This valve adjustment "how-to" is very detailed. It is meant to show the entire process of inspecting and adjusting the valve clearances on a first generation (2004/2005) Honda TRX450R. Although not comprehensive, most of these steps also apply to 2006+ TRX450R's and CRF450R dirt bikes as well.
Disclaimer: I assume NO RESPONSIBILITY for your ATV, parts, or tools. Conduct these steps AT YOUR OWN RISK.
Thanks to all who have helped directly or indirectly in compiling this information.
When removing or torquing bolts, if there is more than one bolt holding anything on that you are removing, follow this procedure. Example: There are 3 bolts holding the valve cover on; put your socket on bolt #1 and barely break it loose, then bolt #2, then bolt #3, then remove bolt #1, then #2, and finally #3. Do NOT remove #1 before you break #2 and #3 loose. If there are 4 bolts follow the same procedure using a crisscross pattern. The same goes for tightening, install all 3 bolts and hand tighten, then cut the torque spec in half and start with #1, then #2, finally #3. Then reset your torque wrench to the full amount and repeat. If the torque amount is high, like 40 ft/lbs, then start at 10, then 20, 30 and finally end at 40...do not just cut a large amount like that in half. Use this procedure anytime there is more than one bolt. This may take a little longer, but not in comparison to a broken bolt or stripped threads.
Before getting started, I recommend getting organized. I generally clear a space in my garage to put the larger parts such as the rear plastics, seat, and gas tank. I also put down a sheet of carboard with several paper towels to lay out the various bolts and small parts in the order they come off the quad (see the picture below).
Remove the seat from the quad by pulling up on the lever located on the underside of the rear of the seat. Then, pull the seat towards the rear of the bike so it will slip out. Refer to the picture below to see the seat lever.
Remove the rear plastics from the quad by completing the following tasks: Pull the kick start lever out into the starting position so the plastics will clear it when they are removed. Pull the three rear plastics tabs out of the rubber grommets. Two are located on the heat shield under the gas tank, the third is located behind the gas tank near the intake snorkel. Next, remove the two bolts (10mm) on top of the plastics which are located above the air box assembly (third picture below, circled in green). Remove the four bolts (10mm), two on either side of the quad that are located on the underside of the rear plastics (fourth picture below, circled in red). Lastly, remove the rear plastics by lifting them up and off of the bike.
Remove the gas tank from the quad by completing the following tasks: Pull the gas cap breather hose out from inside the steering stem hole (first picture below, circled in green). Turn the petcock to the OFF position (second picture below). Remove the fuel line clamp using needle nose pliers (third picture below, circled in red). Pull the fuel line off of the gas tank's fuel line fitting. Note: there could be a smal amount of gas left in the line. Remove the two rubber straps from the frame which are located on each side of the ATV (fourth picture below, circled in blue). Next, remove the two bolts (8mm), one below each of the front fenders (fifth picture below, circled in green). Remove the four bolts securing the front plastics to the tank and frame, two bolts (8mm) on each side of the ATV, one holding the plastic to the tank, and one holding the plastic to the frame (sixth picture below, circled in red). Remove the two bolts (8mm), one on each side of the bike, securing the gas tank to the frame (seventh picture below, circled in blue). Lastly, lift the tank off the quad and place it to the side.
Remove the heat shroud by completing the following tasks: Remove the three black plastic tabs (pictured below, circled in green). Use a flat screw driver to pop the inner push tabs up, then use the screw driver to pry the entire tab out of the frame and plastic shroud. After removing all three tabs, pull the three wires up and out of the heat shroud so that there is plenty of slack in the wires. Then, pull the heat shroud up and off of the frame while carefully maneuvering it out from under the wires. Place the heat shroud aside.
Remove the valve cover by completing the following tasks: Zip-tie the two wires on the right side of the bike to the plastic snap tab hole on the frame (first picture below). Zip-tie the thick wire on the left side of the bike to the frame (second picture below). This will keep those three wires out of the way. Next, use needle nose pliers to remove the clamp and vent hose from the rear of the valve cover (third picture below; stock hose and clamp are not pictured). Remove the spark plug boot (third picture below, circled in red). Then remove the spark plug from the engine using a spark plug socket and long ratchet extension. Remove the three valve cover bolts (fourth picture below, circled in green). Lift the valve cover off the head. Be sure that the gasket stays on the bottom of the valve cover - it can be re-used several times.
