<VV> Rod caps and balancing

[tony.underwood at cox.net]

---- Eric Aos <ericaos at yahoo.com> wrote: 
> I don't buy that. Think of a two cylinder opposed engine, the big ends go around together.   

...uh, no.    The big ends are 180 degrees apart.    

This is why the 'Vair crank has no counterweights.   Balance the big ends together (then the pistons and rod pin ends) and that pair will run smoothly regardless of what the other pairs of pistons/rods weigh IF they are also balanced to one another.   (within reason, of course)   


> The small ends going back and forth are going the same direction,  

No... they NEVER go the same direction together.   They always move either towards one another or away from one another.   


If the pairs of rods shared a journal, the crank would MANDATE counterweights or the engine would rattle itself out of the engine bay in short order.   

> so they are not canceling each other, they are helping each other.   

No, sorry.   They "help" each other by indeed "canceling" each other out.   


>   The total of 1&2 needs to equal the total of 3&4 which needs to equal the total of 5&6.  

Not at all...  I've mixed and matched pairs which were NOT balanced to one another and the engine ran smoothly.   I DID make sure the rods were the same weight and the big ends close as I could get them.   Pistons too, which is kinda easy since they only have to weigh the same as one another (per pair) and not what any other pistons in the engine will end up weighing.  

This is one of the reasons a 'Vair engine is easy to balance (if done right) with relatively simple tools.   

    
>   Long story short... balance ALL rods & pistons.

Balance the pairs together, sure.   But 1+2 do NOT need to be balanced to 3+4 or 5+6.   They CAN be, but it's simply wasted time and effort to do so.   

That includes racing engines as well as street grocery getters... 


tony..