[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.