Notching pistons for oil squirters after assembly has been balanced
10-31-2018, 01:25 PM
#41
Racer
Yep, particularly for the small block Chevy GM has spent hundreds of millions in the factory in Tonawanda NY so it's one of the highest quality low cost engine plants in the world (for the volume.) Apparently one reason they keep bore centers the same as the original 265 cid 1955 V8! No doubt much smaller tolerances today on the C7 engines. I think about that as my 378 cid LT1 spins at 6600 rpm
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JerryU (10-31-2018)
10-31-2018, 01:27 PM
#42
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“The fact is pistons are balanced within 2 grams,” Lieb says. “The rods are balanced plus or minus 2 grams end for end. Most people don’t know what a gram is. One gram is 1/28 of an ounce. The actual weight of a gram is the weight of a dollar bill. When people talk about balancing within half a gram or balancing to zero, it’s nearly impossible to do that with 100 percent accuracy. If they take that same thing that they supposedly balanced to within half a gram and put it back on the scale, they might find out they’re half a gram off. You have to understand the repeatability of the scales of the equipment you’re using and how minute it is.”
Not true. If you have repeatability differential/problems at 1/2 gram range, you need a new scale. I know plenty of industrial Mettler Toledo scales that can repeat less than 1/2 gram.
Now, Lieb stresses that engine builders shouldn’t be discouraged from striving for doing the best, but balancing within half a gram is unnecessary.
Tell NASCSR builders that.
Most rotating assemblies from a manufacturer come with a basic balance that has the rods at a 1.5-2 grams variance and the pistons at .75-1 gram variance. While some people might claim that isn’t balanced properly, the truth is, you’re not going to get it much closer. “Nobody in the industry does that,” White says. “You will not believe how few cars on the planet get a closer balance than that. When you buy a rotating assembly from anyone, they keep their tolerances usually around 2 grams on rods and pistons. We check all those and if they’re over that then we correct it, but we’re not getting down to a half gram on all those parts unless they pay us to do so.”
These 2 sentences almost contradict each other.
I just don't agree unless this is just covering drag racing, quick run then shutdown. My last 2 builds my G8 and my current C7 were balanced to less than 1/8 and was repeatable. They are also endurance engines. I put a heavy *** ultra billet crank in both. When asked why, I would say mine does not run at a more or less fixed rpm. My load...frequency...harmonics are constantly changing. A heavier crank, as opposed to a lightweight crank can handle the load changes better. A tighter balance covers the exponential increase and sudden changes in load and the harmonics throughout the rev range.
Not true. If you have repeatability differential/problems at 1/2 gram range, you need a new scale. I know plenty of industrial Mettler Toledo scales that can repeat less than 1/2 gram.
Now, Lieb stresses that engine builders shouldn’t be discouraged from striving for doing the best, but balancing within half a gram is unnecessary.
Tell NASCSR builders that.
Most rotating assemblies from a manufacturer come with a basic balance that has the rods at a 1.5-2 grams variance and the pistons at .75-1 gram variance. While some people might claim that isn’t balanced properly, the truth is, you’re not going to get it much closer. “Nobody in the industry does that,” White says. “You will not believe how few cars on the planet get a closer balance than that. When you buy a rotating assembly from anyone, they keep their tolerances usually around 2 grams on rods and pistons. We check all those and if they’re over that then we correct it, but we’re not getting down to a half gram on all those parts unless they pay us to do so.”
These 2 sentences almost contradict each other.
I just don't agree unless this is just covering drag racing, quick run then shutdown. My last 2 builds my G8 and my current C7 were balanced to less than 1/8 and was repeatable. They are also endurance engines. I put a heavy *** ultra billet crank in both. When asked why, I would say mine does not run at a more or less fixed rpm. My load...frequency...harmonics are constantly changing. A heavier crank, as opposed to a lightweight crank can handle the load changes better. A tighter balance covers the exponential increase and sudden changes in load and the harmonics throughout the rev range.
10-31-2018, 01:46 PM
#43
Racer
I might chastised here but I would say rebalance. I tore apart 3 engines once because I found a cam thrust bearing that was supposed to be installed. It happened to be someone else's and came back on a hook. I removed those headers I just bought 4 or 5 times to get the routing of the O2 sensors correct and away from all the heat.
10-31-2018, 01:54 PM
#44
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I might chastised here but I would say rebalance. I tore apart 3 engines once because I found a cam thrust bearing that was supposed to be installed. It happened to be someone else's and came back on a hook. I removed those headers I just bought 4 or 5 times to get the routing of the O2 sensors correct and away from all the heat.
