balancing

[steelcomp]

OK engine gurus. lets balance a motor. I'd like some discussion on the different techniques used, and why one is better than another.
How's it done?? When do you stop "chasing" the mark? Over balance? Under balance?
Lets hear it. :D :coffeycup

[BUSBY]

balance - shmalance ... just run it, straight out of the box
isn't that what everyone else is doing?
j/k, where do we start ... this could go into another one of those deep, deep conversations ... are you trying to stir the pot Scott?

[steelcomp]

With a big ass wooden spoon, c'mon. Just want to hear from some smart guys. Balancing is one of "those" subjects, if ya know what I mean! :D

[DeputyDawg]

This could definitely get good. Here is a little article I copied and pasted from Reher Morrison Race Engines with their permission that might help some folks understand crank balancing.
"While external balancing is less expensive than internal balancing, I believe it’s better to balance the crankshaft internally even if it’s necessary to install heavy metal in the counterweights. These heavy metal plugs must be installed parallel to the crankshaft axis by drilling holes through the counterweights and pressing the plugs in place. Plugs installed in the counterweights perpendicular to the crank axis can be dislodged by centrifugal force, turning them into heavy metal projectiles.
When we install heavy metal in a crank at Reher-Morrison Racing Engines, we don’t put all of it in the end counterweights. We drill through the first counterweight and into the second counterweight; in some instances, it’s necessary to drill through to the third counterweight as well. We then repeat this procedure on the other end of the crank. Each hole is progressively smaller, and the corresponding plugs of heavy metal are turned on a lathe to produce the correct interference fit. Distributing the weight throughout the crank in this manner also reduces the torsional loads on the crankshaft.
Hollow rod journals are a real asset for a long-stroke crankshaft. Drilling the crank pins to lighten the throws has the same effect on balancing as adding mass to the counterweights, but it produces a lighter overall rotating assembly. The longer the stroke, the more important it is to drill the crank pins. Most manufacturers offer drilled crank pins as an option, and it’s money well spent. Don’t be tempted to buy an “economy” crank when building a big motor; the cost of balancing with heavy metal can more than offset the low initial cost of an undrilled crank.
The position of the counterweights is also important to proper balancing. Unfortunately it’s difficult to determine whether the counterweights are in the right positions unless the crank is mounted on a balancing machine. If a crank needs a lot of material to be removed from one side of a counterweight and then a plug of heavy metal inserted at the opposite end, it’s likely that the entire counterweight is in the wrong place. It’s possible to balance a crank with this problem, but the fact that the counterweights aren’t indexed properly means that more weight is required to balance it than if the counterweights were in the correct positions.
A crude example of this is an out-of-balance tire. If a tire is mounted on a wheel and it’s way out of balance, often the easiest solution is to rotate the tire to a different place on the rim. Perhaps the wheel and tire are both heavy in one place; if both heavy sides happen to be together, it takes a lot of lead to balance them. But if the heavy sides of the wheel and rim are opposite each other, the overall balance is better and less lead is required. Applying this principle to crankshafts, if the counterweights aren’t in the right place, the balancing job is much more difficult and ultimately requires more weight to achieve a balanced state. An engineer could analyze the moments and angles of force that are involved, but I just know what I see on the crankshaft balancer.
Crankshafts are a complex subject, and I’ve already filled the available space for this column. Next month I’ll get into knife-edged counterweights and why you should never use a cross-drilled crankshaft.

[Fiat48]

