Explain it like I'm 5: Why do six pack rods require external balance weights?

[pettybird]

The answer is "because they weigh more", but this is a reciprocating assembly...why would the rods be heavier in only one direction?  And why are lighter rods OK with zero balance?  I can't make those two things compute.

[cdr]

the 6pack, 1970 up hp 440 rods are so heavy ,the counter weights on the crank are not heavy enough to off set the heavy rods ,so they put a weight on the balancer.

[pettybird]

So the crank is inherently imbalanced?  Are there more "throws" in one direction than others?  It's been a while since I've had a crank in my hand.

[cdr]

So the crank is inherently imbalanced?  Are there more "throws" in one direction than others?  It's been a while since I've had a crank in my hand.

yes, the crank without the rod & piston weight would be OUT of balance, high dollar racing cranks have counter weight throws for each pair of rods, others have very heavy throws at the front & rear of crank.

[cdr]

this is a regular type crankshaft, notice the counter weight, NOT in the middle.

[cdr]

this is one with weight for every pair of rods.

[BSB67]

The answer is "because they weigh more", but this is a reciprocating assembly...why would the rods be heavier in only one direction?  And why are lighter rods OK with zero balance?  I can't make those two things compute.

only the small end reciprocates.  The big end rotates.

The counter weights are simply not big enough to balance the rest of the stuff.  It can be internally balanced with mallory metal.

[Challenger340]

Why in the world anyone would use those 6-pack CLUBS anyways ?

Waaay heavier.... but exactly the same Rod Bolt fastener as the much lighter LY Rods ?     

Guess what the first "weak link" in any Rod Assembly is ?

If you said the Rod Bolt ?  BINGO !

[pettybird]

Ok thanks all.  I just couldn't visualize it for some reason.

As for 'why the six pack rods' I asked because my friend was having a balance issue with his torque converter on his #'s matching V code '71 R/T.  He's since had an original six pack converter redone.

[green69rt]

Why in the world anyone would use those 6-pack CLUBS anyways ?

Waaay heavier.... but exactly the same Rod Bolt fastener as the much lighter LY Rods ?     

Guess what the first "weak link" in any Rod Assembly is ?

If you said the Rod Bolt ?  BINGO !

You answered my question before I could even ask it!  I guess Mopar didn't expect anyone to race their 440 6bbl (yeah, right.)