A wood chipper makes quick work of even the most sturdy pieces of wood, quickly reducing them to useful mulch. A typical wood chipper has several rotating blades that chop chunks from solid pieces of wood as the wood is fed into the chipper. These blades are subjected to very harsh conditions and must be sharpened or replaced after every few hours of use. Most manufacturers have designed their machines so that blade replacement can be performed with a minimal amount of work. Even if replacement is relatively easy, safety is paramount, so always exercise extreme caution when working on a wood chipper.
Make absolutely certain that you have turned off the engine, disconnected the spark plugs, and put the key in a known location.
Remove the spark plug from the engine using a spark plug wrench by twisting it counterclockwise. This will allow you to turn the engine manually in the event that the cutting blades are not clearly visible through the inspection plate.
Remove the inspection plate using a socket wrench. Turn the hex-head screws counterclockwise to remove them, then pull the plate free. Most chippers feature an inspection plate as a convenient access path freeing jams and servicing the blades. The plate is located on the forward side of the machine, about 18 inches from the ground. It is usually centred so that is covers the cutting-head assembly.
Put on heavy work gloves. Remove the Allen bolts holding the blades to the disk or drum by turning them counterclockwise to loosen them. Regardless of the type of wood chipper, the blades will be visible, appearing as sharp steel blocks bolted to parts that revolve. If you cannot see the blades or get the Allen wrench in the correct location to remove the screws, slowly rotate the disk or drum by hand until you are able to do so.
Remove the old blades from the chipper. This may require some persuasion with a rubber mallet if the blades are rusty, bent or have not been changed in a long time. You should be able to pry the blades from their positions with a slotted screwdriver after a few taps with the rubber mallet.
Compare the old blades to the new ones side by side so that you can verify that they are an exact match. Be sure the new blades are fully sharpened prior to installation; sometimes they are not pre-sharpened before shipping.
Install the new blades in the place of the old blades, making sure that all of the new ones face the same way as the old ones. Torque the bolts according to the manufacturer's specifications; if you don't have that information, tighten to 50 foot-pounds of torque.
Spin the chipper slowly by hand to be sure no parts of the blades make contact anywhere. This could cause severe damage to the chipper and usually indicates that the blades were installed incorrectly or are not the correct type. Reattach the access plate and reinsert and tighten the spark plug before testing the machine for normal operation.