Okay gang, I’m posting this again because no one replied the last time. I hope that some of the more technically minded members(Jim Greek, that means you) will respond
The subject of how to lighten V6 flywheels and the effect of this on the balance of the motor has being much discussed in this forum. I think I now understand the nature of the counterweight balances in the V6 flywheel and front pulley.
The following quote comes from a book called “V6 Performance” by Pat Ganahl, published by SA Design.
In terms of balance, the 60-degree V-6 produces both primary and secondary rotating couples due to reciprocating forces. But, since the primary rotating couple varies directly with crankshaft speed, it can be balanced by a pair of counterweights on the crank, one at each end. Since the secondary rotating couple varies at twice crankshaft speed, it could only be counteracted by a separate balance shaft turning at twice engine speed.
I think that the primary rotating couple in the Alfa V6 is balanced by weights in the flywheel and the crankshaft pulley. I’ve seen pictures of the cranks of other 60 degree V6 motors with six throw cranks and they have larger crank throws at the front and back of the crank. The Alfa crankshaft doesn’t have these oversized throws, so the counterweights, I think must be in the flywheel and the crankshaft pulley.
Now here is a quote from an Alfa Romeo press release
The 60o angle selected for the two cylinder banks allows ideal evenly spaced ignition at 120o intervals. For this reason, the particularly short and sturdy crankshaft, featuring 100% balancing with extra counterweights applied to the flywheel and front pulley, is subjected to a minimum amount of torsional vibration and is effectively protected against the 1st and 2nd order vibration periods produced by the pistons' reciprocating motion.
The source of this paragraph is the 1987 Alfa Romeo Product Bulletin, Engine Section which is reproduced in the 164 section of the Alfa Digest
On the old GTV6.org) a Bob Boniface made the following post.
I am installing a 3.0 in my GTV6 and have a flywheel question. My 3.0 came sans flywheel and used ones seem to be unavailable. I got a late 2.5 flywheel to use since it has the proper offset at the the mounting boss to ensure proper engagement with the GTV starter. I am told that this flywheel has 98 grams of counterweight whereas the 3.0 has 114 grams. These weights are also used on the crank pulley at the other end of the crank. Therefore, I now have 114 grams of counterweight at the front of the crank and 98 grams at the rear. I intend on cutting weight off the 2.5 flywheel and then rebalancing to 114 grams of counterweight to match the front pulley.
Has anyone else done this? Also, how much weight can reasonably and safely be removed from the flywheel?
Bob Boniface
Apparently Bob isn’t on this forum anymore. Can anybody else confirm Bob’s number of 98 grams of counterweight for a 2.5 liter motor, and 114 grams of counterweight for a3.0 liter motor?
The upshot of all this is that I think you can lighten your flywheel as much as you think prudent as long as you retain the factory counterweight. Thus if you take a stock 3.0 flywheel which weights 22.2 pounds (10 KGs) on my scales you can lighten it by say seven pounds as long as the machining process doesn’t alter the counterweight
Okay, anybody want to tell me where I’ve gone wrong in the above?
Bye
Hi MG, you giving us a hard time here! I figure that Barry with the SA gang would have gone a long way into the lightened or special flywheel business (why shouldn't I pass the buck?) with all the racing going on down there. C'mon guys, out with it!
I've toiled with the idea for a long while, but haven't done squat yet. However, for the sake of what I'm trying to write, I'm ready to experiment on this. I have a complete set of crankthrow counterweights which I use to balance the 3liter crank with, 2 3liter std rwd flywheels and 1ea Jetronic, Motronic and 24v front pulleys and of course, a 3liter crank. I also have the 24v Q4 flywheel. It weighs stock ~8,5kg, whereas the rwd flywheel weighs ~11kg! (The fwd press.plate weighs ~5,5kg.Does it come into play? I don't know). Here's the plan then: I take the 24v flywheel to the machine shop and skim the p$ss out of it. Then, I go to the balancing guy and see if the assembly can be balanced with all 3 pulleys in turn. If yes, we will answer most of our questions, won't we? The reason I'll use the fwd flywheel is because its expendable! I wouldn't want to ruin one of the 2 rwd flywheels, if the experiment fails. If everything works out, then one of the 'good' pulleys will be lightened. I will not touch the almost semicircular milled area on the flywheel, which obviously is there for the 'external balancing' of the whole assembly. I will remove as much weight as possible from the outside as it should be. I should be ready with this in about a month.