10-31-2018, 02:39 PM
#45
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^^
As someone stated if this is for drag racing where the extra loads will be for a very short time probably not worth the cost. A NASCAR engine running at a constant high rpm it would be a very good idea. Just my thought.
As someone stated if this is for drag racing where the extra loads will be for a very short time probably not worth the cost. A NASCAR engine running at a constant high rpm it would be a very good idea. Just my thought.
Last edited by JerryU; 10-31-2018 at 02:42 PM.
10-31-2018, 02:39 PM
#46
Racer
ok so I just called the balance shop, (well known and highly trusted company) and talked with the head guy there and went over everything with him. He said I did everything exactly as I should have with rearranging the rods and wrist pins to better offset the piston weight differences and that the final variations I have are totally fine and he doesn’t recommend redoing the balance. He could have said “sure, you need it done and I’ll do it” and took my money but he said he really things its fine and that the bob weight will be good..
10-31-2018, 02:52 PM
#47
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11-03-2018, 02:30 AM
#48
Racer
The pics make it appear as if there are decent sized tooling ridges left from the machining along the underside. Must be a good camera. Did your spreadsheet show the before and after piston weights, along with big.little rod end weights and I overlooked it? That's what will matter regarding whether or not you would need a re balance. Looks like you did a great job mixing up the parts to get a nice balanced piston/pin/rod combos. I have no idea what you're going for in the end here but once it's completed I call shotgun! lol
Just built a 350 for my dad a couple 3 days ago, tight stock-ish low end tq towing motor, and wished he had the funds to build it a little more "fun" as looking at your pistons pics makes me want to build something a bit more wild again. This one makes peak power around 4k, so it's more tolerant to deviations in weights than a high revvvvving motor like you are building up. I know I have a set of Venolia pistons in a box somewhere....hmmm lol
Last edited by Yourconfused; 11-03-2018 at 02:46 AM.
11-03-2018, 02:42 AM
#49
Racer
“The fact is pistons are balanced within 2 grams,” Lieb says. “The rods are balanced plus or minus 2 grams end for end. Most people don’t know what a gram is. One gram is 1/28 of an ounce. The actual weight of a gram is the weight of a dollar bill. When people talk about balancing within half a gram or balancing to zero, it’s nearly impossible to do that with 100 percent accuracy. If they take that same thing that they supposedly balanced to within half a gram and put it back on the scale, they might find out they’re half a gram off. You have to understand the repeatability of the scales of the equipment you’re using and how minute it is.”
Not true. If you have repeatability differential/problems at 1/2 gram range, you need a new scale. I know plenty of industrial Mettler Toledo scales that can repeat less than 1/2 gram.
Now, Lieb stresses that engine builders shouldn’t be discouraged from striving for doing the best, but balancing within half a gram is unnecessary.
Tell NASCAR builders that.
Most rotating assemblies from a manufacturer come with a basic balance that has the rods at a 1.5-2 grams variance and the pistons at .75-1 gram variance. While some people might claim that isn’t balanced properly, the truth is, you’re not going to get it much closer. “Nobody in the industry does that,” White says. “You will not believe how few cars on the planet get a closer balance than that. When you buy a rotating assembly from anyone, they keep their tolerances usually around 2 grams on rods and pistons. We check all those and if they’re over that then we correct it, but we’re not getting down to a half gram on all those parts unless they pay us to do so.”
These 2 sentences almost contradict each other.
I just don't agree unless this is just covering drag racing, quick run then shutdown. My last 2 builds my G8 and my current C7 were balanced to less than 1/8 and was repeatable. They are also endurance engines. I put a heavy *** ultra billet crank in both. When asked why, I would say mine does not run at a more or less fixed rpm. My load...frequency...harmonics are constantly changing. A heavier crank, as opposed to a lightweight crank can handle the load changes better. A tighter balance covers the exponential increase and sudden changes in load and the harmonics throughout the rev range.
Not true. If you have repeatability differential/problems at 1/2 gram range, you need a new scale. I know plenty of industrial Mettler Toledo scales that can repeat less than 1/2 gram.
Now, Lieb stresses that engine builders shouldn’t be discouraged from striving for doing the best, but balancing within half a gram is unnecessary.
Tell NASCAR builders that.
Most rotating assemblies from a manufacturer come with a basic balance that has the rods at a 1.5-2 grams variance and the pistons at .75-1 gram variance. While some people might claim that isn’t balanced properly, the truth is, you’re not going to get it much closer. “Nobody in the industry does that,” White says. “You will not believe how few cars on the planet get a closer balance than that. When you buy a rotating assembly from anyone, they keep their tolerances usually around 2 grams on rods and pistons. We check all those and if they’re over that then we correct it, but we’re not getting down to a half gram on all those parts unless they pay us to do so.”
