Lightweight Flywheels - Be VERY cautious
DJM RX7
Joined: Dec 2007
Posts: 48
Likes: 0
From: Northeast Ohio
balancing of rotating assembly is only needed when using different rotors...(ex. a 20B running high compression 13BT rotors instead of factory rotors) Running a lightened flywheel has no effect on the balance of internal components, just allows better throttle response due to lower drivetrain rotating mass.
Is there any reason people who want to switch to a lightweight flywheel without taking apart their motor couldn't just pull off the old flywheel, send it and the new flywheel/auto counterweight to someone and have them match the two? Seems like you should be able to do that fairly easily?
It had 9 k on it and went out wile Kan tunned it according to the seller, I had it spec'd by a machine shop and they said everything seem to be almost to new spec so I will lean towards that it did have 9k on the housings and plates but I don' t know about the bearings if they were reused or not and being the front bearing it could have been a O ring but nothing looked too bad when I opened it up; but doesn't mean that the O ring didn't fail.
Joined: Mar 2001
Posts: 30,804
Likes: 646
From: FL-->NJ/NYC again!
It has no effect on the main (stationary gear) bearings or the rotor bearings.
Did I confuse anyone yet
?
Bumping an old thread here, but wouldn't the orientation of the rotors during a rebuild also cause an inbalance in the engine? The rotors have 3 corners each with each corner being balanced to the corner of the other rotor, so effectively, both rotors could be re-installed in different orientations over the original orientation.
Lets say you did a rebuild, and only labelled the rotors F & R but nothing else.
Lets say you did a rebuild, and only labelled the rotors F & R but nothing else.
I'm sure there are errors in the thread. Let's point them out so people are more educated.
Dale Clark has a ton of knowledge so I'm sure he has something more to say than let the thread die in a fire. His input on the subject should be very useful.
Dale Clark has a ton of knowledge so I'm sure he has something more to say than let the thread die in a fire. His input on the subject should be very useful.
Ok? But this is 4 pages of crap with a misleading title. The front counterweight is a counterbalance to the rear. A flywheel that is properly made will have no balance issues. End of story.
The weight of the flywheel in of itself has nothing to do with engine balance, it's how the weight is distributed on the flywheel. The question is are rotaries internally or externally balanced? And then what's the role of the counter balancer in lightweight flywheel applications?
http://en.wikipedia.org/wiki/Flywheel
Understanding Crankshaft Balancing - Engine Builder Magazine
http://en.wikipedia.org/wiki/Flywheel
Understanding Crankshaft Balancing - Engine Builder Magazine
You also see the drill holes underneith that solid section of the factory flywheel? This particular flywheel is balanced to both my "c" weight rotors and front counter weight. If I were to remove this flywheel, I would also be removing that counter weight as they are one in the same.
Now look at these two front counter weights. Notice the drill holes and the very different locations their drilled. The one on the right is matched to my flywheel above. It has only 2 holes drill to balance it. The weight on the left came off an auto engine I had. It has 3 holes drilled. The factory auto rear counter weights also have holes drill to match it's rotating assembly.
Now the OP wasn't clear on his explanations but he technically is correct. When you remove that manuel tranny flywheel to install a light weight flywheel, the balance of the rotating assembly will be changed because the new auto rear counter weight that comes with that flywheel won't be balanced to your rotating assembly. They are full weight counter weights that don't have holes drilled to match your rotating assembly.
Just to add in to this . I had a new motor built . and I just swapped over the rear counterweight / light weight RB flywheel onto the new motor . and I am getting alot of vibrations over 6k rpm
same motor mounts This was my mistake .
My old motor WAS balanced , THis one was sort of just swap on situation . So just so you know it DOES! INDEED MAKE A DIFFERENCE !
i'm debating now weather to swap in the OEM flywheel back on that was balanced for this motor , Or weather to find a new rear counterweight , that has not been previously balanced and hope it goes into spec .
My rotors are E/F weights
once I make the swap I will let you guys know if the out of spec rear counterweight was indeed the cause of the vibrations
same motor mounts This was my mistake .
My old motor WAS balanced , THis one was sort of just swap on situation . So just so you know it DOES! INDEED MAKE A DIFFERENCE !
i'm debating now weather to swap in the OEM flywheel back on that was balanced for this motor , Or weather to find a new rear counterweight , that has not been previously balanced and hope it goes into spec .
