Are LT1 rotating assemblies really neutral balance in front?

[Spartan7]

This is purely out of curiosity.

Like many of you probably have, I've heard that the LT1 is external balance in the rear (made obvious by weights on flywheel/flexplate) and neutral balance in the front. But are they really neutral in the front?

I ask because the GM manual has some interesting info about the balancer. For removing/installing the hub (part the balancer bolts to), it says "Do not crank engine over after match-marking crankshaft hub and engine front cover. Rotating crankshaft will misalign installation of balancer to crankshaft possibly resulting in engine imbalance." And for the balancer, it says "If balancer is replaced, new balance weights of the same size must be installed on the new balancer in the same hole locations as the old balancer."

So if it's internally balanced, why would any of this matter? I've seen pictures of hubs and balancers drilled for balance, and a couple balancers of other cars with weights in them. But up until now, I've always assumed it was for balancing the individual piece to neutral. However, if the hub/balancer is neutral balance, then it really shouldn't matter how you reinstall it. And if the balancer is neutral balance, then why does GM say to transfer old weights to a brand new balancer?

This all leads me to believe that LT1's are really externally balanced in the front. Any of you experienced engine builders have some input on this? I'd also like to hear from any of you that may have replaced your balancer with a new GM one.

[Sahara54]

I reused the factory balancer from my stock LT1 on my new motor which completely internally balanced...no vibes. It's def. neutral balanced.

[Injuneer]

This article suggests that the stock damper was used to "trim the final engine assembly".

http://www.enginebuildermag.com/2000...et-lt1-engine/

Not sure how accurate that is. For example, the article indicates the LT4's higher CR was due to smaller 54cc combustion chambers, when in fact the actual difference between the LT1 and LT4 heads was 0.4cc.

Then there's the issue of accuracy of the factory manuals. The 94 manual indicates the PCM can flash the codes by shorting the ALDL pins.... no, won't work on a 94. This was carryover info from the 93 manual. The 95 manual shows two fan configurations, based on whether it was an early or late production model. In fact, it was 94 model year where the change occurred, and the diagrams used in the 95 manual are carryovers from the 94 manual. One can only wonder if the cautions regarding the damper are carryovers from the earlier manual for the L98.

Obviously, the Engine Builder magazine article is the most credible possibility - final trim with tiny weights pushed into the holes in the damper. Definitely not the same as the huge weight that is part of the Gen 1 SBC balancer.

[Spartan7]

I reused the factory balancer from my stock LT1 on my new motor which completely internally balanced...no vibes. It's def. neutral balanced.

Good to know. I'm glad I could get your encyclopedic input on this Injuneer, that definitely sounds like a good explanation. It would help to explain why GM didn't key the hub, if it was so important to reinstall it how it was taken off. Leave it to those crazy LT1 engineers to keep us guessing about stuff 20 years after it was designed. Thanks for quelling my curiosity guys.