Ordered a bunch of parts from Texas speed and had to have them ordered from a shop in Chico because I’m in California and they could bring them into the state. I just picked everything up after my stock crank was balanced with the forged rods and pistons that they ordered for me. Guy told me that it doesn’t matter which piston and rod goes with which cylinder. Does this sound right? Just trying to make sure they did the machining right. Thanks for any input

 

Replacement rods & pistons are usually made to be as close to identical as possible, and racing (NOT corner parts store) machine shops treat them that way as well. So yeah, it shouldn't matter which one goes where.

Not the same deal as messing with an intact stock assembly. Those, weird things can happen if you move rods around. Sometimes it's OK but sometimes ... not so much.

 

thanks so much! Just wanted to check. They’re wiseco and tsp parts so hopefully they’re good stuff!!

 

I was told the same thing when I purchased mine and call me OCD but I weighed everything to try and match all of it up to be as close to being balanced by weight as possible. Had a couple of rod, piston, wrist pin, ring combinations that came out 1-2 grams heavier than all the others and decided to put those on the 1 and 6 cylinders.

 

Cylinders 4&5 get less oil to the pistons. What do you do to compensate for the less oil weight?

 

Oh for those I just remove the 4&5 plugs and inject about 20cc into each cylinder..

 

What I'm getting at is, balancing to the single gram isn't useful. If it just makes you feel better, okay. But is doesn't have to be that precise. You also have crank twist under a load that puts things out of alignment, that you can't compensate for either.

 

It really doesn't matter which cylinder they go in. A crank is balanced with bobweights. Not the rods and pistons on them. Just make sure the rods and pistons are mounted and facing the correct way. I've built and balanced an engine or two over the years.

 

Crank bob weights are adjusted according to the weight of rods & pistons, usually by drilling, so that as the reciprocating parts go up and down, the mass of the crank parts moving in the opposite direction, counterbalances the other parts. They are not "fixed" and unchangeable.

 

I’d be curious to know how GM balances mass produced engines.
My guess would be the cranks are balanced with an assumed bob weight +/- a few grams.
I’d also guess rods are weighed at birth and coded in reasonably matched sets.
If someone knows different, do tell.
There are no balance pads in the stock stuff, not even sure how a guy would balance them.

I really can’t imagine there would be any issue with swizzling rod locations in a stock engine.

BTW, LS rods can go in in either direction. Even the goofy Gen 3 rods. Although they don’t look the same side to side.
Gen 4 are identical side to side.

This info from my machinist who has built 100’s of LS engines.

 

Last I knew, what they did was to sort rods & pistons into an n-dimensional array of bins, each holding parts within a weight range; total, big end, small end, and so on, all sorted out. Each bin might cover a 2 or 3 gram or so range, that being as close as they really care about. They made cranks with incremental bob weights to match, then when a bin of rods filled up, go pull a crank to match whatever they were, and build a motor out of it. AFAIK they weren't actually "balancing a motor" as such, the way we'd do it out here in shadetree land. But that was A LONG TIME ago. They may have slickened up their processes since then. Most of my teardown and building experience was with 60s and 70s motors, which were MUCH more crude than what we have today. You NEVER KNEW what you were going to find when you tore one down. Sometimes it became REAL OBVIOUS why some motors just always seemed to run better, or smoother, or made more power, or whatever, than other supposedly "identical" ones... quality control was SO POOR, they were anything but "identical" under the skin.

 

Perhaps the powdered metal technology is more consistent for weight.

Was just looking at digital scales....perfect if you want a kitchen scale.....about went cross eyed looking at Amazon stuff.

 

This is correct. It all gets sorted into bins and locations, according to weight.
Balancing an engine is not a cut and dry deal. Should I overbalance? Under balance? The machinist/builder must know and understand the use of the engine he’s balancing. The best way to look at balancing is from a harmonics point of view. You are trying to combat harmonics, which is a frequency, at a certain rpm range. Harmonics cause the assembly to go into a sort of battle with itself. Not a big deal if this happens at 7k and it’s a street engine that won’t ever see over 6k under load. But if it’s a race build, you must tune the harmonics...by balancing...much higher, or much lower. Harmonics at 5k in a race engine won’t effect anything, as the engine has the power in it to accelerate through the range. If the harmonics are present at 7.5k, you can prolly call it quits there. The engine is going to fight itself at that point, and it’s too close to its edge of power falloff to pull through it. Harmonics are present throughout the entire engine assembly, from the valvesprings, to the pushrods, timing set, etc. But speaking only of the rotating assembly here, it’s an issue that must be addressed according to the useable rpm range it will see.
A really good example of harmonics “fighting” against an object is found in tires. I raced asphalt latemodels for several years, and we could find a half a tenth by balancing our tires. The weight of our Hoosiers and our steel wheels at 95 mph was always at the threshold of a limitation. I ran on a 3/8 mile short track and 95 mph was our max speed on the straights. We actually spent more time in the corner than out on the chutes. Once we figured out the balancing thing, we could pick up a half a tenth per lap, and the tachometer would read a couple hundred more rpm on its settings after the run. Harmonics 101 right there.