Balancing drivetrain

[gtw940]

Here we go! 78 motorhome 440, external balance. rebuilt the motor, some goodies in it etc etc. New BM flexplate 237, the one with crescent notch. and a New Hughes 24-30 stall convertor.
Engine has a large vibration first startup and a little tuning, literally too much vibration to adjust idle mixture.
So, I have the bullet nose stock balancer, the notched BM plate, but i do not remember if the Hughes convertor has a weight on it. The Factory convertor has the triangle weight! I will check this morning but I am pretty sure the New Hughes convertor is not weighted and the notched Flexplate is causing the imbalance.
I am assuming when changing from the "factory" flexplate to an aftermarket flexplate, it is notched to account for the weighted "factory" torque convertor and not a neautral balance aftermarket convertor. Soooo, I am thinking i just need to put in a flexplate without a notch OR add weight to the convertor. ????? Does this sound right? I tell ya these mopars have a learning curve and i keep going straight! 73 challenger, 440, aftermarket pistons, tfs270, tfs cam, tfs intake, HCR spacer, 727 etc etc

 

[Xcudame]

You have the correct flex plate if the torque convertor doesn't have a weight. Do you have the cast crank dampener on the front? It has offset weight as well.

I like this one from 440 Source as it can be used on either an external balance or internal balance by adding or removing the extra counter weight.

Internal / External Balance Black Damper

 

[Chryco Psycho]

Was the engine balanced fr the different pistons internally when it was built if so no external balance is nessisary , any time pistons are replaced the rotating assy must be balanced with a matching flex plate , if it wa not balanced who know what is needed to balance it properly .

 

[Xcudame]

Yes, I should have asked what all was done internally to the short block. If you swapped pistons, still have a cast crank, and didn't have someone balance it, you may have a situation where you will have to tear the egine all back apart. What pistons did you use? How is their weight compared to the pistons you replaced? Stock cast crankshaft (turned)? Stock connecting rods (reconditioned)? I assumed, wrongly, that with the money you spent on the top end, you spent the time and money to properly build the short block and forgot which external balance you need or don't need.

 

[moparleo]

Yes. Much more information is needed to help answer your question.
Did you build the engine your self or did a shop do it ?
If it was a shop did you tell them what your plans were for a coverter and flex plate ?

 

[gtw940]

Yes, I should have asked what all was done internally to the short block. If you swapped pistons, still have a cast crank, and didn't have someone balance it, you may have a situation where you will have to tear the egine all back apart. What pistons did you use? How is their weight compared to the pistons you replaced? Stock cast crankshaft (turned)? Stock connecting rods (reconditioned)? I assumed, wrongly, that with the money you spent on the top end, you spent the time and money to properly build the short block and forgot which external balance you need or don't need.

All is good, talked to Hughes and the shop that did my shortblock. balance is good, i have the trick flow .600 lift cam, kind of a thumper at idle. The vibration smooths out with acceleration, if it was an actual imbalance or mismatch of balancer, flexplate etc, it would try to come out of the mounts accelerating. I have seen that in other circumstances and its not pretty.
Engine was balanced correctly and convertor is neutral, just need to finish the tuning.