Balanced rotating assemblies
 

I didn't want to mess up another gentleman's thread so I started this one.

Please tell me your expectations when you purchase a "balanced" rotating assembly. Are you thinking they will be balanced within a certain tolerance, as good as the factory job or just hoping it doesn't shake or vibrate.

Also would you expect the same quality of job if it was purchased from a large Pontiac vendor as you would say from Scat or Eagle or your favorite machine shop.

Anyone have any past issues with the balance job on their rotating assembly.

I would not trust any balance assembly. My machine shop has gotten balanced assemblies from Pontiac vendors, with issues. Everything is checked rods, pistons..crank. Its well worth the bucks you pay to have everything checked. To prevent a nightmare down the road.

For me, if I was doing this and purchased a balanced assembly from Butler, my expectation would be that I could take that assembly, and the block to my machine shop for the block machining and assembly and end up with an engine that would live for 50K+ miles. I wouldn't necessarily expect it to be a pristine piece that's 100% perfect in every facet, but I'd also not expect to get a much higher bill because the machine shop had to redo everything.

Or, if I was assembling myself and don't have the ability to even check balance, I should be reasonably certain that I have a product in hand that isn't going to vibrate itself to pieces a year after I assembled it.

That's my threshold anyway. If those can't be met with a kit, I'd prefer to work directly with a machine shop and buy the parts needed individually and have them balance and assemble everything. In this case I'd certainly pay a premium for that type of service, but then I want to know the engine is right. In my case that would be what is necessary to have a smooth functioning and reliable engine that would be seen as a moderate street build, not a racing engine.

I bought a complete assembly from Butler for my engine. My engine builder said despite all the other horrors I have endured it was primo

I don't trust them Paul and I know you've seen this too. And this isn't meant to bash anyone, but there are balancers out there and then there are balancers. Some are just pickier than others. Some get it close enough and you'll likely never see a problem, while others care about their work and will get them down to the 9th degree.

Just as an example, here are some pictures that show why I go to Paul C.

This assembly was already balanced, sent out the door because I guess they felt it was good enough, I then had Paul check it (first picture)

So Paul rebalanced it (second picture)

Here is more of the balance job that was supposed to be "perfect"

First pic is the before, second pic is after Paul was done with it. I think this was the flexplate.

I don't disagree with that idea at all JL and in a perfect world that 's the way it should be.
I'm on the fence about that very thing with my next engine build waiting in the wings. A brand new 502 GM crate engine that I want to turn into a 540. Rotating assemblies make the most sense and are about $3000 from Scat. However I'd be giving all that to Paul to sort out, rebalance, go through the rods etc... I'll have to sit down with Paul when this project gets closer and see if he just wants to piece meal the parts, picking certain brands that he knows will work that may be a better product to start with, or if he doesn't mind working with a complete rotating assembly from any one brand. I'd like Paul to make that decision. Either way in the end it will likely cost nearly the same anyway.

YouTube videos, of three different Pontiac guys who bought rotating assemblies from Butler that have checked put good. It’s a pretty good record I’m sure there’s more videos.

I have said it before, Mike Lewis told me not to mix up my pins with the pistons. So he must have balanced it to very close tolerances.
I need to have my other Scat, Ross, Molnar assembly balanced before he retires for good.
Thing is, as minute as those differences in the pin weights had to be, then you file fit the rings and you do not get them exactly all the same.

Wow, that's a nice balance. Our balancer can't get that close. It is a 1998 Sunnen DCB750. It can balance a heavy crank like a Pontiac to a 3 gram tolerance overall in high speed mode. +-1.5G. That's the best the software will allow. For reference, a 5/16" little stainless washer from ARP weighs right at 1 gram. The software give a fudge factor of 2 to 4 grams for 10W-30 vs 20W-50 oil sticking to the crankshaft and being flung around in the crankcase. Yes, a balance of 0-0 would be best and perfect. But a commercially rotating assembly kit within 8 grams left and right would be considered pretty darn good IMO.

At what rpm were those force values recorded?

How did the force values look moving up the rpm scale?

Sorry I don't know which balancer Paul uses. That was a Pontiac 455 rotating assembly

I don't know the answer to that mchell but I'll ask when I talk to him.

That's a Hines balance machine.... Nice unit

How much can a Pontiac be off before it shows up as a problem or vibration?

That other thread mentioned an LS being off 14 front and 26 back, and a Ford being off 35 and 55. Mike did not mention what the Ford was. I know of one 4.25” Butler rotating assembly that was off about the same as the Ford mentioned, it was checked then rebalanced. Would Pontiac’s heavy crank maybe be a factor in a good way masking balancing issues?

stupid noob question - I understand the concept of the balancing but what did they mean back in the day when they said "blueprinted"?

Does that mean factory tolerances?

Generally, yes. All dimensions checked and adjusted to within factory specs.

Should also mention that being within factory specs does not mean they are the right specs for all applications. Factory bearing clearances were allowed to be super tight, and you would not want to build a performance engine with .001" of oil clearance.

With respect to Paul's question, I don't know what specific amount of balance is acceptable.

If I was buying a "balanced rotating assembly", my expectations are that piston and rod weights are similar, and that the actual out of balance amount is tighter than factory specs. In almost all cases, a rotating assembly is using parts of higher quality for more durability/performance, so overall balance should be better than factory.

After reading posts about balancing, it occurs to me that I actually have no idea what is good or not, so if my assembly was off by 10 grams I really don't know if that is an issue or not.

I had my rotating assembly balanced, but have no idea to what value. Ignorance is bliss!!

I think the definition of "blueprint" varies.... Often I order pistons for guys and explain the compression height has to be determined off a "blueprint" dimension. Meaning the height of the deck. The factory used a specified dimension which varies a bit. A blueprinted specification would be a specific number. As you rebuild an engine there are many specific dimensions that have a tolerance. A blue printed engine would be set at a specific dimension. Alteast that's my definition of blueprint .... and "balanced" ;) Back in the day every high performance car in the Auto Traders had a "balanced & blueprinted" engine. Now those guys are ruling the performance pages on FB.

Thanks for your answer. Last I looked most rotating assemblies cost about $150 extra. Most shops seem to charge about $250 to balance a rotating assembly. I was curious why folks were buying the "balanced" assemblies. Most the balanced assemblies we see have one of each part weighed and the crank balanced. Most shops weigh every part and match each part to the lightest unit, then spin the crank. The spinning the crank is the biggest deal and there is no way to "check" that without going through the process of (balancing) spinning the crank on a balance machine.

If one is particular about the quality of their build, one would be better off letting the shop of their choice balance things rather than paying to have the assembly balanced and then asking their favorite shop to check it.