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(From: TT member z4me, TT member Sceptor, TT Archives, TT member MotoMan393) |
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The WRF exhaust valves open at
127.5 degrees while the YZF exhaust valves lift at 105 degrees. The reason for
this is likely the choked stock exhaust. Changing to the YZF timing on the WRF
improves mid-range and top-end power without a significant sacrifice in
low-end, according to most riders who have done this mod. Adjusting carburetor
jetting may be necessary after this mod (see below). For additional information
search YZ timing on www.thumpertalk.com. |
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Make sure the frame
under the tank is clean. Dirt and sand will have a tendency to rain down
into the head of your engine. For added safety, wrap
the frame above the engine and
radiators with plastic wrap (saran wrap) as the frame would be very
difficult to get totally clean. |
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Do not allow the engine to rotate once the camshaft cap has been removed - it should remain
at TDC until the job is finished. If this happens, see below for the
proper procedure to time the cams from scratch. When you remove the
cam cap, there is a half round clip inside that will seek to enter your
engine cavities. Be prepared to catch it. If you miss and it drops in
don't panic - go to Home Depot and get a magnet on a telescoping wand and
simply fish it out. |
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Generally the cams/retainers/etc would be put
back together again using "moly fortified" engine assembly lube.
This is OK practice on an auto engine. The problem on the 250F engine is
that the moly lube will not make the clutch happy (the 250F engine uses a
common engine/clutch oil system). So instead of using premixed moly
assembly lube, take a tablespoon or so of clean new motor oil and coat
each of the cams/retainers/etc before reinstalling all the pieces. |
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The Yamaha manual has more tips on camshaft removal and installation; it would be a good
idea to familiarize yourself with the appropriate section./li>
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If it is in good condition - you can reuse the camshaft cover gasket. |
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Remove seat, fuel tank, and shrouds. The manual says to remove the radiators but you can achieve similar
clearance by removing the upper engine brackets (Figure 1).
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Now remove the valve cover.
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Remove the timing hole plugs and turn the engine with a ratchet until "I" is
in the center of the small plug hole (Figure 2). This is top dead center (TDC).
At TDC the cams will be facing away from each other. The exhaust cams will have
punch marks at 9:00, 12:00 and 3:00. The intake cam will have punch marks at
9:00, 12:00 and 3:00.
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Remove the cam chain tensioner (Figure 3). Use a screwdriver to tighten the screw
inside the tensioner until it locks. Then in a criss-cross pattern remove the
cam chain tensioner.
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Loosen the cam cap bolts in a criss-cross pattern and remove the cam cap. Be careful of the
c-clip on the exhaust camshaft when you take the cap off.
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It is best to loop a zip tie thru the intake sprocket, up over the chain and pull it tight. This
insures you won't loose index when you lift the exhaust cam to spin it and also
that you won't accidentally drop the chain into the case. When you are finished
be careful cutting the zip tie off (don't want a piece falling into the case).
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For WRF timing there should be 13 chain pins between the top marks on the cam sprockets. For YZF timing there
should be 12 chain pins between the marks. Count the 12 teeth positions to the
exhaust sprocket and mark with a Sharpie (Figure 4). Only then take off the
exhaust cams and skip a tooth.
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Turn the exhaust cam one tooth clockwise. The timing mark on the exhaust cam will now be
at 1:00 (Figure 4).
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Make certain you have a good torque wrench to incrementally tighten the camshaft cap bolts up in a criss-cross pattern
and torque to 7.2-ft. lb.. Then reinstall the cam chain tensioner and unlock it.
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Click on images to enlarge
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Photo of YZ timing procedure from May 2001 issue of Dirt Bike Magazine: |
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Click picture to enlarge |
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You cannot simply rotate the exhaust cam to achieve YZF timing on the 2003 model. This is because of the new
auto-decompression feature of the 03 bikes. Although the bike will run properly,
it will not start. The 03 WRF exhaust cam lobe is the same as the 03 YZF. The auto-decompression nipple is in
the same position. The timing mark is one tooth different, same as in 01 and 02.
Even with that said, you CANNOT move the WRF cam one tooth to simulate YZF
timing on the 03. The difference in the two cams is that the nipple on the WRF
cam sticks out about 1mm more than the YZF and therefore opens the exhaust valve
too far when adjusted to YZF timing. To obtain YZF timing on the 2003 WRF you must purchase and install the YZF exhaust
cam (see autodecomp).
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ThumperTalk Archives
(updated by TT member Gallo 12/10/04)
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