Have it balanced anywhere you want and then bring it here and I will show you it ain't balanced. How's that?
On an analog scale .0004 ounce inches is the closest I can get it.
Now all that does not make sense to you...but anyway....just balance it straight up unless 8000 rpm or higher. Then I like to do 1% of the reciprocating.
I did a lot of testing with BBC running internal and external balance. I proved to myself that although it is a hassle to internal balance it is worth it in terms of crankshaft flex. Heavy metal is a pain to put in these hard cranks. But now even the eagle cranks are offered internal balance.
There are some assumptions in balancing. One of which is weight of oil on the crankshaft. Some guys do 4 grams, some do 5 or more.
I believe everything in a performance engine should be as close to tolerance as you can get it. But many believe "Well it's only a gram heavy..what the hell" on a rotating part. I see this all the time. More like 5 grams. Yet the motor has run for years.
I use a Stewart Warner Industrial balancer with roller bearings that support the assembly. I use a shadow graph which has been adjusted to show the slightest variations in weight. This machine has an analog scale of out of balance. The trunions are very sensative. If you were to take a pencil and take the eraser out of the end of that pencil....and place that tiny eraser on the crankshaft that you just finished balancing...the strobe light would show that eraser as a heavy spot. It's very slow compared to the new digital "drill a hole here" machines available today.
Process: Connecting rods are weighed big end and small and all made to weigh the same. Ditto on pistons. A rod bearing is weighed, rings weighed, pin keepers and pins weighed.
This is to get your bobweight...an artificial weight of 2 rods and pistons connected to each journal of the crank (V-8). 100% rotating weight and 50% reciprocating weight is how you get the total bobweight.
Now..since flying pistons have mass....this is where weight would be added to the bobweight to simulate that mass at rpm. Pro stock used to do 1% of the recip..maybe a little more now with 10,000 rpm motors.
The bobweights are made and added to the crankshaft. If internal balance that is all you need. If external you need the flywheel and the balancer. The assembly is put on the balancer. The machine is set up and adjusted. A chalk mark or reference point is put on the flywheel or end of crankshaft. The crank is spun 500 rpm (if you can get it there without the crank flying off the machine due to it's so far out of balance).
The strobe light shows the heavy. If the heavy is on the counterweight you drill the crank. IF it's not on the counterweight then the counterweight is too small and you get to add heavy metal till you get the heavy back on the counterweight side.
You drill, grind the crank till you get the out of balance as low as you can get it.
Then..you speed the machine up to 90% speed...usually 540 rpm. Now the machine gets more sensative and out of balance goes up. You work on that till you get it as low on the scale as you can.
Now you reset the machine and check at 600 rpm or more. If it's right..the needle on the analog reader just lays way back.
Now..if it is internal balance...you add the balancer and the flywheel. Now you work on those to keep you balance. Or they can be done seperate of the crank with another fixture.
That's all there is to it.
That ...is...balanced.

[BUSBY]

There you go Scott ... true old school ... and from what I've been told, the proper way.
Now, of course someone who uses a Sunnen DCB-750 and/or DCB-2000 will come back and say it's way more accurate ... but I have had rotating assy.'s rechecked after coming from some big name shops here in so cal using the digital machines ... and the old analog machines seem to be more accurate.
I'm sure if Fiat (it's Bob right?) had one, he would figure out that he could be just as accurate. I believe it all about the operator ... not just the machine.
my .02

[sdpm]

What oil? Who uses oil? With my 5 1/2 stage dry sump and a vac. pump pulling 17 in. vac I don't think my crankshaft knows what oil is!! :D

[Fiat48]

There you go Scott ... true old school ... and from what I've been told, the proper way.
Now, of course someone who uses a Sunnen DCB-750 and/or DCB-2000 will come back and say it's way more accurate ... but I have had rotating assy.'s rechecked after coming from some big name shops here in so cal using the digital machines ... and the old analog machines seem to be more accurate.
I'm sure if Fiat (it's Bob right?) had one, he would figure out that he could be just as accurate. I believe it all about the operator ... not just the machine.
my .02
Well...here's my take on that. It's kinda like a tire balancer. The digital deal says "add 1 oz here" and you do it and then it says "add 0 weight". My aren't we good! Or are we? What is the tolerance when that puppy reads "add 0 weight?"
I don't know.
But the analog is a scale. "You're this good. Not 0..but you are this good. Wanna go for better?" Sure I do. What it is all about. The best it can be.
When I bought the balancer from a friend who closed his machine shop I had problems. My current motor was apart so I figured my own race motor would be the perfect learning device. I'd just weigh everything up, make a bobweight and balance my already balanced assembly. I found pistons that were heavy by 2 grams. One light rod and they hadn't cut the other rods to match it. So I recorded what I found and made the bobweight like they would have..without correcting those problems.
At 400 rpm the crank was bouncing. I figured I had done something wrong in the setup or bobweight. The previous owner came over..checked what I had done and we spun up the crank. He said "Yep, it's out of balance."
That is from our premier shop in Reno...who is not shy of charging $$$ to balance one.
I can say that my main bearing life increased after I started doing my own stuff.
It would be interesting to use both machines on the same assembly. It could quite be the operator. One thing is for sure. Time wise...money wise...the old analog is no match for the drill press mounted digital.

[BUSBY]

Fiat,
I'm in agreement with you, that's why I said I figured that you would figure out a way to be just as accurate (with the digital machine) ... I'm not a fan of digital machines all of the time, but if the right person get a hold of one ... and understands COMPLETELY how it works and it's inaccuracies, I'm sure that it would be a close call.
I trust only two balance shops that I have been using for 15+ years ... but I sure would like to get to know all of the secrets like Scott is trying to.
Brian

[Fiat48]

I just did some checking and looks like I have some pictures of a crank being balanced. Trying to remember what these pics are and why I took them. Maybe you guys will find them of interest. Least you can see the bobweights and whatnot.
This is a 454 crank...Eagle I think...going to internal balance. About a bobweight of 2200 grams as I remember. Picture #1 is the analog scale. The piece of duct tape is there for a reason. Sometimes I tape a small weight or a piece of clay to move things around a bit to tell better where the weight needs to be taken out.
http://www2.***boat.com/image_center/data/520/374400fmeter.JPG
The pictures aren't good enough to see the buttons very good. But you have 3 "out of balance" scales...X1..X10...X100. Right now the machine is turning the crank 400 rpm and I am on the X10 scale. If I were to turn the crank faster than this..it would try to bounce off the machine because it has a long way to go to get to balanced.
Picture #2: The X is where I am going to add a stick of heavy metal.
http://www2.***boat.com/image_center/data/520/374400r.JPG
Picture 3: Note the X's down on the front counterweight. She wants heavy metal there also.
http://www2.***boat.com/image_center/data/520/374500f.JPG
Picture 4: 1 stick in and she wants more. Follow the x's.
http://www2.***boat.com/image_center/data/520/374DSCF0001.JPG
Picture 5: Little trick of a bolt on weight on the end of the crank. Feeling it out to see what it wants.
http://www2.***boat.com/image_center/data/520/374DSCF0002.JPG

[BUSBY]

very cool ... I sure would like to have you as my next door neighbor! :D

[gottaminute?]

the reason digital machines have a margin of error is due to the complicaticated math involved in seperating the balance vectors and converting the sensor output into a simple display. A VERY small error from the sensor whether amount or angle when you multiply, divide, factor in the cross effect etc. can end up way off base. There are machines on the market that allow you to plug in a bobweight number and spin the crank empty. think what happens when the throws are not the EXACT stroke or not EXACTLY 90 degrees apart or if the keyway (used as a rotational reference) is not EXACTLY lined up with the #1 journal.
BTW... ive been building balancers and balancing parts since i was 10 (the only job ive ever had) everything from industrial to aerospace .... cranks, the fans that lift up the big military hocercraft, impellers etc.
pat

[steelcomp]

Bob, that's the only way I've ever had it done, was analog. You raised the exact point I was always worried about, and could never get an answer to, and that is, when a dig. balancer says "zero", what exactly is that, because I know it's not absolute zero, and no way near .0004 ounce /in. Analog is infinately intelligent.
Do you use an analog scale when weighing parts as well?? I'm assuming there is no tolerance, that the part is correct when the line on the scale is at zero? I know some factory tolerances are as high as 6-7 gms.
On the Eagle cranks that they claim are internal balance, there is a counterweighted flange. Do you consider this a truely internally balanced crank?
If a guy was to get a rotating assy back from balance, would he hurt anything to further match-balance the rods and pistons, knowing they could get closer than what was already done? Would this throw the bob weight off enough to matter?
Great posting, and great info. This is what I was hoping for. I pretty much understand what the deal is, but I thought it would be fun to get some new thoughts and/or techniques. Thanks for all your time here. :D
.