My rotors are E/F weights
once I make the swap I will let you guys know if the out of spec rear counterweight was indeed the cause of the vibrations
...When you remove that manuel tranny flywheel to install a light weight flywheel, the balance of the rotating assembly will be changed because the new auto rear counter weight that comes with that flywheel won't be balanced to your rotating assembly. They are full weight counter weights that don't have holes drilled to match your rotating assembly.
Tem120...Mazdatrix's site has a how-to for identifying the correct generation of counter-weights. Identifying Rear Counterweights
Before you give up on a LWFW, you might want to make sure the one you have is correct. There are really subtle differences in some cases. Initially I was given the wrong one with a LWFW I bought. Only realized it after doing some measurements. Fortunately it was BEFORE install. Got a used correct one, and zero issues with vibration since.
Don't believe they're individually balanced to the particular engine. My thinking is they are simply balanced within a certain tolerance and then just bolted on in the assembly line. Same for the manual flywheels. I've never see either without some holes drilled for balancing.
You may be correct on that. As many engines Mazda has built, they probably have pre-drilled flywheels and counter weights set aside for whatever combination of rotor weights that are put into an engine for assembly. This of course would speed assembly time.
I doubt they balanced the assembly unless someone can show me the 2nd plane balance location. We can see corrections in the flywheel, but there are no correction points on the front of the engine. Also, if the FSM does not require rebalancing when changing the flywheel that tells the story too.
Anyway, it's good to discuss the question because getting things wrong has high costs. Better to consider carefully first, IMHO.
David
OK, let's try and shut this thread down.
First empirical evidence. I've installed light flywheels on a number of FD's and FC's over the years, including my own personal vehicles. I have never found it resulting in any sort of vibration, resonance, or anything. I have also never seen an engine failure I would attribute to an imbalance, like damaged bearings or the like.
The balance assembly in the motor consists of the E-shaft, the rotors, and the front and rear counterweights. The stock flywheel has a built-in counterweight - it's heavy, but a small portion of the mass is offset to balance everything out. The front and rear counterweights are keyed onto the eccentric shaft so they can only go on in one position, insuring their balance.
Rotors have weights. There are 5 weight ranges, the letter codes are A,B,C,D,E and F. Rule of thumb is to match letters if you have to replace a rotor, or get within one letter (a B with a C, for example). Rotors are balanced by themselves, if you spin them in the middle of their axis they spin smoothly. The fact that they're offset on the e-shaft makes having the front and rear counterweights a necessity.
If you look at a few different stock front and rear counterweights, you will notice different amounts of material removed for balancing. This is OK. They are cast iron, which means they are poured into a mold, cooled, then machined. This process is not perfect, you can have minor voids inside, irregularities in the material, etc. The factory then balances that component by itself to a known bob weight.
Same goes for rotors - they are balanced to themselves as a static spinning assembly. Different rotors have different amounts of material removed to balance, again this is because they are cast iron.
The factory doesn't balance rotating assemblies, they just make sure each component is built to a balance tolerance and bolt them together.
If changing to an automatic counterweight WAS a problem, we would see lots of "my motor shakes" and "I just spun my bearings" threads. You don't. By the same token, this would happen with nearly every rebuilt engine as you almost always swap at least one rotor out, sometimes changing many parts, like e-shafts and maybe even a different stock flywheel.
This thread is just screaming FIRE in a packed theater. It does no good, it's not based on fact, and it's looking for a problem that doesn't exist. A light flywheel is a great mod that makes the car even more fun to drive. I would not hesitate to recommend doing this to anybody.
Dale
First empirical evidence. I've installed light flywheels on a number of FD's and FC's over the years, including my own personal vehicles. I have never found it resulting in any sort of vibration, resonance, or anything. I have also never seen an engine failure I would attribute to an imbalance, like damaged bearings or the like.
The balance assembly in the motor consists of the E-shaft, the rotors, and the front and rear counterweights. The stock flywheel has a built-in counterweight - it's heavy, but a small portion of the mass is offset to balance everything out. The front and rear counterweights are keyed onto the eccentric shaft so they can only go on in one position, insuring their balance.
