383 Flexplate balance

[mjl91xj95xj]

Quick question for you Chevy veterans. I bought a 383 for my 80 Chevy K10. A machine shop in my area had it for a year after a guy dropped it off to be built and left town without paying them. They sold it to me and I had them put in an RV cam with a Performer RPM intake. The machine shop put the entire motor together and I picked it up on Saturday. The damper was installed, but it needed a flexplate. I have 3 questions, before I drop this into my truck.

1. How do you tell the difference between an externally and internally balanced damper?
2. Do I need to get the flexplate balanced, since a 383 is normally externally balanced? Does it need to be balanced with respect to the crank and damper(the rest of the engine.)?
3. Is it possible to neutral balance a 400 crank(internally) and then get a neutral balanced damper and flexplate?

I do trust this machine shop, I just want a little info before I call them and make myself look like an idiot. Its also been almost a year since they put the shortblock together, so if there are things missing, I need to get them looking.

Thanks,

Mike

[wrath]

Externally balanced harmonic dampers have a weight on them. The easiest way to tell is to look at the damper or roll it on something flat. If it always stops at the same spot then it isn't "neutrally balanced".

Summit #SUM-161400 is a bit pricey.

Externally balanced flex plates have a weight on them as well. You can purchase a weight that goes between your crank and flex plate for around $35 or you can buy a new flex plate for $65.

Summit #TRD-8951 is a bit pricey too.



If it's a stock replacement crank then any externally balanced harmonic damper and flex plate will work. However, the whole thing should be balanced together on a machine for use above 5,000 rpm I'm told. Your motor is already together though.


Forged 3.75" stroke cranks can be internally balanced. It usually requires 6" rods to help it balance and then they impregnate Mallory Metal (actually tungsten, a really dense metal) in the crank by drilling out a hole and then welding the hole back up. Some of the forged cranks they don't use mallory metal and just stick pieces of heavier metal in the counterbalancers and weld it up.
I've never seen a cast stroker crank that was internally balanced. Forged internally balanced stroker cranks are in the $540 neighborhood last time I checked.

[mjl91xj95xj]

Thanks for the info. I'm going to talk to them when I go to pick up the flexplate that I ordered. I've got a good feeling that he balanced the crank when he ground and polished it. He told me that I would need a 400 damper and flexplate when I met up with him the first time, but I was kind of surprised when he had already installed the damper when I went to pick it up. Either way, as long as all parts are neutral balanced, I ought to be OK. I don't plan on going over 5000, I'm not much of a lead foot in my truck.