connecting rods weighing question

[Belgian1979]

What would be a good way to weigh small ends and big ends on an improvised way ? How much difference can there be between the small ends and big ends of a set of rod before the balance is thrown off ?

Thanks

[Wolfplace]

What would be a good way to weigh small ends and big ends on an improvised way ? How much difference can there be between the small ends and big ends of a set of rod before the balance is thrown off ?

Thanks

You need some sort of arbor to find the center of the bores to weigh them correctly
The rod also has to hang level

Like so



How much is very subjective,, guess it depends on what you will accept
I have seen so called balanced assemblies that had parts over 10gms different so I guess this is "acceptable" to some,, not to me

I balance to .5 gm per end & .5 total rod weight if possible
That is not ± .5 it is .5
You can also "juggle" parts to come up with acceptable numbers because all if the reciprocating weight is cumulative

[Baprace]

What would be a good way to weigh small ends and big ends on an improvised way ? How much difference can there be between the small ends and big ends of a set of rod before the balance is thrown off ?
Thanks

When I rebuild most customers engine's , I always try to sell balance the engine as the results are justified. normaly a decent street engine will come in for rebuild and when we find the balance out by 10 grams or more the customer always say's WOW I didn't feel a shake before BUT I can certainly feel the difference now. Wolfplace has it correct, in my opinion.

[Wolfplace]

You can also "juggle" parts to come up with acceptable numbers because all if the reciprocating weight is cumulative

I can't edit the damn post so to make it clear
The last sentence is supposed to say
You can also "juggle" parts to come up with acceptable numbers because all of the reciprocating weight is cumulative
NOT
if the reciprocating weight is cumulative

[hodge]

When the weight unbalance is greater than 15 grams per throw it will have a shake so I have found. Where it comes in as a shake may vary.

[hodge]

I find that just for the customers satisfaction knowing it needs to be balanced I show them two complete piston rod assembles on the scale, and how bad they come.

[panic]

Against my better judgment, I'll ask:
what does the rod's center of gravity have to do with reciprocating vs. rotating weight?

[Wolfplace]

Against my better judgment, I'll ask:
what does the rod's center of gravity have to do with reciprocating vs. rotating weight?

I don't understand the question?

[Belgian1979]

What would be a good way to weigh small ends and big ends on an improvised way ? How much difference can there be between the small ends and big ends of a set of rod before the balance is thrown off ?

Thanks

You need some sort of arbor to find the center of the bores to weigh them correctly
The rod also has to hang level

Like so



How much is very subjective,, guess it depends on what you will accept
I have seen so called balanced assemblies that had parts over 10gms different so I guess this is "acceptable" to some,, not to me

I balance to .5 gm per end & .5 total rod weight if possible
That is not ± .5 it is .5
You can also "juggle" parts to come up with acceptable numbers because all if the reciprocating weight is cumulative

Ok, I was trying to measure things with a wrist pin on a scale, but I can see now that it would not yield good results.

Does anyone here have an idea how good Oliver rods are concerned balancing of small/big end. I seem to have a difference of 1 gr across the total rod weight.
My crank had to be rebalanced and used one rod to do so.
I found some more differences between the small/big ends. But apparently my method is no good.

BTW : how accuratly are cranks balanced. I hear that it would be futile to go really small.

[CNC BLOCKS]

What would be a good way to weigh small ends and big ends on an improvised way ? How much difference can there be between the small ends and big ends of a set of rod before the balance is thrown off ?

Thanks

You need some sort of arbor to find the center of the bores to weigh them correctly
The rod also has to hang level

Like so



How much is very subjective,, guess it depends on what you will accept
I have seen so called balanced assemblies that had parts over 10gms different so I guess this is "acceptable" to some,, not to me

I balance to .5 gm per end & .5 total rod weight if possible
That is not ± .5 it is .5
You can also "juggle" parts to come up with acceptable numbers because all if the reciprocating weight is cumulative

Ok, I was trying to measure things with a wrist pin on a scale, but I can see now that it would not yield good results.

Does anyone here have an idea how good Oliver rods are concerned balancing of small/big end. I seem to have a difference of 1 gr across the total rod weight.
My crank had to be rebalanced and used one rod to do so.
I found some more differences between the small/big ends. But apparently my method is no good.

BTW : how accuratly are cranks balanced. I hear that it would be futile to go really small.

I worked with the great Smokey Yunik on a engine project years ago and asked him about engine balancing and his reply was balancing is an imperfect science and I think he makes sence with that statement.

A few years ago I went to another shop a guy was picking up his rotator and the shop owner was saying he had everything with in one tenth of a gram and was pretty proud of that and on the final spin it was with a couple tenths, After the bob weights we off I told him to put them back on a respin the crank and he did and the crank did not spin up the same it was out a few grams on both ends and he looked like the little boy that shit his pants

Its like the oil weight its only a gestimate at best. I have had rods out more then 5 grams on the big end and had to make up 3 different bob weights to make it come out right rather then hack up a new set of Lunati Pro mod rods.

[MotionMachine]

How close a crank is balanced all depends on who did it. I tell customers to get rotating assy's unbalanced because mail order balance jobs are rarely very good. How can they balance an assy when no pistons or rods have been removed from their original packaging? The worst I saw was an LS assy that the customer had ordered balanced but it shook so bad he had to take it back out and it required 80 gram removal on both ends. An extreme case but it happened none the less. Some OE's are very close to balance from the factory. Anything German and surprisingly most British inline cranks are very close, most of the time requiring no balance at all, go figure. Like Mike said, .5 gram is what I shoot for. If you're going to do it, it doesn't take that much longer to do it to near perfect so why not? I think the accepted industry standard is 3 grams. My balancer will read 0 if the crank is less than 3 grams. I have to go in and change the calibration every time so that it will read to two decimal points. I think it's probably more important to have all the rotating parts weigh the same than it is to balance the crank to the bobweight.

[Belgian1979]

FYI just read Olivers website and it states they have their rods balanced within .5 gram. My scale here only goes to 1 gram so seeing the total weight on the rods I tend to believe them somehow.

[engineguyBill]

Against my better judgment, I'll ask:
what does the rod's center of gravity have to do with reciprocating vs. rotating weight?

By ensuring that the rod is level doesn't really have anything to do with finding the rod's "center of gravity". By having the rod level, the weight of the big end is not influencing the weight of the small end and vice-versa. The ultimate goal is to segregate the weights of small end and big end from each other. The small end of the rod is reciprocating weight and the big end is rotating weight.

[PackardV8]

FWIW, I've never needed to touch an Oliver to the grinder. They are always within spec. However, trust, but verify.

jack vines

[panic]

The small end of the rod is reciprocating weight and the big end is rotating weight.

But... it's not. The separation of motion paths* isn't related to how much weight is on either end, but on what a molecule in any position is doing.

* very little of the rod mass is pure reciprocating or pure rotating weight.