Now, about the 98 and 114 grams you mention, I think its a simplistic approach to the problem.If you look at the Jetronic/Motronic pulleys vs the 24v one,you'll see great differences in the slab of extra metal used as counterweight, albeit on identical cranks! I want to believe that if metal is evenly removed from the circumference, balancing properties are not altered. This engineering-wise correct statement, means that lightening is on the cards as usual, just don't touch the slab in the front or the gouge in the back! I've been very curious about this for years but Pat Ganahl hadn't given me any answers and neither had the great Smokey Unick. There aren't that many people around seriously modifying V6 motors you can ask and those that do, well...ain't saying much! It'll cost me 30E to skim the flywheel and 100E for balancing (once!). Chalk it up to education, it'll be worth it.
Thats about it. I know I haven't helped any, but in a few weeks we'll know. As for AR literature, I wouldn't give a rat's @ss what they say. They must write their stuff between hickups and then have some sort of contest! To give you a sample, they describe in the 164 3liter Quadrifoglio brochure (1990) how they succeeded in broadening the engine torque curve, by using different valve timing and different intake tract design PER BANK of cylinders!!!
Jim K.
I've toiled with the idea for a long while, but haven't done squat yet. However, for the sake of what I'm trying to write, I'm ready to experiment on this. I have a complete set of crankthrow counterweights which I use to balance the 3liter crank with, 2 3liter std rwd flywheels and 1ea Jetronic, Motronic and 24v front pulleys and of course, a 3liter crank. I also have the 24v Q4 flywheel. It weighs stock ~8,5kg, whereas the rwd flywheel weighs ~11kg! (The fwd press.plate weighs ~5,5kg.Does it come into play? I don't know). Here's the plan then: I take the 24v flywheel to the machine shop and skim the p$ss out of it. Then, I go to the balancing guy and see if the assembly can be balanced with all 3 pulleys in turn. If yes, we will answer most of our questions, won't we? The reason I'll use the fwd flywheel is because its expendable! I wouldn't want to ruin one of the 2 rwd flywheels, if the experiment fails. If everything works out, then one of the 'good' pulleys will be lightened. I will not touch the almost semicircular milled area on the flywheel, which obviously is there for the 'external balancing' of the whole assembly. I will remove as much weight as possible from the outside as it should be. I should be ready with this in about a month.
Now, about the 98 and 114 grams you mention, I think its a simplistic approach to the problem.If you look at the Jetronic/Motronic pulleys vs the 24v one,you'll see great differences in the slab of extra metal used as counterweight, albeit on identical cranks! I want to believe that if metal is evenly removed from the circumference, balancing properties are not altered. This engineering-wise correct statement, means that lightening is on the cards as usual, just don't touch the slab in the front or the gouge in the back! I've been very curious about this for years but Pat Ganahl hadn't given me any answers and neither had the great Smokey Unick. There aren't that many people around seriously modifying V6 motors you can ask and those that do, well...ain't saying much! It'll cost me 30E to skim the flywheel and 100E for balancing (once!). Chalk it up to education, it'll be worth it.
Thats about it. I know I haven't helped any, but in a few weeks we'll know. As for AR literature, I wouldn't give a rat's @ss what they say. They must write their stuff between hickups and then have some sort of contest! To give you a sample, they describe in the 164 3liter Quadrifoglio brochure (1990) how they succeeded in broadening the engine torque curve, by using different valve timing and different intake tract design PER BANK of cylinders!!!
Jim K.
Hey, as far as seriuos Alfa litterature goes, the only technical piece I know is written by the guy who replied before me!!
