Balancing

N2BRK

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Dec 31, 2009
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Hopefully you guys can educate me a bit with regards to balancing a “built engine” Duramax.

My buddy finally got his build back and it shakes like a f’ing paint mixer.

Build:
Fingers pistons were purchased balanced, the rods were purchased balanced, and the machine shop was supposed to balance the entire rotating assembly. We assumed that he would need to buy a neutral balanced harmonic damper and not reuse his stock replacement fluidampr.

We went back to the machine shop last night to show how bad it is, and the owner said that he balanced everything to within 1 gram, by removing weight from the existing fluidampr. Huh?!?! I’m ignorant to building these engines, but that did not make sense to me.

30 seconds later I googled on my phone straight from fluidampr that you cannot balance an engine with a fluidampr installed because of the movement of the inner ring not being adequately deflected in a balancer that way that a running engine will.

Shop wants to have the truck for a few days to remove connection to trans and to try a stock harmonic balancer. The idea of disconnecting the trans makes sense if they are trying to claim it’s not the engine. But wtf would they want a stock balancer?!

So long story short - is it
Normal practice to balance a built Duramax externally instead of internally when requesting engine balancing? Does their admission of improperly balancing with the fluidampr mean that it’s now mandatory to tear down the engine and rebalance the rotating assembly? If yes, should it be internally balanced or is that not normal for a Duramax build?

Small words and hand holding are always appreciated. Lmao.

Thanks,
Wally
 
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Chevy1925

don't know sh!t about IFS
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Balancing the rotating assembly is general terminology compared to externally or internally balancing the engine.

All Dmax engines come externally balanced meaning the counterweight if the pistons/rods/wrist pins/rod journals/etc are not solely counter weighted by the fly weights off the crank, instead there is off center weight added to the balancer and fly wheel/flex plate on the same side as the crank fly weights to create the balance. Hence why machine shops need both the fly wheel/flex plate and balancer.

Internally balancing means you ditched the balancer and fly wheel/flex plate weight to counter act and drill the fly weights of the crank shaft to accept heavy metals like Mallory or tungsten so the fly weights match the rods/pistons/wrist pins/rod journals/etc weight as its slung around.

Balancing a rotating assembly is just that, you are balancing it but you didn’t specify which type? Most people that ask for that mean they just want it balanced to the stock configuration (external or internal). In either case of balancing, machine shops go further in the fact that they will find the lightest piston, then match the rest of the pistons to it by weight removal (piston, wrist pin and rings together), same with the small end of the rods and the big end of the rods. This helps make sure all 8 cylinders are seeing the same weight thrown around and makes the actual balancing of the rotating assemble easier. Also now gives the machinist the bob weights needed to balance the crank.

They should have used a good stock style balancer up front for balancing and then put the other on after all assembled. If he drilled the dampener, I fear he may have ruined it. Putting the stock one on will tell right away.

They shouldn’t have to touch the dampener as far as drilling it with a stock crank. They don’t have enough weight in the fly weights. Now if it was a Callie’s ultra billet or SoCal diesel or any other heavier billet crank, that’s where you can get creative in fly wheel/flex plate and damper drilling but then those are matched solely to that crank. Other wise you are drilling the crank fly weights or converting to internally balanced.

As far as which way you should go if they have to redo it, it’s up to you. Externally and internally balanced last close to the same with a little edge to internally balanced imho on stock cranks because it’s not addressing the real issue but it instead taking weight off the snout of the crank.
 
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N2BRK

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Thanks, James! It was his stock LMM crank that was keyed and re-used.

So if I’m reading this right, if they wanted to stay externally balanced, they should have put on a stock balancer and left the damper alone as they drilled/filled the crank as needed.

If they swap to the stock balancer now, it should balance pretty much the same as his engine was before the work; maybe a little better since it now has matched pistons and rods.

Assuming that slapping the stock balancer on makes a marked improvement, I guess the choice is to leave it or have them tear it down just to re-balance.

I’ll opine they took a lazy way out that would have worked on a stock balancer, instead of drill/fill on the crank itself. But because they hogged out the fluidampr it didn’t work. Funny since they are a fluidampr dealer and should have known better.
 

56taskforce

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Mar 30, 2014
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Your first step is to find our what was actually done... if it was being externally balanced and neutral balance damper and flex plate installed the assembly would be way out of balance. Note: you can buy the dampers with or without counter weight whether it's an elastomer or fluid damper does not make the difference.
Internally balancing a Duramax is quite expensive, as there is not enough room within the confines of the block for counter weights big enough without the use of very heavy and expensive metals such as Mallory.
Find out what exactly was being done in the balancing of this motor that is your fist step. My guess is the motor is externally balanced and you have installed a neutral balance damper and flex plate.
 

N2BRK

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The engine was externally balanced. He did not touch the crank. The flexplate was a Suncoast and I do not know what he did with that. He said that he balanced by cutting weight off the Fluidampr (regular That Chris was running on the stock engine, they did not use a neutral balanced fluidampr).
 

N2BRK

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Also, ASSuming the shop tears it down to rebalance, what would be a reasonable up-charge to internally balance? We were under the assumption he was doing that from the get-go until he said he hogged out weight on the fluidampr instead.

Thanks
 

Chevy1925

don't know sh!t about IFS
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You still drill or add weight the cranks fly weights when doing a rotating assembly balance. I would not drill the damper/flex plate. It’s a better practice. My case was difference as we are talking a 10lbs heavier crank than stock.

