BBC connecting rods

[prairiehotrodder]

I took a stock set of BBC truck connecting rods into the machine shop to get re-sized and new pistons pressed on. I never looked closely at them or anything, i just had them all on a wire from some motor i took apart years ago. The machinist called me to let me know that he was hesitant to work on them because he noticed there was alot of difference in the weight pads on the ends of the rods so he weighed them. He found there was 11 grams difference from the heaviest to the lightest. Is this normal ? I checked a few other sets of rods i have and it looks to me like there is a big difference within a set on the size of the weight pads. My scale is a cheap chinese kitchen scale which gives a different weight every time i place a rod on it.
Brian

[Ericnova]

Normal for a factory balance. Actually pretty close if only 11 grams spread between the whole set, I've seen 30+ difference in factory stuff.

They didn't balance stuff to the high tolerance performance shops do.

Sounds like your machinist is too used to modern parts and aftermarket parts, which are matched much closer.

Back in the old days, the biggest part of doing a balance job on a performance build using stock rods was the time spent weighing, grinding, and equalizing the weights of each end of the rods.

[Geoff2]

Hardly worth spending money on old rods that might be out of balance, out of round, old fasteners...considering the cheap cost of new rods made from better steel.

[ProPower engines]

I took a stock set of BBC truck connecting rods into the machine shop to get re-sized and new pistons pressed on. I never looked closely at them or anything, i just had them all on a wire from some motor i took apart years ago. The machinist called me to let me know that he was hesitant to work on them because he noticed there was alot of difference in the weight pads on the ends of the rods so he weighed them. He found there was 11 grams difference from the heaviest to the lightest. Is this normal ? I checked a few other sets of rods i have and it looks to me like there is a big difference within a set on the size of the weight pads. My scale is a cheap chinese kitchen scale which gives a different weight every time i place a rod on it.
Brian

For what its worth when selecting stock rods look for the smallest balance pad on either end.
If you take the time to carefully measure the rods all over you will find more material in some places with the smaller pads and less in other places where strength is needed.

[mag2555]

Back then GM ruff matched the Rods weight wise and then once assembled spun up the whole darn short block to balance the motor ( yes, your reading that right, they spun up the whole thing! ) which was only to a low tolerance so that on average the motor felt good to the average driver and did not tare itself apart up to 5000 rpm or so .

[BILL-C]

Only 11 grams difference from lightest to heavy is actually average for a stock set of bb chevy rods. If your new pistons are press fit pins, then the stock rods with new arp bolts are still a good choice for a moderate build.

[vortecpro]

11 grams is typical for thumb type rod. But I'd be more worried about the small end press myself. It seems shops that do a 180.00 balance job are concerned with the "spread" I say tool up, and charge more and don't worry about the "spread".

[PackardV8]

For what its worth when selecting stock rods look for the smallest balance pad on either end. If you take the time to carefully measure the rods all over you will find more material in some places with the smaller pads and less in other places where strength is needed.

For true. I've learned the hard way not to trust eyeball balancing. Way back when, I ground the balance pads on both the big end and small end so they were smooth and looked identical. Then, when I put them on the gram scale, expecting to only remove a bit to make them weight the same, there was way more difference in small end weight than the eyeball said there should have been.