[Norseman]

Fiat;
Thanks!!
That's the same way my machinist does them and it looks like you two have the same machine, or had. Ed just closed up his shop after 40 years!!
Now I'll have to find another machine shop !!! :cry:
Too bad the guy that bought the equipment doesn't know how to use it!!! :frown:

[steve d]

very cool ... I sure would like to have you as my next door neighbor! :D
Damn Busby---AS I was reading this, the same exact thought came to mind. The house next door may come up for sale....Fiat---- any interest?....Steve

[Fiat48]

Damn Busby---AS I was reading this, the same exact thought came to mind. The house next door may come up for sale....Fiat---- any interest?....Steve
I can't move as moving all my stuff plus equipment would be more than I could bear. LOL.
Steelcomp:
The scale I use is a shadowgraph. There is an adjustment inside that lets you set the dampening. Mine is set very light for accuracy. Again..makes things take longer.
Yes..the line on the scale in the very center. I weigh several times. You weigh the rod big end. Then the rod small end. The sum of these should equal the rods overall weight. If not..you missed it somewhere.
The counterweighted flange deal has been around for years. Fine since the rear main bearing has twice the surface area of the other main bearings. But the counterweight is also heavier on the rear of an eagle internal balance crank. You can't get em from external to internal on the rear by just a flange...it isn't heavy enough. Unless you are way down there on bobweight...like less than 2000 on a BBC.
And "If a guy was to get a rotating assy back from balance, would he hurt anything to further match-balance the rods and pistons, knowing they could get closer than what was already done? Would this throw the bob weight off enough to matter?"
The answer is...the guy didn't do the job right in the first place....who knows what weight he called the parts that were way off...and you think you might help matters by further matching? Not hardly. Zero is Zero....make the guy weigh the stuff in front of you. You're paying for it.
I try to have the guy here when I spin up the crank...and like to have him here for sure when it's balanced before it comes off the balancer. Stops the bullshit. He knows it's as balanced as it can be.
Oh and I forgot to mention. Go back and look at the analog reader picture.
Note the red scale and the black scale. 1.0 is considered balance for street on the red scale. .5 is considered race balance. That is 1 ounce inch and 1/2 ounce inch.
Now look at the black scale and the tiny lines just above the 0. At 90% run speed (usually 540 rpm or higher)...you shoot for that 2nd little line as the final balance. I can't get it below that. But we think that's because we think the earth shakes a little...so we live with that. :D

[INEEDAV]

I can't move as moving all my stuff plus equipment would be more than I could bear. LOL.
Steelcomp:
The scale I use is a shadowgraph. There is an adjustment inside that lets you set the dampening. Mine is set very light for accuracy. Again..makes things take longer.
Yes..the line on the scale in the very center. I weigh several times. You weigh the rod big end. Then the rod small end. The sum of these should equal the rods overall weight. If not..you missed it somewhere.
The counterweighted flange deal has been around for years. Fine since the rear main bearing has twice the surface area of the other main bearings. But the counterweight is also heavier on the rear of an eagle internal balance crank. You can't get em from external to internal on the rear by just a flange...it isn't heavy enough. Unless you are way down there on bobweight...like less than 2000 on a BBC.
And "If a guy was to get a rotating assy back from balance, would he hurt anything to further match-balance the rods and pistons, knowing they could get closer than what was already done? Would this throw the bob weight off enough to matter?"
The answer is...the guy didn't do the job right in the first place....who knows what weight he called the parts that were way off...and you think you might help matters by further matching? Not hardly. Zero is Zero....make the guy weigh the stuff in front of you. You're paying for it.
I try to have the guy here when I spin up the crank...and like to have him here for sure when it's balanced before it comes off the balancer. Stops the bullshit. He knows it's as balanced as it can be.
Oh and I forgot to mention. Go back and look at the analog reader picture.
Note the red scale and the black scale. 1.0 is considered balance for street on the red scale. .5 is considered race balance. That is 1 ounce inch and 1/2 ounce inch.
Now look at the black scale and the tiny lines just above the 0. At 90% run speed (usually 540 rpm or higher)...you shoot for that 2nd little line as the final balance. I can't get it below that. But we think that's because we think the earth shakes a little...so we live with that. :D
I have a lot of faith in that machine in that garage, as well as in its operator. Spinning mine pretty hard right now, and looking to spin it harder. Hopefully with a blower and alcohol in the next year or so.
I think, Bob, if you would pour several more feet of concrete there under the garage you could stabilize the building to hold the balancer better. :wink:

