Huntr1117

iTrader: (18)

I've finally got my parts together for my new motor and I'm kind of stumped on what to do about my flexplate. I got a built short block that has 0 miles on it from local guy. I talked to the machine shop that did all of the work before I bought it. They verified that they had built the motor. The guy I bought it from gave me a brand new scat flexplate that is weighted and an ati balancer. He said that the flexplate was balanced to the new short block and that he had got it from the same machine shop. I talked to the machine shop again and they said that the motor was balanced but they couldn't find the records that said it was balanced with that flexplate or not. So what will happen to my motor if I install this weighted flexplate instead of a neutral balance flexplate? Will it cause any damage?

SS RRR

iTrader: (2)

It can cause damage. If you run it the way it is you'll pretty much know right away when you take the engine into the RPM band whether or not it is out of balance. The only way to be 100% sure as to how it is balanced is to disassemble and have it checked out by the shop, and possibly have it balanced using that flexplate. IMO this is a perfect example as to why an assembly should be internally balanced. That way all you have to worry about is having a flywheel/flexplate neutral balanced, throw it on and go. None of this guessing nonsense. Also, if for some reason you have to change out the flywheel/flexplate, you'll have to keep the original as a reference so the new one can be balanced the same as the original. PITA.
If you say the machine shop cannot find record, does that mean they are looking at a build sheet stating they have no record or does that mean they have no record of the block being built?

Huntr1117

iTrader: (18)

The machine shop has records. The problem is that there isn't just one record. The guy that had it built did it slowly when he had extra cash. The block got machined then it would sit there until he could afford more parts. Then he would have some work done under his personal name and some done under the name of the shop he worked for. It was there probably a year before he finally had it done. So now there's numerous records under different names that he's looking for.

BALLSS

OP

you will know IMMEDIATELY when you start the engine with a weighted flexplate on a "internal" balanced motor. It will vibrate like a dog shiating razor blades. You don't want to run the engine long this way.

If the shop can't find it's records as to "how" they balanced the rotating assembly...you have a 50-50 odds of the flexplate you have working

One + is the guy you got it from gave you the flexplate & damper (ATI is a very good one) and those parts are not cheap so there is a likely chance the flexplate was balanced with rotating assembly

If you can't get the confirmed records from machine shop you either roll the dice and try what you have or tear the short block apart and have the balance confirmed by machine shop

as SSR notes, you will have to have any replacement flexplate (should you ever need one) balanced to = whatever the Scat weighted one is

Huntr1117

iTrader: (18)

I just talked to a couple of builders near me and both said they've seen this before on a couple of Lt1 builds. Both said that I will notice immediately if its the wrong flexplate. They said don't run it long until I get the right one. One even said that he knocked the weight off while it was still installed and it worked fine after that. Not sure I'd be comfortable trying to knock a weight off installed still without damaging the flexplate.

BALLSS

the weight on a stock flex plate can be knocked off while installed. you rotate motor until you can see it (drop starter) and use a chisel. Aftermarket flexplates may have a stronger weld.

Would the flexplate be perfectly zero balanced then, possibly but ideally you want the machine shop to neutral balance one...even if it says it is zero balance, always worth checking before install IMHO