Valve Clearance Adjustment

Valve Clearance Adjustment

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.

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.

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.

IT IS VERY IMPORTANT TO KEEP THE CRANK AT TDC WHILE THE CAMSHAFTS ARE REMOVED SO TIE THE BREAKER BAR TO THE FOOTPEG!

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.

I had one tight exhaust valve clearance and one loose intake valve clearance so both cams had to be removed and the appropriate shim/pad replaced to get their clearances back into specification. The measurements on 7/8/06 before the adjustments were as follows:

The valid range for the exhaust clearance is 0.17 to 0.22mm
Left exhaust valve (pad/clearance), #182/0.152mm - out of spec.
Right exhaust valve, #180/0.229mm - in spec.

The valid range for the intake clearance is 0.10 to 0.15mm
Left intake valve, #185/0.152mm - in spec.
Middle intake valve, #184/0.152mm - in spec.
Right intake valve, #179/0.229mm - out of spec.

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.

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.

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.

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.

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. Since this is the first time dealing with my 06 YZ250F, I wanted to note the shim sizes on all of the valves hence all valve lifters were removed in order to check the shim sizes.

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).

With both cams removed, use the magnetic tool to remove the valve lifters (see picture 2 below) and check the shim sizes. Picture 3 below shows the right intake valve with the valve lifter and shim removed. BE SURE to put the valve lifters and shims back to their respective valves once the measurements are done - it is best to do only one valve at a time to lessen the chance of mixing up the parts.

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).

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 first picture 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 picture 2 below (i.e. with the number facing up), then put the valve lifter back on.

For 2006 YZ250Fs that have had the recall job done to them, while both cams are removed, make sure to torque down your head bolts to 27 ft-lbs using a 12mm socket in a criss-cross pattern. There are 4 head bolts to check, 2 are located under the camshaft bearing pockets (see picture 1 below) and the other 2 head bolts are located on the outside of the head on the kick start side (see picture 2 below). All 4 of my head bolts were NOT tighten to 27 ft-lbs leaving the possibility of a leaky head gasket or even a blown head gasket if they were unevenly tightened.

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).

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.

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, spark plug, vent hose, gas tank and seat.

Use this link for help with checking valve clearances.

The measurements on 7/8/06 after the adjustments were as follows:

The valid range for the exhaust clearance is 0.17 to 0.22mm
Left exhaust valve (pad/clearance), #178/0.178mm - in spec.
Right exhaust valve, #180/0.229mm - in spec.

The valid range for the intake clearance is 0.10 to 0.15mm
Left intake valve, #185/0.152mm - in spec.
Middle intake valve, #184/0.152mm - in spec.
Right intake valve, #190/0.102mm - in spec.

Measurements on 1/13/07 (no change):

Measurements on 1/12/08 (using millimeter feeler gauges now):

The valid range for the exhaust clearance is 0.17 to 0.22mm
Left exhaust valve (pad/clearance), #178/0.21mm - in spec.
Right exhaust valve, #180/0.21mm - in spec.

The valid range for the intake clearance is 0.10 to 0.15mm
Left intake valve, #185/0.15mm - in spec.
Middle intake valve, #184/0.14mm - in spec.
Right intake valve, #190/0.11mm - in spec.

Measurements on 2/14/09: