I gotta be honest, I'm starting to pull my hair out trying to figure out how my setup got balanced 9 years ago. Since the short block was built 9 years ago, I've taken it out to put in a different car and not running a T56 any longer but will run an automatic. So now the issue is figuring out what kinda flexplate to run. There was some confusion about it being a one piece rear stroker with an externally balanced crank, but the T56 needed an LT1 flywheel that I'm not sure if I found as "externally" balance or not? I remember talking to the guy on the phone about the balance issue (not local) and he told me if I could send them the flywheel and balancer that I was going to run....they would "make it work". I'm pretty sure that he mentioned something about possibly "neutrually" balancing it, but I'm not exactly sure what happened though. The whole internally/external balance thing can get a little confusing, so here's a couple pics of the flywheel and balancer. Can anyone tell what may have happened/how it was balanced?

 

Your flywheel was balanced by the removal of the metal in the making of the 14 holes of approx 1" diameter at the bottom of the photo . That was the heavy side , and they removed metal till it matched the light side ....

As to your Dampener , I don't recall seeing the extra bolted on weight that's on there being on any that I've seen lately , but then lately I've been tinkering with a six , so that may or may not be normal for an eight .....

 

The weight added on the balancer indicates a true "EXT " balance as only used on 400ci cranks.

 

Maybe not
If crank is true ext ( 400 ) balance they they would not be neutral balancing the flywheel as you suggest
400 flywheel is only true EXT balance flywheel

 

Do you think my best bet would be to get an external balance flexplate?

 

Your best bet is to not even WORRY about all that "internal / exteranl" carp at all.

Just get a stock-weighted flex plate, and send that AND your flywheel (assuming the flywheel ran smooth) to the balance shop to have the flex plate made the same as the flywheel. Which is SUPER easy to do; they just bolt em up together but 180° apart, and make the combo neutral.

Leave the damper alone. (assuming the motor ran smooth before)

It is the art of cutting through the intellectual confusion and clutter, and getting right straight to the point of what it is you want to accomplish.

 

Hmmmm...great minds must think alike cause that's exactly what I was hoping could be done but wasn't sure as I had not gotten down to my local machine shop yet. I'm gonna try and make it down there later today to see what they say. Hopefully they have a "can do" attitude today seeing how on most days, this machine shop tends to whine and cry a lot about how they can't do certain things, lol.

 

Well I went down to the shop today, but still a little confused. I'm not 100% confident that he knew what he was talking about. He said that if I got a flexpate that had a weight on it, he was "99%" sure it would balance the same without doing anything else. He even said that you're not supposed to do anything to the flexplate to balance it anyway, only the crank. But he noted to cast in weight on the flywheel and said that as long as a new flywheel had a weight on it, it should be the same. But if I understand correctly, a weight on a flexplate would be for an "internal" balance application right? I would have thought that I would need an "external" balance application (without weight) since the orginal crank was supposed to be external balance and the dampner being weighted like a 400?

 

That looks like a standard everyday LT1 flywheel to me. Many stock ones have those balance holes on the back including my stock replacement. Mine has 6 I think and I have seen some that have as many if not more than yours. I would tend to side with the machine shop in that if you bolt up a stock 1 piece RMS flexplate everything will be fine.

 

True to the extent that if you have a "stock " engine ; you should be able to bolt on any other stock flywheel / flexplate ( correct for that engine; 1 or 2 pce RMS ) without problems

In a " built" engine it is common for the flywheel to be balanced along with the rest of the rotating assembly to fine tune the balance better than the factory
and take into account different weight of non stock parts ; such as lighter pistons
In that case the flywheel has been balanced to one particular engine combo and a replacement needs to be balanced the same

 

Do you have any info on what crank was actualy used?
You may have something like this ;
http://www.summitracing.com/parts/ESP-103523750/
a 1 pce crank with 400 ci true EXT balance requiring a 400 weighted balancer and flexplate
As I noted earlier it is posible the shop balanced your flywheel to the 400 balance required wth this style crank

In any case as Sofakingdom said ; any compentent shop should be able to duplicate the balance on a new flexplate

 

No, that's the thing, I don't have any info. I even contacted the shop that built the engine 9 years ago but as I figured, didn't have any record of the build from that long ago.

And if memory serves me correct, that would have been the type of crank used...1 PMS with external balance. I'm just not sure how a 1 PMS can be called an "external" balance if it doesn't have the weight on the rear of the crank like the 2 PMS's do.

 

You are confused
Has been debated here many times in the past BUT
both 1 and 2 pce cranks have same ( internal ) balance arrangement.
The change of seal arrangement on the 1 pce crank meant the weight you speak of could not be cast on the crank flange so the weight was moved to the flywheel
The crank bolt pattern was changed at the same time to prevent guys accidently installing wrong style one

On a 400 with the larger stroke they could not get the metal they needed to balance the engine inside the block so a 400 has the counter weight on the flange like any other 2 pce crank
PLUS addition weight on the flywheel and balancer.This makes the 400 crank the only EXT balance arrangement SBC
They make a plate ( for 2 pce crank at least ) that allow the use of a lighter neutral balance flywheel on a 400 ext balance crank
http://www.summitracing.com/parts/SES-3-60-11-026/

1 pce cranks are referred to by sellers as EXT balance because they have a weight on the flywheel but this just confuses everyone