How to Adjust the Valves on Bikesby Contributing Writer; Updated June 12, 2017
Adjusting the valves or ports on a 150cc scooter involves delicate work grinding away at the existing surfaces to allow more fuel and air to pass. If done wrong, the work can ruin the engine case, creating a weakness where the case walls begin to crack. Shaped incorrectly, the work ends up being a waste of time and provides no improvement in engine performance. Using the steps below, you can minimize the risk. This approach assumes the engine case is stripped and bare before starting the work.
Under The Hood:
- How to Adjust the Valves in a Yamaha 650
- How to Adjust the Valves on the Yamaha Raptor 700
- How to Adjust the Valves on a 2001 Yamaha Kodiak
- How do I Adjust Valves on an XR400?
- How to Adjust Valves on a 2005 Kawasaki KFX 400
- How to Adjust the Valves on the Kawasaki Mule 3010
- How to Adjust the Valves on a Suzuki GS Motorcycle
- How to Adjust the Valves on a Suzuki 800 Volusia
- How to Adjust the Valves on a 150Cc Scooter Engine
Remove both spark plugs with a socket wrench and spark plug socket. Shift the transmission into first gear. Place the motorcycle on its center stand.
Use a wrench (preferably a crescent wrench) to remove the cap located behind the cylinders, underneath the carburetors. Inside the hole is a threaded stud with a lock nut on the end. Inside the stud is a small pin, which should be even with the end of the stud. If it is not flush, it needs to be adjusted.
Rotate the rear wheel forward. While rotating the tire, the pin should move in and out an equal distance in both directions. Stop turning the tire when the pin is in the middle of its stroke. Loosen the lock nut with a wrench and turn the stud until the end is even with the end of the pin. Tighten the lock nut and replace the cap. The cam chain is now adjusted.
Look into one of the spark plug holes using a flashlight. Turn the rear wheel until the top of the piston is visible in the spark plug hole. The engine is now at top dead center.
Remove the valve covers using a crescent wrench. Four valve covers are located on the front and back of the two cylinders; three are round and the left front cover is square. The exhaust valves are at the front of the cylinder and the intake valves are at the back.
Adjust the valves on the cylinder at the top of its compression stroke, which is the one with the closed exhaust valve. Insert a feeler gauge of the correct thickness between the rocker-arm bolt and the top of the valve stem. The clearance is correct when the next size up feeler gauge will not fit in between. Adjust using a crescent wrench by turning the bolt on the top of the rocker arm counterclockwise to tighten or clockwise to loosen. Bring the other cylinder to the top of its compression stroke and repeat. Remount the four valve covers.
Items you will need
3/8-inch drive socket wrench
Metric socket set
Metric wrench set
Small metric crescent wrenches (optional)
Pull off the spark plug wire. Loosen and remove the spark plug with a plug wrench. Removing the plug eliminates engine compression so you can rotate the engine crank when adjusting the valves.
Loosen and remove the timing cover bolts at the right side of the engine with a metric socket and ratchet. Pull off the timing cover to access the timing flywheel and timing marks.
Use a metric Allen wrench to remove the crankshaft end-cover at the right side of the engine to access the crankshaft bolt.
Clean the area at the base of each valve cover with blasts from a compressed-air canister. This prevents dirt or off-road debris from getting into the valve springs and rocker arms.
Loosen and remove the pair of intake valve covers at the front of the cylinder head with an adjustable wrench. Loosen and remove the pair of exhaust valve covers at the rear of the head.
Attach a metric socket and ratchet onto the end of the crankshaft bolt where the end-cover was removed. Rotate the bolt counterclockwise as you observe the timing marks at the flywheel inside the timing housing. Rotate the bolt until the timing mark “I” is directly in line with the timing indicator at the upper side of the flywheel. This indicates the piston is at top-dead-center and the intake valves are fully closed.
Loosen the lock nuts at the base of both tappet stems on the intake valves.
Insert a 0.10 mm feeler gauge between the base of a rocker arm and the corresponding valve stem below. Turn the tappet stem clockwise or counterclockwise with the screwdriver, as necessary, until the feeler gauge slides in and out with light resistance. Repeat this step to adjust the other intake valve. Tighten both lock nuts with the wrench.
