Rotating Assembly Balancing Question
Thread Starter
TECH Regular
iTrader: (7)
Joined: Aug 2009
Posts: 444
Likes: 2
From: Muscle Shoals AL,
Rotating Assembly Balancing Question Ok here is my question, back in the old days on the old small blocks. When you had your rotating assembly balanced, the shop required that the complete assembly be balanced with the harmonic balancer and the flex plate. However when I spoke with a ( BIG ) supplier concerning purchasing a rotating assembly from them. I was going to have them balance it before it ship's out to me. After speaking with a couple of local machine shops about doing my machine work, they said that the assembly needs to be balanced with the balancer and flex plate. I am at a loss as to if the LS engines actually have to be balanced with or without the other items. I need some questions from others please fast. As I want to order my rotating assembly by the end of the week Please help!!!!!
In for the answer, as I'll be facing this soon. From what I understand, the LS does not need to be balanced with any external parts. That said, I replaced the manual trans flywheel on my engine with a neutral balanced flexplate and now have a lot of vibration from 3k up...
Many people here replace their balancers (which are not even keyed anyway) and clutch/flywheel assembly without worrying about balance issues. So I would just balance your internals.
Lets see if memory serves ,,,,,,,,,,,I believe the sm bl 400 is externally balanced meaning if You were to have the rotating *** balanced it would require the flywheel/flexplate to be on the crank and the harmonic balancers on the older engines were heavier because My guess is that They were'nt balanced as close internally to start with hence the heavier balancer/pulley.
So the 350 and every other sm bl gen 1 was internally balanced . But were talking factory balance which is'nt as close as having a machine shop balance You're **** so that would be why They still want the flywheel/flexplate because They are close only so You're ending up with an engine that just because of the aftermarket balancing will have maybe 10 more hp and be a little more efficient and potentially last longer .
The LS engines are much "closer" to the perfect balance than the gen1 chevy's were including the flexplate and fr pulley/balancer so They probably won't require those parts to balance You're rot *** and then with the parts on You'll still have a very well balanced engine ,,,,,,,,but every mach shop is prob diff so check first with You'rs .
So the 350 and every other sm bl gen 1 was internally balanced . But were talking factory balance which is'nt as close as having a machine shop balance You're **** so that would be why They still want the flywheel/flexplate because They are close only so You're ending up with an engine that just because of the aftermarket balancing will have maybe 10 more hp and be a little more efficient and potentially last longer .
The LS engines are much "closer" to the perfect balance than the gen1 chevy's were including the flexplate and fr pulley/balancer so They probably won't require those parts to balance You're rot *** and then with the parts on You'll still have a very well balanced engine ,,,,,,,,but every mach shop is prob diff so check first with You'rs .
Launching!
Joined: May 2012
Posts: 209
Likes: 1
From: NC
The old 400's needed the flywheels and HB to balance externally because they relied on counterweighted flywheels/flexplates for proper engine balance. With internally balanced rotating assemblies it does not matter as mallory is used instead. As a matter of fact you can get lightweight nodular iron flywheels for the old SBC's that do not have externally balanced flywheels which reduce an engine's rotating inertia and improve throttle response. They also make it harder to drive on the street with manual transmissions because of the reduced rotational mass.
older smallblocks were often neutral balance far as the damper but had a certain weight counterweight on the flexplate/flywheel that was consistent and the final adjustments were made internal.
This is how the LT1s are and I think at least the other one piece rear main smallblocks been so long since O worked on a 2-piece rear main SBC I don't remember.
I wouldn't see anything wrong with a shop wanting the damper and flexplate/flywheel so long as they were using them to just make sure it was all balanced nicely together. If they wanted to drill or weight one of them to do the balancing I would stay the hell away from them.
This is how the LT1s are and I think at least the other one piece rear main smallblocks been so long since O worked on a 2-piece rear main SBC I don't remember.
I wouldn't see anything wrong with a shop wanting the damper and flexplate/flywheel so long as they were using them to just make sure it was all balanced nicely together. If they wanted to drill or weight one of them to do the balancing I would stay the hell away from them.
Trending Topics
The 400's were externally balanced, requiring the fly and balancer. The 2 piece 350's and such were semi internally balanced. They were balanced internally with holes and slugs, but still had a counterweight "external" of the block, making it semi internally balanced.
The 1 piece rear engines as well as ls were totally internally balanced.
The 1 piece rear engines as well as ls were totally internally balanced.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Five Reasons the Camaro Was the Most Pivotal Player in the Pony Car Wars 2.0
Brett Foote
10 Reasons the LS7 Is GM's Most Extreme Naturally Aspirated V8 Engine Ever
Verdad Gallardo You want me to go take a pic of an LT1 flexplate with the external weight? I think it safe to assume the LT1 would have been handled the same as the other one piece rear main SBCs.
I agree the 400 was external front and rear.
If you are saying the 2-piece were done with a standardized external weight on the rear then that is the same as the LT1 and that said I think it safe to assume all the other one piece rear main SBCs would have been the same, why would they change for a few years in the middle between the 2-piece and LT1?
