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its not hard at all. just need a feeler gauge and make sure that no dirt gets in your engine. o and make sure the engine is at tdc (top dead center) the manual explains it.

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Here is a how to that I have written:

This is a paper I wrote for English on checking the valves:

This how to article will walk you trough the steps for checking the valve clearances on a CRF250R. You will need some basic mechanical knowledge and some tools such as a torque wrench, feeler gauges, and a set of sockets. You can save money by doing this piece of required maintenance by yourself instead of spending a wad of cash at the bike shop. A couple of tips before we begin. You will want a really clean bike, cleanliness is super important; you do not want any debris falling into the engine. If you end up needing to re shim the valves, buy a hotcams valve shim kit. These kits cost $80, and they come with 3 of every shim, instead of spending $10 per shim at the dealership. So if you are ready to begin, read on.

First get your bike up onto the work stand. Next remove the seat and radiator shrouds. Turn the fuel off and remove the fuel line and tank. Once the tank is out of the way, remove the spark plug lead and clean around the valve cover area. When clean, remove the valve cover; making sure the gasket comes off with it. The next step is to set the motor at top dead center. To do this rotate the motor until the cam lobes are facing rearwards, and then the lines on the cam gear are flush with the top of the cylinder head. Once the motor is at top dead center, it is time to check the valve clearances. When checking the valves, ensure the feeler gauge has a slight resistance when it is under the cam and rocker arm. Do not force it in; it would create an inaccurate measurement. The specs for the valve clearances are .004-.006 inches for the intake valves, and .010-.012 inches for the exhaust valves. If your valves measure out of spec, re shim them; this will be covered in a separate how to article.

Now that you have checked the valve clearances, it is a good idea to record them along with the number of hours on the bike at the time of checking. This is useful to track how much the valves have tightened up over time. Generally as a rule of thumb, once the clearances start tightening up, after the initial break in of the bike when the valves “seat in”, they will keep getting tighter and tighter. You may only get a few rides out of the adjustment; this means that the valves are starting to “cup”, so a valve rebuild is needed. This entails of getting the guides checked, seats cut and installing new valves, springs, cotters, and retainers. If you do not get the seats cut, the new valves will not last.

After you have checked and recorded the valve clearances, it is time to put the bike back together. Make sure the rubber gasket is seated on the valve cover properly, and it is clean; then, install the valve cover, and torque the bolts to 7 foot pounds. Next, put on the spark plug lead, tank, and fuel line. After those are all secure, finish up the job by installing the radiator shrouds and seat. The bike is now ready to ride. Once you get good at this, you should be able to check the valve clearances in 15 minutes and adjust them in 45 minutes.

It is important to keep up on the maintenance of your bike so that it will keep working well for you. Frequent oil changes after every one or two rides, and airfilter cleanings after every dusty ride is necessary to keep your bike working it top condition. I hope this article has proved useful to you, let’s see you out at the track this weekend.

And to adjust them:

To adjust them:

Make sure the motor is at top dead center.

Loosen the middle bolt from the cam chain tensioner, and then remove the other two bolts and take out the tensioner

Use a sharpie to mark the cam chain and sprocket to help with timing the motor when you put the cam back in.

Remove the cam cap bolts in steps, a little on one side and a little on the other.

Then using the bolts in the cam caps you can rock them back and fourth, they will eventually come out. You may need a slight tap with a rubber or plastic hammer. Do not drop in the bearing clips that go under them.

Now you can remove the exhaust rocker arm, remove the allen head plug on the right side of the cylinder head, then slide out the rocker arm shaft and then take out the rocker arm.

Now the left cam bearing can slide to the left, slide it to the left and then wiggle the cam downwards so you can get the chain off of the cam. Wire up the chain so it doesn't fall in, be careful to not let it fall off the bottom sprocket. Remove the cam, set aside.

Remove the valve buckets and shims, the shims may stick in the buckets. Make sure you keep left and right separated.

Remove the exhaust shims, keep left and right separate.

You want to set your intakes at .005" and exhausts at .008"

.127 mm for intakes and .2032mm for exh.

To figure out your new shims sizes: (to measure old shims use a good digital caliper)

Convert all of your measurements to metric

multiply thousands of an inch by 25.4 to get metric.

divide metric by 25.4 to get thousandths of an inch.

Then to figure out your new shim sizes do this math:

Measured clearance – specified clearance + measured shim size

Here is an example

So for example your valve clearance is .0025 your old shim is 1.85 and the specified clearance is .127 (.005”)

You would convert the .0025 to metric (multiply by 25.4) = .0635mm

Then take .0635 - .127 + 1.85

You get 1.7865 – you would put in a 1.75mm (175) hotcams shim to get your valve to the .005” spec.

Now install the proper valve shims in their places. Install the valve buckets, put some oil on them.

Now install the cam shaft - line up the sharpie mark on the cam gear with the mark on the chain. Put the cam back in, slide the bearing over. Now you want to check to make sure you got your timing correct.

To do that line up the marks on the cam gear flush with the cylinder head. You want to putting your finger in the hole where the chain tensioner goes and putting tension on the chain to get the correct reading. Also hold down the cam so it doesn't flop out of place. Then you want to look in the plug on the ignition cover. There are 2 marks on the flywheel, you want it so that you can see the two marks and it is lined up inbetween/ around the second mark (second mark is TDC, first is firing).

Now you can install your rocker arm and rocker shaft.

Then install the cam bearing caps [long bolts on the exh side, and shorter on the intake side), make sure you have the clips inside of them in place. Install them on the cam, be careful to get the clips in the groove of the cam bearing. Make sure they are totally seated with the cylinder head before you torque them up to the 12 ft lbs. Use a rubber hammer or something to help aid in seating them. Do not beat on them though. Before torquing them up make sure that each end of the cam cap is flush with the head. To torque them go a little on one side and a little on the other until you get to 12 ft lbs.

Install your cam chain tensioner. Use a screw driver to wind in the tension, and keeping the tension winded in thread in the bolts all of the way with your hand. You can release the tensioner once the bolts are torqued up. Taking out the screw driver allows the tensioner to put tension on the cam. (the tensioner only goes out, does not come back in, thats why you want to keep it retracted when you install it)

Re check to make sure your timing is correct. Cam lobes facing rearward, 2 lines lined up with the cyl head. And the ignition cover marks lined up properly. There is also a mark on the right crank gear. Just pull out the right crank plug and you can check to see if that mark is lined up as well.

If your timing isn't good, fix it.

If it is, put on your valve cover, etc.

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