Engine balancing

[blykins]

Originally Posted by 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.

It just depends on how you look at that...

If the rotating assembly has been balanced in a 28oz imbalance and you stick a 50oz balancer on there, then yes, changing balancers will solve the problem.

[Keithc8]

Balancing an enigne is not exact sience but there are formulas that work with most engine under 7000 rpms just fine. You get into race engines over that and you may want to over balance or under balance the engine. That is a topic for another time.
The 302 Ford came originaly as a 28 oz balance engine. It had a weight on the damper and on the flywheel. The weight is bigger looking on the damper because it is closer to the center. The weight on the flwheel is not as big as the flywheel because it is farther from the center of the crank.
When you are balancing the farther out from the crank you get the less weight you need to balance. Most Fords are external balanced with a weight on the damper and flywheel. this is problem because most balance shops will drill on the damper and or the flywheel when balancing the crankshaft and all. If you have a problem down the road and need another flywheel or damper your engine will be out of balance. We use a factory 28 oz damper and flywheel to balance these engines to then check the damper and flywheel that we will use to make sure they are to spec. This is more time consuming but the right way to do it. you want to drill on the crank and not the other parts. If our customer have a problem with the damper or flywheel or want to change them we can then get them a new 28 oz damper or flywheel and they will be ok. We can even check the new stuff.
This all causes a problem and later Ford went to a lighter crank in the 302 with a 50 oz damper and flywheel, 1980 I think to help with the mass of the crank and to help power and economy. The external balance is very bad for race engines and anthing over about 6500 rpms. The longer the stroke the worse the case is on this. Well when Ford came out with this 50 oz stuff it caused even more problems because people would install a 50 oz set up on a 28 oz engine and vise versa. Got to love this Ford stuff.
The 352, 390 and 427 Ford are zero balanced but the 428 is external on the back only and the 428SCJ is external on the front and back. this is has also screwed a few FE guys over the years.
To make matter worse a lot of the pressure plates are out of blanced and need to be balanced with the flywheel and then marked so that they bolt back up the same as balanced. If the flywheel pressure plate bolt pattern is even shifted just a little it will affect the balance. If you surface the flywheel it will more than likely knock the engine out ot balance because most of the time a little more comes of one side than the other, I have seen that several times. And everybody thought this stuff was easy.
Then you get into making cranks that were orignally external to zero or internal balanced which takes heavy metal in the crank counter weights. You can also drill the rod pin side if it has not been drilled.
I have balanced engines now for about 30 years and seen about everything. On the first race steel cranks we were doing we have put as many as 16 pieces of mallory in a crankshaft and ended up with a 800.00 to 900.00 balance job. We now have much better cranks that are made for zero balancing. I remember working with Scat on the first Ford steel cranks back in the late 80s, counter weight placement and size to try and get them to zero balance much easier.
Well this could go on for a while and I would have even more mis-spelled words. Hope some of this helps. Street engine external ok up to about 6500 rpms, race engine just go internal/ zero balanced. The external weights start to flex the crankshaft at high rpms and can even break it but normally takes the #2 and #4 main bearings out first. Road Race and Circle track enigne are harder on them than Drag racing. We need to write a book on this stuff.

Good luck, Keith Craft

[xb-60]

Originally Posted by Keithc8

Balancing an enigne is not exact sience .... We need to write a book on this stuff.

Good luck, Keith Craft

Thanks Keith. What's becoming clear is that the guy at the local machine shop down the road may not be the best bet for skimming your flywheel, let alone to build an engine for you.
What spelling errors? You should do the book.
Cheers,
Glen

[Jerry Clayton]

There are two types of engines which require two different types of cranks--the inline engines and the "V" engines---With the inline engines they don't require the bobweights to be on them for spinning during balancing--
The V types require that bobweights be attached to the rod throws for spinning during the balancing process--The bobweights are made up of 100% of the rotational weight and 50% of the recipricating weight of 2 cylinders ( V8)--since the front two rod throws(4 cylinders) are at 90* to each other as are the back 2 rod throws also 90* while the two center rod throws( OK, so I'm up to 6 rod throws ?) are 180* to each other, the V8 cranks will have counter weights to the front and back but generally not at the center throws---( unless it has been CENTER COUNTER WEIGHTED for strength )

SOOOOOOOO---the addition/subtraction of weight for balancing is generally done on the first and last counterweight---

The 28 and 50 OZ numbers relate to inch/ounces--thats why the flywheel on the external jobs have less correction than the front dampners---differance between something 6-8 inch dia and 12-14 inches flywheel

The pics that I posted that show the imbalance(when I took the pictures) relate to grams. at the time the crank was at 2 grams on a 3 inch radius---

[Mike Huddart]

[quote=Jerry Clayton;1165114]There are two types of engines which require two different types of cranks--the inline engines and the "V" engines---With the inline engines they don't require the bobweights to be on them for spinning during balancing--

Not strictly true, an inline 5 cylinder requires bobweights.