Rotors have weights. There are 5 weight ranges, the letter codes are A,B,C,D,E and F. Rule of thumb is to match letters if you have to replace a rotor, or get within one letter (a B with a C, for example). Rotors are balanced by themselves, if you spin them in the middle of their axis they spin smoothly. The fact that they're offset on the e-shaft makes having the front and rear counterweights a necessity.
If you look at a few different stock front and rear counterweights, you will notice different amounts of material removed for balancing. This is OK. They are cast iron, which means they are poured into a mold, cooled, then machined. This process is not perfect, you can have minor voids inside, irregularities in the material, etc. The factory then balances that component by itself to a known bob weight.
Same goes for rotors - they are balanced to themselves as a static spinning assembly. Different rotors have different amounts of material removed to balance, again this is because they are cast iron.
The factory doesn't balance rotating assemblies, they just make sure each component is built to a balance tolerance and bolt them together.
If changing to an automatic counterweight WAS a problem, we would see lots of "my motor shakes" and "I just spun my bearings" threads. You don't. By the same token, this would happen with nearly every rebuilt engine as you almost always swap at least one rotor out, sometimes changing many parts, like e-shafts and maybe even a different stock flywheel.
This thread is just screaming FIRE in a packed theater. It does no good, it's not based on fact, and it's looking for a problem that doesn't exist. A light flywheel is a great mod that makes the car even more fun to drive. I would not hesitate to recommend doing this to anybody.
Dale
OK, let's try and shut this thread down.
First empirical evidence. I've installed light flywheels on a number of FD's and FC's over the years, including my own personal vehicles. I have never found it resulting in any sort of vibration, resonance, or anything. I have also never seen an engine failure I would attribute to an imbalance, like damaged bearings or the like.
The balance assembly in the motor consists of the E-shaft, the rotors, and the front and rear counterweights. The stock flywheel has a built-in counterweight - it's heavy, but a small portion of the mass is offset to balance everything out. The front and rear counterweights are keyed onto the eccentric shaft so they can only go on in one position, insuring their balance.
Rotors have weights. There are 5 weight ranges, the letter codes are A,B,C,D,E and F. Rule of thumb is to match letters if you have to replace a rotor, or get within one letter (a B with a C, for example). Rotors are balanced by themselves, if you spin them in the middle of their axis they spin smoothly. The fact that they're offset on the e-shaft makes having the front and rear counterweights a necessity.
If you look at a few different stock front and rear counterweights, you will notice different amounts of material removed for balancing. This is OK. They are cast iron, which means they are poured into a mold, cooled, then machined. This process is not perfect, you can have minor voids inside, irregularities in the material, etc. The factory then balances that component by itself to a known bob weight.
Same goes for rotors - they are balanced to themselves as a static spinning assembly. Different rotors have different amounts of material removed to balance, again this is because they are cast iron.
The factory doesn't balance rotating assemblies, they just make sure each component is built to a balance tolerance and bolt them together.
If changing to an automatic counterweight WAS a problem, we would see lots of "my motor shakes" and "I just spun my bearings" threads. You don't. By the same token, this would happen with nearly every rebuilt engine as you almost always swap at least one rotor out, sometimes changing many parts, like e-shafts and maybe even a different stock flywheel.
This thread is just screaming FIRE in a packed theater. It does no good, it's not based on fact, and it's looking for a problem that doesn't exist. A light flywheel is a great mod that makes the car even more fun to drive. I would not hesitate to recommend doing this to anybody.
Dale
First empirical evidence. I've installed light flywheels on a number of FD's and FC's over the years, including my own personal vehicles. I have never found it resulting in any sort of vibration, resonance, or anything. I have also never seen an engine failure I would attribute to an imbalance, like damaged bearings or the like.
The balance assembly in the motor consists of the E-shaft, the rotors, and the front and rear counterweights. The stock flywheel has a built-in counterweight - it's heavy, but a small portion of the mass is offset to balance everything out. The front and rear counterweights are keyed onto the eccentric shaft so they can only go on in one position, insuring their balance.
Rotors have weights. There are 5 weight ranges, the letter codes are A,B,C,D,E and F. Rule of thumb is to match letters if you have to replace a rotor, or get within one letter (a B with a C, for example). Rotors are balanced by themselves, if you spin them in the middle of their axis they spin smoothly. The fact that they're offset on the e-shaft makes having the front and rear counterweights a necessity.
