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1998 KX500 ENGINE BUILD For Tim
sandblaster:
Thanks for another good job Todd 8-)
dave916:
Anyone know why todd drills those 4 holes {17mm] in the crank?
Guessing he is using them with some kind of alignment pins for truing the crank/ but i could be wrong
alward25:
Balancing with a Wossner rod and piston. Gets the crank to the right balance factor .
sandblaster:
What balance factor do you use?
sandblaster:
Ok, that explains a few things.
I know Todd uses 59% for the K5.
Now I'm really gonna step in it here.... :-o
From everything I have researched, it is difficult or almost impossible to cancel out all the forces involved especially on a single cylinder engine.
So, at some point, you have to compromise on all the different forces.
At first thought it seems simple.
Balance the crank, rod, and piston assembly so that if you set the assembly on a balance beam resting on the mains, the crank will not move regardless of the timing just like this video demonstrates:
https://www.youtube.com/watch?v=LzUjXA_aesM
Ready to rip?
Not so fast...
While the assembly is balanced statically, this will do nothing for the other forces involved.
Keeping it really simple and disregarding tertiary forces and such, think about what the piston is doing when it is moving really fast and then it has to change directions.... That's right, we have to factor in acceleration and deceleration of the piston, pin, bearing, rings, and top half of the rod.
To make matters worse, the top 90 degrees of crank rotation happens faster then the lower 90 degrees of crank rotation due to the angle of the rod.
Even if you could totally cancel out all the forced generated by the assembly changing direction at the top 90 degrees of crank rotation, you will then have a imbalance at the bottom 90 degrees of crank rotation.
What all this means is that depending on the balance factor used, the crank asy will vibrate more at certain RPM range then at others.
The object then is to move the major vibration causing imbalance to a rpm range that isn't used.
In the end, 59% seems to be the best compromise for the K5 crank asy....
Let the carnage begin :-D
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