Mike

[xb-60]

Originally Posted by Jerry Clayton

There are two types of engines which require two different types of cranks--the inline engines and the "V" engines---With the inline engines they don't require the bobweights to be on them for spinning during balancing--
The V types require that bobweights be attached to the rod throws for spinning during the balancing process--The bobweights are made up of 100% of the rotational weight and 50% of the recipricating weight of 2 cylinders ( V8)--since the front two rod throws(4 cylinders) are at 90* to each other as are the back 2 rod throws also 90* while the two center rod throws( OK, so I'm up to 6 rod throws ?) are 180* to each other, the V8 cranks will have counter weights to the front and back but generally not at the center throws---( unless it has been CENTER COUNTER WEIGHTED for strength )

SOOOOOOOO---the addition/subtraction of weight for balancing is generally done on the first and last counterweight---

The 28 and 50 OZ numbers relate to inch/ounces--thats why the flywheel on the external jobs have less correction than the front dampners---differance between something 6-8 inch dia and 12-14 inches flywheel

The pics that I posted that show the imbalance(when I took the pictures) relate to grams. at the time the crank was at 2 grams on a 3 inch radius---

Thanks Jerry. My experience up until recently has been with inline four and six cylinder engines. I couldn’t work out why you would add 28oz (or getting close to a kilogram) to the front and rear ends of the crank – in order to balance it!!
Cheers,
Glen

[Jerry Clayton]

So what does that add to this conversation??? no one has a 5 cylinder inline in their Cobra and I was using the inline to v type engine as a means to identify how there are some differances and why the counter weights are on the ends of the crank and not usually the middle.

[Jerry Clayton]

I'm surprised that Mark let that tape out

[CHANMADD]

Most engines have an imbalance at 1400_2000 rpm. This is harmonic imbalance.The harmonic balancer helps to absorb that frequency. Most harmonic balancer have arubber ring sandwiched berween two parts. This type of balancer should be balanced with the crank. A fluid filled type balancer cannot be spun balanced because the fluid moves around. The 28 oz thing is like balancing a wheel and on one side there is a big hole drilled , so that before you stick it on the machine you know that you drilled out 28oz, so that exactly opposite at the same circumference you attach a 28oz weight to get the balance close before spin balancing on the machine.
A single cylinder motor would have all the components meticulously polished ,shaped etc.
A blueprint is making sure that all the components match exactly the designers specs.
A multicylinder blueprint is making sure that all the cylinders and all related components are exactly the same, down to 0.002 of a gram. When they are all same the harmonics will be minimized and then spin balancing will require less addition or removal of metal. This is what makes motors live.
Look at the pulley on a good timiing chain set...it should have some balancing drill marks.
So....yes balance everything if you can..it can only make things smoother
John

[xb-60]

Originally Posted by CHANMADD

Most engines have an imbalance at 1400_2000 rpm. This is harmonic imbalance.The harmonic balancer helps to absorb that frequency. Most harmonic balancer have arubber ring sandwiched berween two parts. This type of balancer should be balanced with the crank. A fluid filled type balancer cannot be spun balanced because the fluid moves around. The 28 oz thing is like balancing a wheel and on one side there is a big hole drilled , so that before you stick it on the machine you know that you drilled out 28oz, so that exactly opposite at the same circumference you attach a 28oz weight to get the balance close before spin balancing on the machine.
A single cylinder motor would have all the components meticulously polished ,shaped etc.
A blueprint is making sure that all the components match exactly the designers specs.
A multicylinder blueprint is making sure that all the cylinders and all related components are exactly the same, down to 0.002 of a gram. When they are all same the harmonics will be minimized and then spin balancing will require less addition or removal of metal. This is what makes motors live.
Look at the pulley on a good timiing chain set...it should have some balancing drill marks.
So....yes balance everything if you can..it can only make things smoother
John

John - if you drill a hole on one side and then add material exactly opposite, would that not make the imbalance worse?
Cheers,
Glen

[CHANMADD]

K

Originally Posted by xb-60

John - if you drill a hole on one side and then add material exactly opposite, would that not make the imbalance worse?
Cheers,
Glen

yes...:I was typing on the move......little brain phart right there....but I trust you understood what I meant.

[xb-60]

Originally Posted by CHANMADD

K

yes...:I was typing on the move......little brain phart right there....but I trust you understood what I meant.

phart understood

[Jerry Clayton]

If a customer showed up here with those parts, I would send him on his way--that crank is scrap and the balance guy would be looking for work doing something else---

[CHANMADD]

The crank in the video became scrap because too much material was removed. If parts selection and balancing had been done it would not have required such extreme drilling.