Part 2a: The math of STATIC BALANCING and doing it in practice.
The math is different from dynamic balancing. But the result is the same.
So it often happens that the persons using one and the persons who uses the other method, don't understand each other.
We now want to calculate a replacement weight, the bob weight. This weight is acting on the crank pin, such as pistons, rings, etc. , but only with the intended percentage.
When we add this bob weight to the down hanging conrod and the crankshaft stops in each position, the crankshaft is balanced statically.
Preliminary: Determine the weight of the
2 piston rings
Small end bearing
Reciprocating part of the connecting rod
The first 5 positions are easy to determine.
The 6th makes some difficulties.
Position the connecting rod in that way that it lies as level as possible. The upper conrod end will now be weighed. (The weight of the lower connecting rod does not interest at all.)
...done. When we add our six positions above we get 110 grams.
Now we think. We want to compensate the 6 weights together, let us say with 40% of their true mass. 110g x 0,4 = 44g for the bob weight?
BUT THE CONNECTIONG ROD is hanging there with 100% of its weight.
It should hang with 28g X 0,4 = 11,2g. But it doesn't. From the rod there are hanging 16,8 grams too much. Problem...16,8g too much. So the 44g bob weight is wrong.
Don't laugh at me. You know the solution: Reduce the first calculated bob weight by 16,8 grams. 44g - 16,8g = 27,2 grams is the correct bob weight in this example.
Sum all 6 positions => result1;
result1 x percentage /100 => result2;
upper conrod part x percentage /100 => result3
upper conrod part - result3 => result4
result2 - result4 => bob weight
Now take some nuts, washers or whatever you have laying around and fasten it somehow at the conrod. Ribbons, wire, a bag - no matter. But its weight becomes part of the bob weight and must be considered.
It should only hang freely and must not disturb the rotation of the crankshaft.
The appropriate base for our work:
You can position the crankshaft with the main bearing journals on two flat and exactly horizontal surfaces.
The easier and probably exacter way is to use absolutely new not oiled or greased 6202 bearings and some brake pads. You will be astonished how difficult it is to prevent this unit from rolling off. Even if you thought the base was horizontal.
The HT engines with 3 part crankshafts have kidney-shaped notches on the inside. This is the balancing from the factory. And this is the area, where we should take away some more material or add some.
Here is the state of the flywheels from factory
Miniature cutters in action
Here, the state afterwords. 38g less. I can fill the holes again. Either to add some weight for tests or to keep the original crancase volume.
(There will be a part 2b and a youtube video and an excel sheet for you to download. And the parts 3 and 4)
Kind regards to Biknut. He discribed the procedure correctly in another thread.