IMHO, just lighten the shit of everything and bring it to any shop who lightens and/or balances drag racing engines. They will make it work.
PS! Looking at the beninca web page they should be experts in this field as well.
IMHO, just lighten the shit of everything and bring it to any shop who lightens and/or balances drag racing engines. They will make it work.
PS! Looking at the beninca web page they should be experts in this field as well.
hi jim,i had my flywheel done exactly the same way like yours.
i sent foto's to some engineers and they told me that it is very dangerous and that the original alfa material would explode!!!
original it was about 11 kg and after lightening it was 3 kg and a little bit.it was terrible!!almost undrivable in city traffic.i took it of the car and threw it away!what you think of the strenght.
they told me i had to buy a aluminium or a solid steel one and then lighten it?
i sent foto's to some engineers and they told me that it is very dangerous and that the original alfa material would explode!!!
original it was about 11 kg and after lightening it was 3 kg and a little bit.it was terrible!!almost undrivable in city traffic.i took it of the car and threw it away!what you think of the strenght.
they told me i had to buy a aluminium or a solid steel one and then lighten it?
RZ, thanks for the very impressive picture! I wonder if there is a label on there somewhere, saying:''break along dotted line''!
The picture I posted is from a German AR performance store and it looks like a std 4cyl flywheel, weighing 2,8kg!!! I would be interested in more info from you about driving with your drilled flywheel. How was the behavior at high rpm? Any vibration? What did it do at low rpm to become undriveable? Did you sense any vibration from the rear of the car (gearbox)?
The drilling pattern, reminds me of a waterbrake dyno disc! Leaving obvious mechanical weakness aside, we can discount any problems due to vortices generated (Micke,Mats,Maurizio?), its only air!
Zamani, I suspect that RZ's observations may have something to do with front/rear flywheel mass imbalance, leading to great torsional vibration, especially during rpm change periods (acceleration/deceleration). We all agree that lightening must be done on both ends in correct proportions (???).
Any more views??
Jim K.
The picture I posted is from a German AR performance store and it looks like a std 4cyl flywheel, weighing 2,8kg!!! I would be interested in more info from you about driving with your drilled flywheel. How was the behavior at high rpm? Any vibration? What did it do at low rpm to become undriveable? Did you sense any vibration from the rear of the car (gearbox)?
The drilling pattern, reminds me of a waterbrake dyno disc! Leaving obvious mechanical weakness aside, we can discount any problems due to vortices generated (Micke,Mats,Maurizio?), its only air!
Zamani, I suspect that RZ's observations may have something to do with front/rear flywheel mass imbalance, leading to great torsional vibration, especially during rpm change periods (acceleration/deceleration). We all agree that lightening must be done on both ends in correct proportions (???).
Any more views??
Jim K.
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Maurizio
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- Joined: Wed Dec 01, 2004 4:49 am
- Location: the Netherlands, 153.1km from the N'ring :-)
The RZ flywheel (hey Mark 
) looks a bit scary.
But is much better then the picture posted by Jim.
(First look without real calculations etc.)
If you look at the small amount of steel left as springs and the mass still on the outside, the natural frequency of RZ’s flywheel will be much higher. And mass pulling on the small springs due to centrifugal forces is also low.
But starting and high compression
A lot of stiffness could be added to make the holes not completely through. Leave a thin bottom of 1 mm thickness and could work fine!
But still this is cast iron with a lot of enclosed imperfections etc
Torsional vibration will not be a issue due to front and back imbalance, is my opinion.
My theoretical explanation: The imbalance between front and back works on a arm (radius flywheel), the counterpart will be the crank supported on the first and last main bearing. The crank is a very stiff and supported by a total of 5 bearings! Imbalance will only wear out the first and last.
Rotational imbalance is more scary it wears out the first and last main bearing very fast.
Btw: what about the prop shaft and the gear box flywheel, they are also working on the backside of the engine!
But, first weight is not important, what we are looking at is inertia.
