Crank Balance Calculator Instructions

Here's the Excel file screenshot. All the light blue boxes (cells) are where you enter the needed info. The info for my Suzuki 100 crank is in there as an example. You can refer to my video on how to figure out equivalent balance holes for cranks with metal removed around the con rod pin area instead of holes. You will need a digital food scale and digital caliper. You can buy a scale at Amazon for $19 or one at WalMart for less. WalMart sells a digital caliper for $19 or you can buy one from Amazon for $23. This screenshot shows my balanced engine.


Notice the usage instructions starting at C44. First, enter all the necessary data in the light blue cells and click the "Graph V/H Forces" macro button to the right of the crank photo to display the vibratory forces throughout the RPM range in the graph starting at F1 (but this isn't essential if your spreadsheet program can't use macros). Then adjust the counter balance hole sizes (or add more holes or fill in holes) till the # at E46 is close to 1.0 (within .03). If it's more than ±3% then change the size of the balance holes accordingly. Click onto the macro button after every change to update the chart if you can use macros. If not then just go by the value at E46.

If you are measuring where the current balance holes are and you want to calculate what the angle is between the hole and where the center of the con rod pin is then just measure the radius and the chord according to the picture below and use the angle calculator below K46 on the spreadsheet.


Any of four "hole sets" can be two or four holes each. The example on the spreadsheet shows four holes 25 degrees from the conrod pin (set #1), two holes in line with the conrod pin (0 degrees, set #2), and 2 holes opposite the conrod pin (180 degrees, set #3). The "filler" of holes can be any of the five things listed at A29 to C29 and B30 and C30 (air, ABS plastic, aluminum, brass, lead). Filler #6 is anything of your choosing. Just find its density online and then enter it at D30 with ".00" before it. The example here is beryllium copper with a density of 8175 which I entered as .008175. The hole filler # (1-6) is to be netered at row 33. Some people like to fill holes to not lose any crankcase compression. Or if the setup is over-balanced then holes can be filled with steel or lead to correct that. I wouldn't fill a hole just for concern about crankcase compression because that affects engine power very little if any at all and crankcase pressure wears down crankshaft seals.



The remaining necessary data is the length of the holes (usually same as the width of the crank wheel), the distance from the hole center to the center of the crankshaft, and the degrees of the holes from the vertical (which goes through the conrod pin). Most holes are close to the con rod pin but if the holes are too big then you can counter that by having two holes at 180 degrees which would be on the opposite side of the crank than the con rod pin.

Some engines also have an extra balancer shaft which reduces the average radial force by 25% - 30%. Here's two pictures of one:


On the spreadsheet starting at row 141 is this section which is needed to help you find the center of gravity of the balancer and its weight. First you should find the weight of its end shafts. Put water into a cup that is level with the top when the shaft end is submersed. Then remove the shaft and measure how far down the water level now is. Enter the vessel inner diameter at E159 and the height change of the water at E161. Multiply the result at E163 by 2 and subtract that from the measured wieght of the balancer. That final amount should be entered at E26. (Make sure E26 is 0 when working with a crank without an extra balance shaft.)


You'll need to glue something to the balancers flat surface which will extend away from it so you can hang a weight from it. Before glueing or taping the extender on then weigh it and enter its weight at E146. After it is attached then measure the two distances D1 and D2 to be entered at E142 and E144. Then add weights to the string/wire till the shaft will stay still without turning. Enter that weight in grams at E148. The calculated distance from shaft center to balancers center of gravity will appear at E155 which needs to be entered at E24.

The main goal is to have the # at E46 as close to 1.0 as possible. The max engine RPM at E2 is the maximum RPM that you normally use.



To change millimeters to inches just divide by 25.4, so that as an example 8.7mm divided by 25.4 is .342 inch which can then be translated to 16ths of an inch by multiplying by 16 which gives 5.5 which isn't a whole # so it has to be converted to 32nds which is 11/32" (multiplying both numbers by 2). So a 11/32" drill bit would work to drill a 8.7mm hole.

Questions about each bit of data to be entered can often be answered by hovering the pointer over the description box. That will reveal the note I have saved that explains more. But if you still have questions after reviewing this page then contact me at 19jaguar75@gmail.com

Here is a compete description of what is required for each data entry cell of the spreadsheet.

celldescriptionvisual ref.About this
B2piston pin mm diameterthe outer diameter of the piston pin in millimeters
B3conrod center-center mmcenterhole to centerhole connecting rod length in millimeters
B4con rod weight (grams)the weight of the naked rod in grams
B5piston assembly weightthe weight of piston, rings, bearing, circlips
B6wrist pin weightthe weight of the piston wrist pin
B10piston stroke mmif unknown either measure the piston stroke in the cylinder or multiply by 2 the distance from the center of the crank to the center of the conrod pin.
B11rod small end I.D.connecting rod small end inner diameter
B12rod small end widthconnecting rod small end width
B13rod small end thicknessconnecting rod small end thickness of the metal wrapping around the bearing
B14rod big end I.D.connecting rod big end inner diameter
B15rod big end widthconnecting rod big end width
B16rod big end thicknessconnecting rod big end thickness
B17conrod big end pin diathe outer diameter of the big end conrod pin
B18big end pin lengththe length of the big end conrod pin
B19BE pin inner hole diathe inner hole diameter of the big end conrod pin
B23big end bearing weightthe weight of the big end bearing. Use the weight estimator at E8-10 if you can't measure it.
B24crank half thicknessthe crank wheel thickness where the big end conrod pin goes thru it.
E1# of piston strokesenter "2" for a 2 stroke engine, or "4" for a 4 stroke engine
E2max engine RPMend of pipe powerband RPM
E3graph RPMThis is optional and exists just to have all the graphs sync to that RPM except for the Vertical Minus Horizontal graph (just to see what happens at said RPM)
E5compression ratioenter the engine compression ratio if known and the cranking pressure is not known. If the cranking psi is known then change the compression ratio at E5 till the right pressure is shown at D7.
E8(optional) bearing I.D.bearing inner diameter
E9(optional) bearing lengthenter bearing length if you can't measure the bearing weight. Usually its the same as the width of the conrod where it covers the bearing.
E10(optional) individual pin dia.the diameter of each little pin in the roller bearing. If not sure then look up your conrod at the Hot Rods site to get the inner diameter of the rods big end. Use that minus the outer diameter of the conrod pin and then divide the difference by 2.
B32# of holes per setthe total number of the "same" holes in both crank halves.
B33identity # of hole fillermenu: 1) air, 2) ABS plastic, 3) aluminum, 4) lead
B34diameter of each holethe inner diameter of each hole
B35length of each holethe thickness of the crank wheel if the balance hole goes completely thru it.
B36holes center to crank ctrthe distance from the center of the crankshaft to the hole center.
B37degrees from BE pin ctrthe degrees from center of conrod pin to center of hole.


Here's my YouTube videos about crank balance: #1   #2   #3   #4 The last video explains how to figure out
the equivalent balance holes for a crank with sculpted out areas instead of balance holes. The method
and the graph is different in the video because that was made before my latest update but still it is
worth watching.


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