external to internal balance

[flatheadgary]

i have a motor home 440 engine that i assume is externally balanced. i also have a neutral balance steel crank. can i have the rods and pistons balanced to use the steel crank? it is backed by a neutral convertor 727 trans. i don't have the harmonic balancer and haven't cleaned the motor to see the stampings. do i need to buy different pistons and rods? i am just trying to build the motor as cheap as possible.

 

[steve340]

I am not an expert but here is an opinion for you.
You should be able to use your rods and pistons with the steel crank. It comes down to flywheels dampers etc having counterweight built in or not, as you know they are neutral if not counterweighted.
From what I know an external balance engine can be made internal by removing the external counterweights, and adding the weight to the crankshaft internal counterweights. This is done with a very dense metal called mallory metal.
If it works out cheaper and you want to save money just leave it externally balanced it is not a problem for 99% of engines.
A decent machine shop should be able to advise you the best way forward.

 

[Lefty71]

I think Steve340's assessment is correct, but I will add that it may be cheaper to find the right damper, put the weights back on the converter and just run it that way depending on its intended use, which he alluded to. But maybe too many parts have been changed?? Are these original rods, pistons, steel or cast crank originally?? Shouldn't be too hard to find the right damper, if that's all you need. Any part numbers on the crank, like a 7-digit stamping?? HTH, Lefty71

 

[66Satellite47]

The steel crank is an internally balanced part. Look at the rods, check if they are LY or "Six Pak" wide beam style. The steel crank with LY rods is neutral balance, although if it's apart I'd have the assembly balanced, crank, rods, whichever pistons you choose. Pistons are a function of what you want the compression to be & the condition of the cylinder bores.

 

[flatheadgary]

thanks for the replies. let me tell you about my situation. i have a fed with a 440 stock externally balanced motor in it. i can't find a balancer for racing that is externally balanced. i also have the other motor and was told it was a late model so i assume it is externally balanced too. it is covered up with tarps and i don't want to uncover it right now. i haven't seen the other crank for a while and am not sure where it is either. you can find internally balanced dampers all day long, not so much for the other kind. i got the steel crank with the fed with other parts so i would think the previous owner ran it that way. i also assume the convertor is neutral balanced. the fed isn't running yet so i will probably sort this all out when i get to it. the fed motor will go in my belvedere and the other motor will get the race heads and cam i got with the fed parts. thanks again

 

[wyrmrider]

with LY rods or other light rod you can make the swap with a minor internal reballance
with 6 pack rods an internal balance with non 6 pack dampner and converter/ flysheel or flexplate is expensive
best to change to lighter rods and pistons
back when we were running "stock" we used long 6 cyl rods- even lighter- never broke one

 

[66Satellite47]

The LY rods hold up well to lots of power. Good rod bolts, shot peened, good to go. 7000+ RPM. Stock steel crank has a limited life span at 7000. 6500 RPM or less, you are good for a long time with LY rods & stock steel crank. Light pistons are also great for both performance & durability.