Balance Question

[Virg464]

Had my motor built by a shop (Petit Racing, in Mich) that my good friend recommended, they do all his engine work. My question is balancing: the motor is a 400 (external balance), the rotating assy was balanced during the build, do I still need to run an ext-bal flex-plate (the one with a scallop cut)?
I have a ext-bal flex-plate, but I'm concerned if I install it and don't need it, will that make the motor want to jump out of the car, damage the trans, crack the flex-plate, all of the above?

 

[beanhead]

If they balanced it internally (removed/added weight to the rotating assembly), then you should be using a neutral damper and flexplate, spec'd for internally-balanced engines. Best bet is to ask the builder...

 

[Grabbergreendream]

If you have an original external balance flywheel from that engine and the crank was not changed out, it would have to be a cast crank. The amount of Mallory metal needed to zero balance the crank would be VERY expensive. I doubt it was zero balanced, because the builder would have also needed a harmonic balancer as well as the flywheel, I believe.
Sounds like you will need to contact the builder for details.

 

[Gunner1]

You can call the shop. They can tell you if you need external or internal accessories.

 

[bm02tj]

There is a flex plate for use with unweighted converter
Or you can add metal to your flex plate as I had done 45 years ago

 

[Virg464]

Thanks guys, I'll call the shop and ask which flex-plate to use. That's the only thing that didn't come with the motor when I picked it up, hence the question.

 

[Lefty71]

Your shop can not do a proper balance job on a motor
Iike that without the balancer and converter in question IN HAND, not just a flexplate. Therefore, this is a question best answered by them, not us. Good luck, they will know.

 

[MoparLeo]

Amazing that they didn't give you this very important information..