Internal Balancing Tolerance?

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mopowers

mopowers

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I recently bought a "balanced" rotating assembly. The balance sheet shows a rod big end weight of 464g and small end weight of 162g (total - 626g). I took one rod out of the box and it weighed 579g, which is 47g lighter than what's shown on the sheet. Is this a problem, or is it within an acceptable tolerance?

I don't know much about balancing, but I would think the actual weight of the rod should match the total rod weight used to determine the bobweight during balancing - at least within a few grams, right?
 
Total rod mass is not equal to big+small end mass. Whatch some YouTube videos to see how their measured. 65
 
I watch my daughter balance one and weighed everything. She weighed the big end and the weighed the rod. The program after entering those weights calculates the weight of the small end. Then take the lightest small end to the heaviest piston. and the heaviest piston to the lightest small end and so on.
 
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Just got off the phone with a guy at the machine shop that does the balancing. From what he was saying, the big and small end weights should equal the total rod weight. Sounds like someone may have written down the wrong number for the big end on the sheet, which explains the 47g discrepancy. I'm just glad I caught it.
 
Who did the balancing?
My last build, I had Rex Hutchinson balance the assembly for my 440/495. This dude runs smoother than it ever has.
 
I suggest studying up on reciprocating mass vs rotating mass.
It is very hard to accurately measure the big end and small end independently of each other without a proper fixture and scale. You can quickly screw up a matched set and if you got a balanced/matched set from a respected manufacturer (scat, callies, etc) then you stand a very good chance of messing them up if you try to make them better.
 
TT5.9mag said:
I suggest studying up on reciprocating mass vs rotating mass.
It is very hard to accurately measure the big end and small end independently of each other without a proper fixture and scale. You can quickly screw up a matched set and if you got a balanced/matched set from a respected manufacturer (scat, callies, etc) then you stand a very good chance of messing them up if you try to make them better.
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Thank you. I think I understand that. I guess my question is - if you weigh the small end and the big end (using a proper fixture), should the sum of those measurements equal the weight of the rod?
 
mopowers said:
Thank you. I think I understand that. I guess my question is - if you weigh the small end and the big end (using a proper fixture), should the sum of those measurements equal the weight of the rod?
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yes
 
mopowers said:
Thank you. I think I understand that. I guess my question is - if you weigh the small end and the big end (using a proper fixture), should the sum of those measurements equal the weight of the rod?
Click to expand...
Yes
 
Thanks guys. I got everything resolved. I'm swapping the whole shebang out for an unbalanced assembly and will have it balanced locally.
 
Oldmanmopar said:
I watch my daughter balance one and weighed everything. She weighed the big end and the weighed the rod. The program after entering those weights calculates the weight of the small end. Then take the lightest small end to the heaviest piston. and the heaviest piston to the lightest small end and so on.

So I called my son at the shop just now and he said your numbers are not acceptable after entering them. Do not assemble it until you have it balanced at a shop you trust. Never trust a supplier all they do is box and ship parts. Most all the sheets for the same engines are identical. What are the chances of that . He finds most needing to be balanced.

I remember him starting and running a 360 on our run stand for someones fresh build they assembled with "out of the box" parts. It vibrated so bad it shook the floor. The customer needed to have the engine tore down and balanced.

A slightly unbalanced rotating mass will will not spin up. I learned that racing slot cars in my teens. We balanced our armatures on leveled razor blades stuck in cork. primitive but it worked.
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I've tried to preach that on here for along time. For some reason it always falls on deaf ears. People have no problem spend 3K plus on a "good" reciprocating assembly, but they balk at having the balance checked again. A rebalance might be what? 250-500? It makes no sense.
 
I went to the shop today. My daughter was balancing the 426 Max wedge Took some pics and she wrote a sheet out to be typed into the shop papers.

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67Dart273 said:
WOW....when someone finds an ACTUAL "barn find."
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It was in a pole barn right up the street. About 12 years back I found the car. I went there to look at a 86 GLHS. Since that time my son started doing engines for Alex who owns several MAX wedge cars. I told him I knew about the car. The owner since died and Alex purchased the car.

I Met Alex in the 80's he helped me with parts for my 62 conv. When he came to my son to build his engines. At the time he had no idea who I was until we started talking. we are old and I didn't recognize him. Its a small world.

Now my son and Daughter get to have part of the history of some famous historic race cars. There is a 64 Dodge factory HEMI race car. also local find . My son related to me that Alex may be getting that also .

Steve's machine shop teacher at HTA machine owns the original HEMI Hunter. Big Daddy wants the car for his museum. The original drivers nephew is helping on a Demon that is here.

The world gets smaller. My oldest daughter lives over 150 miles from here . I was down there just driving around and found one of Muldowney's Dragsters sitting in the woods by a junk yard with a Hemi Dart where I bought a Barracuda .

If only I had the extra cash to buy some of these old Drag cars we are finding from meeting old farmer customers fixing tractors at the shop hiding in the Pa. barns. We are located in the middle of Several well known 1/4 mile drag strips where I frequented in my young years. Maple grove, Island, Atco, Cecil County, English town, Nuemedia, and many more 1/8 mile tracks and air ports.

I can think several old race cars and rare mopars sitting in barns and fields. I showed some and they went and bought them and I never received a thank you let alone a finders fee. Like most I am waiting to hit the lottery.

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