Checking and Adjust Valves on a Honda CRF250

We all know how important valve maintenance is on the water-cooled Honda CRF's. Proper valve maintenance includes checking clearance and adjusting the valves as necessary. As frequently as this needs to be done, paying a mechanic to do this for you can get expensive fast. This "How-To" written by CRF's Only member "Heckler" will show you step-by-step how to check and adjust (shim) your valves on a Honda CRF250X. This process is very similar to other CRF models.

1. First remove the seat by removing the two bolts on the rear sides of the seat and slide it back.

2. Next remove the rubber strap holding the rear of the tank down.

3. Using an 8mm socket remove the bolt holding the top of the tank to the frame.

4. Remove the fuel line from the petcock. (Don’t forget to turn the gas off...)

5. Remove the bolt holding the petcock.

6. Next remove the two lower shroud bolts on both sides, leave the top ones in place.

7. Remove the tank and shrouds as a single unit and set aside.

8. Clean the top of the valve cover off to remove any dirt and debris.

9. Remove the spark plug cap by pulling up firmly, it may take a good tug, move it off to the side.

10. Next remove the vent hose on the rear of the valve cover and remove the two 10mm bolts.

11. Carefully remove the valve cover making sure you don’t damage the gasket. (You can re-use this gasket if you don’t damage it.) There is also a rubber sealing ring on the spark plug tower, don’t loose it or let it fall into the cam chain tower.

12. Next remove the cover on the lower right side case, I believe it's an 8mm allen.

13. Turn the motor over clockwise until the punch mark on the gear lines up with the arrow mark on the side case. Check to be sure that the cam lobes are facing to the rear of the bike, if they are pointing toward the front keep going until they face back and the punch mark aligns up with the mark on the case.

14. Check the cam gear to make sure the two marks on the gear are level with the surface of the head.

15. Inset your feeler gauge under the intake lobes, it should slide in with a slight drag. .005" is spec for the intake valves; if it won’t fit try the next size down etc. Write down your measurements for both left and right valves.

16. Next do the Exhaust valves by sliding your feeler under the rocker, spec for the exhaust valves are .011" I use 12" long auto type feeler gauges that are nice and flexible. Again, write down your measurements for both left and right valves.

17. Make sure the rubber sealing ring is firmly seated in the under side of the valve cover and set it back on.

18. Using a "QUALITY" torque wrench (1/4" drive) Torque the valve cover bolts to 84 inch lbs (or 7 ft. lbs.) Be very careful when tightening those bolts, they thread directly into the cam bearing caps and can only be replaced by buying the whole head assembly, you can’t buy them separate. Replace everything else in reverse order. Don’t forget to replace the cover on the lower right case! IT"S REALLY EASY!!!!! Takes about 15-20 minutes tops once you get the hang of it.


PART 2 Reshimming

1. Assuming you have recorded your measured clearance (From valve check post) and installed shim size (You will get the installed shim size later in this post) use this spreadsheet (Please right click and “save target as”) to calculate your new shim size. All Honda shim sizes and part numbers are listed at the bottom of the spreadsheet. If you have a valve at zero clearance it will take a few tries before you can get the correct values, you must have some clearance for the spreadsheet to work.

Click Here to Download Valve Shim Calculator Spreadsheet

2. Remove the bolt on the cam chain tensioner.

3. I use a small flat blade screwdriver to release the tension, turning it clockwise will release the tension on the chain.


4. I use a small set of vise grips to hold the screwdriver in place, the tension will hold the vice grips against the side cover holding it in place. If you wish to avoid this step or don’t have the vice grips or screwdriver you can completely remove the chain tensioner by removing the two bolts that attach it to the head but you will need to release the tension before re-installing it.

5. Remove the cam cap bolts in steps in a crisscross pattern, loosen a little at a time to avoid warping the caps


6. Notice I stuffed a rag in the cam tower opening; this is in case something like the cam cap bearing retainer clip or shims fall it won’t end up in your crank case.


7. Work the caps loose by moving them back and forth, once you have them loose place a finger underneath them to hold the bearing retainer clip in place so they don’t fall out, if they do that’s ok…. That’s why you have the rag in the cam tower to catch them in case this happens. Do the same for both sides.


8. This is what the bearing retainer clip looks like, it fits in a groove on the cap and aligns in a groove on the bearing.

9. Put a little grease in the groove to hold the clip in place when you re-install the caps.

10. I use a perm marker and mark a spot on the chain and gear as a reference when re-installing the chain.

11. Slide the bearing on the cam gear side to the left, the cam will then drop down on the left side.

12. Next wire up the chain so it won’t drop into the tower, if this happens its ok, it won’t go too far, you will just need to fish it out of there before you install the cam back.

13. Remove the chain then the cam from the head assy. and place it aside.

14. The shim buckets are the round silver parts near the rear of the head that were directly below the cam.

15. Lift the buckets up to expose the shims, you can also use a magnet to remove them and often it will lift the bucket and shim out together.

16. Usually even without the magnet the shim will stick to the underside of the bucket. If not it will be on the bottom of the valve that was under the bucket. Remove the shim and it should have the size on it. The size will read something like 195 which is 1.95mm. If the writing has worn off you will need to use a caliper or a micrometer to get the size, you will need this to calculate your new shim size. Use the spreadsheet at the beginning of this post to enter your measured values. Once you have the correct shim size ordered and in hand just place them where the others were and replace the buckets. When replacing the buckets put a little clean oil on them.

17. To get to the exhaust valve shims remove the small cover on the right side of the head. If all you need to adjust is the exhaust valves your in luck, you don’t need to remove the cam or cam caps, you will need to remove the cam cap bolts but that’s way easy...

18. Using a small screwdriver push the rocker shaft out the hole in the side of the head you just removed the cap from.

19. The rocker will now just lift out.

20. The shims are directly under the rocker, there are no buckets over the exhaust valve shims. Remove the shims with a magnet and replace them with your new ones.

21. Replace the rocker, shim buckets, and cam in reverse order of removal. Make sure your timing marks are lined up (or use the permanent marker reference mark) when you put the chain back on the cam gear.

22. Place the cam bearing caps back on. This may take a bit to get them lined up as you need to be sure the bearing retaining clip is properly lined up with the groove in the bearing. The bearings slide around so you may need to move them into position a few times before you get it rite. You should be able to get the caps all the way down flush with just your fingers, “DO NOT FORCE THEM DOWN WITH THE BOLTS”

23. Next torque the cam cap bolts to 144 inch pounds or 12 foot pounds with a torque wrench. Again do this in steps in a crisscross pattern. (Example: Tighten them at 60 in lb then 90 in lb then 100 in lb then 144 in lb. etc.)Next remove the screwdriver from the cam chain tensioner or replace it if you removed the whole assy.

24. Using a "QUALITY" torque wrench (1/4" drive is best) Torque the valve cover bolts to 84 inch lbs (or 7 ft. lbs.) Be very careful when tightening those bolts, they thread directly into the cam bearing caps and can only be replaced by buying the whole head assembly, you can’t buy them separate.

25. Put everything back together in reverse order. Now save yourself some money and do this yourself. It really is very easy.

CRF's Only "How-To" By "Heckler" August 2005


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