Step by step crankshaft balancing?

LS614

LS614

Well-Known Member
Hi everyone. I am no idiot when it comes to engines, I have read both of the books in my signature cover to cover, but what I don't understand, still, is HOW you balance a crank. I would love a step by step explanation. For me it's the little things, like I don't understand how you weigh half of the con rod, or when you put the crank in a rig so it hangs freely what result are you trying to achieve there? do you want the heaviest part of the counterweight up or down? How do you know how much to drill out of the counterweight and where to drill it. I've read people's posts and I've read the books, but I still don't get it. I'd love if at least one person could give a step by step explanation. Thanks :)
-LS.wee.
 
LS,
The simple answer is: You CANNOT ballance a single piston crank shaft.
All you can do is affect the major frequency resinance to a point that has less effect in your operating range.
I suspect your overhtinkng it. :)
It is exactly as described here:
http://motorbicycling.com/f13/homemade-crank-balancing-4498.html
or here:
Balancing Small Engines by ET Westbury: Page 2
Look for an upcoming step by step pictorial of the proccess in an upcoming thread. I am building a 48cc giant killer with stock HT parts
 
Thanks for the reply, yeah I saw that thread but I didn't really understand how he did it. I know that you can't ACTUALLY balance a single cylinder engine, but he reduced vibration and I want to do the same. What I'm not clear about is how he actually used that rig for it to be effective. If someone could explain how he did it so I can understand better, I would appreciate the help :)
 
the "rig" is a simple pr of rods that are measured perfectly level in both X&Y planes

you can see the "ballance pig" bolted through the center of the big end bearing. (50 something % of recipricating mass)

& the rod is correctly hung on the level horizon to cancel its offset weight.
once set on the rods the cranks heavy spot will fall to the bottom. That is the area he drilled materal away to create a crank that would rest in any position.(with the rod still level)

To be NASA acurate you need to remove the con rod & elliminate any friction from the rod bearings or residual drag from any lubricant in the bearing itself.

Once you set up a ballance fixture like that you will be suprised at how tiny weights show how out of ballance something truly is.
 
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