Engine Balancing - Five Cylinder

[FRP]

Greetings from Four Ring Performance Engineering

Finally getting time to talk with all of you through this excellent forum. Thanks, to Hank , Marc and Ed for the invite to share here. I had not been involved with any forums up to this point but I thought this was one worth getting involved with and I really respect the mission of the site and the way the protocols were set up.

I have done just enough reading of this and other sites of late to know that the first area I wanted to help with was on the subject of engine balancing on the five cylinder VAG motors and specifically on the AAN, 3B and 7A. There is obviously a great deal of confusion out there on the subject and most of it seems to center around whether the motors are "internally" or "externally" balanced. I understand how this controversy can exist due to the presence of the big lug inside the front damper on these motors and with the use of weights on the flywheels for same.

Ok. These motors are very much "internally balanced". These motors, and any others, that have a full set of counterweights, that is, a pair of weights opposite of each crank throw, are all internally balanced. Motors with external balancing will be missing several of the internal counterweights and will have huge sizeable weights built into their external dampers and flywheel assemblies.

This is not to say that internally balanced motors never have some kind of adjunct or additional balance weights added to their flywheels or crank damper. And, a great deal of confusion may have been introduced over the years as people have often referred to the crank damper as a "harmonic balancer".
Just remember, when you look at the crank of any engine and see a full set of counterweights on all the rod throws - that motor is internally balanced.

Now, what about the weights on the Audi 5 cylinder flywheels and that big lug on the front damper?
With regard to the flywheels, they are all "zero" balanced in whatever part of the factory makes them and can therefor go onto any engine that they end up with. That is what the welded on weights on the back of the flywheel are for - to get them to zero balance.

Now the bigger question. Is the lug in the damper hub, which engages the holding tool that must be used to torque the damper bolt, part of the Audi 5 cylinder balance scheme? I can't say for certain and it is not for lack of trying to find out! I have never been able to gain access to an VAG engineer to ask him that question! But here is what I strongly suspect: I think it is not and that they just did not care about that amount of weight, that close to the axial centerline of the crank, and, it was just a cost issue with needing to put a very robust lug in there to support the insane torque (525 pounds ft.) required to hold the damper on with essentially zero engagement with the crank nose. I suspect that in the rpm operating range of the stock engine, they just weren't worried about it due to the very robust internal counterweighting and its close proximity the the axial centerline .

I could be wrong on this, it may be an adjunct weight in the balance scheme, but I can tell all of you this: When I developed the dry sump system on the Bonneville car and adapted an Ati Super Damper to the factory crank, the result was near electric motor smoothness from the old I5. And all Ati dampers are, of course, zero balanced. (For those of you interested you can see the damper and hub assembly on the web site - fourringperformance.com).

Now with regard to another area of confusion, mostly regarding just how it is properly done, here is how the crank assembly on these motors is balanced.

First all of the parts in the rotating assembly are individually weighed and the lightest of each is identified, i.e. the lightest piston and lightest rod,( bearing shells and rings not included here). Then the balance tech, through machining or grinding in the appropriate spots, reduces the weight of the other four rods and pistons to match the weight of the lightest down to within about 1/2 to 1/4 gram depending on how particular he is. Pistons are normally machined under the crown and rods ground and polished just above the bolt bosses.

The balance tech then uses a very special type of scale to measure the weight of the piston, pin, clips, rings and the small end of the rod to establish the "reciprocating weight". He then measures the weight of the big end of the rod and the bearing shells to establish the "rotating weight". Next a "balance factor" is assigned. The I5 uses the same balance factor as a V8 which is referred to as "a 1.5 balance factor". What this means is that the bob weights, which are to be placed on the crank throws, will represent the sum of 100 percent of the "rotating weight" and 50 percent of the "reciprocating weight".

All of the pertinent info is entered into the balance machine's software tables which allows the balancer to electronically read and understand where the "imbalances" exist and indicate to the balance tech where to add or remove material from the crank's counterweights. Once the balancer "zeros out" or gets to a really miniscule imbalance (again depending on how picky he is) the process is complete and you are ready to receive the invoice!

