289 balancing question
03-27-2014, 11:16 AM
#1
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289 balancing question
This should make for a short thread, as I'm sure someone will provide a good answer pretty quick. I have a '65 289 which is running a 50-oz balancer off a 5.0 HO engine, and a 28-oz 164-tooth flywheel off a '69 Boss 302. Engine was built by PO about 7 or 8 years ago, and still runs smooth. My question: how, exactly, was the engine balanced to run this mix of parts? In another thread, someone said it was "easy" to have balanced the flywheel for this, but I'm not a machinist...so explain to me exactly how this would have been done.
03-27-2014, 02:57 PM
#2
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The flywheel and balancer have an imbalance factor to them. There is offset weight on part of them so it would normally wobble on it's own. The balancer and flywheel are imbalanced to match each other and the crankshaft, so that when it's all spinning around, the imbalances cancel each other out.
On a flywheel it's as simple as putting it on a balancing machine, and removing weight from certain parts of the flywheel to give it the imbalance where you want it. It's usually done with a drill press or something similar, drill some dimples into one side of the back of the flywheel until it's correct.
Some of the newer flywheels have removable weights, so you bolt down the one you are going to use, 0/28/50.
On high end crankshafts for 0 balance factors, weight is typically added using something like a tungsten slug in different parts of the crank counterweights; which is one of the main reasons getting 0 balance factor setups is so expensive, the slugs are quite pricey. But they have the best balance characteristics, and are typically used only in high end high performance and racing applications.
On a flywheel it's as simple as putting it on a balancing machine, and removing weight from certain parts of the flywheel to give it the imbalance where you want it. It's usually done with a drill press or something similar, drill some dimples into one side of the back of the flywheel until it's correct.
Some of the newer flywheels have removable weights, so you bolt down the one you are going to use, 0/28/50.
On high end crankshafts for 0 balance factors, weight is typically added using something like a tungsten slug in different parts of the crank counterweights; which is one of the main reasons getting 0 balance factor setups is so expensive, the slugs are quite pricey. But they have the best balance characteristics, and are typically used only in high end high performance and racing applications.
03-27-2014, 04:35 PM
#3
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i am one of the people that answered your other thread.
thry would have had to add 22 oz of weight to the flywheel.
no balance shop in their right mind would have done this, therefore it is unlikely it was done which might account for your vibration you said you had.
you either yank it apart to see what they did and fix it if need be or drive it as is.
thry would have had to add 22 oz of weight to the flywheel.
no balance shop in their right mind would have done this, therefore it is unlikely it was done which might account for your vibration you said you had.
you either yank it apart to see what they did and fix it if need be or drive it as is.
03-27-2014, 08:36 PM
#4
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You can balance a flywheel by removing weight from one side rather than adding it to another. Accomplishes the same thing. The weight imbalance factor is actually for purposes of centripetal force. It's ounce-inches rather than a weight in pure ounces, so it's ounces x distance from center of rotation.
You could balance a flywheel by adding weight to it, but it wouldn't be worth the time or money. I used a factory 28oz flywheel for years on a 50oz HO setup, just drilled out some material when they balanced it.
That said, if you're pulling the flywheel or building a new engine, flywheels DO wear out after a time. Engagement with the clutch and resurfacing remove material, less material means less ability to handle heat. Good SFI steel flywheels are available today. Cast iron isn't that terribly strong.
You could balance a flywheel by adding weight to it, but it wouldn't be worth the time or money. I used a factory 28oz flywheel for years on a 50oz HO setup, just drilled out some material when they balanced it.
That said, if you're pulling the flywheel or building a new engine, flywheels DO wear out after a time. Engagement with the clutch and resurfacing remove material, less material means less ability to handle heat. Good SFI steel flywheels are available today. Cast iron isn't that terribly strong.
03-28-2014, 12:12 PM
#5
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Thanks, folks, for the replies. I went back and looked at some photos I took of the flywheel,etc. when I was replacing the clutch and pressure plate, and sure enough, it has 3 "dimples" or shallow holes drilled into the front (engine side) of the flywheel. The crank mounting surface where you bolt the flywheel also has one such dimple drilled. Attached are a couple photos. So...looks like they did balance it after all. Like I said...the engine runs smooth, and what little vibration I do have on the open road at about 50 mph may likely be a u-joint starting to go bad. If so..it should slowly get worse as time goes on.
Again...thanks for the explanations.
Again...thanks for the explanations.
03-28-2014, 05:55 PM
#6
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You are not getting it.
It is IMPOSSIBLE, IMPOSSIBLE, IMPOSSIBLE, IMPOSSIBLE to balance a 28 oz flywheel to a 50 oz crank without adding 22 oz of weight by the counter weight or removing 22 oz of weight directly opposite of the counterweight . IT CAN NOT BE DONE.
Your holes mean NOTHING!
look at the weight with the numbers on it, now, that is 28 oz. to make is a 50 balance by removing weight, they need to remove material close to the same size as that weight EXACTLY directly across from it. It is onbvious that this was not done.
look at your crank damper, if the weight is not 1/2 way around the damper is is a 28 oz damper not a 50.
E
It is IMPOSSIBLE, IMPOSSIBLE, IMPOSSIBLE, IMPOSSIBLE to balance a 28 oz flywheel to a 50 oz crank without adding 22 oz of weight by the counter weight or removing 22 oz of weight directly opposite of the counterweight . IT CAN NOT BE DONE.