I agree the 400 was external front and rear.
If you are saying the 2-piece were done with a standardized external weight on the rear then that is the same as the LT1 and that said I think it safe to assume all the other one piece rear main SBCs would have been the same, why would they change for a few years in the middle between the 2-piece and LT1?
55-86 small block internal balanced. 400 small block external balance front and rear. 86 and up 1 piece small block including LT internal balance front and external rear. Why I have no clue but those are the facts. The one piece rear main must be balanced with the flywheel/flexplate unless it is converted to neutral balance. If a machine shop asks for all parts it is because they want to check the balancer and flywheel or flexplate to be sure they are zero balanced. People need to quit posting incorrect ****.
You want me to go take a pic of an LT1 flexplate with the external weight? I think it safe to assume the LT1 would have been handled the same as the other one piece rear main SBCs.
I agree the 400 was external front and rear.
If you are saying the 2-piece were done with a standardized external weight on the rear then that is the same as the LT1 and that said I think it safe to assume all the other one piece rear main SBCs would have been the same, why would they change for a few years in the middle between the 2-piece and LT1?
I agree the 400 was external front and rear.
If you are saying the 2-piece were done with a standardized external weight on the rear then that is the same as the LT1 and that said I think it safe to assume all the other one piece rear main SBCs would have been the same, why would they change for a few years in the middle between the 2-piece and LT1?
I don't know about a weight on the LS engines but the weight on the LT1 flexplate is WAY more than would be needed to balance the flexplate.
I understand that even a neutral balance plate would likely have a spot where some weight could be added or removed to make it neutral.
google pic search for LT1 flexplate turned this up as the second pic.
http://www.google.com/imgres?imgurl=...QEwAQ&dur=2549
That hunk of metal isn't to balance the flexplate it is to balance the rotating assembly.
I understand that even a neutral balance plate would likely have a spot where some weight could be added or removed to make it neutral.
google pic search for LT1 flexplate turned this up as the second pic.
http://www.google.com/imgres?imgurl=...QEwAQ&dur=2549
That hunk of metal isn't to balance the flexplate it is to balance the rotating assembly.
I don't know about a weight on the LS engines but the weight on the LT1 flexplate is WAY more than would be needed to balance the flexplate.
I understand that even a neutral balance plate would likely have a spot where some weight could be added or removed to make it neutral.
google pic search for LT1 flexplate turned this up as the second pic.
http://www.google.com/imgres?imgurl=...QEwAQ&dur=2549
That hunk of metal isn't to balance the flexplate it is to balance the rotating assembly.
I understand that even a neutral balance plate would likely have a spot where some weight could be added or removed to make it neutral.
google pic search for LT1 flexplate turned this up as the second pic.
http://www.google.com/imgres?imgurl=...QEwAQ&dur=2549
That hunk of metal isn't to balance the flexplate it is to balance the rotating assembly.
Using the balancer and flex plate to balance internals is a thing of the past.
^ You really have a lot to learn if you think the rear of an 86 and up 1 piece rear main is internally balanced. Go read a book and learn something. It has to do with the added weight at the rear of the crank/ different hub.
After some more thought if you look at the back of a 2-piece rear main SCB there is an additional counterweight at the rear of the crank, that is how they are internally balanced.
The one piece rear main gen 1 and gen 2 stuff doesn't have that weight so there is the big hunk of metal at 6oclock on the flexplate in the pic I linked. If the LS engines are comparably externally balanced please post a picture of said weight.
I think your missunderstanding is that the weight on the flexplate of the one-piece rear main stuff is generally not modified it is left alone and the actual material removal or weight adding to fine tune the balance is done internally, but the weight on the flexplate is still a counterweight, the flexplate is not neutral it just has a standardized imbalance.
The one piece rear main gen 1 and gen 2 stuff doesn't have that weight so there is the big hunk of metal at 6oclock on the flexplate in the pic I linked. If the LS engines are comparably externally balanced please post a picture of said weight.
I think your missunderstanding is that the weight on the flexplate of the one-piece rear main stuff is generally not modified it is left alone and the actual material removal or weight adding to fine tune the balance is done internally, but the weight on the flexplate is still a counterweight, the flexplate is not neutral it just has a standardized imbalance.
The counterweight on the back of the crank of a 2 piece rear makes it externally balanced. It is external of the crank case. This is the same logic your using, saying the weight on the flex plate makes it externally balanced. It doesn't change the fact it is external of the crankcase.
I understand there is some debate to that which is what we are seeing here being that the counterweight is part of an internal engine component, but that still does not make a whole lot of sense.
If this were the case, no 1 piece rear small block or ls engine would run on an engine dyno because of the absence of the flywheel or flexplate.
I understand there is some debate to that which is what we are seeing here being that the counterweight is part of an internal engine component, but that still does not make a whole lot of sense.
If this were the case, no 1 piece rear small block or ls engine would run on an engine dyno because of the absence of the flywheel or flexplate.
I see what you said about the rear only. I agree with you. The counter weight was moved from the crank to the flex plate. But that does not make a 2 piece engine internally balanced as some are stating.
