CR500 Crank Balancing

 Straight Talk

With so much controversy over crank balancing in general, I figured I would give more insight on the subject. Since the Honda CR 500 seems to be the most popular item of discussion, I’ll start there.  First of all you have to realize that every crank is different in some way. The vendors who make the cranks change over time and so does the process. There are so many variables to consider.

First the forging itself, the density of the material, the mold it’s conformed to . Next you have the process of taking the raw forging and machining the appropriate journals and the position of the crank pin holes.  The locations vary to the forging as well as amount of material removed, etc.  The thickness of each web is not the same and the location of the hole to the web is also not consistent.

So now we bring ourselves to the balance procedure. I‘ll try to give you some insight without giving up any proprietary information.  As some of you may already know, the same motor in different applications and mounts makes for different vibrations. For instance a YZ 450 in a dirt bike frame is relatively smooth where as the same motor in the quad chassis has noticeably more vibration.  

We have been stroking and balancing cranks at STR for 5 years now and have had nothing but praise for how smooth our motors are.  Where there are many different balance factors you can use, the most important part is how the cranks are balanced. To do it right it is very time consuming. The crank must be disassembled and put back together with nothing on it. Then after weighing the appropriate parts you create a formula using rotating mass and reciprocating mass to establish what’s called a bob weight. Keep in mind now that all these cranks are different .

After spinning in the balance machine, a specific amount of weight is added or removed at a specific rotation of degrees (different on each crank half). This completes the balance process and the crank must be disassembled and reassembled in the same manner.  Dead balls true!! Crank width perfect!! Without the proper jigs and fixturing this would be impossible. Now add the skin feature of the CR 500 and you can see how this can create a problem. The reason some people take the skins off is mostly because they are damaged in the rebuilding process. They are meant to be crank stuffers to increase crankcase pressure and to reduce friction.

So in conclusion I can tell you that depending on the weights and balance factor, some get weight added and some get weight removed. It is always in a different location. So having the experience and knowing what I’ve heard, some companies may just pick a consistent location and add or remove material without going through the process of proper balance technique (no disassembly at all).  Most people think it’s always 180 degrees form the crank pin. They couldn’t be more wrong. The machine reads the vibration on the journals and has to take into consideration what I call the gyro effect. It’s not only up and down, but side to side as well. Maybe these are the critics who say it doesn’t matter. 

All I do is build race motors and to do it right takes time and pride. I don’t just wing it! My reputation is all I have to grow my business and it seems to be working nicely.

Good Luck

“The Wizard”