This picture is my TS flywheel inertia is about 50% of original and ~4.7 Kg (~7.2 Kg). This flywheel leaves enough material to take the cast iron imperfections into account. I only did a static rotational balance of the flywheel just to ease my mind.....
) looks a bit scary. But is much better then the picture posted by Jim.
(First look without real calculations etc.)
If you look at the small amount of steel left as springs and the mass still on the outside, the natural frequency of RZ’s flywheel will be much higher. And mass pulling on the small springs due to centrifugal forces is also low.
But starting and high compression
A lot of stiffness could be added to make the holes not completely through. Leave a thin bottom of 1 mm thickness and could work fine!But still this is cast iron with a lot of enclosed imperfections etc
Torsional vibration will not be a issue due to front and back imbalance, is my opinion.
My theoretical explanation: The imbalance between front and back works on a arm (radius flywheel), the counterpart will be the crank supported on the first and last main bearing. The crank is a very stiff and supported by a total of 5 bearings! Imbalance will only wear out the first and last.
Rotational imbalance is more scary it wears out the first and last main bearing very fast.
Btw: what about the prop shaft and the gear box flywheel, they are also working on the backside of the engine!
But, first weight is not important, what we are looking at is inertia.
This picture is my TS flywheel inertia is about 50% of original and ~4.7 Kg (~7.2 Kg). This flywheel leaves enough material to take the cast iron imperfections into account. I only did a static rotational balance of the flywheel just to ease my mind.....
Banned.. ? 
Daily donky.. ==> BMW 325d 
E36M3 (3.0) Ringtool
==> definitely BANNED!
AR 75 TS Ringtool '90, AR Spider 2000 veloce '79
Daily donky.. ==> BMW 325d E36M3 (3.0) Ringtool
==> definitely BANNED! AR 75 TS Ringtool '90, AR Spider 2000 veloce '79
This is my flywheel, haven't mounted it yet and I need to balance it. Down 3Kg (to 5Kg), all in the outer perimeter of the flywheel.
Did the front pulley too. turned off the two outer slots, needs balancing too.
I honestly can't think that my lightening can have any impact on durability, basically I just took off dead weight on the outer part of the flywheel and the narrowest part of the flywheel is still intact, should be less stress in that area now and since I'm going to balance it there will be no vibrations to rip it apart either.
BTW, here is a couple of pics I took of the Factory GTA flywheels on the -02 ETCC cars. Pretty cool huh?
Did the front pulley too. turned off the two outer slots, needs balancing too.
I honestly can't think that my lightening can have any impact on durability, basically I just took off dead weight on the outer part of the flywheel and the narrowest part of the flywheel is still intact, should be less stress in that area now and since I'm going to balance it there will be no vibrations to rip it apart either.
BTW, here is a couple of pics I took of the Factory GTA flywheels on the -02 ETCC cars. Pretty cool huh?
Last edited by Mats on Wed Oct 19, 2005 5:56 am, edited 1 time in total.
Mats Strandberg
-Scuderia Rosso- Now burned to the ground...
-onemanracing.com-
-Strandberg.photography-
GTV 2000 -77 - Died in the fire.
155 V6 Sport -96 - Sold!
-Scuderia Rosso- Now burned to the ground...
-onemanracing.com-
-Strandberg.photography-
GTV 2000 -77 - Died in the fire.
155 V6 Sport -96 - Sold!
Excellent feedback guys and great pics!!
Mats, inline engine stuff doesn't count, we all know we can lighten till it disappears, like a 4cyl setup-no problems! Its the V6 that puzzles us here with its special problems.
Maurizio, when I said front to back I didn't clarify, I meant front flywheel and gearbox flywheel-my mistake. Its there that I think torsional vibrations may arise, due to front/rear mass differences, upon rpm changes. The existence of the driveshaft donuts will also allow small oscillations to take place between the two sections.
I personally would prefer Mats' lightening method which is a tried and tested scheme and thats what I'll try at the machine shop.
Jim K.
