26 replies to this topic

[S pack]

Here's an idiots thoughts- (me)


If you could work out the weight of each conrod and piston and what position they are going to be in the block once fitted,

would you be able to work out the weight differences between 1&6, 2&5, 3&4 and machine off all the counterweights on the crank except for the differences between 'pairs' so they are evened up on the crank- purely to counterweight the differences?



Or would that just create another harmonics problem?


Would matching the balance of the flywheel to the crank help? ie. some mopar engines which are 'externally balanced'?

I don't think any high performance engine builder would attempt to balance an engine that way. But I could be wrong.

AFAIK.
Basically.
Take the all the pistons, weigh each one and then machine enough metal off the inside (somewhere it won't weaken the piston) of the heavier pistons to make them all weigh the same.
Then you take all the conrods, weigh the big ends (with caps, bolts and nuts fitted) and machine enough off the pads until they all weigh the same as the lightest one.
Then do the same for all the small ends.
Each end of a conrod must be balanced individually as the big end is part of the rotating mass (crankshaft) and the small end is part of the reciprocating mass (pistons).
Then you can calculate the bob weights, fill and attach the bob weights to the crankshaft and balance it.

Externally balanced engines must be balanced with the harmonic balancer and flywheel fitted to the crank. Once the rotating mass is balanced (usually by adding weight to or removing weight from the crank, flywheel and harmonic balancer) you must always install the balancer and flywheel in exactly the same position on the crank or the balance of the engine will be out of whack.

Internally balanced engines shouldn't need the harmonic balancer or flywheel attached when balancing the crank, as long as the flywheel, harmonic balancer and clutch pressure plate (if manual) themselves are balanced.

I'm not an expert in engine balancing but I suspect that the old Red 6 might actually benefit from a combination of internal and external balancing techniques.
Where as the Blue and Black 6's with their fully counter weighted cranks would be much easier to balance using internal balancing only.