How to Remove a Spark Plug in a Yamaha YFZ450by Chris Gilliland
A Yamaha YFZ450 ATV relies on a single spark plug to operate its engine. Under normal circumstances, the spark plug is fairly durable and can provide hundreds of hours of reliable service. However, Yamaha recommends a monthly inspection of the spark plug to avoid possible engine failures brought about by a damaged or failing spark plug. If the spark plug is damaged in any way, it must be replaced immediately. Only a few tools are necessary to remove and replace the spark plug, but you may need to make a few adjustments to the plug before it can be installed.
Unlatch the seat, using the release lever at the rear of the seat. Lift the rear of the seat up, and then pull it away from the ATV.
Unscrew both upper fuel tank cover bolts, located below the handlebars, using a 5 mm Allen wrench. Unscrew the lower fuel tank cover mounting bolts, using a socket wrench and a 10 mm socket. Lift the fuel tank cover slightly, and then pull it toward the rear of the ATV until it can be removed completely.
Unscrew the mounting bolts from the left and right side covers, located below the fuel tank and the ATV's seat rails, using a socket wrench and a 10 mm socket. Pull the side covers away to access the fuel tank mounting bolts and the engine.
Unscrew the upper fuel tank mounting bolts, located in front of the handlebars on the ATV's frame, using a 5 mm Allen wrench. Lift the front fuel tank cover away from the fuel tank. Unscrew the lower fuel tank mounting bolts from the ATV's seat rails, using a socket wrench and a 10 mm socket. Set the tank's fuel valve to the "Off" position, and then pull the fuel hose from the valve outlet. Lift the fuel tank off the ATV.
Reach between the ATV's seat rails and grasp the ignition coil, positioned on the top of the engine's cylinder. Pull the ignition coil off the spark plug. Unscrew the spark plug, using a socket wrench and a 16 mm spark plug socket.
Check the new CR8E spark plug's gap, using a gap tool. Your YFZ450 requires a gap range of 0.028- to 0.031-inch. If the spark plug gap is not within this range, bend the spark plug's electrode slightly with the gap tool and recheck the gap.
Screw the spark plug into the engine by hand. Tighten the spark plug to 9.4 foot-pounds, using a torque wrench and a 16 mm socket wrench. Push the ignition coil over the top of the spark plug.
Mount the fuel tank onto the ATV. Screw the lower fuel tank mounting bolts into place with a socket wrench and a 10 mm socket. Tighten the lower mounting bolts to 5.1 foot-pounds, using a torque wrench. Place the front tank cover over the fuel tank, and then screw the upper mounting bolts into place with a 5 mm Allen wrench. Push the fuel hose onto the fuel valve outlet.
Install the left and right side covers onto the ATV's frame. Screw the side cover mounting bolts into place with a socket wrench and a 10 mm socket. Tighten all of the side cover mounting bolts to 5.1 foot-pounds, using a torque wrench
Slide the fuel tank cover over the fuel tank and around the handlebars. Screw the upper mounting bolts into place with a 5 mm Allen wrench. Screw the lower mounting bolts into the ATV's frame, using a socket wrench and a 10 mm socket.
Slip the seat's mounting tongue under the base of the fuel tank, and then lower the seat onto the seat rails. Press down on the rear of the seat until the seat latch locks.
- "Yamaha YFZ450S Service Manual": Yamaha Motor Corp.; 2003
Things You'll Need
- 5 mm Allen wrench
- 10 mm socket
- Socket wrench
- 16 mm spark plug socket
- CR8E spark plug
- Gap tool
- Torque wrench
- An improperly gapped spark plug can affect the ignition timing and cause misfires. Always check the gap before installing the spark plug onto your YZF450's engine.
An avid motorcyclist, Chris Gilliland has immersed himself into the two-wheeled world while balancing work life and raising three daughters. When he is not managing the parts department of a local, multi-line motorcycle dealership, Gilliland can often be found riding, writing or working on his motorcycle blog, Wingman's Garage.