Some engine builders will specify different balance factors based on the particular rpm range that the motor runs in. This variation is called "under balancing" or "over balancing". The Bonneville motor is slightly overbalanced to allow it to run even smoother, with less parasitic shaking forces, between 7,000 and 10,000 rpm. It incorporates a 1.52 balance factor. This does cause it to be a little less smooth below about 3,000 rpm and I would not recommend this strategy on a normal street / track motor.

This is just the very basics of a very complicated engineering art. I am certain that on the Audi 5 cylinder, it is a bit of a "black art" where really, really, smart people are able to calculate what are called "dynamic forces" like the "weight" of the compression, power and intake strokes, figure it all into the motor's balance scheme and apply it to "second and third order" harmonics etc. etc. etc.

Hope this helps settle the dust a little on this subject. Next time I will talk about "torsional deflection" in the crank assembly and what the crank damper is really there for.

[EDIGREG]

Fantastic info...glad to finally have that confusion cleared up. Thanks Jeff!

[alxdgr8]

Fantastic info...glad to finally have that confusion cleared up. Thanks Jeff!

+1, can't wait to see the other info you bring to this forum. Thanks for signing up and taking the time to share your knowledge!

[Mcstiff]

Great read, thanks!

[PRA4WX]

Thanks for joining and sharing, Jeff. Greatly appreciated here! I've been keen on your project since hearing about it when i spent a good part of a day at Mike Schowengerdt's shop better than 5 years ago now. Glad to see you have decided to contribute here!

[mushasho]

Very concise info right there...

Would you care to share insight on when balancing becomes more of a need? Do power goals play a factor? Is it rpm range? Where does the stock balance start to show considerable "imbalance?" (for lack of a better word)

Any/All "black magic" info on any of the above would be much appreciated...

TIA

Sent from my HTC One using Tapatalk 2

[loxxrider]

Thanks for posting Jeff. Great info there! I'm looking forward to the damper too as this is just what I've been most interested in lately Welcome!

[Hank]

Welcome Jeff and thanks for the awesome "ingredient" to make this forum more valuable than any other forum for the niche.

Hank

[PRY4SNO]

This is phenomenal info and perfectly timed for me to take my spare block to the machinist.

Highly regarded and appreciated, thanks for taking the time to put that down in laymans terms

Looking forward to more information regarding the crank damper.

[PITTS]

Jeff great read, and congratulations on the achievements of you car!

I am hoping you can clarify for us:

You advised your balance factor is 1.52... was this a figure arrived at by an a fore mentioned dark-arts practitioner through some detail oriented process? Or was this just some ballpark guess based on 2nd hand story trading (some guy knew a guy, who was an Audi engineer back in the day and his cousin said 1.52 was the balance weight all the real cool kids use). Just curious how you arrived at this figure.

Thanks for sharing!

[4v6]

Im currently doing a build for a friend and balancing is in progress for his new internals/crank etc so this is an extremely interesting piece jeff, thanks for that.
I always thought for some reason that the I5 was externally balanced due to being indexed to the flywheel but seems im wrong.
Not complaining none, that makes me very happy indeed.

Thanks again for the in depth info!

Tony.

[mushasho]

Im currently doing a build for a friend and balancing is in progress for his new internals/crank etc so this is an extremely interesting piece jeff, thanks for that.
I always thought for some reason that the I5 was externally balanced due to being indexed to the flywheel but seems im wrong.
Not complaining none, that makes me very happy indeed.

Thanks again for the in depth info!

Tony.

I hear you. It sort of goes against what's been heard before... Clarification would be nice and could possibly be easily resolved by just spinning a stock damper or a stock flywheel to see if they are zero from the manufacturer. Then it would make sense that it's internally balanced.

http://theprojectpad.com/viewtopic.php?p=22580#p22580

Sent from my HTC One using Tapatalk 2

[FRP]

Regarding questions:

Out of balance forces try to deflect the crankshaft perpendicular to the direction of rotation. The magnitude or "weight" of these shaking forces multiply exponentially with rpm i.e. if you double the speed you quadruple the forces. So balancing just becomes more critical as the max rpm of the motor is raised.
Concerning over and under balancing: This is always limited to between 1 and 4 percent plus or minus. And it is trial and error to figure out what a given type of engine "likes" and does not like. I have attended balancing workshops at various motorsports trade shows and been exposed to some really smart people in this field. One particular gentleman who had worked for several OEM's suggested the I5's like between plus and minus 2 percent. I have tried it both ways and was happiest with the 2 percent over balance for extreme sustained high rpm.

[Lord_Verminaard]

Thanks for joining Jeff, it will be fantastic to have a resource like you on the forums!

And thanks also for clarifying the I-5 balance issue and confirming what I have been trying to tell people for a while now. haha.

I would be interested to hear if you have any thoughts on the balancing of a very long-stroke high compression TDI 4-cylinder engine, and if it can benefit much on an engine that even in modified form probably won't hit more than 6,000 rpm. Don't want to hijack this 5-cylinder discussion though.

Thanks again for joining the forums.

Brendan

[85oceanic]

Fantastic stuff Jeff! Glad to see a guy with your kind of experience/expertise joined the board! I love this stuff!!!

[FRCFD5]

Nice to see you on here Jeff

-Rafael

[Derracuda]

Regarding the internal/external balancing comments from the 1st post. I cannot technically say which is true, but I do however have some findings of my own about the extra nub in the damper.

I had my engine balanced about 5 years ago by a well known engine building shop in Sacramento. They balanced it as an internally balanced engine, starting with zero'ing the crank, then so forth. When guy put the damper on, it went WAY out of balance and he had no real explanation. He asked if the engine had a balance shaft, to which i responded no, and then said there must be some counter balancing weight on the water pump or something... those were his words. I had no expertise in the field and had nothing to counter with, so I went with it.... No corrections were made to the damper itself.

My engine never felt particularly smooth IMO. Stock cars felt smoother. I ended up taking the engine down for some other work and had the balance checked by a local shop here in Salem, to whom I explained my previous experience. He found that the front 4 cyl counterweights have depressions cast into them, and the #5 is completely solid. This is where the first guy removed the bulk of materials (turns out about 20grams). His logical conclusion is that it's the counterbalance to the nub in the damper at the front. Once the material was added back to the holes drilled in the #5 counter weight arms, the crank came back into balance with the damper in place. The shop who had now last balanced it found the flywheel to be zero balance, and the crank needs to be balanced with the damper on it. It also required 5grams of adjustment on through the OEM pistons being unequal.

Beyond that, I have no other technical experience or advice regarding the balance and what the engineers did and why, but what my last balancer found and explained sure made a bunch more sense than the first guys "well, there must be a counter weight on the water pump or something". I hope my findings are of some use to you all.

Good article and information above. Thank you for the read!

[GTJeff]

That is interesting information and confirms what I have been told by a couple of machinists; to be safe you should have the entire rotating assembly balanced together whether or not the engine is internally balanced.

Also I researched bobweight percentages when i was rebuilding my Alfa V6. I find it interesting that the bobweight percentage used for many street engines that don't have a balance shaft is 50%. Or it is 51% to 52% if you want to overbalance it for high rpm use. Doesn't matter if it is an Inline 5, VR6, 60 degree Alfa V6, or Chevy 350.

It is a long story but my balancing lesson from my Alfa V6 was to beware of any shop that doesn't wany your flywheel and crank pulley or wants to balance your engine to something other than 50%. Also if your motor was running smoothly before and you get it back from the shop and the machinist had to add or remove a bunch of metal to get it to balance you should probably ask some questions.

