Technical Dodge 318 harmonic balancer

I plan on running a 1970 318, with a 1995 3.9L AX-15 5 spd. From what I know, the 318 is internally balanced. I have the flywheel from the 3.9L, but not sure if I can use it, because I believe the 3.9L is externally balanced. What is the easiest, and the most economical way to solve this problem?

 

You could take it to a machine shop and have it 0 balanced.

 

You could grind the counterweight off of the flywheel. I did it to a GM 2.8 flywheel once and used it. No real guarantee that will make it "balanced" but you could try it.

 

just combine both ideas...first grind off the weight, then take it to be zero balanced.

 

According to the Mopar engine bible the 1970 318 has a cast crank and should therefore be externally balanced I believe.

 

Look at the front balancer. If it has a noticeable lump on one side it's external. If it is equal all around (as if it was made on a lathe) it's internal balance.

 

Haven't looked at a 3.9 'wheel lately but if it is like a 360 wheel then there are NO weights...there are, or should be, three very large drillings in the back side. You could duplicate the drillings on the exact opposite side of the wheel or you could just get a new wheel. NOTE: the AX15 bell housing will require a 143 tooth flywheel, NOT the uber common 130 tooth. I have bought new flywheels from O'Riellys for as little as $100....just a thought.
As to whether or not your 318 has a cast crank, AFAIK, a 1970 should be forged. My 1972 service manual only indicates a cast crank in the 360 and my Engine Manual, 9th edition, says in the intro, pg 43, that the 318 from 68-72 is forged, but in a chart on pg 51 it indicates cast.....
Yes, 1972 is generally considered the start of cast cranks but in this particular FSM the 318 and 340 are omitted from the cast crank discussion.
As mentioned, look at the 318 dampener. If it is gone then you will need to pull the pan and look at the crank.

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318 was internally balanced when they had a cast crank, too. The 360s were all external balance.

 

So if the balancer is there it will almost settle the internal- external question but be aware that shade tree mechanics have been known to switch out inappropriate parts! It's a 40 year old engine.

 

The motor came out of a 1970 Dodge Tradesman rust free camper van. 68,000 miles. I might have the motors backwards on witch ones are balanced how. After reading this and looking at my parts, I think the flywheel is balanced and the harmonic is not.

 

Is it a bad thing if the flywheel and harmonic balancer are balanced the same? What if they are both externally balanced?