# Hit&Miss Balance



## cobra428 (Apr 16, 2009)

Hi All,
In getting my engine to run for the first time and there was a terrible vibration. I had to clamp and just about chain it down. I get Gas Engine Mag (full size engines) so I looked thru some issues and at the pics and saw that some had grooves cut in the flywheels some had extra weights added either in the casting or screwed to them. I messed with adding weights similar to those they balance your car wheels with. I ran the engine and still vibration. Well to make a long story short, I put out a post on engine balance and Marv sent me to a site with a formula and procedures to figure all this out. I didn't do the math (sorry Marv) but I did the essence of the math. Here are the results, I took my model airplane prop balancer out and used it to fine tune my FW, crank, piston and rod assy. After this......sa...moooooth. Thanks Marv :bow: :bow:





You can see the radial groove cut in the FW at the outer rim (both wheels =)




Once I get it Blinged Out I will post a video of it running
Thanks Again for the Help
Tony

http://www.modelenginenews.org/etw/etw_bal/p2.html

PS&#160; Marv I didn't use the math because....It I believe it was set up for a moment arm of a counterweight = to the arm of the the crank throw. I had a arm = to 2* that, so I had to play!!! But the formula was a great help in understanding.


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## Hal (Apr 17, 2009)

Tony

Thanks for the pics.

I can understand how to balance the fly wheels and the crank.

But how and what position do you hold the rod to balance it ??????

Hal


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## cobra428 (Apr 17, 2009)

Hey Hal,
That pic does not show exactly how I did it but it shows the assy in balance. The way I did it for real....

 I adjusted the height of my balancer to be ~9/16" above the surface plate (1"cyl /2)+1/16. With the crank assy in the balancer I rested the piston on the surface plate. Now I did the "Egyptian" I took 3 pin gages .060 .061 .062 and placed them under the piston so that they will roll when the piston goes back and forth (this saved me making some fixture of some kind). I then placed weights opposite the crank throw till all&#160; was balanced and stayed at any position I put it in. The weights just gave me an idea as to how much material I had to remove to obtain the balance without the weights. Or if I decided to go the other way how big do I have to make the counter balance weight to add on. This will only work for a horz. motor. A vert motor I think you would just hang the piston a rod and balance till the crank throw would always return to the horizontal. I'm not sure about that, we need Marv to chime in on that one. This is just a static balance. Dynamic balancing, like they do on your car wheels, well that takes a very expensive machine. But for our purposes I think static balance is good enough.

Tony


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