Engine balancing

[xb-60]

Could I draw on the forum’s experience again for explanations on engine balancing terminology and processes?

For example, what does balanced to 28oz mean when describing an engine?
How does this affect clutch choice?
Also what is external balancing?
How does a harmonic balancer work?
What items are subjected to internal balancing? And is this balancing static or dynamic?
Is material typically added (weights) or removed?
Do flywheels need to be balanced?
Do clutches need to be balanced?
I assume gearboxes, as supplied, don’t need balancing unless it’s for all-out racing applications?
Do tailshafts normally need balancing?
At what rpm point does extensive/comprehensive balancing become essential?
Does extensive/comprehensive balancing affect engine life significantly?

I understand the common-sense logic of balancing rotating and reciprocating components, but apart from simple static balancing, I don’t know how it’s accomplished.

Advice or input on any or all is much appreciated. Thanks.

Cheers,
Glen

[patrickt]

Glen, I think you asked too many questions in one single post. That said, if none of the real engine builders give you a detailed response, then I'll tell you the story of my 428 build, that started out life as an externally balanced engine with a goofy flywheel from the Ford factory, many, many, years ago. Then, almost 50 years later, a stork would drop my new bundle of joy on the doorstep and it was now an internally balanced FE of 447 cubes. The harmonic balancer, unfortunately, stayed the same (maybe that's why it spun apart). Hopefully blykins, barry, or keith will give you an experts post and you won't have to rely on an enthusiastic hobbyist and his story (that has absolutely nothing to do with a small block anyway).

[xb-60]

Originally Posted by patrickt

Glen, I think you asked too many questions in one single post. That said, if none of the real engine builders give you a detailed response, then I'll tell you the story of my 428 build, that started out life as an externally balanced engine with a goofy flywheel from the Ford factory, many, many, years ago. Then, almost 50 years later, a stork would drop my new bundle of joy on the doorstep and it was now an internally balanced FE of 447 cubes. The harmonic balancer, unfortunately, stayed the same (maybe that's why it spun apart). Hopefully blykins, barry, or keith will give you an experts post and you won't have to rely on an enthusiastic hobbyist and his story (that has absolutely nothing to do with a small block anyway).

Too many questions? Maybe Pat, but there's too much I don't know....
Looks likely further down the list there's detailed expert responses a comin', but this forum is about the stories as well as the detailed, reasoned, analytical responses, so don't hang back, buddy!
Cheers,
Glen

[bobcowan]

Most SBF's are externally balanced. Meaning that the extyra weight is added to the blancer AND the flywheel. Early engines add 28oz to balancer and flywheel; later engines use 50oz.

Some custom engines will be internally balanced. And then the harmonic balancer and flywheel do not have weights attached. Internally balanced engines add Mallory metal to the crank throws if needed, or metal is drileld out of the crank throws.

Balancer and flywheel weights need to match the crank.

The crank is balanced dynamically - spinning. Bob weights are usually attached to the crank throws to simulate the weight of the reciprocating assembly.

Clutches and transmissions are generally not balanced, except in extreme rpm applications.

Any time the engine is tressed - regardless of rpm - then balancing becomes more important. It's a time consuming and tedious process, but worth the effort for racing.

[blykins]

Q: For example, what does balanced to 28oz mean when describing an engine?
A: It means that the engine uses a 28oz imbalance (externally balanced). This typically means that the harmonic balancer and flywheel/flexplate are 28oz items.

Q:How does this affect clutch choice?
A: It doesn't. However, some guys want to have the pressure plate balanced with their rotating assembly as an option.

Q: Also what is external balancing?
A: An externally balanced engine uses a weighted harmonic balancer and/or flywheel to keep the engine in balance.

Q: How does a harmonic balancer work?
A: It uses different materials, such as rubber, fluid, polymers, etc. to help eliminate the vibration harmonics out of an engine.

Q: What items are subjected to internal balancing? And is this balancing static or dynamic?
A: Everytime you balance a rotating assembly, it's dynamic. Go to YouTube and look for some rotating assembly balancing videos. The crankshaft is placed in a balancer and spun up to rpm. There are bobweights bolted to each rod journal which simulate the weights of the pistons/rings/rod bearings/rods/parasitic oil, etc.

Q: Is material typically added (weights) or removed?
A: It depends on which setup you have. You can do it either way, although the crankshaft manufacturer will design the counterweights on the crankshaft so that a target bobweight will be used.

Q: Do flywheels need to be balanced?
A: Not typically. They come from the manufacturer intended for a specific application.

Q: Do clutches need to be balanced?
A: The pressure plates are balanced from the manufacturers, but I have seen a few that need to be installed in a certain position to be perfectly balanced. You always balance the pressure plate only as a clutch disc is a consumable item.

Q: Do tailshafts normally need balancing?
A: If you're talking about a driveshaft, then yes.....always.

Q: At what rpm point does extensive/comprehensive balancing become essential?
A: There's really not an "extensive" balancing. It's either balanced or it's not balanced.

[xb-60]

Reworded questions...