If you look at a few different stock front and rear counterweights, you will notice different amounts of material removed for balancing. This is OK. They are cast iron, which means they are poured into a mold, cooled, then machined. This process is not perfect, you can have minor voids inside, irregularities in the material, etc. The factory then balances that component by itself to a known bob weight.
Same goes for rotors - they are balanced to themselves as a static spinning assembly. Different rotors have different amounts of material removed to balance, again this is because they are cast iron.
The factory doesn't balance rotating assemblies, they just make sure each component is built to a balance tolerance and bolt them together.
If changing to an automatic counterweight WAS a problem, we would see lots of "my motor shakes" and "I just spun my bearings" threads. You don't. By the same token, this would happen with nearly every rebuilt engine as you almost always swap at least one rotor out, sometimes changing many parts, like e-shafts and maybe even a different stock flywheel.
This thread is just screaming FIRE in a packed theater. It does no good, it's not based on fact, and it's looking for a problem that doesn't exist. A light flywheel is a great mod that makes the car even more fun to drive. I would not hesitate to recommend doing this to anybody.
Dale
OK, let's try and shut this thread down.
First empirical evidence. I've installed light flywheels on a number of FD's and FC's over the years, including my own personal vehicles. I have never found it resulting in any sort of vibration, resonance, or anything. I have also never seen an engine failure I would attribute to an imbalance, like damaged bearings or the like.
The balance assembly in the motor consists of the E-shaft, the rotors, and the front and rear counterweights. The stock flywheel has a built-in counterweight - it's heavy, but a small portion of the mass is offset to balance everything out. The front and rear counterweights are keyed onto the eccentric shaft so they can only go on in one position, insuring their balance.
Rotors have weights. There are 5 weight ranges, the letter codes are A,B,C,D,E and F. Rule of thumb is to match letters if you have to replace a rotor, or get within one letter (a B with a C, for example). Rotors are balanced by themselves, if you spin them in the middle of their axis they spin smoothly. The fact that they're offset on the e-shaft makes having the front and rear counterweights a necessity.
If you look at a few different stock front and rear counterweights, you will notice different amounts of material removed for balancing. This is OK. They are cast iron, which means they are poured into a mold, cooled, then machined. This process is not perfect, you can have minor voids inside, irregularities in the material, etc. The factory then balances that component by itself to a known bob weight.
Same goes for rotors - they are balanced to themselves as a static spinning assembly. Different rotors have different amounts of material removed to balance, again this is because they are cast iron.
The factory doesn't balance rotating assemblies, they just make sure each component is built to a balance tolerance and bolt them together.
If changing to an automatic counterweight WAS a problem, we would see lots of "my motor shakes" and "I just spun my bearings" threads. You don't. By the same token, this would happen with nearly every rebuilt engine as you almost always swap at least one rotor out, sometimes changing many parts, like e-shafts and maybe even a different stock flywheel.
This thread is just screaming FIRE in a packed theater. It does no good, it's not based on fact, and it's looking for a problem that doesn't exist. A light flywheel is a great mod that makes the car even more fun to drive. I would not hesitate to recommend doing this to anybody.
Dale
First empirical evidence. I've installed light flywheels on a number of FD's and FC's over the years, including my own personal vehicles. I have never found it resulting in any sort of vibration, resonance, or anything. I have also never seen an engine failure I would attribute to an imbalance, like damaged bearings or the like.
The balance assembly in the motor consists of the E-shaft, the rotors, and the front and rear counterweights. The stock flywheel has a built-in counterweight - it's heavy, but a small portion of the mass is offset to balance everything out. The front and rear counterweights are keyed onto the eccentric shaft so they can only go on in one position, insuring their balance.
Rotors have weights. There are 5 weight ranges, the letter codes are A,B,C,D,E and F. Rule of thumb is to match letters if you have to replace a rotor, or get within one letter (a B with a C, for example). Rotors are balanced by themselves, if you spin them in the middle of their axis they spin smoothly. The fact that they're offset on the e-shaft makes having the front and rear counterweights a necessity.
If you look at a few different stock front and rear counterweights, you will notice different amounts of material removed for balancing. This is OK. They are cast iron, which means they are poured into a mold, cooled, then machined. This process is not perfect, you can have minor voids inside, irregularities in the material, etc. The factory then balances that component by itself to a known bob weight.