Set the engine to top dead center (TDC) by completing the following tasks: Remove the crankshaft hole cap (10mm allen wrench) on the bottom right side of the engine (near the transmission fluid check hole). Inside the crankshaft hole, use an 8mm allen wrench to rotate the crank manually to line up the timing marks on the crank gear and case (first picture below, circled in green). After setting the crankshaft marks correctly, ensure the timing marks on the cam assembly and cam chain sprocket are aligned properly (second picture below, circled in red). Finally, if all the timing marks line up, the cam lobes should be pointing to the rear of the quad, and slightly up - as shown in the third and fourth pictures below. This means the engine is now at top dead center, and you are ready to check your clearances.
Some prefer to set the engine to TDC by removing the flywheel inspection plug on the left side of the engine (stator cover) and aligning the "T" mark on the flywheel with the slot within the flywheel inspection plug hole. If this method is used, be aware that there is also an "F" mark on the flywheel; do not use this mark as a TDC indicator. Although the flywheel inspection plug method may be a more preferred timing method, it is not shown here since it's difficult to capture pictures of the flywheel marks and alignment.
Before checking your valve clearances, its recommended to find out what the clearance specifications are for the cam you are using. Most stock and shelf cams have an intake valve clearance of .006" (+/- .001") or 0.16mm (+/- .03mm) and an exhaust valve clearance of .011" (+/- .001") or 0.28mm (+/- .03mm). To find out what your cam's clearance specs are, contact the cam manufacturer or your engine builder.
The "(+/- .001")" is the allowed variance in the clearance specification. Example: If the intake valve clearance spec for your cam is .006" (+/- .001"), and your measured clearance is .005", .006", or .007", then you are still within spec.
The first picture below shows the location of the four valves. The two intake valve clearances are measured between the "bucket" and cam lobe (circled in blue), and the two exhaust valve clearances are measured between the rocker arm and exhaust valve shims (circled in red). Use a straight feeler gauge (second picture below) to measure the exhaust valve clearance by sliding it between the rocker arm and exhaust valve shim (third picture below). Try different feeler gauge sizes to see which size feeler gives you the best feel. You're looking for a snug fit, but you should still be able to move the feeler gauge around with a little bit of resistance while it's between the shim and rocker. Record your measurements on what clearances you have for each valve on a piece of paper for reference. Next, check the two intake valve clearances. It's important to get an accurate feel for the intake valve clearances, so I suggest using angled feeler gauges as shown in the fourth picture below. Slide the feeler gauge under each of the two cam lobes, you are feeling for the clearance between the cam lobe, and the bucket under the cam lobe. Refer to the fifth picture below to see how to properly check the intake valve clearance. Again, you are looking for a snug fit while still being able to slide the feeler gauge back and forth while it's between the lobe and bucket with some resistance. Record your measured clearances for each intake valve. If one or more of your valves is not within the cam manufacturer's specifications, continue on to step 9 to adjust your valve shims. If all four of your valve clearances are within the cam manufacturer's specs, you don't need to make any shim changes and can re-assemble the bike by reversing the previous steps and referring to the torque specs for the spark plug, valve cover bolts, and crankshaft hole cap in step 10.
To adjust the valve clearances, the thickness of the valve shims has to be changed. To make shim changes, the cam sprocket and cam carrier/assembly need to be removed. It's recommended to put a large rag in the open area of the engine (where the cam chain descends) to ensure no small parts fall inside. First, break the two cam sprocket bolts loose (first picture below, circled in red), but don't remove them yet. When breaking the cam sprocket bolts loose, you will need to keep the cam sprocket from turning. Have a helper place an 8mm allen wrench on the crank nut that can be seen through the crankshaft check hole as mentioned in step 7 to keep the engine from turning over. It's generally much easier to break each cam sprocket bolt loose when its at the bottom, away from the top frame rail. To accomplish this - turn the engine over via the 8mm crank nut on the right side of the engine; but be sure to return the engine to the top dead center position before removing the cam sprocket or cam/carrier assembly. Additionally, to keep the machine in time, it is also recommended to zip-tie the cam chain to the cam sprocket (first picture below, circled in green), to ensure the timing chain does not become advanced or retarded. Next, remove the cam chain tensioner bolt (8mm), and use a small flat screw driver to turn the cam chain tensioner bolt all the way in as shown in the second picture below. The cam chain tensioner bolt is spring loaded, and turning it in removes all of the tension from the cam chain. While holding this screw all the way in, remove the two cam sprocket bolts completely while being careful not to drop them into the engine. While still holding the tensioner screw all the way in, pull the cam sprocket off the cam and zip-tie it to the frame as shown in the third picture below. After the cam sprocket is secured to the frame, you can now slowly back the cam chain tensioner screw out to put tension back on the cam chain.
Another method for dealing with the cam chain tensioner is to just remove then tensioner assembly completely from the cylinder.
Next, remove the four cam carrier bolts (fourth picture below, circled in green). Lift the entire cam/carrier assembly up and off of the cylinder head as shown in the fifth picture below. You may have to wiggle the assembly a bit to get it to pop off. Take care to ensure that you don't drop the small shims or the intake buckets down into the engine. After lifting the cam assembly off, the top of the head should look like the seventh picture below, note the shims circled in green.
With disassembly now finished, its time to make the needed shim changes and reassemble.
Keep this logic in mind - if the spec. valve clearance is .006", and your current valve clearance is .004", a smaller shim is required to increase the size of the gap. If the spec. valve clearance is .006", and your current valve clearance is .008", a larger shim is required to decrease the size of the gap. Additionally, before installing any new shims, coat them with oil; do not put a dry shim into the engine.
If you already know what size shims are in your quad or the size of the shim can still be seen on its face, use this calculator to calculate the size shims you need for each intake and exhaust valve. The valve shim calculator linked above is in millimeter measurements, so if you recorded your measurements in inches, convert them to millimeters.
Every .001" is equal to approximately 0.025mm. Therefore, if your spec intake valve clearance is .006", this converts to 0.16mm. If your spec exhaust valve clearance is .011", this converts to 0.28mm.
To use the calculator, enter your spec valve clearance in the appropriate calculator (either intake or exhaust), put in your current valve clearance, and then enter your current shim thickness (example: a shim with 1.65 printed on it measures 1.65mm). Press the "Calculate New Shim Thickness" button the calculator should display the new shim size you need to bring you clearance back into spec. Repeat this step for each shim that needs changed. If you don't know what size shims are in your bike, there are two methods you can use to find out what size shims you need.
The easiest method, is to use a digital caliper to measure the shim thickness as shown in the second picture below. Then use the valve shim calculator as outlined earlier in this step to calculate the correct shim thickness.
The second, and most time-consuming method, is to "guess and check". Install shims which you know the thickness of, and take new valve clearance measurements. For this method, it is recommended to put a 1.95mm shim in both exhaust valves and a 1.65mm shim in both intake valves. Then, re-install the cam carrier assembly (with buckets) and torque the four bolts back down to 10 ft/lbs. Ensure the cam lobes are facing towards the rear of the quad, and slightly up in the TDC position when re-installing the cam assembly (just as it was removed). Re-measure the valve clearances (as outlined in step 8), and record the measurements. Remove the four cam carrier bolts and remove the cam assembly as outlined in step 9. Now, use the new shim thicknesses and clearance measurments in the the valve shim calculator to get the correct shim sizes.
Now that your shim sizes have been adjusted, record the shim sizes for each valve for future valve adjustments. Reverse step 9 to install the cam carrier and cam sprocket. Install the cam assembly and ensure the cam lobes are facing towards the rear of the quad and slightly up, in the top dead center position (just as it was removed) and torque the four bolts to 10 ft/lbs. At this point, it is recommended to re-check your valve clearances to ensure all of the measurements and calculations were accurate. Re-install the cam sprocket and bolts. When re-installing the cam sprocket, the cam chain tensioner will need to be screwed all the way to remove the tension from the chain. Before installing the cam sprocket bolts, clean the old loc-tite off the bolt threads and re-apply red loc-tite to the bolts. Torque the cam sprocket bolts to 14 lb-ft. Allow the loc-tite to set at least 20 minutes to before starting the quad. Remove the zip-ties holding the cam chain in place on the cam sprocket. Before installing the valve cover, turn the engine over manually by using the 8mm allen wrench on the crank to ensure the cam and timing chain are functioning correctly. It is recommended to ensure the timing marks on the crank, flywheel, and cam tower/sprocket are all in alignment at this point. Reinstall the valve cover and make sure the gasket is properly seated. Torque the valve cover bolts to 7 lb-ft. Re-install the spark plug and torque to 17 lb-ft. Re-install the crankshaft hole cap and torque to 11 lb-ft. Re-assemble the remainder of the quad by reversing the steps above. Take your time, and double check that everything is in place and that there are no parts or hardware leftover.