How do you counterweight a crankshaft?
By placing counterweights on opposite sides of the Conrod journals of the crankshaft it is possible to compensate for outer moments, minimise internal moments and therefore reduce the amount of vibration and bearing stresses.
What is a crankshaft counter weight?
The counterweights are wedge or disc-shaped cylindrical sections positioned laterally in between the crank throws (each throw includes two connecting rod journals, generally in a continuous machined surface), and positioned rotationally opposite the throws (180° away) to “counter-act the weight” of the journals, rods.
Why must a crankshaft be balanced?
The real goal of balancing a rotating assembly is to make sure that the crankshaft counterweights offset the rotating and reciprocating forces created by pistons and rods. The mass of the crankshaft counterweights should equal 100 percent of the rotating mass and 50 percent of the reciprocating mass.
Why are counter weights provided in a crankshaft?
Counterweights are used because they nullify the reaction caused by the rotation. This is helpful because it helps in achieving higher RPM’s in an engine and makes the engine run smoothly.
Do I need to balance a new crankshaft?
The reason for dynamically balancing a rebuild/upgrade is because the component weights can be quite far off from stock. For instance, the counterweights on the stock crank are built to compensate the mass of stock rods, pistons, wristpins, bearings etc. If you get forged pistons, they’ll most likely be lighter.
How are counterweights used to balance a crankshaft?
A crankshaft is statically balanced when the weight of the entire assembly of crankpins, crank cheeks, and counterweights is balanced around the axis of rotation. When testing the crankshaft for static balance, it is placed on two knife edges. If the shaft tends to turn toward any one position during the test, it is out of static balance.
How to calculate the torque for a counterbalance?
Using the equation, _Fe × de = Fl × dl, the torque for the weight, or effort force, is then 2,000 pounds times 50 feet, or 100,000 pound-feet for the weight. The counterbalance weight, or load force, is then, 100,000 pound-feet divided by 20 feet, or 5,000 pounds.
How are counterweights used to balance Pistons and rods?
In other words, the size, positioning and mass of the counterweights is designed to offset a specific piston and rod weight, (plus or minus a couple percentage points). With stock cranks, the bobweight is more or less equal to the weight of the stock pistons and rods.
How does the conrod and Conrod affect the crankshaft?
The conrod and the piston of the first cylinder “pulls” the crankshaft up, the second down, while it is fixed at the main bearings. The crankshaft will be deformed at the main bearings, which means a lot of stress at the fillets next to the bearings, and has a negative effect on the lifetime of the bearing shells.
If the counterweights are the correct weight to offset the weight of the rods and pistons, the crankshaft is balanced. If the counterweights are too heavy, material must be removed by drilling or milling the counterweights. If the counterweights are too light, weight must be added to the counterweights.
How does a externally balanced crankshaft work?
Pictured here is a crankshaft with no center counterweights. An externally balanced engine is one in which the counterweights are not heavy enough to fully compensate for, and therefore balance, the engine components, so (in addition to the usual eccentric counterweights) the missing fraction must be re-located to outside the engine block.
How do you calculate bobweights for a crankshaft?
Using the geometric center of the connecting rods, I used SolidWorks mass properties to obtain the rotational and reciprocating component weights of the connecting rod/piston assemblies. Based on the SolidWorks derived weights, I created an Excel Spreadsheet to calculate equivalent bobweights based on the various factors presented in the papers.
What kind of counterweight does a K301 crankshaft use?
The K301 crankshaft’s counterweights are machined flat for the lighter-weight K301 piston/rings assembly, while the K321, K341 and K361 crankshaft’s counterweights are rounded for the heavier K321, K341 and K361 piston/rings assemblies.