Mats, inline engine stuff doesn't count, we all know we can lighten till it disappears, like a 4cyl setup-no problems! Its the V6 that puzzles us here with its special problems.
Maurizio, when I said front to back I didn't clarify, I meant front flywheel and gearbox flywheel-my mistake. Its there that I think torsional vibrations may arise, due to front/rear mass differences, upon rpm changes. The existence of the driveshaft donuts will also allow small oscillations to take place between the two sections.
I personally would prefer Mats' lightening method which is a tried and tested scheme and thats what I'll try at the machine shop.
Jim K.
-
Maurizio
- Verde
- Posts: 680
- Joined: Wed Dec 01, 2004 4:49 am
- Location: the Netherlands, 153.1km from the N'ring :-)
OK Jim,
Yes the engine will rev better.
So imagine a simple mass/spring system hanging on a rotating disk, which will give an amplitude up/down to the spring.
Lowering engine parts inertia will only will enlarge the ampitude, but mass and spring are still the same. So natural frequentie stays the same of the gearbox / drive shaft combo.
So the engine will wind the torsional spring a bit more, but that is all.
This will not give any extra vibrations. Only will wear out the guibo's faster....
But did alfa match the inertia of engine and gearbox?
Gearbox inertia would be something which is extremely difficult and inconsistant. Oil warm/cold, different gears engaged etc.....
The guibo stiffness is also changing a lot through its life.
Yes the engine will rev better.
So imagine a simple mass/spring system hanging on a rotating disk, which will give an amplitude up/down to the spring.
Lowering engine parts inertia will only will enlarge the ampitude, but mass and spring are still the same. So natural frequentie stays the same of the gearbox / drive shaft combo.
So the engine will wind the torsional spring a bit more, but that is all.
This will not give any extra vibrations. Only will wear out the guibo's faster....
But did alfa match the inertia of engine and gearbox?
Gearbox inertia would be something which is extremely difficult and inconsistant. Oil warm/cold, different gears engaged etc.....
The guibo stiffness is also changing a lot through its life.
Banned.. ? Daily donky.. ==> BMW 325d
E36M3 (3.0) Ringtool ==> definitely BANNED!
AR 75 TS Ringtool '90, AR Spider 2000 veloce '79
Daily donky.. ==> BMW 325d E36M3 (3.0) Ringtool
==> definitely BANNED! AR 75 TS Ringtool '90, AR Spider 2000 veloce '79
Hi guys. Like mats has done in skimming(when I first converted to 3.0l 24v) I took 1.1kg off a 2.5 flywheel(skim) and used the 24v pulley (also skimmed). The first time I dId this without stripping the motor as I took 2.5flywheel and pulley to our balance shop and matched it to the counterweights of 3.0l flywheel(not mine) which was already saved in his balancing machine computer and repeated thet process with the pulley. Lucky my old man always got his balancing work saved. However when converting to 3.2GTA -) I obviosly had to balance crank ,flywheel and pulley as a unit as there definitly no info on this saved yet. I also found that new GTA pistons had a variance of 8grams and conrods 3grams.
Ive seen some of of Dawies flywheels have been skimmed to hell but thet was on front mounted gearboxes.
There was not really a major difference of skimming 1.1kgs off but I was going to be rather save then sorry after seen well DRILLED fly wheel come out the side 2.L Bertone GTV door many years ago.
I will ask Dawie next time I see him on what was the most he has teken off flywheels and where as he also raced a modified class 3.0l gtv apart from his team of ''standard'' production 3.0l in the eighties.
Ive seen some of of Dawies flywheels have been skimmed to hell but thet was on front mounted gearboxes.
There was not really a major difference of skimming 1.1kgs off but I was going to be rather save then sorry after seen well DRILLED fly wheel come out the side 2.L Bertone GTV door many years ago.
I will ask Dawie next time I see him on what was the most he has teken off flywheels and where as he also raced a modified class 3.0l gtv apart from his team of ''standard'' production 3.0l in the eighties.