Attach the metric socket and ratchet onto the end of the crankshaft bolt. Rotate the bolt counterclockwise until the timing mark “I” is at the lower side of the flywheel and directly vertical to the timing indicator above. This indicates the exhaust valves are closed.
Loosen the lock nuts at the base of both tappet stems on the exhaust valves with the metric wrench.
Insert a 0.18 mm feeler gauge between the base of a rocker arm and the corresponding valve stem. Adjust both valves with the screwdriver until the gauge slides in and out with light resistance. Tighten the lock nuts with the metric wrench.
Reattach the valve covers and tighten each with the adjustable wrench. Reattach the timing cover and tighten the bolts with the socket and ratchet. Reattach the crank-bolt cover with the Allen wrench. Install the spark plug with the plug wrench and reattach the plug wire by hand.
Items you will need
Spark plug wrench
Metric socket and ratchet
Metric Allen wrenches
0.10-mm feeler gauge
0.18-mm feeler gauge
Remove the seat from your Kodiak, using the latch on the rear of the seat. Pull the gas tank side covers off your Kodiak's frame. Unscrew the gas cap. Unscrew the bolts at the base of the gas tank, using a 10 mm socket and a socket wrench, then lift the gas tank's cover off your Kodiak. Unscrew the gas tank's mounting bolts with a 10 mm socket. Lift the tank off your Kodiak's frame and unplug the gas line.
Unbolt the front rack and bumper from your Kodiak, using a 12 mm socket and a socket wrench. Pull the plastic rivets out of the front fender's center panel, then pull the panel away to access the headlights' wiring. Unplug the headlights from their connectors. Unbolt the front fender from your Kodiak's frame, using a 5 mm Allen wrench and a 12 mm socket.
Unplug the spark plug cable from the left side of the motor. Unscrew the spark plug with a spark plug socket and a socket wrench. Remove the intake tappet cover from the top of your Kodiak's motor and the exhaust tappet cover from the bottom of the motor, using a 6 mm Allen wrench.
Remove the pull-start cover from the left side of the motor, using a 10 mm socket and a socket wrench to access the timing port and the motor's crankshaft. Unscrew the plug from the timing port, positioned to the right of the crankshaft, using a flat screwdriver.
Place a 17 mm socket and a socket wrench over the end of the crankshaft. Turn the crankshaft counterclockwise until a "T" mark is centered over the notch on the bottom of the timing port.
Slide a .0039-inch feeler gauge between the intake valve and its rocker arm on the top of the motor. The gauge should slide between the valve and rocker arm with a small amount of resistance. If there is no resistance, the clearance between the valve and the rocker arm is too great. If the gauge cannot be inserted between the valve and the rocker arm, rotate the crankshaft one complete turn and take another measurement. If the gauge cannot be inserted after rotating the crankshaft, the valve clearance must be increased.
Loosen the lock nut from the adjuster bolt on the top of the rocker arm, using a 10 mm box wrench. Turn the adjuster bolt clockwise with a flat screwdriver to reduce the valve's clearance or turn it counterclockwise to increase the valve's clearance. Check the valve clearance again with a .0039-inch feeler gauge. Hold the adjuster bolt steady with your flat screwdriver and tighten the lock nut against the rocker arm with your 10 mm box wrench.,
Inspect the exhaust valve's clearance, using a .0079-inch feeler gauge. Follow the same method used to inspect and adjust the intake valve's clearance.
Reassemble your Kodiak, following the reverse order of removal.
Items you will need
10 mm, 12 mm and 17 mm sockets
5 mm and 6 mm Allen wrench
Spark plug socket
.0039 inch and .0079 inch feeler gauges
10 mm box wrench
Turn off the fuel petcock. Follow the directions in the shop manual to remove the side covers, seat and gas tank.
Remove the crankshaft access cap and the timing access cap. The crankshaft cap is in the center of the engine cover on the left side of the bike. The timing cap is just above the crankshaft cap. Remove both -- turning counterclockwise with a hex wrench.
