DIY dynamic crank balancing

For do it yourselfers.

Its an extra step but it should help bring your crank to a more accurate dynamic balance.

Remove the flywheel. Rotate one side so it is like a 180 degree crank (journals 180 degrees from each other). Bolt it up without the flywheel and drill the heavy cheek until its balanced (use knife edges, lathe ways etc). This will reduce the rocking from side to side. Its not super accurate machine balancing but it should get you close enough.

Finish up with static balancing by replacing the flywheel with a bob weight and drilling the flywheel.

You can also DIY static balance by hanging a string through the journal holes with your balance factor weight on the string. When done check that the crank sits exactly straight up on the knife edges with the bob weight removed.

Would be interesting to see some pics/vids of each balance technique.

Great and interesting solution to this problem.
For those near enough to a shop that can static/dynamic balance a crank ($200?) is this effort worth it?
I like your thinking though!

I balance each cheek individually and start on the flywheel once both cheeks are perfect - not earlier.

Yes the cheeks should be balanced first (the dynamic balance).

Here's the dynamic balance technique again:
Remove the flywheel. Rotate one side so it is like a 180 degree crank (journals 180 degrees from each other). Bolt it up without the flywheel and drill the heavy cheek until its balanced (use knife edges, lathe ways etc).


Then the flywheel should be added and balanced (static). The images below are for static balancing - taken from my race manual.

Primary balance is more important than secondary. When you have a crank with a balance factor in the low 50s, it usually runs vibrationless at fairly low revs - any secondary imbalance is probably more likely to be felt.