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Checking & Adjust Valve Clearances - 06 Yamaha YZ250F


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Remove the seat and gas tank in order to have easy access to the valve cover. Remove the spark plug and the valve cover vent hose, then use a 5mm Allen wrench to remove the valve cover.

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Use a quarter, a big flat head screw driver or a pair of needle nose pliers to remove the 2 caps to check for the top dead center (TDC) mark.

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Use a 17mm socket and a breaker bar to turn the crank counter clockwise until you line up the '|' mark inside the TDC peep hole. The TDC mark is hard to see unless you have very good lighting.

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At TDC, the cam chain side should look like the first picture below, notice that the 'E' and the 'I' dots on the intake cam are horizontal. There should be 12 pins on the cam chain between the two 12 o'clock dots of both cams. The second picture below shows how the back of the cams should look like - notice how the lobes are pointing at 10 o'clock and 2 o'clock. I used an Allen wrench to touch the piston in order to verify TDC.

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Below, looking from the kick start side, I'm checking the left intake valve, then the middle intake valve then the right intake valve - the valid range for the intake valve clearance is 0.10-0.15mm (0.0039-0.0059 in).

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Below, looking from the kick start side, I'm checking the right exhaust valve, then the left exhaust valve - the valid range for the exhaust valve clearance is 0.17-0.22mm (0.0067-0.0087 in).

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If your valve clearances are out of specification, i.e. if the smallest feeler gauge that you can fit in there is smaller than the lower end of the specification or if the biggest feeler gauge you can fit in there is bigger than the upper end of the specification, then you'll need to get the proper pads (a.k.a. shims) and adjust the clearances back into the required specification.

If your valve clearances are all within specification, then reinstall the valve cover, the spark plug, the valve cover vent hose, the 2 caps on the shifter side of the case for checking TDC, the gas tank (don't forget to reattach the fuel line to the carburetor), the seat and you're good to go. http://www.thumpertalk.com/public/style_emoticons/#EMO_DIR#/ride.gif

Adjusting Valve Clearances

In this article, we are removing both the intake and exhaust camshafts to adjust the valve clearances.

Remove the seat and gas tank in order to have easy access to the valve cover. Remove the spark plug and the valve cover vent hose, then use a 5mm Allen wrench to remove the valve cover.

TN_IMGP5332.jpgTN_IMGP5346.jpg

Use a quarter, a big flat head screw driver or a pair of needle nose pliers to remove the 2 caps to check for the top dead center (TDC) mark.

TN_IMGP5342.jpgTN_IMGP5344.jpg

Use a 17mm socket and a breaker bar to turn the crank counter clockwise until you line up the '|' mark inside the TDC peep hole. The TDC mark is hard to see unless you have very good lighting.

IMGP5352.jpgIMGP5355.jpg

At TDC, the cam chain side should look like the first picture below, notice that the 'E' and the 'I' dots on the intake cam are horizontal. There should be 12 pins on the cam chain between the two 12 o'clock dots of both cams. The second and third pictures below show how the back of the cams should look like - notice how the lobes are pointing at 10 o'clock and 2 o'clock. I used an Allen wrench to touch the piston in order to verify TDC.

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NOTE: Since you will be removing camshafts, make sure you have the breaker bar setting the engine to TDC (see above), then zip-tie the breaker bar to the foot peg to keep the engine at TDC while you're adjusting the valve clearances. It is very important to have the engine at TDC when the camshafts go back on later, so check the TDC mark before installing the camshafts!

Shove a clean rag or some paper towels into the cylinder head cavity to prevent things from falling in there. Tie the cam chain to the frame to prevent it from falling into the cylinder head cavity too. Remove the cam chain tensioner located on the shifter side of the cylinder next to the carburetor.

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Make sure to have a small, skinny flat head screwdriver to turn the screw inside the back of the cam chain tensioner to compress the tensioner rod during the installation process later. Notice the screw inside hole in the picture below.

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Remove the bolts on the exhaust cam cover using a criss-cross pattern. Use a flat head screw driver to gently nudge the cam cover free from the head if necessary. Be sure you don't drop the 'C' clip that sits on the cam's bearing into the cylinder head cavity (see first picture below). The cam may also need some gentle persuasion to get the bearing out of its pocket. Picture 2 below shows the exhaust valve lifters.

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Having a magnetic tool such as the one shown below is a must in order to remove the valve lifters and the shims (a.k.a. pads). The magnetic tool shown below is readily available at most auto parts store.

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Remove the valve lifter that needs the clearance adjustment. The shim may be stuck to the inside of the valve lifter as shown in picture 2 below. Picture 1 shows the exhaust valves with the shims removed.

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Next, remove the intake cam...

Remove the bolts on the intake cam cover using a criss-cross pattern. I removed the inner 2 bolts first then the outer bolts using a criss-cross pattern as shown in picture 1 below. Remove the cam cover and the intake cam. Be careful not to drop the 'C' clip into the cylinder head cavity (see picture 2 below).

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With both cams removed, use the magnetic tool to remove the valve lifters for the valves that need adjusting (see picture 2 below). Picture 3 below shows the right intake valve with the valve lifter and shim removed.

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When removing the valve lifter, the shim tends to stick to the inside of the valve lifter as shown in picture one. Remove the shim from the valve lifter by using the magnetic tool, picture 2 shows the valve lifter with the shim removed. The shim size should be printed on the upper side of the shim, but if the numbers have worn off of your shim then you'll need a micrometer such as the one shown in picture 3 below to measure the shim's thickness (i.e. its size).

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NOTE: The thickness of each shim is indicated in hundreths of millimeters. Round off the last digit of the installed shim number to the nearest increment.

If the last digit of the shim is 0, 1 or 2 then the rounded value is 0

If the last digit of the shim is 4, 5 or 6 then the rounded value is 5

If the last digit of the shim is 8 or 9 then the rounded value is 10

For example, if the installed shim is 148 then the rounded value is 150.

Locate the rounded-off value and the measured valve clearance in the "pad selection table" (see below). The field where these two coordinates intersect shows the new pad number to use. Once you have obtained the appropriate shim size for your adjustment, oil it well and put it back as shown in the picture below (i.e. with the number facing up), then put the valve lifter back on.

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Reinstall the cams and the cam covers. Make sure the 'C' clips are situated correctly on the bearings as well as in the cam covers' grooves. I installed the intake cam first, then the exhaust cam. Be sure the punch marks are lined up correctly with 12 pins between the two 12 o'clock marks (see picture 1 below). The rear of the cams should look similar to picture 2 below. Using a 8mm socket, tighten the cam covers using a criss-cross pattern, each bolt should be torqued down to no more than 84 inch-lbs (I used 80 inch-lbs to be safe).

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There should be just enough room for you to move the intake and exhaust camshafts with your fingers to make sure that they can be rotated easily. If both camshafts can be rotated easily then cut the zip-tie or string that was holding the cam chain in place and reinstall the cam chain tensioner. You will need to use a small flat head screwdriver to turn the screw on the back of the cam chain tensioner clockwise in order to compress the tensioner rod.

Recheck your valve clearances.

Use the 17mm socket along with the breaker bar and turn the engine counter clockwise at least a couple of revolutions to make sure everything is moving freely in the head. Reinstall the valve cover, the spark plug, the vent hose, the 2 TDC caps (on the shifter side of the case), the gas tank and seat.

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