A balanced shovelhead makes for a smooth ride.
Shovelhead motorcycle engines need to be balanced if you want a smooth ride. When it’s not balanced, your shovelhead will cause parts to fall off your bike, oil to leak and gas mileage to decrease. In addition, an off-balanced engine causes the bike to vibrate, which can be exhausting for the rider. Motorcycle machine shops offer shovelhead balancing services, but it’s often quite expensive. You can learn to do it yourself at home if you acquire a balance kit and are patient as you learn.
1. Inspect the engine for parts that look corroded or damaged. Replace any parts that look problematic because it is a waste of time to balance parts that you are going to replace soon. Parts to pay particular attention to include flywheel thrust washers and wrist pin bushings.
2. Weigh all the reciprocating and rotating parts and record their weights on a piece of paper. Record the weights for the front piston, the front piston wristpin, the front piston wristpin clips or buttons, the front piston rings, all the same parts for the rear piston, the crankpin, crankpin nuts, crankpin key, bearing cages, bearings, the small end of the front rod, the big end of the front rod and the complete front rod. The reason you weigh each item individually and then the total weight of each connecting rod is to compare your weights to make sure you have weighed them correctly.
3. Calculate the weight of the bobweight and record it on the piece of paper. Assemble the bobweight that came with the balancing kit. It consists of the main body, the retaining cap and the shim cap.
4. Put the flywheel together for balancing. Check the keyway and oil hole in the flywheel taper for burrs and remove the burrs if you find any. Clean the flywheel with solvent. Secure the assembly in the flywheel with the balance shaft nut. Bolt the bobweight assembly in the crankpin hole.
5. Place the balance stand on a perfectly flat and level surface and bolt it to the workbench. Shim under the 4 corners if necessary to get it completely level.
6. Place the flywheel assembly to be balanced on the balance stand. Place the assembly in the center of the stand edges with the bobweight on top. The bobweight must be able to rotate completely without obstruction.
7. Prepare your drill for drilling holes into the flywheel. There is no set number of holes to drill or how deep to drill them. Make your best guesses and test the flywheel to see if it is balanced. It is best to try drilling the same number of holes on each side. Tap the holes and heat them with a propane torch. Fill the holes with acid core solder, and then use a chisel or punch to stake threads to make sure the solder doesn’t come out.