Crank Balancing revisited

[HeadSmess]

Now I know lots of engines (like my 125 2 stroke dirt bike) vibrate much less when running in their powerband. I'm gonna take a guess and say that the smoother combustion occurring at that point is the missing variable as to why some engines smooth out with rpm.

this is a phjenomenaim (wtf?cool typo!) familiar with. i believe its because the factory sets their balance factor to coincide with the max rpm determined by porting etc, and then the exhaust is tuned to that rpm, all combining to make smooth bands... would you seriously want to get on it if they tried vibrating you off?

but even the HT runs smoother with a pipe...


one small point about this 50% balance factor and so forth which is a bit of an error in your calculations. its not a direct subtraction as you have written.

i believe that when a crank is balanced the procedure is much like this...

the piston, rings, pin and clips are a given weight, with little room for improvement.

these are all weighed.

the conrod, the lil end is weighed, and used as reciprocating...add to piston weight.

the other end of rod is rotating, so weigh that too.

now, a block is made to clamp to the crank pin.

this block weighs, say, 50% of the total reciprocating weight...piston and lil end MINUS the rotating portion of the rod weight.

the crankshaft is then spun to speed and balanced in the same fashion as any other spinning object- removing bits off it.



how to balance a rotary? iunno! hows that thing going anyway?