & flywheel) on a weekend warrior? Not very. Sure, there will be stories like the one Rich just mentioned, but those will be very far and few in between. The vast majority of us won't see any noticeable changes to warrant doing it even when we swap out stock flywheels for lightened flywheels. Ppl on the forum have been running lightened flywheels for over a decade now without any ill effects - myself included.
The argument about wearing out bearings faster...while it may be true, it reminds me of the natural vs. synthetic or Group IV vs Group V motor oil arguments. Is there a difference? Of course. But has anyone (from us weekend warrior drivers) ever lost a motor due to the difference in such tolerances/properties? Never. So is it worth all the worry? Na... Your engine will prob blow from poor tuning, bad fuel, or a fuel system failure YEARS before any premature wear from a lack of balancing/using the sub-optimal motor oil will make a *noticeable* difference in engine longevity
Worry about the tried and true causes of engine failure rather than losing sleep over the least likely scenarios...~Ramy
Thread Starter
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Joined: May 2007
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From: Durban, South Africa
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.
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.
I was just giving a friendly warning to any FD enthusiasts that were new to the game, and i don know if you seen many a thread where it says "If you don like it then don join it", or somethin to that affect. It's not my fault it was your time of the month when you read my thread...
Hey supernanny, pull your panties out and take a chill pill.
I was just giving a friendly warning to any FD enthusiasts that were new to the game, and i don know if you seen many a thread where it says "If you don like it then don join it", or somethin to that affect. It's not my fault it was your time of the month when you read my thread...
I was just giving a friendly warning to any FD enthusiasts that were new to the game, and i don know if you seen many a thread where it says "If you don like it then don join it", or somethin to that affect. It's not my fault it was your time of the month when you read my thread...
when you sign up here... your supose to get a complimentary flame suit in the mail.
Joined: May 2005
Posts: 3,243
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From: Kennewick, Washington
Just an FYI, as long as the flywheel itself is balanced, it will not affect this scenario at all.
However, if your engine exhibits vibration after installing an aftermarket flywheel and oem counterweight (all you are doing is emulating the counterweight that is biult into the stock flywheel), then you need to actually lighten the counterweight you installed . Once you have the correct counterweight mass, then you are hunky-dory.
However, the OEM counterweight will work within spec for probably 90% of engines.
Keep in mind when installing a lightweight flywheel:
The only factor you are changing as far as balance is concerned is the counterweight. that is all. the flywheel is not a factor (as long as the flywheel itself is balanced properly and installed correctly.
You have a higher chance of exhibiting vibration and out-of-balance symptoms from a poorly installed pressure plate, or poorly balanced one.
However, if your engine exhibits vibration after installing an aftermarket flywheel and oem counterweight (all you are doing is emulating the counterweight that is biult into the stock flywheel), then you need to actually lighten the counterweight you installed . Once you have the correct counterweight mass, then you are hunky-dory.
However, the OEM counterweight will work within spec for probably 90% of engines.
Keep in mind when installing a lightweight flywheel:
The only factor you are changing as far as balance is concerned is the counterweight. that is all. the flywheel is not a factor (as long as the flywheel itself is balanced properly and installed correctly.
You have a higher chance of exhibiting vibration and out-of-balance symptoms from a poorly installed pressure plate, or poorly balanced one.
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Joined: Jan 2002
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From: 15143
When building my car's current engine back in 1999, I sent my complete rotating assembly to MazdaTrix for balancing, some people thought I was wasting money.
But I knew that less vibration means longer life and a little more power.
But I knew that less vibration means longer life and a little more power.
Interesting thread.
Question from one of those 'average' owners of a mostly street driven car (as described by adam c)....if an improperly balanced rotating assembly accelerates bearing wear, how much do new bearings cost relative to the cost of a rebuild?
Question from one of those 'average' owners of a mostly street driven car (as described by adam c)....if an improperly balanced rotating assembly accelerates bearing wear, how much do new bearings cost relative to the cost of a rebuild?
question:
my engine is originally balanced for an auto....when i had the swap done i got a 9.5lb flywheel and kept the same counterweight. Does that mean that because the counterweight was balanced for the engine no balancing needs to be done (or very little)
my engine is originally balanced for an auto....when i had the swap done i got a 9.5lb flywheel and kept the same counterweight. Does that mean that because the counterweight was balanced for the engine no balancing needs to be done (or very little)
You would be fine keeping the same counter weight that came with the auto engine. Mainly we are talking about using a new or different counter weight from another engine in place of the one integrated into the stock manuel flywheel. In this case the counter weight you add may not be in perfect balance with the rotors you have inside the engine. The flywheel itself isn't the issue.
Last edited by t-von; Aug 12, 2007 at 10:25 PM.
Adam I already said in some of my later post that most won't notice the vibrations. But it still doesn't change the fact the different counter weight can still through the rotating assembly out of balance. One counter weight can not perfectly balance a rotating assembly that has 5 different rotor weight combinations. Anyone who thinks otherwise is ignorant. My 20b counter weight even has the drilled holes in it.
Mainly we are talking about using a new or different counter weight from another engine in place of the one integrated into the stock manuel flywheel. In this case the counter weight you add may not be in perfect balance with the rotors you have inside the engine. The flywheel itself isn't the issue.
Joined: May 2005
Posts: 3,243
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From: Kennewick, Washington
Question:
Is there some sort of correlation between the front counterweights mass and the rear counterweights mass? If we could find some sort of pattern, it may be possible to get even closer to balanced without a rebuild.
Just a thought. Find a relation and create a band aid fix.
Is there some sort of correlation between the front counterweights mass and the rear counterweights mass? If we could find some sort of pattern, it may be possible to get even closer to balanced without a rebuild.
Just a thought. Find a relation and create a band aid fix.
development
Joined: Aug 2002
Posts: 5,714
Likes: 7
From: Lafayette, LA
I had similar concerns...
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/adding-lightweight-flywheel-reman-581668/
https://www.rx7club.com/3rd-generation-specific-1993-2002-16/adding-lightweight-flywheel-reman-581668/
Adam I already said in some of my later post that most won't notice the vibrations. But it still doesn't change the fact the different counter weight can still through the rotating assembly out of balance. One counter weight can not perfectly balance a rotating assembly that has 5 different rotor weight combinations. Anyone who thinks otherwise is ignorant. My 20b counter weight even has the drilled holes in it.
BTW, you shouldn't call me ignorant. Especially when you cannot figure out the proper use of the word "Through".
Definitions of "through" on the Web:
* from beginning to end; "read this book through"
* over the whole distance; "this bus goes through to New York"
* to completion; "think this through very carefully!"
* in diameter; "this cylinder measures 15 inches through"
* done: having finished or arrived at completion; "certain to make history before he's done"; "it's a done deed"; "after the treatment, the patient is through except for follow-up"; "almost through with his studies"
* throughout the entire extent; "got soaked through in the rain"; "I'm frozen through"; "a letter shot through with the writer's personality"; "knew him through and through"; "boards rotten through and through"
* through(a): (of a route or journey etc.) continuing without requiring stops or changes; "a through street"; "a through bus"; "through traffic"
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I believe the word you are looking for is: "Throw"
From what I understand the atx to mtx and the use of the lightweight flywheel make the job a lot easier because you don't have to pull the counterweight with special tools. Now I just have to find a counterweight holding tool and a big *** wrench for that nut...