[Fiat48]

I used to balance my drag slicks on my crank balancer. Couldn't spin them but I could find the heavy and get them pretty good. A Hell of a lot closer than Goodyear could get them for sure.
Then I went to a swap meet and bought this old relic. She's so old that it actually uses a set of points and a coil and throws a spark where the heavy is on that little dial out front of the machine. Big old bearings and a stout old mounting. I made adapters....can even do Lexus.
I do about everything in house. LOL.
http://www2.***boat.com/image_center/data/520/374bear.JPG

[shaun]

Fiat,
with external balanced does the balancer need the flywheel/flexplate and dampner/balancer? I noticed you said for internal you add those, was just curious if the shop only needs that stuff for external also.

[Norseman]

Bob;
Sure wish you lived closer!!!!!
That coast to coast shipping is a bitch!!!!
I wonder if I could talk Joan into moving ????? :D
Bob

[steelcomp]

Fiat,
with external balanced does the balancer need the flywheel/flexplate and dampner/balancer? I noticed you said for internal you add those, was just curious if the shop only needs that stuff for external also.
Shaun, if I may,
The external balance set up needs the flywheel and harmonic balancer right from the beginning of the process, as they are counterweighted, and serve as part of the balancing. With the internal balance, you can do just the crank, then can add the balancer and flywheel afterwards, since they are zero balance (not counterweighted), and may may need only slight corrections, maybe nothing at all.

[steelcomp]

I used to balance my drag slicks on my crank balancer. Couldn't spin them but I could find the heavy and get them pretty good. A Hell of a lot closer than Goodyear could get them for sure.
Then I went to a swap meet and bought this old relic. She's so old that it actually uses a set of points and a coil and throws a spark where the heavy is on that little dial out front of the machine. Big old bearings and a stout old mounting. I made adapters....can even do Lexus.
I do about everything in house. LOL.
http://www2.***boat.com/image_center/data/520/374bear.JPG
You must have 48 hr. days! :D

[gottaminute?]

Fiat
if you need parts for that "relic" call me Pat @ balance research 310 263-1135 or email me .... balancingshop@yahoo.com.
my grandpa was the western US sales rep for bear mfg (early 50s until applied power bought them out). i may even have a manual hiding around here if i dig real hard

[Infomaniac]

Yep I got one of them balancers. Nope I don't know how to use it. Not enough anyway to ad intelligent conversation to this thread. :confused:
We do balance some really large rollers shafts etc on it. 15' long etc. you can see the extra base in the background for the really wide stuff. Have the gang drill handy against the wall also. Gotta carry a crank to the mill to add mallory.
http://www2.***boat.com/image_center/data/506/211balance.jpg

[78Eliminator]

very cool ... I sure would like to have you as my next door neighbor! :D
I have driven up to his house 1090 miles round trip several times. Every time has been worth it. He's not stingy about sharing his wealth of knowledge and one hell of a hard worker.......and his wife knows how to cook up a storm! Always fun times up in Reno.

[Fiat48]

You guys seem interested in this balance stuff so here is a little update of today. Guy comes over with a 4 cylinder Toyota motor to balance. He races it. Anyway..I balance the pistons and the rods which are aftermarket. The crank is bone stock Toyota crank.
On a 4 cyl internal balance....you do not use a bobweight. You just set up the machine and spin it on the balancer.
This little bitty crank doesn't weigh much. It's got these little drill holes from the factory on every counterweight...all in the same place.
I set up the machine and spin her up. The needle lays almost at 0..just a tiny tad above. I keep increasing rpm clear up to 1000 rpm. Soon as the machine stabilizes the needle just lays above 0.
Nothing to do here. Cannot make it better. Now we know why Toyota motors are so smooth.