Balancing a Motorcycle Crankshaft

Balancing a motorcycle crankshaft will greatly improve the performance and efficiency of the bike. It will also reduce the stress of the machine. A crankshaft, shortened as crank is part of an engine. To improve the balance of the motorcycle’s engine, counterweights are used to do the trick. It is usually attached on the crankshaft that results to an even running engine. If you want to improve the performance of your motorcycle, this article provides you with basic know-how in balancing the motorcycle crankshaft.

Step 1 – Create a Jig

A jig is a gear that serves as a guiding tool or a holding machine. Construct a jig to hold the bearing and the crankshaft in place. Attach the bearing in the jig and the crankshaft unto the bearing. Take a new bearing and get rid of all the grease and immerse it in the break clean. This frees the bearing and allows the crank to spin the heavy spot down.

Step 2 – Weigh the Bobweight

Remove the piston, rod and wrist pin to weigh it in. The wrist pin is a pin attached at the end of a connecting rod either to a wheel, crank or piston. Take ¾ of the total weight as a guide for you to know the ideal bobweight you will need to wrap around the crank pin. Start spinning the cranks using the balancer machine and see where it stops. Make sure that the counterweight of the crank is heavier compared to the overall weight of the piston and rod on the crankshaft.

Bobweight refers to the reciprocating and rotating weight of the assembly. Reciprocating weight is computed starting from the middle of the rod upwards including the piston, wristpin, and rings. Meanwhile, the rotating weight starts from the lower half of the connecting rod.

Step 3 – Balance the Crank

Do the necessary cuts to obtain the ideal weight wherein the counterbalance must be heavier compared to weight on the crank pin. Place back the crankshaft into the engine which may seem that nothing is different. Start the engine and don’t mind the vibration.

Removing weight from the crankshaft to balance the assembly is simple. Use the drill and drill some holes unto the attached crankshaft counterweights. However, if the bobweight is lighter you may add metal to the crankshaft.

Balancing a motorcycle crankshaft also depends on the type of cylinder. There are three cylinders available-single, two, and multi-cylinders. The vibration which was mentioned earlier is normal especially for engines that do not have balancing counterweights. To reduce the vibration, single-cylinder integrates balancing weights.

Counterweights are installed on the crankshaft to balance the effect of inertia between a heavy piston and the connecting rod in two contrasting motions-reciprocating and rotational. The weight of the piston and connecting rod greatly affects the size and the placement of the counterweight. The heavier the piston-rod is, the heavier the counterweight to be used. Counterweights should be placed in front and rear of the cranks to lighten the crank without blocking the case of the crank.
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