Your holes mean NOTHING!
look at the weight with the numbers on it, now, that is 28 oz. to make is a 50 balance by removing weight, they need to remove material close to the same size as that weight EXACTLY directly across from it. It is onbvious that this was not done.
look at your crank damper, if the weight is not 1/2 way around the damper is is a 28 oz damper not a 50.
E
03-28-2014, 07:47 PM
#7
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I'm not saying you balance a 28oz flywheel to a 50oz crank. I'm saying you turn a 28oz flywheel into a 50oz one, then balance that to the 50oz crank setup. At that point the flywheel is a 50oz flywheel, even though it came from the factory as a 28oz.
It can be done, I've had it done before. If it were wrong, the crankshaft would have broken. That's how factory flywheels have their finishing balance done as well, they're typically cast with the weight in it, and then spun up on a machine that measures the size and location of the imbalance, and then additional metal is removed by drilling a bit out where needed to finalize the mass-distance at the proper location (since the flywheel is clocked to the crankshaft via the bolt pattern).
Like I said, it's not pure weight, it's weight-distance (technically force, mass x distance). Less weight a farther distance from the center, has the same effect on centripetal force as more weight closer to the center of rotation. It's a non linear relationship as well, it's actually a function of the square of the tangential velocity to the radius. So if you have some weight at some distance from the center, 1/4 of the weight at 2x the distance generates the same centripetal force.
And that's what you're shooting for with the imbalance on the flywheel, balancer and crank. The goal is to create various regions of centripetal force (flywheel, balancer and the various parts of the crank) such that they cancel each other out. That's why a 50oz imbalance flywheel has to be used with the corresponding balancer (which is actually a 34oz imbalance in a 50oz setup). Then it's matched with the various weights of the assembly bolted to the crank (pistons, rods etc), then spin it up on a balancing machine and then by adding or removing weight on the crankshaft counterweights itself.
In the end it controls harmonic vibrations in the crankshaft along with the harmonic balancer itself, to prevent resonance that shatters the crank.
The easy way you turn a 28oz flywheel into a 50oz flywheel is to remove weight on the opposite side of the flywheel so that the imbalance in the flywheel increases. It's the same as adding weight to the existing balance weight that's cast in place (some newer flywheels bolt them on and they are changeable for the 2 balance factors). You could also turn a 50oz into a 28oz by removing weight on the same side as the imbalance.
And since you're removing weight at a larger radial distance than the existing factory weight, you can remove a lot less weight. That's why you can get away with just drilling some dimples in the outer edge of the flywheel (which is done anyway to finish the flywheel balancing). Typically though when you rebalance a 28oz flywheel to a 50oz balance factor, there end up being quite a few holes on the side opposite of the imbalance weight.
It can be done, I've had it done before. If it were wrong, the crankshaft would have broken. That's how factory flywheels have their finishing balance done as well, they're typically cast with the weight in it, and then spun up on a machine that measures the size and location of the imbalance, and then additional metal is removed by drilling a bit out where needed to finalize the mass-distance at the proper location (since the flywheel is clocked to the crankshaft via the bolt pattern).
Like I said, it's not pure weight, it's weight-distance (technically force, mass x distance). Less weight a farther distance from the center, has the same effect on centripetal force as more weight closer to the center of rotation. It's a non linear relationship as well, it's actually a function of the square of the tangential velocity to the radius. So if you have some weight at some distance from the center, 1/4 of the weight at 2x the distance generates the same centripetal force.
And that's what you're shooting for with the imbalance on the flywheel, balancer and crank. The goal is to create various regions of centripetal force (flywheel, balancer and the various parts of the crank) such that they cancel each other out. That's why a 50oz imbalance flywheel has to be used with the corresponding balancer (which is actually a 34oz imbalance in a 50oz setup). Then it's matched with the various weights of the assembly bolted to the crank (pistons, rods etc), then spin it up on a balancing machine and then by adding or removing weight on the crankshaft counterweights itself.
In the end it controls harmonic vibrations in the crankshaft along with the harmonic balancer itself, to prevent resonance that shatters the crank.
The easy way you turn a 28oz flywheel into a 50oz flywheel is to remove weight on the opposite side of the flywheel so that the imbalance in the flywheel increases. It's the same as adding weight to the existing balance weight that's cast in place (some newer flywheels bolt them on and they are changeable for the 2 balance factors). You could also turn a 50oz into a 28oz by removing weight on the same side as the imbalance.
And since you're removing weight at a larger radial distance than the existing factory weight, you can remove a lot less weight. That's why you can get away with just drilling some dimples in the outer edge of the flywheel (which is done anyway to finish the flywheel balancing). Typically though when you rebalance a 28oz flywheel to a 50oz balance factor, there end up being quite a few holes on the side opposite of the imbalance weight.
03-28-2014, 08:08 PM
#8
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his flywheel has NOT been balanced for 50 oz. it simply hasn't. i can easily see that it has not. i have had engines balanced and flywheels matched balanced for 40 years.
obviously something somewhere has been done but not much of it was done on the flywheel.
obviously something somewhere has been done but not much of it was done on the flywheel.
03-28-2014, 08:55 PM
#10
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he would have at lest 6 holes and likely around 10. we're still talking about removing around 18 -20 [not 22] oz of metal accounting for its increased distance from the center than the weight as you mentioned.