Engine balance

[Rich G.]

Just looking to learn a little bit about internal and external balance on a 340. A long time ago my cuda had an automatic trans and I put in a 5 speed. I had a spare 340 sitting on the floor with a flywheel on it and put that in my car and it vibrated terribly. That's when I found out about internal and external balance. The hard way of course but an easy fix once I changed the flywheel. So the big question is how do you know what type of flywheel or torque converter you need buy looking at an engine without tearing it apart?

[7212Mopar]

Pull the harmonic balancer

[Rich G.]

And do what with it ???

[HP2]

No need to pull it, simply look at it. Internal balance balancers are all round on all steps and ridges. External balance balancers have an offset weight that is visible on the step just forward of the main round body.

[1972V21Cuda]

And do what with it ???

[JonH]

No need to pull it, simply look at it. Internal balance balancers are all round on all steps and ridges. internal balance balancers have an offset weight that is visible on the step just forward of the main round body.

correct above to read    EXTERNAL balance have an offset weight visible on step

[71383bee]

Weren't cast crank 340's a 73 only thing?  Or did 72 get them too?  Otherwise they were always forged.

Balancer is a dead giveaway as explained. The gorged is smooth with no noticeable weights. The cast has an offset weight on the front of it and look more bulky


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[mopartaz]

cast cranks had the external balancer usually 73 340 and 360's. Wider balancer . Good for street duty to 6k.

[Chryco Psycho]

Yes the balancer is the best clue but at that a cast crank engine can be internally balanced ,
Steel crank engines can vary in balance as well by using lighter rods & piston but generally they will remain internally balanced even if metal has to be removed from the crank .
Different 360s can be balanced differently as well , the 360 LA uses different balancing than the 360 Magnum , also the 440 was balanced differently from the 440 HP , the HP was steel crank but still used external balancing of a different weight from the cast crank 440 to compensate for the extremely heavy 6 pack rods used
the best way is to have the receipt or know the builder .

[1972V21Cuda]

Weren't cast crank 340's a 73 only thing?  Or did 72 get them too?  Otherwise they were always forged.

Balancer is a dead giveaway as explained. The gorged is smooth with no noticeable weights. The cast has an offset weight on the front of it and look more bulky


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Early 1972 340's had forged cranks. Eventually, they changed over to cast cranks during the model year.

[HP2]

No need to pull it, simply look at it. Internal balance balancers are all round on all steps and ridges. internal balance balancers have an offset weight that is visible on the step just forward of the main round body.

correct above to read    EXTERNAL balance have an offset weight visible on step

Should have proof read before posting.  Fixed it.