Balance Question - Machine shop screwed up.
01-11-2016, 09:54 PM
#1
Teching In
Thread Starter
Join Date: Nov 2013
Posts: 26
Likes: 0
Received 0 Likes
on
0 Posts
Balance Question - Machine shop screwed up. I brought my 6.0 rotating assembly to the machine shop to be balanced. I supplied hyper pistons (4.030), a 5.3 crank, stock floating rods. Machine shop talked me into selling me the rings because they could get them for the same cost I could...I told them the part number that goes with the pistons. Machine shop also requests my flywheel (manual), and balancer/pulley.
"Hello your balancing is done, bring us our money..."
They had to add a couple slugs to the 5.3 crank to balance it out. Whoopee.
They didn't get the ring part number/brand I suggested, they got Hastings - good brand, I get it- OK.
Forward fast a couple of weeks, and tonight I go to check some basic things, like rings gap etc, and when I go to insert a compression ring into the bore it just falls right in. Check another ring, same thing.
Google the part number on the hastings box, and its a .030 5.3 set, not a .030 6.0 set. Assuming the guy weighed and used the 5.3 rings for his data (like he said he did)...Is this balance job fucked or will it be OK if I just get and add the 4.030 6.0 rings to it?
Its a 6.0, ls9 cam, 6-6500rpm max, street motor.
After dealing with so many shops and people over the years, I do not like where this could be going (trying to bring it all back to be redone-rechecked etc).
"Hello your balancing is done, bring us our money..."
They had to add a couple slugs to the 5.3 crank to balance it out. Whoopee.
They didn't get the ring part number/brand I suggested, they got Hastings - good brand, I get it- OK.
Forward fast a couple of weeks, and tonight I go to check some basic things, like rings gap etc, and when I go to insert a compression ring into the bore it just falls right in. Check another ring, same thing.
Google the part number on the hastings box, and its a .030 5.3 set, not a .030 6.0 set. Assuming the guy weighed and used the 5.3 rings for his data (like he said he did)...Is this balance job fucked or will it be OK if I just get and add the 4.030 6.0 rings to it?
Its a 6.0, ls9 cam, 6-6500rpm max, street motor.
After dealing with so many shops and people over the years, I do not like where this could be going (trying to bring it all back to be redone-rechecked etc).
01-11-2016, 10:22 PM
#3
That's because you don't balance rings, you balance the crank. In order to do that, you have to weigh the pistons, pins, rings, etc.
With that said, there may not be enough of a difference between the 3.780" rings and the 4.030" rings to make a difference, but it sounds to me like its the machine shop's problem. Take it all to them, tell them what you've found, and let them show you how much the bobweight changes with the larger rings. Usually 2-3 grams is no big deal.
With that said, there may not be enough of a difference between the 3.780" rings and the 4.030" rings to make a difference, but it sounds to me like its the machine shop's problem. Take it all to them, tell them what you've found, and let them show you how much the bobweight changes with the larger rings. Usually 2-3 grams is no big deal.
The following users liked this post:
Homer_Simpson (05-19-2023)
01-11-2016, 11:43 PM
#5
That's because you don't balance rings, you balance the crank. In order to do that, you have to weigh the pistons, pins, rings, etc.
With that said, there may not be enough of a difference between the 3.780" rings and the 4.030" rings to make a difference, but it sounds to me like its the machine shop's problem. Take it all to them, tell them what you've found, and let them show you how much the bobweight changes with the larger rings. Usually 2-3 grams is no big deal.
With that said, there may not be enough of a difference between the 3.780" rings and the 4.030" rings to make a difference, but it sounds to me like its the machine shop's problem. Take it all to them, tell them what you've found, and let them show you how much the bobweight changes with the larger rings. Usually 2-3 grams is no big deal.
01-11-2016, 11:52 PM
#6
Although thet don't balance the rings, the ring weight is used to determine total piston weight, therefore "bob" weight. Although I assume the weight difference between the rings is insignificant, I also assume you paid good money for the work. Have the shop weight the 2 different rings, and determine if the bob weight they used works for both rings.
01-12-2016, 12:40 AM
#7
I think you guys are misunderstanding the question. I believe you are thinking of when the components are "balanced" so that each of the pistons, rods, or whatever component weighs within a certain percentage of eachother. This is not what is being discussed.
We are talking dynamic balance. This is when the components are weighed to calculate a bobweight. These bobweights are attached to the rod journals of the crank and spun up to measure the imbalance of the crankshaft counterweights. Here is a link to help explain the concept.
If the 3.780" rings were weighed instead of the 4.030" rings to calculate the bobweight, the crank was not balanced properly. Depending on the weight difference between the ring sets, it may or may not be acceptable to run as is.
FYI, if the bobweight is calculated without the rings at all, then your crank is most certainly balanced improperly and outside normal tolerances.
We are talking dynamic balance. This is when the components are weighed to calculate a bobweight. These bobweights are attached to the rod journals of the crank and spun up to measure the imbalance of the crankshaft counterweights. Here is a link to help explain the concept.
If the 3.780" rings were weighed instead of the 4.030" rings to calculate the bobweight, the crank was not balanced properly. Depending on the weight difference between the ring sets, it may or may not be acceptable to run as is.
FYI, if the bobweight is calculated without the rings at all, then your crank is most certainly balanced improperly and outside normal tolerances.
