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Engine Balancing stuff I found all over

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 Post subject: Engine Balancing stuff I found all over
PostPosted: Fri May 27, 2011 10:06 pm 
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Ok, I have been doing a lot of research on engine balancning, particularly the Audi 5 cylinder we love so much. Anyways, there dont seem to be many places the have much info, at least in one place. This all started out with one of Darins motors. I had a guy balance his motor. He has been balancing motors for close to 50 years. He has probably forgotten more about balancing than I have been able to learn. So, here goes, everything that I have found out.

The 5 cylinder motor is externally balanced, which means that the flywheel and harmonic balancer are both counterweighted to provide a smooth balanced engine. Anyways, the 7A flywheel is not balanced correctly for a 3B or AAN motor, also, I have a JB racing flywheel that I got used. I installed it when I put my 6 spd 01E in, and while the balance is better, it is still off. I have a talk with Jim Green at battle born quattros concerning Balance and he told me he had had his flywheel zero-balanced, which as it turns out is what JB racing said they did when I talked to the tech support. i asked him if they had any data to back up the zero balance on the flywheel and they said that they had just coppied the one that they used for design. Anyways, as it turns out, there is definatly a counter balance on the original flywheel. I had a special fixture made by one of my buddies to mount the flywheel to the balancing machine, so I will be able to custom balance flywheels for the AAN/3B, while it may not be the same as getting a complete balance job, but it will be pretty darn close and much better than a zero balance.
Now, going on, the front crank balancer it counterweighted as well. We spun up a MC balancer, and a stock AAN pulley, they are pretty close, much closer than the flywheels. So, after we get a little more done with the balancing, we should be able to come up with what will together. I also have a 7A balancer that I plan on checking out as well.
Now on to theory. In general, most in-line motors dont require bob wieghts. Bobweights are a mock up of the amount of reciprocating and rotating mass comprised of the pistons, rings, rods, bearings and the film of oil coating the parts. Generally you use 100% of rotating weight and 50% of reciprocating mass. Rotating mass is all of the big end of the rod, bearings and a portion of the shaft of the rod. The piston, little end of the rods, rings and of course all the oil sticking to the components. Generaly, you weigh the rods entirely and then support the little end of the rod while weighing the big end. You take all of these weights, and calculate the amount of weight needed to be placed on the crank throws. Now, in general, the wieghts will only increase the mas, without changing the balance, but apparently it affects the harmonics of the assembly during balance. I am not totally sure why the bobweights are needed for the five, while they are not needed for any other inline, I would suspect that it is because none of the throws are opposite of each other. All "V" motors require bobweights in order to be properly balance. Generally, harmonic vibrations occure sinsoidaly, this means that the amount of energy in a vibration raises and lowers, when the peaks are near the base line, there is not much of a vibration, but when the sine wave comes closer to the peaks, i.e. perceptible vibration, there is much more energy available to cause the vibrations. As a rule, generally, the peaks occure in squares. If the motor shakes at 2000 rpm, it will shake again around 4000 rpm, and luckilly 16000 rpm, which is well above anything we will ever see.
Now, sometimes, in order to balance components, a very heavy alloy called mallory is added to the items. The mallory is heavier than the steel and can help bring things closer to the correct balance. Other times, material needs to be removed. This can be done by drill, milling or grinding material off of the item. When a motor is balance, all of the rods and pistons are weight and the lightest part turns out the be the one everything is matched to. Much easier to lighten a part than to add weight. Between matching components, and balancing the rotating assembly, that is pretty much how balancing is done.

Now, there are other things that come into play as well, which is where experiance comes in. Also, much more expensive machinery to meassure vibrations. The primary vibration is what is usally called first order harmonic, once you get into things, there are sencond, third and so forth orders of harmonic vibration. These can be much hard to get rid of. One way to explain this is related to wheel balancing.
During wheel balance, you can balance statically, meaning weights only on on side of the wheel, the second way is dynamically, where you install weights on two planes, inside edge and outer edge. This is a better balance, but there is more involved than just balancing the tire. When the wheel and tire are mounted up, there is generally a high spot on the tire and a high spot on the wheel, when these aren't positioned correctly, you can get run-out, which can cause vibrations. Now, generally, a tire that is out of balance would be a first order harmonic, and the run-out can cause a vibration as well, this as I understand it would be called second order, and I believe that an interaction between the two can also cause a third order harmonic vibration.
Anyways, this is how I understand it, and I hope that maybe it helps some other people understand this as well. If you find me in error, please correct my ignorance.