These 2 sentences almost contradict each other.
I just don't agree unless this is just covering drag racing, quick run then shutdown. My last 2 builds my G8 and my current C7 were balanced to less than 1/8 and was repeatable. They are also endurance engines. I put a heavy *** ultra billet crank in both. When asked why, I would say mine does not run at a more or less fixed rpm. My load...frequency...harmonics are constantly changing. A heavier crank, as opposed to a lightweight crank can handle the load changes better. A tighter balance covers the exponential increase and sudden changes in load and the harmonics throughout the rev range.
The tolerances grow at quite a significant rate as the rpm increases, so building for the application does matter, kinda like using the right tool for the job if you will. My last 2 sets of "balanced" rods from Eagle were within a couple of grams, which was a nice starting point, but like the OP has measured, stacked tolerances can be dealt with to mitigate material removal when going for a higher degree of accuracy.
Last edited by Yourconfused; 11-07-2018 at 11:22 PM.
11-07-2018, 10:07 PM
#50
Melting Slicks
I did some quick calculations...
I estimated the missing aluminum in the piston at 4 grams; with a balance bob weight of roughly 1950 grams, that's a change of only 1/5 of 1%. Many race teams intentionally overbalance their engines 2% or more to reduce high rpm vibration - even the oil allowance alone is roughly 4 grams in the crank. If this is the only deviation, it would be virtually impossible to notice. If I were you, I'd save the money.
Good luck!
I estimated the missing aluminum in the piston at 4 grams; with a balance bob weight of roughly 1950 grams, that's a change of only 1/5 of 1%. Many race teams intentionally overbalance their engines 2% or more to reduce high rpm vibration - even the oil allowance alone is roughly 4 grams in the crank. If this is the only deviation, it would be virtually impossible to notice. If I were you, I'd save the money.
Good luck!
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FYREANT (11-08-2018)
11-08-2018, 07:35 AM
#51
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I did some quick calculations...
I estimated the missing aluminum in the piston at 4 grams; with a balance bob weight of roughly 1950 grams, that's a change of only 1/5 of 1%. Many race teams intentionally overbalance their engines 2% or more to reduce high rpm vibration - even the oil allowance alone is roughly 4 grams in the crank. If this is the only deviation, it would be virtually impossible to notice. If I were you, I'd save the money.
Good luck!
I estimated the missing aluminum in the piston at 4 grams; with a balance bob weight of roughly 1950 grams, that's a change of only 1/5 of 1%. Many race teams intentionally overbalance their engines 2% or more to reduce high rpm vibration - even the oil allowance alone is roughly 4 grams in the crank. If this is the only deviation, it would be virtually impossible to notice. If I were you, I'd save the money.
Good luck!
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11-08-2018, 09:31 AM
#52
Racer
We have scales at work that go to 1k's of a gram (determining the PPB of HF acid among other things as we are an independent lab for municipalities), so you are spot on in your comments about the quality of the equipment and for the rest of your comments too. I just wait till the weekend to play with the EQ when the overloard isn't there. lol
The tolerances grow at quite a significant rate as the rpm increases, so building for the application does matter, kinda like using the right tool for the job if you will. My last 2 sets of "balanced" rods from Eagle were within a couple of grams, which was a nice starting point, but like the OP has measured, stacked tolerances can be dealt with to mitigate material removal when going for a higher degree of accuracy.
The tolerances grow at quite a significant rate as the rpm increases, so building for the application does matter, kinda like using the right tool for the job if you will. My last 2 sets of "balanced" rods from Eagle were within a couple of grams, which was a nice starting point, but like the OP has measured, stacked tolerances can be dealt with to mitigate material removal when going for a higher degree of accuracy.
I've balanced everything from gas engines to GE Turbines and yes stacked tolerances do count. Weight and balance wise, you could take any part of my assembly and move it to any other part. I go overboard or at least most people would say so but it took me 4 days to balance out my assembly. BUT im spinning a stock bore/stroke at 8500. On top of everything it cost me an extra $500.00, of course not everybody needs it but it builds in a lot of reliability. IMHO every set needs to be balanced, even the package unit short blocks. If your spending 5-7k on a prebuilt short block, spend a few more on checking the balance, you might be surprised what you find. 've came across a few that had defective parts and would have ruined the whole thing if started.....it happens.