Locate the valve adjusting caps. They are on top of the cylinder head; two each on the front and back. Use a shop towel to clean any debris off the caps. Turn each cap counterclockwise with a wrench to remove.
Loosen the lock nut in each valve adjustment port, under the caps you removed in step three. This takes a 7mm wrench.
Use a 12mm or 17mm socket and a breaker bar to turn the crankshaft counterclockwise to align the "T" mark in the timing access hole.
Make sure the rocker arms are at top dead center (TDC). Use a flat blade screwdriver to back each valve adjuster out slightly.
Adjust the intake valves. These are the two valves on the rear of the head. Insert the 0.10mm blade of the feeler gauge between the adjuster in the rocker arm and the sub-rocker just under it. Turn the adjuster screw, until it lightly contacts the feeler blade. You should be able to slide the blade with only slight resistance. Tighten the lock nuts.
Adjust the two exhaust valves on the front of the head. Use the same technique as with the intake valves, except use the 0.12mm blade. Tighten the lock nuts.
Replace the valve adjustment caps, crankshaft and timing caps, and the fuel tank, seat, and side covers.
Items you will need
XR400 shop manual
Metric hex wrench set
Metric combination wrench set
Metric socket set
Park the ATV on a level work surface and allow the engine to cool for a minimum of four hours.
Remove the seat from the ATV using the release lever under the rear fender. Unscrew the gas cap, then remove the pop rivets from the base of the upper fuel tank cover and both side covers using the tip of a Phillips screwdriver. Pull the upper and side covers away from the ATV. Screw the gas cap into place.
Turn the fuel valve lever under the left side of the gas tank to the on position. Pull the fuel hoses off of the fuel valve, using pliers. Remove the bolts from the base of the gas tank using a 10 mm socket and a socket wrench. Lift the base of the tank upward, then pull the tank away from the ATV's frame.
Unplug the spark plug cable from the top of the engine cylinder head cover, then unscrew the spark plug using a spark plug socket. Pull the oil hose and breather hose off of the top of the cylinder head cover. Remove all three bolts securing the cylinder head cover to the cylinder using a 6 mm Allen wrench.
Remove the generator port cap, located at the center of the left engine cover, and the timing port cap, located just above the generator cover cap, using a 6 mm Allen wrench. Place a 17 mm socket and a socket wrench on the end of the crankshaft, located within the generator port.
Rotate the crankshaft clockwise until a T-shaped mark is aligned with the triangle printed into the left engine cover below the timing port. The pointed portion of the intake and exhaust cams, located at the top, left side of the engine cylinder, should be pointing away from each other and toward the front and rear of the ATV. Rotate the crankshaft clockwise 360 degrees and realign the T mark with the timing triangle if the cams are pointing inward, toward each other.
Measure the clearance between the valve tappets and the exhaust and intake cams, located at the front and rear of the engine cylinder, using a blade-type feeler gauge. Ideally, there will be a 0.0039- to 0.0071-inch gap between the intake cam and tappet and 0.0079- to 0.0118-inch gap between the exhaust cam and tappet. The tappet shims must be replaced if either exhaust or intake clearance is out of specification.
Unscrew the cam chain tensioner spring holder bolt and spring, located at the rear of the engine cylinder, using a 12 mm socket. Remove the cam chain tensioner mounting bolts using a 5 mm Allen wrench.
Take note of the direction the cams are pointing, then remove the camshaft holders using a 10 mm socket. Lift the camshafts off of the engine cylinder head to access the intake and exhaust tappet shims. Place a screwdriver under the center portion of the cam chain, located at the top of the engine cylinder head, to keep the chain from falling into the engine.
Remove the shim from the top of the intake or exhaust valve tappet, if the valve clearance is not within the valve's specified range, using a magnetic pickup tool. Take note of the number imprinted into the bottom of the tappet shim, which indicates the shim's thickness in millimeters. For example: A shim with the number 280 indicates a thickness of 0.11 inch. Select a thinner shim if the intake valve clearance is less than 0.0039 inch. Select a thicker shim if the valve clearance is greater than 0.0071 inch. Coat the top and bottom of the new shim with a molybdenum-based grease, then slide the shim onto the top of the tappet.