You need to first ask if the shop can do it. Everyone’s rates are different. I’d say 1k-2k. The material isn’t cheap either.

Personally I’d rather sink that money into an internallly balanced SoCal or Callie’s billet with narrowed rod journals.
 

Ne-max

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What crank, damper and flexplate did you use? Lbz/lmm are way different from lb7/lly/lml.
I would find a new machine shop. Do not suggest taking weight off the damper or flexplate if not needed.
Whats your power goal? I would not do a internal balance for anything under 1200hp. Or even use a compstar or stock crank at that point.
 

56taskforce

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I am a little confused as to why counter weight would be removed from the balancer??? I am relatively sure the Figures pistons are heavier than stock especially if the pins aren't ground meaning it is more likely weight needed to be added to counter weights not subtracted. The reason I asked about the neutral balance damper is you stated in your original post that you thought you would need one. Did the machinist have the weight of the piston and rod assemblies and know the operating rpm? This is information needed to choose the weigh of bob weights used.
 

N2BRK

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Stock LMM crank. Flexplate is Suncoast. Damper we thought would be neutral since we thought it was going to be internally balanced. Pistons are Fingers cast. Rods are Carrillo (I think). Goals are for now are max out 68stg2r and then after saving up more money it will be to compound with S485. This is a semi daily driver, so nothing will be max effort so to speak.

Given the above, are you recommending that my friend has them tear down and balance with a stock balancer, adjusting weight with crank and flexplate, or what?

Thanks!!
 

N2BRK

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We thought he’d need a neutral balanced damper because we thought that the machine shop was doing an internally balanced build. The shop got everything - engine, pistons, etc - they did all of the work and they assembled the engine. Why they hogged the balancer is unknown to me, but I’m no expert - hence why I’m asking advice :) It sounds like it was a cheap way to balance instead of drilling or filling the crank, but fluidampr says you cannot do this with their damper and the paint mixer idle backs that up! The question is now wtf.
 

56taskforce

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I guess make the discussion if you trust him enough to fix it or find someone else. Not an easy one to figure out. Many machine shops require they choose and purchase from their own suppliers as they are familiar with those parts. If you bring the parts they may not give a complete warranty. I am in the middle of a build and can't find a local shop that I trust and or will even do a performance deisel. It is looking like I will be shipping all down to SoCal for machine work where most of it came from. I hate having to bite the bullet and pay to ship it around the country but it is looking like my best option.
 

N2BRK

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The shop came highly recommended by a local shop, and they have built many engines for Duramax sled pull trucks in the area. This should have been routine for them.
 
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KyleC4

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If the machine shop is that good i would just work it out with them. Talking it all over as to what exactly was performed and the light bulb should go off for the machine shop as to what the culprit is. If they didn’t touch crank at all, don’t know why they would think they needed to remove material from balancer. But I’m curious as to what they’ll find or say
 

56taskforce

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Mar 30, 2014
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The shop came highly recommended by a local shop, and they have built many engines for Duramax sled pull trucks in the area. This should have been routine for them.
Sounds like the situation should be able to be resolved, good luck.
I hope I can find a good local machine shop to do Duramax work.
 

N2BRK

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I hope so. The other side of me says that lots of guys are in business for many many years... doing shit wrong. I hope it all works out. I’m betting they wind up rebalancing the engine by putting on a stock balancer and starting over.

I thought about the removing weight on the balancer, and a fluidampr is much heavier than a stock damper, so maybe that’s why they hogged it out. I think this is going to be an expensive lesson for them on how not to use a fluidampr for balancing.
 

Ne-max

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I dont think you understand how balancing a engine works. Your machine shop should have a balancing machine. They will mount your crank, damper, and flexplate. Then add weights to resemble your rods, bearings, pistons. It shows them where to remove or add weight.... soo if yours is that bad they should havr noticed it before assembly.

External balance. They use stock style damper and flexplate. Then take away material or add material to crank itself. Leaves more spinning mass at the end of the crank.

Internal balance. They use zero balanced damper and flexplate. Then turn around and add weight to crank to balance it out. Its expensive but the best way to do it.

You MUST match your damper to flexplate when doing this. Can't use a zero balance damper with regular style flexplate. Also knowing the difference betweem lb7/lly to lbz/lmm/lml is huge.

Take it to another machine shop if they dont know this.
 

N2BRK

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Thanks, but I understand. Respectfully, I think that you don’t understand what they did. Correct me if I’m mistaken.

They used a fluidampr when they balanced. You cannot use a fluidampr when balancing, according to fluidampr themselves. The forces on the balance machine are not enough to mimic a running engine, and fluidampr acts differently on a running engine. They also cut weight off the fluidampr to balance. When we talked about drilling/filling the crank, all they said was they cut material off the fluidampr to balance - they never said they touched the crank. It seemed like they did not, but I didn’t press for an answer on that because we already established the mistake made.
 

Ne-max

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Thanks, but I understand. Respectfully, I think that you don’t understand what they did. Correct me if I’m mistaken.

They used a fluidampr when they balanced. You cannot use a fluidampr when balancing, according to fluidampr themselves. The forces on the balance machine are not enough to mimic a running engine, and fluidampr acts differently on a running engine. They also cut weight off the fluidampr to balance. When we talked about drilling/filling the crank, all they said was they cut material off the fluidampr to balance - they never said they touched the crank. It seemed like they did not, but I didn’t press for an answer on that because we already established the mistake made.
Ok. I guess I misread your initial post saying you got a neutral balanced balancer. As long as you did not use it then it makes sense.
 
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