How To Adjust the Valves on Other Vehiclesby Contributing WriterUpdated June 12, 2017
Adjusting the valves on a Honda other ATV is relatively uncomplicated. The most time-consuming aspect of the procedure is removing parts and components to access the rocker arms and valve adjusters. Anyone with basic mechanical knowledge and a set of metric tools can adjust the valves on a Honda other. Many experienced riders and mechanics can do the job in less than an hour.
Under The Hood:
- How To Adjust the Valves on a Honda 300EX
- How to Adjust the Valves on a 2006 TRX450R
- How to Adjust Valves on a Suzuki LT 125
- How to Adjust the Valves in a Suzuki LT 125 Quadrunner
Remove the rear fender-seat assembly to access the battery. Disconnect the negative battery cable and move the end of the cable away from the battery. Turn the fuel petcock lever to the closed position.
Pull the vent hose off the gas cap by hand and remove the cap. Depress the push pins that hold the gas tank cover in place using the butt of a ratchet handle. Pull the cover toward the back of the ATV and lift it off.
Locate and remove the metric bolts and Allen bolts that secure the one-piece front fender unit to the frame. Ease the fender unit forward enough to disconnect the headlight wires and ignition wire at the back by hand. Lift the fender unit off to access the fuel tank heat protector.
Depress the push pins where the carburetor air vent attaches above the heat protector. Remove the clutch cable from the cable guide above the protector and move the cable to the side. Loosen the metric bolts that secure the heat protector in place and lift the heat protector off to access the valve caps at the top of the cylinder head.
Loosen and remove the valve caps at the cylinder head with a metric wrench to access the intake and exhaust valve rocker arms and valve adjusters.
Remove the small timing cover at the left side of the engine crankcase with an Allen wrench to provide a view of the timing marks and the indicator-pointer. Remove the larger cover below to access the crankshaft bolt.
Put the 300EX transmission in neutral. Attach a metric socket on the crankshaft bolt where the larger timing cover was removed. Rotate the bolt clockwise as you observe the intake valve rocker arm at the carburetor side of the cylinder head. Rotate the bolt until the rocker arm is fully up. If necessary, rotate the crankshaft bolt again to determine the fully up position.
Note the position of the timing mark “T” in relation to the timing indicator-pointer where the smaller timing cover was removed. Rotate the crankshaft bolt a small amount either way until the mark is directly in line with the indicator.
Loosen the lock nut at the intake valve rocker arm adjuster with a metric socket and ratchet. Slide a .004 mm feeler gauge between the lower face of the rocker arm and the top of the valve stem. Turn the rocker arm adjustment stem with a flat-tip screwdriver and adjust the clearance so the feeler gauge slides in and out with some resistance. Tighten the lock nut securely.
Rotate the crankshaft bolt clockwise as you observe the exhaust valve rocker arm at the opposite side of the cylinder head. Rotate the bolt until the rocker arm is fully up. Loosen the lock nut and adjust the clearance using the feeler gauge and the screwdriver. Tighten the lock nut securely.
Reattach the valve caps and tighten each. Reattach the heat protector and reposition the clutch cable in the cable guide. Reattach the carburetor air vent. Reattach the remaining components, wires and the fender unit in the reverse order as removed. Reconnect the negative battery cable before reattaching the rear fender-seat assembly.
Items you will need
Metric sockets and ratchet
.004-mm feeler gauge
Park the TRX450R on a flat, level surface and let the engine cool for a minimum of four hours if it has been ridden recently. Remove the rider's seat, using the release lever at the bottom of the rear fender, directly below the rear of the seat.
Grasp the sides of the top cover between the front fenders and just above the headlight. Pull the cover upward to separate its mounting bosses from the grommets installed on the fenders. Pry up the trim clips securing the front fenders to the ATV, using the tip of a flat-head screwdriver. Remove the bolts from the underside of the fenders, using a ratchet.
Remove the bolts from the inside of the seat's mounting point along the rear fender, as well as the bolts located under the sides of the fender. Unhook the rubber strap securing the heat guard at the front of the fender to the ATV's frame. Lift the rear fender off of the ATV.
Set the fuel valve lever under the left side of the fuel tank to the Off position. Remove the screw from the fuel valve lever, using a Phillips screwdriver. Pull away the lever and fuel valve cover. Unhook the fuel tank straps and remove the tank mounting bolts. Lift the tank off of the ATV's frame, then pull the fuel hose off of the valve outlet.
Remove the round crankcase hole cap from the left side of the engine, identified by the hex-shaped indention at the center of the cap, using an Allen wrench. Look through the crankshaft hole at the primary drive gear. Rotate the crankshaft clockwise, using a ratchet, until the triangular punch mark on the primary drive gear is visible and aligned with the matching index mark on the right side of the crankshaft hole.
Remove the bolts from the top of the cylinder head cover. Pull the cover and gasket away from the engine to reveal the intake and exhaust valves. Look at the valve rocker arms. If the valves are touching the round valve shims, rotate the crankshaft clockwise in complete turns to bring the piston into top dead center with the valves closed.
Measure the clearance between the intake valves, located toward the rear of the cylinder head, and their corresponding cam lobes with a feeler gauge. There should be 0.006 inch of clearance between both components. Measure the clearance between the exhaust valves, located toward the front of the cylinder head, and their corresponding cam lobes. These valves should have 0.011 inch of clearance.
