Just curious if anybody has any tips on easy ways to check and adjust their valve clearence at home. I attempted it once but decided to let the dealer do it. I would like to learn to do it myself with confidence that it would not get messed up.
Thanks

 

My owners manual on all my honda's have step by step instructions on how to adj them, maybe honda is shying away from that so the dealer can make more money It is easy, just use a feeler guage and it should have just a slight drag on it as you pass it under the adjustor... make sure they dont loosen up when you tighten the nut

 

This post originally appeared over 18 months ago under the old forum format, and was lost when the change to the new forum format occurred this past July. So, for the benefit everyone who ever wondered how to adjust the valves on their machine, and for the idly curious, here it is again.

Army Man

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Ten Easy Steps To Perfect Valve Adjustment
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Valve adjustment is a relatively simple procedure that requires no special mechanical expertise, and one that even a beginner should be able to handle without undue difficulty. You are more likely to have difficulty gaining access to the valves, i.e., removing the various plastic body panels, than you are adjusting them. Modern four-stroke engines of the type generally found in motorcycles and ATVs most usually employ a single overhead cam (SOHC) and rocker arm arrangement to perform mechanical actuation of the valves. The Honda Foreman, however, is a notable exception to this general rule.

There are only four major components to any SOHC setup. (1) The cam chain, which transmits the circular motion of the crankshaft to the cam at a 1 to 2 ratio, i.e., for every two revolutions of the crankshaft, the cam makes one revolution. (2) The cam, which uses elliptical lobes to change that circular motion to a reciprocating motion. (3) The rocker arms, which have two distinctly different ends. The cam-follower end of the rocker arm is broad and flat. It rides directly on the cam lobe. Its purpose is to mimic the reciprocating motion of the elliptical cam lobe. The valve-tappet end of the rocker arm is small and narrow. It is positioned directly over the end of the valve stem. Its purpose is to transmit the reciprocating motion of the cam-follower to the valve. Shim and bucket valve setups are not generally found on ATVs and so will not be covered here. And (4) The valves, which allow the air/fuel mixture to enter the cylinder and the exhaust gases to exit.

Too much valve clearance will cause the valve to open late and close early because the initial movement of the ramped portion of the cam lobe is wasted taking up the excess clearance. This decreases power output because it decreases flow through the engine. It also tends to make the engine noisier because the excess clearance allows the cam follower to accelerate without resistance and the tappet smashes into the valve stem at a higher speed than normal. This can also cause peening of the valve stem, thereby further increasing valve clearance and exacerbating the problem. This by its very nature is a slow process and will only be a major problem somewhere down the road.

Too little valve clearance will cause the valve to open early and close late. This decreases power output because it increases valve overlap, the period of time when the intake and exhaust valves are open simultaneously, which allows some of the air/fuel mixture to escape. In cases of zero, or even negative, valve clearance, the valve is actually held slightly off of its seat and never closes. This certainly causes a loss of power, primarily due to loss of compression, but the real damage occurs when the air/fuel mixture ignites and the high temperature combustion gases burn the edges of the valve and burn the valve seat. This can very quickly turn into a major and hugely expensive problem.

A loss of power could, at least in part, be caused by improperly adjusted valves, especially if there is too little clearance. But, generally speaking, during the break-in period for a new machine valve clearance tends loosen rather than tighten. Either situation can cause a loss of power, but too little valve clearance is more harmful than too much. The following step-by-step procedure will walk you through a standard rocker arm cam-follower/valve-tappet valve adjustment.

1. Determine the proper clearance for the intake and exhaust valves. This can be done by consulting the specifications section of your machine’s owner’s manual, a shop manual, or the dealer’s service manager.

2. Procure a good quality set of English or Metric “feeler” gauges. These gauges are thin strips of tool steel of varying thickness. The nominal thickness is stamped on each gauge in thousandths of an inch, or tenths of a millimeter. If the set of feeler gauges you have is not in the same measurement system as the valve clearance specifications, then divide tenths of millimeters by 25.4 to convert to thousandths of an inch, or multiply thousandths of an inch by .003937 to convert to tenths of millimeters.

3. Start with a cold engine. The manufacturer has based the valve clearance specifications on the known thermal expansion characteristics of the materials from which the cam, rocker arm, and valve are made. Any adjustments made on warm/hot engine will be too loose when the engine reaches actual operating temperature. Gain access to the engine and remove the valve cover inspection caps. Locate the rocker arm adjusting screws and lock nuts. For engine designs that use eccentric rocker arm shafts, these are usually located near one end of the camshaft. For engine designs that use integral adjusting screws, they are located at the end of the valve tappet part of the rocker arm. Remove the alternator cover, or engine side cover, to gain access to the nut on the end of the crankshaft that will allow you to manually rotate the crankshaft. Remove the spark plug. It is much easier to turn the crankshaft by hand when you are not compressing the air in the cylinder.

4. Using the appropriate wrench/socket, rotate the crankshaft until the piston reaches top dead center (TDC) of the compression stroke. You should now be able to stick your finger in the valve inspection port and wiggle the intake and exhaust valve rocker arms thus confirming that the engine is at TDC on the compression stroke. While the amount of movement is very slight, it should nonetheless still be detectable. There should also be markings on the alternator housing indicating TDC, and a timing mark on the alternator stator which can be aligned to be sure the engine is at TDC. On some machines this mark takes the shape of the letter “T”. If you can not wiggle the rocker arms, or if any of the valves appear to be open, then you are not at TDC and you must rotate the crankshaft another full turn. Repeat Step 4 as necessary until you are sure the piston is at TDC of the compression stroke.

4A. Check/set the cam chain tension. This must always be done with the piston at TDC of the compression stroke. Do not proceed with this step until Step 4 has been successfully completed. Most manufacturers use some type of automatic cam chain tensioner. Some can be adjusted and some can not, consult your owners-manual/shop-manual for the specific procedure for your machine. The most common form of automatic cam chain tensioner is the spring-loaded wheel and plunger arrangement. This is usually positioned somewhere near the center of the cam chain run. For those setups that are adjustable, the actual adjustment procedure is usually quite simple. Most often there is a lock bolt that holds the plunger in place. Loosening this lock bolt allows the spring to push the plunger/tension-wheel assembly forward thereby taking up any slack created as a result of cam chain stretch. Tightening this lock bolt sets the cam chain tension. Do NOT forget to retighten this lock bolt. Severe engine damage can result if the cam chain tensioner comes out of its housing and bounces around inside the crankcase when the engine is running.

5. Measure the existing valve clearance by starting with a feeler gauge smaller than the minimum stated clearance for the valve in question. Slip the feeler gauge in between the valve stem and the tappet. It should slide in between the two with little or no resistance. Then using progressively larger feeler gauges, repeat this step until the feeler gauge you have selected will no longer slide in between the two. The last feeler gauge to successfully slide in between the valve stem and the tappet represents the current valve clearance. Write this number down along with the name of the associated valve. Repeat Step 5 for all remaining valves.

6. Compare the measured valve clearances, the ones you previously wrote down, with the valve clearance specifications, if all of the measured clearances are within specification, put everything back together and clean up, otherwise for those valves that are out of specification, go to Step 7.

7. Loosen the valve tappet adjustment screw lock nut. Gently turn the slotted adjustment screw with a screwdriver until you determine which direction increases the valve clearance, usually counterclockwise. Increase the valve clearance just slightly. Select the feeler gauge that represents the exact valve clearance, or the middle of the valve clearance range, as specified by the manufacturer. Slide this gauge in between the valve stem and the tappet. Gently turn the slotted valve tappet adjustment screw with a screwdriver to decrease the valve clearance. When the clearance has been reduced to the point where the feeler gauge is held snugly between the valve stem and the tappet, but not so snug as it can not be extracted with gentle finger pressure, then gently tighten the valve tappet adjustment screw lock nut while being careful not to move the valve tappet adjustment screw itself. This operation requires a certain amount of finesse and a great deal of patience as the valve tappet adjustment screw sometimes tends to turn with the lock nut, and a small amount of contrarotating force must be applied to the valve tappet adjustment screw to prevent this from occurring, but not so much as to disturb the setting you have worked to achieve.

8. Check your work on the lower end of the valve adjustment range. Remove the correct size feeler gauge from in between the valve stem and the tappet. Select the next smaller feeler gauge one increment down from the correct size feeler gauge and slip it in between the valve stem and the tappet. It should slide in between the two with little or no resistance. If it does not, then you applied too much contrarotating force to the valve tappet adjustment screw and the valve clearance is too tight. Go back to Step 7.

9. Check your work on the upper end of the valve adjustment range. Remove the correct size feeler gauge from in between the valve stem and the tappet. Select the next larger feeler gauge one increment up from the correct size feeler gauge and try to slip it in between the valve stem and the tappet. It should not slide in between the two. If it does, then you applied too little contrarotating force to the valve tappet adjustment screw and the valve clearance is too loose. Go back to Step 7.

10. Have patience and repeat Steps 7, 8, and 9 as many times as necessary until you achieve the correct valve clearance. Once you get the hang of things, it should only take an hour or two to perform a thorough and precise valve adjustment.

Finally, since you have removed the sparkplug to make the valve adjustment procedure easier, check and adjust the sparkplug gap prior to replacing it. Using the “feeler” gauge technique described above, check the existing sparkplug gap. If the gap requires adjustment, use a small pair of needle-nose pliers, or a specially designed sparkplug gapping tool, to bend the ground electrode on the sparkplug in the direction that will bring the gap into specification. Recheck the gap, make any final adjustments as necessary, then replace the sparkplug.

After break-in, most engines will hold their valve clearance fairly consistently, and will only require verification, and perhaps adjustment, on an annual basis.

Army Man




[This message has been edited by armyman (edited 11-12-1999).]