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  1.  
    I saw an article on balancing crankshafts somewhere and now I don't remember where. I need to find some information to balance the peewee crankshaft, or get it closer. The article involved rolling the crank on 2 knifebladed pieces of steel. Where did I see that article?

    Steve
  2.  
    Steve
    Like you I can recall a few articles - mainly on single cylinder engines. One is a Geometer article from Model Engineer 6 June 1957, but much of that material is covered in the MEW reference below. I'll keep looking and pass anything along.

    Dynamic Balancing
    ->link<-

    Technique;
    ->link<-

    Some theory;
    ->link<-


    Garry
  3.  
    here's the Geometer article

    ->link<-

    Garry
  4.  
    Thank you. I'll get to reading!
  5.  
    Model engine news!!

    That was it!!

    Thanks again

    Steve
  6.  
    I just ordered a scale that will get me to .01 Grams. One thing that is not mentioned is how close to the same everything has to be. I think i'm going to shoot for everything to be within .1 grams. My big block chevy was within .5 grams.

    Do i expect to much? Anybody ever gone down this road before. Should I write another article? (Kidding)
  7.  
    your next clue.....

    ->link<-

    Garry
    • CommentAuthorjay rich
    • CommentTimeFeb 15th 2009
     
    balance lol i am lucky if i even come close the best way i have tryied to do this is by useing 2 glass rods and some wax by placeing the rods on a flat surface and laying you crank on it and give it i light spin it will tell you where it is off it works but here is a joke on my new engine the fron and back plate that hold the crank in with bearings is egged but whe the engine starts and fires it all goes straight so i think i will leve it alone so far i got a rpm of 6k out of it till i pulled the plug wires the engine started to scare me so until i fix it 6k and thats it ....jay
    • CommentAuthorkamran
    • CommentTimeFeb 16th 2009
     
    Is it also possible to balance the crankshaft by adding weight to one side of the flywheel?
    If so, what's the procedure for doing that?

    Thanks
    Kamran
    • CommentAuthordavid
    • CommentTimeFeb 16th 2009
     
    Many real farm hit and miss engines used weights on the fly wheels to balance the crank. The weights were cast in and I doubt any fine balance adjustment was done.
    When I build faster models I balance the crank shaft on knife edges till it will rest at any angle. I don’t include connecting rod or piston weight. I always check the flywheel and cut out some to balance it.
    • CommentAuthorkamran
    • CommentTimeFeb 16th 2009
     
    Hello David
    What is the reason for not including the connecting rod or piston weight when balancing the crankshaft? Wouldn't you be off when adding the piston, ring, pin, and connection rod to the crank?

    Thanks
    Kamran
  8.  
    Here is the way i understand it.

    Weigh the pistons with the rings on, and find the lightest one. Remove material from the heavy pistons untill they are all the same You cant modify the rings so they are added to the piston.

    The rods are hung horizontal and the big end is weighed with the bearing. Weight match the big ends. Now do the same for the small end.

    The wrist pins are done like the pistons.

    Balancers, flywheels, ect are spin balanced individually on there own.

    Then you take the weight of the piston, rings, wrist pin, and small end of the rod and add them together and devide by 2. So using half that weight and add the weight of the big end with the bearing. This will give you the weight of the temporary weight that is put on the crank throw when you spin the crankshaft on the leveled knife edges.

    Other than that, there is nothing to it.

    Steve
    • CommentAuthordavid
    • CommentTimeFeb 17th 2009
     
    Kamran,
    Over the years I have read a lot of ways to balance a simple crank.
    Based on no sound engineering, I believe the piston and the drag from the rings and a connecting rod with 2 pivot points, is separate from the crank. Its motion is purely reciprocating in the cylinder. I suspect half the connecting rod (because one end is supported by the piston) should be included at times but have never bothered.
    These are models. Mine are small and operate at low speeds (<5K RPM). If the crank weighed several pounds or was going to reach over 10K RPM I would be more concerned. When my engines run there is little vibration and I don’t have short bearing life.
    It works for me.
  9.  
    KAMRAN, what STEVEHUCKSS396 said in the post above you on ballancing is the correct way to do it.
  10.  
    Get this!

    I weighed my rings and pistons and put the light rings on the heavy pistons and the heavy rings on the light pistons. Then i installed the rings and reweighed the pistons.

    Then I weighed the rods and matched the heavy rods with the light pistons ECT and reweighed.

    Then I weighed the wrist pins and did the same thing.

    Final weight of the piston, rod, ring, wrist pin assemblys.

    8.79 grams
    8.79 grams
    8.79 grams
    8.78 grams.

    who's the luckiest person you know NOW!!