About
Balancing Engines for Less Vibration An imbalance in the crankshaft in relation to the reciprocating weight of the upper end causes vibration and a loss of power. Making sure your engine is balanced correctly is essential, especially if you are modifying the engine to work in a different RPM range than what it was designed for. Using a lighter wrist pin can help if the vertical forces are too much. Click here to read why I don't recommend using the balance factor method.
Click here to read of my tests which helped me develop my crank balance program. centrifugal force calculator (don't
enter linear speed. change m to mm, change kg to grams, change N
to lbf) Here
is a picture of my crank assembly with an additional balancing hole
just above the conrod pin. The 6 blue holes are lightening holes (although I wouldn't recommend any more than 4 if
the bike is for street use). The blue is foam filling half the hole.
The ends of each hole were later filled with JBWeld. I used foam just
to reduce the amount of expensive JBWeld used. The conrod hole and two
factory balance holes are already filled with JBWeld for increased
crankcase compression (although the change is very small). ![]() You can drill extra balance holes
with any good electric drill although it's a bit tough. Much easier to
take it to a machine shop and let them put it on a drill press. Also
the holes can be drilled at the TDC location of the crank wheels
without even taking it out of the crank cases. Just put duct tape on
the crank wheels (after cleaning them with alcohol) to keep metal
shavings from going into the crankcase, and then keep the crank in
correct position by using vise grips on the primary gear above and
below where it meshes with the clutch gear. You can measure from
halfway through the angled tip and mark the drill bit at the correct
distance with black electrical tape. That way you have a visual
reference while drilling. Click here to read more about my spreadsheet which can be used to calculate the size of counter balance holes needed in any single cylinder crank. |