Rotating assembly balance?

[loud2004marquis]

Researching into balancing the rotating assembly for a forged lower end and was wondering if anyone here who has gone through the process can tell me the tolerances held for their build?

[Ourobos]

They're zero balanced. Usually pistons come within a gram, preferably a half gram of each other. What are you looking for in particular?

[loud2004marquis]

Got a rebuild book and the author is saying to have the assembly "Dynamic Balanced." Said to have connecting rods and pistons precision balanced to within .1 gram of each other. Not sure how common this spec is?

Sounds like it's above and beyond, but I'm still learning.

[Ourobos]

Half a gram is pretty much as close as most machine shops are going to get it. Most quality piston and rods sets are pretty close from the get go. Some piston sets don't even require balancing, but should be check of course. For example, I put a set of Diamond pistons in my 03 Cobra, stock rods and crank, and the weight on the diamonds was so close to the stock pistons, we put it together and cranked out 455rwhp with the stock blower no issues.

[Marauderjack]

Dynamic Balancing uses attached weights to represent rod & piston weights on each journal.......spin and add or remove weight from the crank counterweights as necessary!!

https://www.youtube.com/watch?v=J-skHy97PFQ

Good shops usually attach the harmonic balancer and flywheel to achieve best balance for the entire combination!!

My 408W was balanced to 0.10 gram!!

Here is a more detailed video:

https://www.youtube.com/watch?v=M_PeWKnTchI

[Ourobos]

With these engines being neutral balanced, the flywheel and dampened shouldn't be necessary, but if they want it, hey more power to them. If a manual transmission, a good shop will want the pressure plate sometimes as well.

[BeeDamn]

Sorry for Hijack but, What is the weight gram for our Rods and Pistons? So if I ignore the rotating balance because nobody here can doin it I have to match the weight gram? is that it?

[Curless]

On any of our builds we zero balance the entire rotating assembly, always use the balancer and the flywheel when balancing. We also add in the weight of the rings and bearings when calculating... if you don't, you are not accurately doing the job.

[Ourobos]

^ Can you elaborate on why you say to have the dampener and flexplate to balance a zero / neutro balanced engine? Doesn't make sense to me.

[Curless]

^ Can you elaborate on why you say to have the dampener and flexplate to balance a zero / neutro balanced engine? Doesn't make sense to me.

It will not affect the "balance" of the engine's internal components, however if they are not "zero" balanced (none of them are perfect or even close for that matter) out of the box, you can pick up a vibration. For the extra 10 minutes it takes to mount them both, we have them done. Read this article and learn about how much weight changes when spinning on an axis... ever hold a harmonic balancer? They are not light... want one slightly out of balance on your engine?

http://www.enginebuildermag.com/2013...increase-life/

[Ourobos]

I understand the balancing concept, I was an ASME certified machinist for 8 years.. And I do agree, if you already have the dampener and flexplate, supply them to the machinist, ESPECIALLY if it's a manual, the pressure plates are hardly ever uniform.. BUT..

Here is the only thing in that article I could find about a neutral balanced engine :

"The flywheel and clutch are neutral or zero balanced, which means engine balance is unaffected if the flywheel or clutch have to be replaced later."

Tells me if you balance the pistons and rods to the counter weights of the crank, to ZERO imbalance, the supporting pieces are not necessary to balance..

Only reason I ask is I've had many engines balanced when I hadn't purchased the flywheel / flexplate or dampener yet, and never had any issues with neutral balanced engines. If the machinist is good, they're not needed IMHO.

[Curless]

I understand the balancing concept, I was an ASME certified machinist for 8 years.. And I do agree, if you already have the dampener and flexplate, supply them to the machinist, ESPECIALLY if it's a manual, the pressure plates are hardly ever uniform.. BUT..

Here is the only thing in that article I could find about a neutral balanced engine :

"The flywheel and clutch are neutral or zero balanced, which means engine balance is unaffected if the flywheel or clutch have to be replaced later."

Tells me if you balance the pistons and rods to the counter weights of the crank, to ZERO imbalance, the supporting pieces are not necessary to balance..

Only reason I ask is I've had many engines balanced when I hadn't purchased the flywheel / flexplate or dampener yet, and never had any issues with neutral balanced engines. If the machinist is good, they're not needed IMHO.

You did not read what I wrote.... "It will not affect the "balance" of the engine's internal components"

If you want to have a #7 pound weight, hanging off of the front snout / hub of your crankshaft, spinning at 6500 RPMS and not know if its truly zero or not have it... Like I said, it costs no more and takes very little time... to each his own.

[Ourobos]

Guess that attests to the need to buy a quality dampener and flexplate.

[MOTOWN]

Only a complete idiot would attempt to balance a rotating assembly without the flexplate/flywheel , and the harmonic balancer.

[Ourobos]

The voice of LOGIC.. Muahahah

No valid reasoning to add to the discussion, let's use our inner city upbringing to throw around some dirty name calling..