Same goes for rotors - they are balanced to themselves as a static spinning assembly. Different rotors have different amounts of material removed to balance, again this is because they are cast iron.
The factory doesn't balance rotating assemblies, they just make sure each component is built to a balance tolerance and bolt them together.
If changing to an automatic counterweight WAS a problem, we would see lots of "my motor shakes" and "I just spun my bearings" threads. You don't. By the same token, this would happen with nearly every rebuilt engine as you almost always swap at least one rotor out, sometimes changing many parts, like e-shafts and maybe even a different stock flywheel.
This thread is just screaming FIRE in a packed theater. It does no good, it's not based on fact, and it's looking for a problem that doesn't exist. A light flywheel is a great mod that makes the car even more fun to drive. I would not hesitate to recommend doing this to anybody.
Dale
Based on the above info, someone blows an engine that has all A code rotors. They replace those rotors with all F code rotors. Since your saying that all the components are built to balance tolerance, will the above engine stay in balance?
Gordon the thread title should make you think about it as the OP is saying be CAUTIOUS. I think the differences may not be enough to worry about in most cases (street wise) because a street engine spends much of it's life in lower rpm ranges. Now someone like Fritz who does nothing but track his Fd, is a different storey. 1/4 mile runs at a drag strip isn't the same as someone going WOT for 15-20min track sessions at a time. I mean who's to say that a rotary engine that's slightly out of balance wont amplify the frequencies/harmonics of engine knock under boost? Isn't engine knock virtually vibration to some extent?
I've only had maybe 4-5 lightweight flywheels over time, though only one with my 3 rotor. Never noticed any issues with vibration, but this thread made me think about it. Making sure the rotating assembly is really well balanced with my 3 rotor has proven important. It would seem to make sense to me that, while I might not necessarily notice any vibration, I would think it would be better to balance the flywheel assembly, though I'm not sure what difference it would make. Maybe I just put it down to having a balance thing. I wonder if this becomes more of an issue as people stiffen up their cars with various braces, like Banzai's transmission brace and the various differential braces etc?
G
G
Imbalance is imbalance. The parts we all use are balanced, and remain balanced unless you grind material off of them or machine them in some way.
The only major effect on imbalance causing vibration is RPM. Since none of us are running past the factor 8-9k redline, the factory specs are good enough.
As far as rotor weight codes go, you just need to keep the same/similar codes in the engine. Having balanced rotors of different weight will cause a two-plane imbalance on the e-shaft. If you want to get fussy, send the rotors out for rebalancing and exact weight matching, then the letter codes won't matter.
David
Last edited by dgeesaman; Jan 25, 2015 at 03:05 PM.
See this is what I accidentally did wrong on my own S5 NA rebuild back in 2005. I had damaged A-B rotors and replaced them with a matching C set. I thought I was doing ok with keeping the rotors 1 letter of each other but what I didn't realize was that I was installing a set of rotors that were lighter than what I orginally had. So yea that engine runs rough. Didn't take me long to realize what I had did so I just kept the rpms low and drove it. Other than the extra vibration, that engine ran great for 45k until the tephlon coolant seals went out.
This thread is a GREAT example of do you research before you make a thread! I have been looking into swapping out my flywheel with a light weight one and this tread started to scare me off before I got to the end.
Senior Member
Joined: Oct 2012
Posts: 434
Likes: 16
From: Manassas
I have just a bit of input about lightweight flywheels. I'm a veteran auto technician and I specialize in Asian car repair. I have only ever seen two aluminum flywheels with the iron insert. Both of those cars came to me with excessive clutch chatter, about as bad as I've ever seen. Both had badly deformed wear plates. It appears to me that the junction between the iron wear plate and aluminum flywheel isn't very good at heat transfer and results in overheating the wear plate.
So based on the fact that 100% of the two that I've seen caused problems, I'd suggest if you want a lightweight flywheel, get one of the billet steel ones.
I've installed the lightweight billet flywheels on several cars, different makes and models and have only had positive results. I am always amazed at how much of a difference it makes in performance.
So based on the fact that 100% of the two that I've seen caused problems, I'd suggest if you want a lightweight flywheel, get one of the billet steel ones.
I've installed the lightweight billet flywheels on several cars, different makes and models and have only had positive results. I am always amazed at how much of a difference it makes in performance.