Trending Topics
01-12-2016, 12:44 AM
#9
I think you guys are misunderstanding the question. I believe you are thinking of when the components are "balanced" so that each of the pistons, rods, or whatever component weighs within a certain percentage of eachother. This is not what is being discussed.
We are talking dynamic balance. This is when the components are weighed to calculate a bobweight. These bobweights are attached to the rod journals of the crank and spun up to measure the imbalance of the crankshaft counterweights. Here is a link to help explain the concept.
If the 3.780" rings were weighed instead of the 4.030" rings to calculate the bobweight, the crank was not balanced properly. Depending on the weight difference between the ring sets, it may or may not be acceptable to run as is.
FYI, if the bobweight is calculated without the rings at all, then your crank is most certainly balanced improperly and outside normal tolerances.
We are talking dynamic balance. This is when the components are weighed to calculate a bobweight. These bobweights are attached to the rod journals of the crank and spun up to measure the imbalance of the crankshaft counterweights. Here is a link to help explain the concept.
If the 3.780" rings were weighed instead of the 4.030" rings to calculate the bobweight, the crank was not balanced properly. Depending on the weight difference between the ring sets, it may or may not be acceptable to run as is.
FYI, if the bobweight is calculated without the rings at all, then your crank is most certainly balanced improperly and outside normal tolerances.
01-12-2016, 01:35 AM
#10
Reason i ask this btw is because in previous experiences with balancing cranks (on other builds ive done, 4 cylinders mostly) the cranks are zero balanced independently and the rotating assemblies are balanced separately so that the pistons and rods all weigh the same or close to the same within 1 gram. I've never had a crank balanced with things that are on the rotating assembly factored in, we send the crank out, and it comes back zero balanced.
Most V8 cranks are 90 degree cranks, which don't work the same way. The counterweights have to counter the weight of the rods and pistons as they travel up and down so the crank is balanced with the bobweights which simulate those components. Then the necessary weight is removed or added to the counterweights.
01-12-2016, 10:24 AM
#12
Somehow I doubt the difference in weight of a 5.3 ring vs. a 6.0 ring is enough to cause the whole thing to be unbalanced.
The rotating assembly as a whole, with the flywheel and crank pulley probably weighs in excess of 40kg (90lbs). The difference in weight of the rings is probably a few mg.
There are 4,000,000mg in 40kg. Do you think 5mg out of 4 million will make a difference?
The rotating assembly as a whole, with the flywheel and crank pulley probably weighs in excess of 40kg (90lbs). The difference in weight of the rings is probably a few mg.
There are 4,000,000mg in 40kg. Do you think 5mg out of 4 million will make a difference?
01-12-2016, 10:49 AM
#13
I know plenty of shops that do the bob weight with a ring pack that they keep in house simply labeled as "BBC," "SBC," etc. But I also know of shops that want to use your exact ring pack to be precise. If the shop doesn't have you bring your rings, they are using a set they have at the shop to add in for the bob weight. With all that said, they should have a sheet laying around somewhere (maybe even on the invoice) that says what all of the weights were that they can compare to. Lots of places I've seen balance to .5g, so if they know what the 3.78 rings weighed vs what the 4.030 rings weigh, they should be able to either correct it, or let you know for certain if it's good to go.
01-12-2016, 11:58 AM
#14
4 cylinder cranks are different. They're 180 degree cranks, aka flat plane cranks, so as two journals go up, the other two go down. They almost cancel eachother out.
Most V8 cranks are 90 degree cranks, which don't work the same way. The counterweights have to counter the weight of the rods and pistons as they travel up and down so the crank is balanced with the bobweights which simulate those components. Then the necessary weight is removed or added to the counterweights.
Most V8 cranks are 90 degree cranks, which don't work the same way. The counterweights have to counter the weight of the rods and pistons as they travel up and down so the crank is balanced with the bobweights which simulate those components. Then the necessary weight is removed or added to the counterweights.
01-13-2016, 10:05 PM
#15
Teching In
Thread Starter
Join Date: Nov 2013
Posts: 26
Likes: 0
Received 0 Likes
on
0 Posts
Weight Machine shop got the 4.030 6.0 rings in and compared them to the data carded on the .030 5.3.
Claims its only a little over a 1/10 of a gram difference due to the fact that the 6.0 top ring and oil ring are thinner then the 5.3.
Says it wont make a difference...
Have to take his word as I really have now way to tell, or to test if that were ever true...
Claims its only a little over a 1/10 of a gram difference due to the fact that the 6.0 top ring and oil ring are thinner then the 5.3.
Says it wont make a difference...
Have to take his word as I really have now way to tell, or to test if that were ever true...
01-14-2016, 07:55 AM
#17
Machine shop got the 4.030 6.0 rings in and compared them to the data carded on the .030 5.3.
Claims its only a little over a 1/10 of a gram difference due to the fact that the 6.0 top ring and oil ring are thinner then the 5.3.
Says it wont make a difference...
Have to take his word as I really have now way to tell, or to test if that were ever true...
Claims its only a little over a 1/10 of a gram difference due to the fact that the 6.0 top ring and oil ring are thinner then the 5.3.
Says it wont make a difference...
Have to take his word as I really have now way to tell, or to test if that were ever true...