Reinstall the camshafts onto the engine cylinder head, pointing the cams away from each other in the same position they were removed. Reinstall the camshaft holders, then tighten the holder bolts to 7 foot-pounds using a torque wrench.
Push the release latch, located on the inner tip of the tensioner, into the cam chain tensioner body. Push the tensioner push rod into the chain tensioner body, then mount the tensioner onto the engine cylinder. Screw the chain tensioner mounting bolts into place and tighten the bolts to 7 foot-pounds. Push the tensioner spring into the tensioner body, then screw the spring holder bolt into place. Tighten the spring holder bolt to 21.5 foot-pounds.
Turn the crankshaft two complete turns to seat the shim, then realign the T mark with the triangle at the bottom of the timing port. Recheck the valve clearance. Replace the shim with a thinner or thicker shim, if needed to bring the intake valve clearance between 0.0039 to 0.0071 inch or the exhaust valve clearance between 0.0079 to 0.0118 inch.
Reinstall the engine cylinder head cover. Tighten all three bolts to 7 foot-pounds, then tighten the bolts again to 10 foot-pounds. Push the oil and breather hoses into place, then screw the spark plug into the center of the engine cylinder head. Tighten the spark plug to 8 foot-pounds, then push the spark plug cable into place.
Reinstall the gas tank, then push the fuel hose onto the fuel valve. Reinstall the upper and side covers onto the ATV. Reinstall the seat.
Items you will need
10 mm socket
Spark plug socket
6 mm Allen wrench
17 mm socket
Blade-type feeler gauges
12 mm socket
5 mm Allen wrench
Magnetic pickup tool
Park the Mule on a level work surface and set the parking brake. Let the engine cool for a minimum of two hours; the engine must be completely cold to accurately measure and adjust the valve clearance.
Unlock the rear cargo bed, using the release lever, and lift the bed into its fully raised position. Remove the alternator cover and gasket from the right side of the engine, located just in front of the right rear wheel, using a socket and a ratchet.
Grasp the front cylinder spark plug boot, located just below the rocker cover marked with "OHV". Twist the boot a half-turn to release it from the spark plug, then pull the boot off of the end of the spark plug. Remove the spark plug using a ratchet and a spark plug socket. Remove the rear cylinder spark plug using the same method.
Remove the rocker covers and gaskets from both cylinder heads using a ratchet.
Place a socket and a breaker bar over the nut at the center of the alternator flywheel. Turn the flywheel clockwise until the front cylinder timing mark -- indicated by the number "1" -- is aligned with the mark imprinted into the crankcase breather cover directly above the flywheel. Wiggle the front cylinder rocker arms by hand, which should move slightly. If the rocker arms are stiff, rotate the flywheel clockwise a full turn.
Slide a blade-type thickness gauge between the front cylinder rocker arms and the valve tappets in the cylinder head. There should be a 0.010-inch air gap between the rocker arms and the tappets. With a 0.010-inch gap, the thickness gauge will slide through the gap with a slight resistance.
Hold the adjuster screw lock nut, located on top of the rocker arm, with a box-end wrench. Loosen the adjuster screw with a flat-head screwdriver. Turn the adjuster clockwise to decrease the air gap, or counterclockwise to increase the air gap. Recheck the clearance between the valve tappet and the rocker arm. Hold the screw in place and tighten the lock nut, once the valve clearance has been set to 0.010-inch. Repeat on the remaining valve, if needed. Skip this step if both front cylinder valves are within specification.
Turn the alternator flywheel clockwise one full turn until the rear cylinder timing mark, indicated by the number "2," is aligned with the mark on the crankcase breather cover. Wiggle the rocker arms to check for free play. Turn the flywheel a complete turn if the rocker arms are tight.
Check and adjust the rear cylinder valve clearances as described in steps 6 and 7.
Reinstall the rocker covers and gaskets onto the engine cylinder heads. Tighten the cover bolts to 16 foot-pounds using a torque wrench. Screw the spark plugs into both cylinder heads by hand. Tighten the spark plugs to 12 foot-pounds. Push the spark plug cable boots over the spark plugs until they snap into place.
