Does anybody care to educate me on how rotating assemblies are balanced these days? I'm apparently not up to speed. I always thought that the rods & pistons were put onto the crank and the whole thing got spun in order to balance it. I'm guessing that's not the case anymore? I bought a balanced rotating assembly from Texas Speed, and noticed that all 8 pistons have their weight in grams written on the underside of the pistons. The rods are still in their original sealed plastic, with a single card stating one weight (average of the 8?). I see that one or two of the crank weights have been drilled, so I'm guessing that the crank is balanced based on the measured piston weight and the, uh, assumed connecting rod weight?

Thanks in advance for the education.

 

rod assemblys are weighed with each end seperatly to distinguish between rotating weight and reciprocating weight.

ofcourse, the big end, bolts and bearings is rotating and the piston, pin, circlips and small end of the rod are reciprocating.

once the asseblies are weighed, you make up bob weights accordingly and strap them to the crank.

spin it, check your screen....works pretty close to a tire balancer

the computer tells you where to drill, how deep and what size bit to remove enough weight.

and typically, only the front and rear counterweights are drilled unless its seriously bad.

 

I ran into this same thing. They are suppose to equalize all pistons add weight of rod bearings and oil allowance. Come up with a bobweight and balance. I was told by one of the sponsers I received my rotating ***. from they try and match each rod and piston on opposite sides. Yet nothing was marked as to where it was to go and nothing had been removed from it's sealed package. I was told the bob weight method was blueprinting. duh. Had to have it rebalanced. Thank goodnes it was checked.

 

Is it standard procedure to just use the included weight number that's included with the rods for this? Although the pistons apparently all weighed within one gram of each other, I have a hard time believing that all 8 rods have identical weights.

Similarly, I don't see where any of the pistons were numbered to be assigned to a specific location, but since they're all within one gram of each other, I guess that wouldn't matter anyway.

 

the tolerance most people shoot for is within 1 gram. thats what i use anyways. reasoning is, you will spend a month on that balancer chasing a gram across the screen. drill, weld, drill, weld...if each piston assembly is within 1 gram, it doesnt matter where it goes in the block, as long as the pistons are pointing the right direction etc....

a little note, most factory engines are balanced within 25-50 grams...ish.

 

Take a look at Helicoil's thread. Start about port#53
https://ls1tech.com/forums/generatio...te-dyno-3.html

Great description and pics on the entire process.

 

Thanks for the info. Considering what Texas Speed charges for their balancing, it would have been nice if they measured the rods instead of just using the card.

 

Mr. Irace, I'll shed a bit more light on the tolerances here since nobody has yet.

Callies Compstar rods are +/-1gram of each other in their boxes when we get them. That is a tolerance Callies created and keeps up with for the aftermarket. They hold to it strictly. Your Wiseco pistons are weighed the same way and held to the same tolerance. The rods come with a sheet that says what they weigh, and it's always accurate from Callies....but, our machine shops weighs one anyway to ensure they are balanced properly. Anything beyond that, is "spinning the tires" so to speak.

Now a few examples of balancing tolerances that make you think a bit about how precise our balance jobs are. Say whomever balances your rotating kit gets the job done and sets the crank on the ground overnight. He comes in the next morning, and can't remember if he finished it or not, so he puts it back on the machine and checks it. Even though it was finished, it could read off by about 5-10 grams just due to the slight difference in how he hung the bob weights on the crank. You can see that much difference just by the slight difference in how the weights are centered on the crankshaft! You can also see 10-15 grams difference between two different machines, just due to the slight differences in the setup on the machines.

Now to put this into perspective: OE assemblies are typically balanced to within 25-35 grams....Our ROUGH balance is about the same as the OE's FINISHED balance! Yet, nobody really tests the OE assembly or complains about any nasty vibrations in them.

Now, to clarify, I am trying to give our machine any more of a high-five than they deserve...there are many machinests on this forum, sponsors and otherwise, that can and do balance their assemblies to the same tolerances and with the same precision and attention to detail. This is not an ad for Texas Speed rotating assemblies (although we do appreciate the business), rather just some more info so you know what you paid for and what you can expect from your kit!

Hope that helps.

 

It does. Thank you.