For example, what does balanced to 28oz mean when describing an engine?
A: It means that the engine uses a 28oz imbalance (externally balanced). This typically means that the harmonic balancer and flywheel/flexplate are 28oz items.
Re-Q: But what do you mean, that the h-b and flywheel/flexplate are 28oz items? And the engine uses a 28oz imbalance? You know me Brent, I'm slow on the uptake.

Q:How does this affect clutch choice?
A: It doesn't. However, some guys want to have the pressure plate balanced with their rotating assembly as an option.
Re-Q: I can't find the email, but I thought you asked me awhile ago what engine imbalance for a particular flywheel or clutch selection?

Q: Also what is external balancing?
A: An externally balanced engine uses a weighted harmonic balancer and/or flywheel to keep the engine in balance.
Re-Q: I take it this is the quick,cheap version of engine balancing. Is this static or dynamic?

Q: How does a harmonic balancer work?
A: It uses different materials, such as rubber, fluid, polymers, etc. to help eliminate the vibration harmonics out of an engine.
Re-Q: Does an engine that is internally balanced have/require a h-b as well?

Q: What items are subjected to internal balancing? And is this balancing static or dynamic?
A: Everytime you balance a rotating assembly, it's dynamic. Go to YouTube and look for some rotating assembly balancing videos. The crankshaft is placed in a balancer and spun up to rpm. There are bobweights bolted to each rod journal which simulate the weights of the pistons/rings/rod bearings/rods/parasitic oil, etc.
Re-Q: Excuse my ignorance, but is the rotating assembly just the crank, or is it the crank/rods/pistons assembly?

Q: Is material typically added (weights) or removed?
A: It depends on which setup you have. You can do it either way, although the crankshaft manufacturer will design the counterweights on the crankshaft so that a target bobweight will be used.
Re-Q: Does the crank manufacturer (say, Scat?) balance his cranks, or does he leave that for the engine man?


Q: Do tailshafts normally need balancing?
A: If you're talking about a driveshaft, then yes.....always.
RE-Q: Halfshafts too?

Q: At what rpm point does extensive/comprehensive balancing become essential?
A: There's really not an "extensive" balancing. It's either balanced or it's not balanced.
Re-Q: OK...is there a a rpm level at which it is advisable to have the crank and rods and pistons all dynamically balanced?

Apologies if this is tedious going, but there'a a lot here that I understand a little, and don't understand a lot. Thanks for the time spent in replying. It's appreciated.
Cheers,
Glen

[blykins]

[quote=xb-60;1165098]Reworded questions...

For example, what does balanced to 28oz mean when describing an engine?
A: It means that the engine uses a 28oz imbalance (externally balanced). This typically means that the harmonic balancer and flywheel/flexplate are 28oz items.
Re-Q: But what do you mean, that the h-b and flywheel/flexplate are 28oz items? And the engine uses a 28oz imbalance? You know me Brent, I'm slow on the uptake.

The pieces don't weight 28oz; they have that much imbalance in them. They have a weight either bolted or welded to them, clocked at a particular spot that makes them out of balance.

Q:How does this affect clutch choice?
A: It doesn't. However, some guys want to have the pressure plate balanced with their rotating assembly as an option.
Re-Q: I can't find the email, but I thought you asked me awhile ago what engine imbalance for a particular flywheel or clutch selection?

Flywheels are categorized by imbalance...0, 28, 50, etc. Flywheels matter, but pressure plates are not rated that way.

Q: Also what is external balancing?
A: An externally balanced engine uses a weighted harmonic balancer and/or flywheel to keep the engine in balance.
Re-Q: I take it this is the quick,cheap version of engine balancing. Is this static or dynamic?

It's often easier because you usually don't have to add metal to the crankshaft. Always dynamic. Always.

Q: How does a harmonic balancer work?
A: It uses different materials, such as rubber, fluid, polymers, etc. to help eliminate the vibration harmonics out of an engine.
Re-Q: Does an engine that is internally balanced have/require a h-b as well?

Yes.


Q: What items are subjected to internal balancing? And is this balancing static or dynamic?
A: Everytime you balance a rotating assembly, it's dynamic. Go to YouTube and look for some rotating assembly balancing videos. The crankshaft is placed in a balancer and spun up to rpm. There are bobweights bolted to each rod journal which simulate the weights of the pistons/rings/rod bearings/rods/parasitic oil, etc.
Re-Q: Excuse my ignorance, but is the rotating assembly just the crank, or is it the crank/rods/pistons assembly?

Everything that rotates or reciprocates. This includes the crankshaft, rods, pistons, rod bearings, piston rings, piston locks, etc.

Q: Is material typically added (weights) or removed?
A: It depends on which setup you have. You can do it either way, although the crankshaft manufacturer will design the counterweights on the crankshaft so that a target bobweight will be used.
Re-Q: Does the crank manufacturer (say, Scat?) balance his cranks, or does he leave that for the engine man?

He has no way of knowing which rods, pistons, etc. that are going to be used. They are designed for a target "bobweight." For instance, a crankshaft is designed to be internally balanced with an 1800 gram bobweight. If the weight of your pistons/rods/rings/bearings,etc. weigh more than that, then you will need to add metal to the crankshaft to keep it balanced. If your bobweight is lighter, then you can likely get away with removing metal from the crankshaft.

