I've heard it both ways... That Lt1 motor is externally balanced and that it is internally balanced. So which is it? And if it is external, is just the flexplate/flywheel balanced, or is the damper also responsible for balancing?

Thanks.

One more thing! Is Nu-Tek motorsports out of business? There phone is disconected and they don't seem to know how to respond to an e-mail... If they are, does anyone know a good machine shop in Ohio?

 

The answer is "yes".

The old 400's were externally balanced front and rear.

All other 2 piece rear seal SBC's are internally balanced.

1 piece rear seal SBC's are internally balanced front and externally balanced rear. Look at an LT1 or TPI flexplate and you'll see a weight spot-welded to it. That's for external balance. Very important: LT1/TPI do not use the same flexplate or balance weight as a 400.

However. . . my 383 LT1, even though it is 1 piece rear seal, is fully internally balanced due to the Eagle crank with larger counterweights. We had to remove the balance weight off the flexplate to get it to balance.

Mike

 

I had the same question when I was installing my new clutch. The stock LT1 rotating assembly is neutral balanced in the front at the damper and counter balanced at the flexplate/flywheel. In other words, it is balanced only at the flexplate/flywheel. All motors are internally balanced to some extent otherwise they would simply shake to bits. The balance weight welded to the flexplate (or cast in the case of a flywheel) is there to take care of minor machining differences. Many members here have also had their rotating assemblies internally balanced while the motor was apart, negating the need for external weights.

 

An LT-1 is set up with the front half internal (no weight on balancer) and the back half external balanced(weight on flywheel or flex plate).1/2 & 1/2

 

The balance weight is there in 1 piece rear seal motors because the rear of the crank is shaped different.

Compare a 2 piece and 1 piece rear seal crank and you'll see that the 2 piece seal crank is not round at the rear.

Mike

 

So if I decide to go with a 383 that is internally balanced... I will need to remove the weight on my flexplate! And will I need to then rebalance the flexplate, or is it good enough.

Also If I throw new pistons on the stock rod/crank. Do I need to keep piston weight in a certain range so that it will balance correctly? Or could someone walk me through the steps to get this assembly properly balanced?

Thanks

 

You don't have to touch anything.Take your crank,rod's,pistons,pins,locks,rings,and brgs to the machine shop an they will be the judge.Let a PRO make the decisions on what to remove.
Your NEW pistons need to be damn close to the original pistons weight to not need rebalancing,A few grams.Again ask your machinist.
Anybody who balances engines can "walk" you through it.Let a PRO do it and quit worrying.The machinest is the only one who needs to know how to do it.You have to have trust in him to get it done.

 

Agree 100% with 1racerdude.

Don't even consider doing this yourself.

Some 383's require the weight to be removed, some don't. I thought they all required the balance weight until we did mine.

Mike.

 

There's a couple recent threads within the first few pages with some GREAT info.

Bottom line is take it to a REPUTABLE machinist and have it done.

 

State you want the flexplate/flywheel balanced separately, in case there is any question.