Reinstall the alternator cover and gasket onto the engine. Screw the cover bolts into place until they are hand-tight. Tighten the cover bolts to between 35 and 43 inch-pounds, alternating between bolts in a crisscross pattern.
Lower the cargo bed until the release lever latches into a locked position.
Items you will need
Metric socket set
Spark plug socket
Blade-type thickness gauges
Metric box-end wrench set
Torque wrenches, foot-pound and inch-pound
Lift the motorcycle onto its center stand. Remove its fairings, if equipped, using a 4-mm Allen wrench. Unlock and remove the motorcycle's seat, using the ignition key. Unscrew the mounting bolt at the gas tank's base, near the seat's rails, using a 10-mm socket and wrench. Turn the gas tank's valve to the "On" position, and pull the fuel lines away from the valve. Lift the gas tank off of the motorcycle's frame.
Unscrew the bolts from the round crankcase cover on the right side of the motor with a Phillips screwdriver or a four-mm Allen wrench. Pull the cover away to access the motor's crankshaft. Place a 19-mm wrench over the nut at the end of the crankshaft.
Unscrew the tachometer cable from the motor's cylinder head cover, if present, using a pair of rubber-jawed pliers. Unscrew the cylinder head's bolts with a 10-mm socket. Lift the cylinder head cover off of the motor to access the valve tappets and camshafts. The GS motors are equipped with two camshafts; the camshaft at the rear of the cylinder head controls the intake valves; the forward camshaft controls the exhaust valves.
Rotate the crankshaft counterclockwise with a wrench to turn the camshafts. Stop when the exhaust camshaft's round-tipped cams on the right side of the motor are pointed at a 90-degree angle away from the top of the cylinder head. Measure the clearance between right exhaust cams and their tappets with a feeler gauge. Suzuki specifies a clearance range of 0.001 to 0.003 of an inch of clearance between the cam and the top of the tappet.
Adjust the exhaust valve's clearance by replacing the existing shim with a new shim that is slightly larger or smaller than the original shim, according to the measurements taken in the previous step. Push the exhaust valve's tappet away from the cam, then pull the shim off of the valve with forceps. Coat the top and bottom of the new shim with 10W40 motor oil, then slide the shim into place over the tappet. Skip this step if the clearance of the first two exhaust valves are within 0.001 to 0.003 of an inch.
Rotate the crankshaft 180-degrees counterclockwise with a wrench so that the intake camshaft's cams are away from the intake valve's shims on the right side of the motor. Measure the valves' clearance with a feeler gauge and replace the shims as needed.
Rotate the crankshaft 180-degrees counterclockwise with a wrench so that the exhaust camshaft's cams are away from the exhaust valve's shims on the left side of the motor. Measure the valves' clearance with a feeler gauge, and replace the shims as needed. Repeat this step to check and adjust the remaining intake valve clearances.
Reinstall the cylinder head cover onto the motor, and tighten its bolts with a 10-mm socket. Reinstall the right crankcase cover and tighten its bolts with a four-mm Allen wrench. Screw the tachometer cable into the cylinder head cover and tighten it by hand. Reinstall the gas tank onto the motorcycle and reconnect the fuel line to the carburetor. Reattach the seat and reinstall any fairings removed earlier. Use a 4-mm Allen wrench to tighten the fairing's bolts.
Items you will need
4-mm Allen wrench
10W40 motor oil
Park the motorcycle on its side stand and let it cool completely. Remove the bolt at the rear of the passenger seat, using a ratchet and an Allen-head socket. Lift the rear of the passenger seat up and pull it away from the rider seat. Remove the two bolts securing the passenger grab strap to the rear fender; this will free the rider's seat from the fender. Lift the rear of the rider's seat up and away from the motorcycle.
