hello all.
i did some researching on the subject of internal vs external balancing and had a couple of questions that maybe i can get some help with.
i have a 383 in my 96 camaro. I purchased a Lunati set from Jim Cook Performance which included the rods, pistons and crank. Jim said that he would balance the set for me. ok, cool. but i did not give him my front balancer or flexplate.
i have the motor out now and am in the process of rebuilding it.
i have purchased a fluid dampner ( i know this is not a cure for vibrations) and have purchased a Vigilanted torque converter. my flexplate is OEM and HAS a weight on it. i have read in other posts about the flexplate being neutrally balanced.
i am looking for advice and recommendations on what to do for my particular set up. any thoughts? sorry for the long post.
now, if i could just get that LT1 to work in my 87 GMC full size truck, that would be awesome!! lol
later and Happy New Years!
Lee
96Z 383

 

when i went to get my bottom end balanced all i gave them was the crank, pistons, rods and they asked for the flexplate because they didnt have anythere at the time, they dont need your harmonic balancer but i think they would need the flexplate, but they do come balanced and dont to be rebalanced that much thats pry why they didnt aske for it but thats what i think.

 

You need to ask the shop to be sure. They may have neutrally balanced the whole rotating assy., in which case you need a new, neutral balance flywheel/flexplate. Or, they may have balanced against a standard 350 SBC external balance flywheel/flexplate. Either is acceptable. It's more expensive to do a full internal balance because of the labor and the need to use Mallory (heavy) metal. You can use your existing flywheel/flexplate even if the motor has been internally balanced by removing the counter weight. It won't be perfect but it will be close.

Rich Krause

 

Am I correct in thinking that an LT1 comes stock with a zero balance flywheel and harmonic balancer? Or are they setup to offset the balance of the rotating assembly?

To make more sense of what I said, if the rotating assembly stock was not zero balanced, did they modify it, or did they correct the out of balance by adding counterweight to either the balancer or flywheel?

 

I am not sure of your terminology. But take a look at an LT1 flywheel/flexplate. It has a counterweight, in fact, the stock pieces all have the same counterweight. Each OEM assy is not individually balanced. They use a standard counterwieght and rely on production tolerances being close enough to give an adequate balance. And it works! The front of the motor is neutrally balanced however.

Rich Krause

 

Ok, so if I have an SLP billet flywheel then does it have the same counterweight? If so then the machine shop would for sure need to have the flywheel at the time of balancing in order to zero balance the entire assembly? The front of the motor however doesnt matter since whether using stock balancer or AM dampner that piece is zero balanced correct?

 

You are close. They may have balanced against the standard external counterweight. In that case, they wouldn't need your specific flywheel. Though, as I said, using a different flywheel would not be quite as accurate. As far as the front goes, that's right. Any neutral balance pieces will work. You really should call them to find out what they did.

Did I mention how expensive internal balancing can be? My new rotating assy cost over $400 to balance. It took 4 pieces of Mallory metal (at over $50 per) as well as the labor. My friends Hemi has over $500 of Mallory metal in the crank

Rich Krause

 

Correct me if Im wrong here Rich, but when you buy a 4340 crank from either eagle or scat or whoever, isnt the crank already balanced, then they just shave off the pistons or rods however they do it to balance the whole rotating assembly. Im all the sudden really confused about how the whole operation works. I was told at first to use a 4130 or 4340 crank so it is internally balanced to make it cheaper. But to internally balance a cast crank is where it becomes expensive since it is not already. Where am I thinking wrong here?

 

All cranks have counterweights. For a given crank configuration, there will be a specific amount of "bob weight" that the counterweights will offset. If you install rods and pistons with that bob weight, the assembly will be balanced with no additional work. That's how the OEM's do it, though in most cases the counterweights don't completely balance the rods and pistons and some additional external weight is required. IOW, back to the situation with the stock rotating assy and flexplate/flywheel.

Aftermarket cranks may have larger counterweights and a forged crank is denser than a cast piece. In fact, when installing a very light set of rods and pistons it may be necessary to take weight off the counterwieghts (by drilling) rahter than add Mallory metal. So, an aftermakret forged crank will be easier to balance to a given set of rods and pistons than the OEM cast crank. And you could say (of any crank) that is "already balanced" against a specific bob weight as manufactured. But for high end engine assembly, the ideal is to check the balance of your specific parts.

External balancing is cheaper than full internal balancing and works well. Some people think that full internal balancing puts less stress on the crank than an external balance. Internal balancing is more convenient because you can switch flywheel/flexplates at will, as long as they are neutrally balanced.

Rich Krause

 

thanks for the help all.
so, do you think i would be ok if i got an aftermarkert 153 tooth flexplate to replace the OEM (with the weight) which is on their now?
i m not gonna ship the rods, pistons, crank and flexplate back to Tennesee where i got the package.
thanks again.
Happy New Year too.
Lee
96Z 383

 

rskrause =

 

You really have to check with where you got the rotating assy, or have someone locally check it. In all likelihood it will be either neutral or balanced against a stock counterweight.

Rich Krause

 

you think i can get away with taking the weight off of the flexplated? wont be perfect but maybe better than before.
also, when i order a new one, do i want an external or internallly balanced flexplate?
I am assuming that the internally one would come without the weight on it.
thanks.
Lee
96Z 383

 

If the assy is internally balanced you can get away with just removing the counterweight. Won't be perfect but should be ok unless you plan sustained high rpm use.

Rich Krause