[audifreakjim]

Now the bigger question. Is the lug in the damper hub, which engages the holding tool that must be used to torque the damper bolt, part of the Audi 5 cylinder balance scheme? I can't say for certain and it is not for lack of trying to find out! I have never been able to gain access to an VAG engineer to ask him that question! But here is what I strongly suspect: I think it is not and that they just did not care about that amount of weight, that close to the axial centerline of the crank, and, it was just a cost issue with needing to put a very robust lug in there to support the insane torque (525 pounds ft.) required to hold the damper on with essentially zero engagement with the crank nose. I suspect that in the rpm operating range of the stock engine, they just weren't worried about it due to the very robust internal counterweighting and its close proximity the the axial centerline .

I could be wrong on this, it may be an adjunct weight in the balance scheme, but I can tell all of you this: When I developed the dry sump system on the Bonneville car and adapted an Ati Super Damper to the factory crank, the result was near electric motor smoothness from the old I5. And all Ati dampers are, of course, zero balanced. (For those of you interested you can see the damper and hub assembly on the web site - fourringperformance.com).

When I had my 20vt balanced (all internal of course:), my machinist zero balanced the pulley by removing metal from the outer portion. Not surprisingly, opposite of the big nub in the center. So far it has worked great, but I would have preferred they drilled out the nub as much as possible and then finished it off on the outer portion. My concern is that without doing this, you are putting more stress on the rubber that bonds the two pieces.

Some long term thoughts, every time Hank rides in my car, he comments on how smooth the engine is. Also, I have an original 034 crank pulley with the 60-2 ring welded to it, that is still in perfect shape and has not broken at the welds after 40,000 miles. I often wonder why this may be the only one in existence that has not failed, but maybe it's due to the balancing of the crank pulley itself.

[jretal]

Jim, out of curiousity, is there any type of gap between the 60-2 wheel and the outter "dampered" portion of your crank pulley?

My theory for why these fail is that there isn't enough clearance b/n the two (i.e. zero). So assuming the center portion of the crank pulley (where the 60-2 wheel is mounted) is stationary, if there is any deflection what-so-ever in the outter (dampered) portion of the pulley during the RPM range, it starts to push on the 60-2 wheel. This will eventually fatigue it and break whatever is mounting the 60-2 wheel to the pulley. SO if the outter portion of yours was balanced, I wouldn't be surprised if that would be a contributing factor to the life of your welded ring.

I am pretty confident that this is why my "improved design" 034 60-2 wheel failed on my 4000 after less than 250 miles (while at a track event). While the crank pulley is brand spanking new (fresh rubber, etc), there is still deflection in the outter portion of the pulley due to high RPMs and driving accessories (for me P/S and alternator). When inspecting the pulley after it sheered 5 of 6 bolts, it was evident that there is no gap b/n the 60-2 wheel and the outter portion of the crank pulley.

I had asked Nate if they designed in a gap, but he never responded to me about that. If I would have realized it, I probably would have had the machinist turn the outter portion of the pulley down a thousandth or so to give more room for deflection, in addition to drilling/tapping bigger holes for larger hardware.

[Derracuda]

Just thinking aloud here. Justin, could it be the opposite of what you are explaining, that the failure is due to the overall diameter of the trigger wheel, and that the crank resonance is causing the screws to fail since they are not on the rubber damped portion of the pulley? Obviously we know that having the trigger on the damper portion can cause an erred signal, but I don't think the outer ring of the damper "vibrates" so to speak.

[audifreakjim]

I vote for not polluting this thread, I didn't intend for this to turn into a trigger ring failure discussion

[morris400]

Just read through Jeffs post, first off thank you for this information. Iam sure ill be reading through this again soon.

Im going to be building an AAN this year (2020) in hopes of either putting it in a Coupe im picking up or maybe in my UrS. My plan is to get the engine balanced and bored to 83mm with Wiseco pistons and forged rods. Also using a fluid damper if that changes things.

Im fully expecting to have to used the information here to assist the machine shop cause i doubt they do many, if any I5 Audi engines.