Unlock the left frame cover -- the plastic cover located directly below the rider's seat rails -- using the ignition key. Remove the bolts securing the right frame cover, using an Allen-head socket. Remove the two bolts from the front of the speedometer housing, and the single bolt at the housing base, using an Allen-head socket. Lift the speedometer off of the fuel tank and uplug the speedometer wiring harness. Set the speedometer aside. Remove the bolt from the base of the fuel tank, using a socket. Lift the rear of the tank upward and unplug the fuel gauge wire harness and fuel hose from the bottom of the tank. Pull the fuel tank toward the rear of the motorcycle and set it aside.
Remove the rectangular valve inspection covers from the tops of both engine cylinders, using an Allen-head socket. Twist the spark plug wire caps a quarter-turn, then pull the caps off of the spark plugs. Remove the spark plugs with a spark plug socket.
Unscrew the round timing inspection plug from the front left crankcase cover, as well as the generator plug on the side of the cover, using an Allen-head cover. Place a socket and ratchet over the flywheel nut, visible through the generator plug port, and observe the timing inspection port. Turn the flywheel nut clockwise until your feel resistance and the FT mark is aligned at the center of the timing inspection port. This will pace the front cylinder at top dead center in its compression stroke.
Measure the clearance between the front cylinder intake valve -- the valve closest to the carburetor between the cylinders -- and the rocker arm adjustment screw, using a thickness gauge. There should be between 0.003 to 0.005 inch of clearance between the valve and screw. Measure the clearance between the exhaust valve, located on the opposite side of the engine cylinder. The exhaust valve clearance should measure between 0.007 to 0.009 inch. Skip to Step 7, if the both valves are within specification.
Hold the valve steady with a flat-head screwdriver, then loosen the lock nut with an open-end wrench, if either valve is out of specification. Turn the adjustment screw clockwise to decrease the clearance, or counterclockwise to increase the clearance. When properly set, you should be able to slide the thickness gauge between the valve and the adjustment screw with a slight drag. Hold the adjustment screw steady and snugly tighten the lock nut.
Rotate the flywheel nut clockwise a full one-and-a-quarter turns to bring the rear cylinder to TDC in its compression stroke. An RT mark will be aligned at the center of the timing inspection port. Check and adjust the rear cylinder intake and exhaust valve clearances, as outlined steps 5 and 6.
Reinstall the valve inspection covers and tighten the cover bolts to 7.6 foot-pounds, using a torque wrench. Screw the spark plugs into place and tighten them to 18 foot-pounds. Push the spark plug caps into place. Screw the timing inspection and generator plugs snugly into place.
Slide the front of the fuel tank onto the rubber bungs behind the front fork, plug in the fuel gauge connector. Push the fuel hose onto the fuel valve at the bottom of the tank, then lower the tank onto the motorcycle's frame. Screw the tank bolt snugly into place. Plug in the speedometer harness, then snugly tighten the speedometer housing bolts. Reinstall the frame covers and seats. Tighten the seat bolts to 7.6 foot-pounds.
Items you will need
Allen-head socket set
Open-end wrench set
Purchase the performance intake valve gasket and cylinder base gasket you want the 150cc engine ports to match. Place the intake gasket against the intake port so that it covers everything except the original valve areas that must be removed.
Mark the intake surface section not covered by the gasket with a black permanent marker. Thoroughly ink it so that the black ink won't wipe off. Remove the gasket when finished. Complete the same process with the cylinder base gasket against the cylinder part of the engine case.
Place the inked engine case under a bright light. Put yourself in a comfortable position to sit or stand for a extended period of time. Attach a soft metal grinding bit to a hand-held motorized grinding tool. Turn the tool on and carefully begin to grind away the engine case metal to match the markings on your case.
Stop periodically to remove ground material from the engine case ports with a brush. Grind carefully so the finished surface is a smooth adjustment matching the marker pattern. Avoid grinding where the ports or valves begin to transition to flat.
Finish the grinding and wipe away all the removed material. Examine the valves for any areas still needing work. Remove the tool and take the engine to a bin. Wash it with water to remove any remaining bits on the engine case. Dry the case off. Prepare to reassemble the engine with the newly widened valves.
Items you will need
Performance intake gasket for a template
Performance cylinder gasket for a template
Black permanent marker
Hand-held motorized grinding tool
Soft metal grinding bit
Large bin for washing