How the Crankshaft Balancing is Done?


Important features of crankshaft balancing including the Bobweight

Crankshaft balancing is the main and major component of giving 100% efficiency and performance, and without its unbalancing, it does not give satisfactory performance. There is the main thing which helps in crankshaft balancing. And that is understanding it. The first step in understanding crankshaft balancing is to understand the purpose of the counterweights. These are shaped to give proper weight to rod and pistons. The main science to take under consideration is that the sum of total forces is roughly equal to zero.

Internal and External Balance

We better know that the engine is effected if the crankshaft is not balanced. At low speed, you do not notice it but when the speed is accelerated, noticeable variations starts to appear. When the counterweights alone can be made to balance the crankshaft, the crankshaft is said to be “internally balanced.” There is also another condition. If the counterweights are too light by themselves to balance the crankshaft and more weight is needed, an “external balance” can be used. There are also main components involved named harmonic dampers or flywheel that has a weight on it in the same position as the counterweight that effectively adds to the weight of the counterweight on the crankshaft.

Test Crankshaft Balance

There are different weights of different rods and different pistons. That’s why it is quite difficult to make a crankshaft that is balanced right out of the box. They must be adjusted to specific rod and piston combinations. There is always a margin of (+-2%) of the bobweight when the crankshaft is taken out of the box. As a standard, the crankshaft has an 1800 target bobweight.

What is Bobweight?

It is simple. When a crankshaft is balanced, the actual rods and pistons cannot be used in the balancing machine. That’s why they are surely stimulated. That specific and stimulated weight is called as the bobweight. When we calculate the weight, it is bolted onto the rod journals to shift the weight of the rods and the pistons during the balancing process.

To get the exact crankshaft balancing, it is perfect to know the information and some internal functionality of the crankshaft.


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