Harmonic Balancer (Internal vs External) for 1970 340 4-spd

[elevenssc]

I need a little education...

I bought a new harmonic balancer for my 1970 340 4-spd.  From what I can determine, I should need the internal balance version.  I say this because there are no weights on the original balancer or flywheel.  The flywheel does have 3 holes drilled in it, but I'm assuming these are for neutral balance.

Before bolting everything together and getting the engine back in the car, I want to make sure I got the right balancer.  Is there anything else that would help me determine if my 340 is internally or externally balanced?  Which "flavor" 340's were externally balanced?

Thanks.

[Topcat]

This is all I could find. Hope it helps.

http://www.moparts.org/Tech/Archive/smallblock/5.html

[challengermaniac]

I just crossed this bridge myself.  I believe you are correct in that the 340 is internally balanced.  When Summit Racing sent my new balancer, it had the weights on it and all I had to do was remove them for my application (internally balanced 340).

[Topcat]

As shown in the picture, the external balance 340 balancer has a raised rib edge on the inside. The internal one's don't.

[72bluNblu]

68-72 340's all had forged cranks and they should all be internally balanced.

'73 340's were the only ones that used a cast crank, they may be externally balanced, but I'm honestly not sure if they were or not. But any of the forged crank 340's should be an internal balance.

[71chally416]

I think the '72 340's also had a cast crank. 

[70 340]

Dont know if it came from the factory that way but my 71 has a cast crank.

[72bluNblu]

Dont know if it came from the factory that way but my 71 has a cast crank.

It shouldn't have. '71 340's were still high compression engines with forged cranks. 72 and 73 were the lower compression, cast crank engines (thanks 71chally416). Then again, if it were a late build '71 who knows.

[Aussie Challenger]

All cast 340 cranks are externally balanced unless somebody has gone to the expense of having it rebalanced like the old internally balanced forged cranks.