con rod balance ?

rod · 06-20-2015, 11:04 PM

I was just weighting a set of rods [I beam small journal 327 SBC], reconed by the machine shop. all are within 1/2 a gram except one which is 2 grams light. [has to be on the big end, cause the small end has nothing to loose].
what is the acceptable +/- spread?
thanks
Rod in AZ

carl hinkson · 06-21-2015, 08:50 AM

Quote:

Originally Posted by rod

I was just weighting a set of rods [I beam small journal 327 SBC], reconed by the machine shop. all are within 1/2 a gram except one which is 2 grams light. [has to be on the big end, cause the small end has nothing to loose].
what is the acceptable +/- spread?
thanks
Rod in AZ

What is meant by the small end has nothing to loose ??? Both ends should be weighed to see which end is out.

That being said I see alot of the GM crate circle track engines and have seen rods per set off as much as 8 grams and those engine run for years with zero problems and look very good when disassembled.

You should be fine.

John Dinkel · 06-21-2015, 11:40 AM

Two grams is the weight of 2 $1.00 bills.

carl hinkson · 06-21-2015, 01:20 PM

Quote:

Originally Posted by John Dinkel

Two grams is the weight of 2 $1.00 bills.

If its 2 grams on the big end that would be double when figuring a bob weight and that would be 4 dollar bills.

Adger Smith · 06-22-2015, 03:45 AM

If you are not swinging the rods and weighing from end to end you are killing time. Assuming a set is equal on each end, big are equal as well as small ends, is a pretty big assumption. I've run into sets that are as far off as 7 or 8 grams. I think that is about the + or - for auto makers tolerance. Read a good tutorial about balancing before you start grinding on anything.
I bought my first balancer in 1977 and there is no telling how many mismatched components I've seen. If the rods were at one time a balanced set the resizing probably did take a couple of grams off the big ends.That happens on every set that is resized and all you can do is equalize them to the lightest one. Or if you want to cut the amount of change of the bob weight in half.... match a heavy rod with a lite one to make a pair.

rod · 06-24-2015, 08:23 PM

the small/little end has been computer cut, there is no extra material. all small ends weigh the same. the big end pads are all there is to cut.
so I assume that 2 grams is within normal race tolerance.
thanks
Rod in AZ

Adger Smith · 06-24-2015, 09:39 PM

Not at my shop. 1/2 gram is the number for me. If you are not re balancing the crank that will put you in an over balance situation on the bob weight If you are talking about a total change of 2 to 4 from where the rod was when it was first balanced it will be ok. The big end is a X 2 multiplier on the bob weight calculations.

06-20-2015, 11:04 PM	#1
rod Member Join Date: Dec 2009 Location: Kingman, NW AZ. in the middle of the longest stretch of Route 66 Posts: 305 Likes: 0 Liked 17 Times in 13 Posts	con rod balance ? I was just weighting a set of rods [I beam small journal 327 SBC], reconed by the machine shop. all are within 1/2 a gram except one which is 2 grams light. [has to be on the big end, cause the small end has nothing to loose]. what is the acceptable +/- spread? thanks Rod in AZ

06-21-2015, 11:40 AM	#3
John Dinkel Senior Member Join Date: Nov 2005 Location: Pinckney, Michigan Posts: 500 Likes: 348 Liked 233 Times in 62 Posts	Re: con rod balance ? Two grams is the weight of 2 $1.00 bills. __________________ John Dinkel 3295 STK

06-22-2015, 03:45 AM	#5
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,348 Likes: 433 Liked 676 Times in 260 Posts	Re: con rod balance ? If you are not swinging the rods and weighing from end to end you are killing time. Assuming a set is equal on each end, big are equal as well as small ends, is a pretty big assumption. I've run into sets that are as far off as 7 or 8 grams. I think that is about the + or - for auto makers tolerance. Read a good tutorial about balancing before you start grinding on anything. I bought my first balancer in 1977 and there is no telling how many mismatched components I've seen. If the rods were at one time a balanced set the resizing probably did take a couple of grams off the big ends.That happens on every set that is resized and all you can do is equalize them to the lightest one. Or if you want to cut the amount of change of the bob weight in half.... match a heavy rod with a lite one to make a pair. __________________ Adger Smith (Former SS) Last edited by Adger Smith; 06-22-2015 at 03:46 AM. Reason: sp

06-24-2015, 08:23 PM	#6
rod Member Join Date: Dec 2009 Location: Kingman, NW AZ. in the middle of the longest stretch of Route 66 Posts: 305 Likes: 0 Liked 17 Times in 13 Posts	Re: con rod balance ? the small/little end has been computer cut, there is no extra material. all small ends weigh the same. the big end pads are all there is to cut. so I assume that 2 grams is within normal race tolerance. thanks Rod in AZ

06-24-2015, 09:39 PM	#7
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,348 Likes: 433 Liked 676 Times in 260 Posts	Re: con rod balance ? Not at my shop. 1/2 gram is the number for me. If you are not re balancing the crank that will put you in an over balance situation on the bob weight If you are talking about a total change of 2 to 4 from where the rod was when it was first balanced it will be ok. The big end is a X 2 multiplier on the bob weight calculations. __________________ Adger Smith (Former SS)