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Fri May 27, 2011 10:40 pm 
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So, you are saying 0 balancing each component separately is better than nothing but not a truly balanced 5cyl?

Also since I have never paid to have a motor balanced, what is a ballpark cost?

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Fri May 27, 2011 11:17 pm 
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Brent, Interesting that you too have been chasing this balance thing. You are absolutely right in that there isn't much info readily available out there. Guys that could balance a small block 350 in their sleep kind of just look at you funny when you talk an I5. In my experience the first thing that comes up is whether bob weights are needed and then of course when they come to the realization that yes bobs will have to be made up, the question of what percentage of the reciprocating weight needs to be taken into account.

A few things that I have learned in the last little bit, but I have yet to test the results are these.

1. Audi I5's are externally balanced motors. The AAN is the easiest to see this on the flywheel as it has welded on weights. The damper/pully is also weighted by drill holes and in the case of older engines the blob for the rotation holder tool. These dampers have holes drilled also to take some of the weight of the blob away.

2. Scat rods are ~45gr. lighter than stock AAN rods.

3. Obviously aftermarket pistons will be lighter than the stock pistons.

4. When spinning an AAN crank without bobs it spun within .5 gr. of balanced. One end was perfect and the front was off .5 gr. Not bad.

What we ended up doing is spinning the rotating assembly with stock damper and flywheel and making up bobs to get it in balance. With this infomation it was determined that the reciprocating weight would be figured in at 37%. With Stock pistons and Scat rods we ended up adding a 28gr. weight (by drilling three holes on the opposite outside) to the aluminum Fidenza flywheel and using a 7A damper/pulley which added another 50gr. The 50gr. in front is an inch or two from the center of rotation and the 28gr. on the rear is out the radius of the the flywheel from the center of rotation.

I'm at work now so I don't have pictures or numbers, but maybe can post something later. I intend to take my stroker rotating assembly to this guy and recheck it. It supposedly is zero balance internally and I was told by a different outfit that they had to take weight off of the crank counterbalancers. I can believe this as the the 92.8mm crank was out of an industrial engine and diesel I believe. If that was the case, going from big clunker diesel pistons and rods to after market pauter rods and wiseco pistons would explain it. I still want to see if it is indeed internally balanced now. The proof is in the pudding however and I have yet to run either motor. :frustrated: :oops:

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Sat May 28, 2011 8:48 am 
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Cool into, someday I'll need to know.

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Sat May 28, 2011 12:39 pm 
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It is easy to remove material to balance but not always as easy to add material. 52 grams is only about 2 onces, and isn't too much energy 1-2 inches off rotation, but 23 grams about an onces 6-7 inches off center of rotation can make quite a bit of centrifical force. I cant wait to get mie smoothef out again.. I am about ready to put the big ass dual mass back in just to smooth it out.

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Sat May 28, 2011 3:15 pm 
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Brent, John you guys really did your homework and are right on the money.


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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Sat May 28, 2011 6:23 pm 
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why dont you guys just add a heavier material so it takes up less physical space to balance? if you cannot remove material for whatever reason, lead is cheaply available, if you want denser then snaggle up some tungsten. its not impossible.

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Sat May 28, 2011 6:57 pm 
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Mallory is the choice material for balancing. Here is a link to the datasheet if you want to read about it. It is a blend of tungston and several other metals, generally copper and silver that is formed as a powder and sintered together. It is denser than lead with compairable strenghs to steel.
http://www.mallory.com/datasheets/1300501.htm

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Sat May 28, 2011 7:20 pm 
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Like Repaair stated in another balance thread, there isn't anything wrong with an external balance. I would rather have an internal balanced motor so that if dampers, flywheels etc have to be changed the motor doesn't have to come apart to rebalance. That is also why data is saved (blueprint) so that the flywheel or whatever needs to be changed can just be match balanced and installed. When we balanced my AAN, when it was all said and done the only thing that was needed was three holes drilled in the outside edge of the Fidenza flywheel to take out 28gr. of weight. I have the feeling that the AAN and 7A damper/pulleys are pretty close to the same, but I wanted a vbelt setup so I opted for the 7A setup. We spun the assembly with it on the front and came up with the 28gr. for the rear on the flywheel.

