The 1998-2004 Honda TRX450 Foreman ATV repair manual by Clymer covers:
Honda TRX450ES, 1998-2001
Honda TRX450S, 1998-2001
Honda TRX450FE, 2002-2004
Honda TRX450FM, 2002-2004
Book Excerpt: 1998-2004 Honda TRX450 Foreman Repair Manual
The selector drive clutch is available only as a unit assembly, except for the final drive pinion shaft and bearing contained in the clutch body.
If the drive clutch is faulty, check for possible damage to the final drive as well. Refer to Chapter Eleven.
An unusual noise is usually the first indication of a drivetrain problem. It is not always easy to diagnose the trouble by determining the source of the noise and the operating conditions that produce it.
Some clues to the cause may be gained by noting whether the noise is a hum, growl or knock; whether it is produced when the vehicle is accelerating under load or coasting; and whether it is heard when the vehicle is going straight or making a turn.
Drivetrain service procedures are covered in Chapter Eleven (front) and Chapter Twelve (rear).
Knocking or pinging during acceleration can be caused by using a lower octane fuel than recommended or a poor quality of fuel. Incorrect carburetor jetting or a spark plug that is too hot can also cause pinging.
Refer to Correct Spark Plug Heat Range in Chapter Three. Check also for excessive carbon buildup in the combustion chamber or a faulty ICM unit.
Slapping or rattling noises at low speed or during acceleration can be caused by excessive piston-to-cylinder wall clearance. Check also for a bent connecting rod or worn piston pin and/or piston pin holes in the piston.
Knocking or rapping while decelerating is usually caused by excessive rod bearing clearance.
Persistent knocking and vibration or other noise is usually caused by worn main bearings. If the main bearings are good, consider the following:
Loose engine mounts.
Leaking cylinder head gasket
Exhaust pipe leakage at cylinder head
Stuck piston ring
Broken piston ring
partial engine seizure
Excessive connecting rod small end bearing clearance.
Excessive connecting rod big end side clearance.
Excessive crankshaft run out.
Worn or damaged primary drive gear
A rapid on-off squeal may indicate a compression leak around the cylinder head gasket or spark plug.