Q: Do tailshafts normally need balancing?
A: If you're talking about a driveshaft, then yes.....always.
RE-Q: Halfshafts too?

I would, yes.

Q: At what rpm point does extensive/comprehensive balancing become essential?
A: There's really not an "extensive" balancing. It's either balanced or it's not balanced.
Re-Q: OK...is there a a rpm level at which it is advisable to have the crank and rods and pistons all dynamically balanced?

Read Keith's explanation above....he did a good job of explaining this part.

Before you ask any more questions, you need to watch a video or two on YouTube about it. It will clear up a lot of things you're having trouble with. You need to forget the static/dynamic questions as it's all dynamic. You don't balance a rotating assembly by just letting it sit there. It's all spun at rpm.

[xb-60]

Originally Posted by blykins

....Before you ask any more questions, you need to watch a video or two on YouTube about it. It will clear up a lot of things you're having trouble with....

Thanks Brent. It's a steep learning curve, and I appreciate all the replies.
I've seen some videos, but they have been the results of out-of-balance, not "how-to", and "why?" I'll look some more.
Cheers,
Glen

[blykins]

Step by step.....

The Balancing Process from Coast High Performance - YouTube

[madmaxx]

I thought the harmonic balancer was to counteract the torsional elasticiy of the crankshaft under load.

[blykins]

Originally Posted by madmaxx

I thought the harmonic balancer was to counteract the torsional elasticiy of the crankshaft under load.

What you said = what I said. Except you just used bigger words.

[madmaxx]

No, you said vibrations, I meant when the cylinder opposite of the other end fires the crank "twist" and the harmonic balancer helps resist this twisting. I dont think it balances anything it is more of a gyroscope.

Originally Posted by blykins

What you said = what I said. Except you just used bigger words.

[Jerry Clayton]

Here are some pics of part of the process of balancing a 3.250 Callies crank for a twin turbo charged small block ford

[Jerry Clayton]

The next group of 5 pics

[blykins]

Originally Posted by madmaxx

No, you said vibrations, I meant when the cylinder opposite of the other end fires the crank "twist" and the harmonic balancer helps resist this twisting. I dont think it balances anything it is more of a gyroscope.

No, I said harmonics. Actually I said vibration harmonics, which is really a redundant phrase....but I digress.

It's a damper. Harmonic damper. Whatever you want to call it, it's a shock absorber for harmonics in the engine.

It's easy to do a Google or Wikipedia search and pull off a big long string of engineering associated words, but I was trying to get the jist of it across, as this is more of a fundamentals type post.

[Luce]

Let me take a stab at this....

A crank is sort of like the crystal wine glass the fat lady sings to and makes it break. If you tap the rim, it rings. If you sing the exact same frequency to it, in the right location, the pressure waves will reinforce the vibrations causing the ring, and the vibration will increase until the forces are stronger than the glass, and it breaks. If you keep a finger lightly touching the rim, the vibrations are dampened and absorbed, and can never reach a dangerous level.

The soft mounted weigh of the harmonic dampener is that lightly touching finger. It dampens high frequency vibration that the pistons and rods can induce. A good crank will ring too if smacked, but not anywhere near as long if the harmonic balancer is installed.

And another reason the clutch disc doesn't need to be balanced WITH the rest of the rotating mass is because it's not indexed. Each time the clutch is engaged, it stops at a different place.

[Jerry Clayton]

I balance a crankshaft about every other day---there's more to it than what is easily visable or talked about on the internet. it sounds much simpler than it really is. I have been working on a book type thingie and have recently taken lots of digital photos of portions of the balance procedure, however haven't gotten all aspects covered yet--I should have enough photos to post in a few days (middle of next week) so be patient with me please and I'll get on it as I have one tomorrow--

[Jerry Clayton]

this is a trial upload--if it works notice the 2 pieces of heavy metal to internal balance this crank


On this pic of a rear counter weight you can see two pieces of mallory heavy metal installed into the crank and then a drill point drilling to remove what was then excessive weight--
Engine shops have charts of the weight of drilled holes, weights of different sizes of mallory AND then the differances of the weight of the removed iron and installed mallory--besides the numbers of the hole sizes, its important to know the weight of the mass removed by the POINT of the drill also---and of course theres a differance in 118and 1358 points

[xb-60]

Originally Posted by Jerry Clayton

...notice the 2 pieces of heavy metal to internal balance this crank

On this pic of a rear counter weight you can see two pieces of mallory heavy metal installed into the crank and then a drill point drilling to remove what was then excessive weight...

Thanks Jerry. Yes it sounds simpler than it really is. Is it similar in priciple to balancing tyres/wheels in that a computerized balancing machine tells you the location along the crank and the angle at which the material is added/removed?
Cheers,
Glen

[madmaxx]

As I understand, you dont balance a crankshaft with a harmonic balancer, if the crank is out of balance changing balancers will not solve the problem.