Remove the camshaft holder assembly bolts, then remove the assembly and valve lifters from the engine, if the clearance between either valve set is out of specification. Pull the valve shims off of the appropriate valve sets. Measure the thickness of the removed shims, using a vernier caliper. Skip this step, if the valves are in specification.
Determine the required thickness of the new shim by subtracting the measured valve clearance from the specified valve clearance, then add the thickness of the removed shim. Skip this step, if the valves are in specification.
Install the new shims and reinstall the camshaft holder assembly. Tighten the assembly bolts to 10 foot-pounds, using a torque wrench. Reinstall the cylinder head cover and gasket, then tighten the cover bolts to 7.6 foot-pounds. Reinstall the crankshaft hole cover and tighten it to 11 foot-pounds.
Reinstall the fuel tank and tighten the tank bolts to 10 foot-pounds. Reinstall the fuel valve cover and lever, then snugly tighten the lever screw. Reinstall the front fenders, front cover, rear fender and seat.
Items you will need
Ratchet and sockets
Allen wrench set
Lift the combination seat/rear fender assembly to access the engine. The intake (rear) valve is closest to you, the exhaust valve is located on the opposite side of the cylinder head, towards the front of the vehicle.
Expose the two valves by removing the threaded caps from the front and rear of the cylinder head of the engine with an end wrench. Threaded caps look like hexagonal bolt heads, but with a broad circular base. The caps cover wells in the cylinder heads which allow access to the valve adjustment screws. Remove the recoil starter from the left side of the engine by taking out the four bolts securing it to the crankshaft mount.
Remove the spark plug wire and take out the spark plug. Put your thumb over the spark plug hole and rotate the crankshaft by hand counterclockwise until you feel the sensation of pressure building inside the cylinder that indicates the piston is on its compression stroke. (If the piston is on an exhaust stroke, the exhaust valve will be open and there will be no detectable pressure in the cylinder at all.) The "T" mark on the crankshaft rotor should be lined up with the pointer on the crankcase.
Checking Valve Clearance
Select a feeler gauge within the 0.08 mm to 0.013 range.
Locate the intake valve at the rear of the engine and slip the feeler gauge between the valve and its corresponding adjusting screw.
Determine the fit of the feeler gauge. If it fits snugly with minimal metal-to-metal contact and can be moved in and out of the gap without binding, the valve adjustment is within limits. If the feeler gauge will not fit between the valve stem and the adjusting screw, the adjustment is too tight. If there is no feeling of drag as it is inserted in the gap and you can wiggle it laterally and up and down without resistance the valve gap is too loose.
Valve Adjustment And Reassembly
Loosen the locknut on the adjusting screw with an end wrench. Using a flat-bladed screwdriver, loosen the adjusting screw until the feeler gauge will fit into the gap or tighten it to remove excess play. Hold the adjusting screw in place with the screwdriver and tighten the locknut with the end wrench. Repeat the procedure on the exhaust valve at the front of the engine.
Re-install the threaded caps on the front and rear of the cylinder head. Bolt the recoil starter on crankshaft mount at the left side of the engine using the four bolts.
Replace the spark plug and attach the spark plug wire. Lower and latch the seat/fender assembly.
Items you will need
Socket wrench and sockets
Spark plug wrench
Accessing the Valves
Access the engine compartment by raising the seat/fender assembly. You'll be looking down on top of the cylinder head. The rear (intake) valve will be closest to you, while the exhaust valve is on the opposite side of the head at the the front of the engine. Both valves are recessed into the cylinder head and covered by threaded caps.
Remove the threaded caps from both the intake and the exhaust valves with a combination wrench. You should be able to see each valve adjustment screw. Unbolt the recoil starter from the left side of the crankcase using a socket wrench and socket to remove the four bolts.
Take off the spark plug wire and remove the spark plug. Put your thumb over the spark plug hole and rotate the crankshaft by turning the crankshaft rotor with the other hand. Stop when you feel pressure build in the cylinder. Look at the pointer on the crankcase. It should line up with the "T" mark on the rotor.
Check the Clearance
Open the feeler gauge and find a gauge strip in the 0.08 mm to 0.13 mm range.
Insert the feeler gauge into the intake valve well on the cylinder head and slip it between the valve stem and its adjusting screw.
Evaluate the gauge result. The feeler gauge should slip into the gap with minimal drag or resistance. If it doesn't fit into the gap, the valve adjustment is too tight. If there is too much play when the gauge is inserted, and it can be moved laterally or up and down easily, the valve adjustment is too loose.
Adjust the Valves
Using the combination wrench, release the locknut on the adjusting screw. Loosen the adjusting screw with a screwdriver until the feeler gauge slips into the gap, or tighten it to until there is no more play or excessive movement of the gauge. Hold the adjusting screw with the screwdriver while tightening the locknut with the wrench. Move to the exhaust valve on the front of the cylinder head and repeat the procedure.
Reinstall the front and rear threaded caps. Install the recoil starter on its crankshaft mount and tighten the four bolts.
Replace the spark plug and tighten it. Connect the spark plug wire. Lower the seat/fender assembly and lock it in place.
Items you will need
Socket wrench and sockets
Spark plug wrench