The extra time and effort of drilling and inserting either mallory, lead, or tungsten into the crank counter weights just wasn't worth it to me. As it is I think with the same internals.....stock AAN pistons, Scat rods, 7A damper and the fidenza flywheel, I think that I could drill the same diameter holes the same depth at the same orientation in the flywheel and come up with a pretty closely balanced motor. I will be interested to see if the stroker assembly, made up with 100% rotating +37% reciprocating bobs, will internally zero balance. I'm hoping so and was told that was the case.

This guy that I use now spent a few years working the circuit with a top fueler drag team doing nothing but their heads and valve train work. He is pretty sharp and now runs a business out of a back yard shop. The first time I went and talked to him about balance work I had a set of valves that I wanted to face. I asked him about them and he pointed to the Sioux valve grinding machine and asked if I could run it since he was busy at the moment. LOL The point being is that instead of being told what was done I went over to his shop and helped balance my motor.

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Sat May 28, 2011 9:17 pm 
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I think that you are on the right track John. My best guess would perfectly agree with yours. there is a lot to it I would guess that Audi knows it best. what else could one do other than, go as light as possible, balance like Audi did, but be extra precise?

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Sat May 28, 2011 9:41 pm 
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I got an AAN automatic. How it this motor balanced? Just with the damper in the front? There seems to be more vibration lately.
I don't want to have to rebuild the motor. How can I check if the damper is still OK?

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Sat May 28, 2011 10:29 pm 
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Don't think you will see much difference with the balancer, unless parts have been changed you might want to look to other things. Maybe motor mounts and trans mounts.

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87 turbo 2L 16V Scirocco 13.2 @115 street tires
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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Sun May 29, 2011 12:27 am 
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savagerocco wrote:
Don't think you will see much difference with the balancer, unless parts have been changed you might want to look to other things. Maybe motor mounts and trans mounts.

Now that I think of it, I think I got the poly snubber mount installed last time at the shop... :roll:

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Tue Aug 02, 2011 7:19 am 
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Brent... any updates on this? Are you set up to balance FWs now?

At some point I'm going to be yanking the AAN out of my 4KQ and putting it into an 80 I just bought. It currently has a 3B (200) flywheel on it, and as I understand it I need to switch to a 7A FW to make it work with the 01A in the 80. Sounds like I should be getting that 7A FW specially balanced before using it with the AAN? The AAN has all stock internals.

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Tue Aug 02, 2011 9:01 am 
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elaw wrote:
Brent... any updates on this? Are you set up to balance FWs now?

At some point I'm going to be yanking the AAN out of my 4KQ and putting it into an 80 I just bought. It currently has a 3B (200) flywheel on it, and as I understand it I need to switch to a 7A FW to make it work with the 01A in the 80. Sounds like I should be getting that 7A FW specially balanced before using it with the AAN? The AAN has all stock internals.

jstu swap the clutch disc and itll work, pilot size differences

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Tue Aug 02, 2011 9:43 am 
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Yeah I've bought a lightly-used 7A PP and disc from someone but it hasn't shown up yet. One thing I'm surprised doesn't get discussed more is seemingly not all 7A discs are created equal. Seems that some are 228mm and others are 240mm (according to ETKA, the 90 20V has the smaller disc and CQ has the larger). I wonder if that's why some people using turbos have better luck than others?

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Mon May 18, 2020 11:37 am 
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Sorry for diggin this old topic. But i have stroker crankshaft,aftemarket rods, pistons, 7A flywheel and damper from 7A and 707 pressure plate. I know a guy which could balance me this parts but without bob weights. I am building stroker (diesel block) engine so almost every part is from different engine (flywheel,damper, crank). Is it worth this balancing?

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 Post subject: Re: Engine Balancing stuff I found all over
PostPosted: Mon May 18, 2020 4:03 pm 
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try this: the project pad.com/viewtopic.php?f=32&t=325" onclick="window.open(this.href);return false;

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