Understanding External Balance

Helping my brother with his 360 we are going to be sending to the machine shop. I had my 360 all internal balanced when we stroked it to a 408 and have never messed with external balance.

Please correct me on any misconceptions I have. My understanding is that the 360 harmonic balancer is not externally balanced to that exact engine but a standard amount of weight is added to all 360 cranks to keep them within a certain balance tolerance? Also you need to either have an external balanced flexplate or Converter. The flexplate preferably external balanced so you can use any converter. When we bring everything to the machine shop we need to make sure they have the external balanced balancer that was on the engine or another 360 balancer and the external balanced flexplate we are going to use. This way they can be sure everything is in balance when they put the new KB flat top pistons on and add or remove weight from the balancer and flexplate to make sure it's right.


Thanks a lot

As assembled from the factory, yes, they are balanced to the parts they are assembled with. However, the tolerance was such that parts could be interchanged. If that makes sense.

The “balancing” is done on the crank itself at the machine shop.
You prefer to not mess with the damper or flexplate for balancing.
This is so they can be replaced if necessary with other standard parts.

For externally balanced cranks, the correct damper and flex plate need to be mounted on the crank during that operation, but any adjustments that need to be made....... are made to the crank.

That is just the crank portion of the balancing process.
There is also the weight matching of all the components to each other.

So, yes...... for a 360 SBM, to have a normal balance job done, the shop will need all of the rotating assy parts, including the weighted damper and flexplate.

That really clears it up.


Thank you

PRH said:

The “balancing” is done on the crank itself at the machine shop.
You prefer to not mess with the damper or flexplate for balancing.
This is so they can be replaced if necessary with other standard parts.

For externally balanced cranks, the correct damper and flex plate need to be mounted on the crank during that operation, but any adjustments that need to be made....... are made to the crank.

That is just the crank portion of the balancing process.
There is also the weight matching of all the components to each other.

So, yes...... for a 360 SBM, to have a normal balance job done, the shop will need all of the rotating assy parts, including the weighted damper and flexplate.

Click to expand...

with todays lighter pistons (and rods), most all Mopars can be made to be internally balanced. Really the way to go as it opens up damper selections. Flex plates are not enough mass to balance and cast cranks were not heavy enough to counterbalance the stock pistons and rods so they had to add metal to the balancer and convertor/flywheel