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The 2002 and 2003
YZ250F and WR250F exhaust cams are identical except for the decompression device.
So for about $160, the 2001-2002 250Fs can start just as easily as a
2003 model. This isn't true for the old 426F. The 450F cam
gear has a different tooth pitch, even though the tooth count is the same.
The new cam will work for a while, but the chain and gear will have
accelerated wear. |
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The 2001-2002 E-cam is shown on the
left. The 2003 E-cam and autocompression device is seen on the right. |
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Close-up pictures of the 2003
E-cam with autocompression device. |
Click images to enlarge |
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Your valve cover gasket and chain tensioner gasket can be reused. Get some Permatex 6B RTV Silicon to re-seal the valve cover gasket as
per manual.
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Technically speaking you may need to re-shim the valves so measure your valve clearance first. No one on ThumperTalk has had to re-shim. If you do, your valves
needed it anyway. And you really won't know what size shims you'll need until after you measure the gap.
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One thing to beware of is the circlip under the cam cap. Stuff a rag in the timing chain opening so the circlip doesn't fall down
into the engine. Many (including myself) have had to fish it out with a magnet.
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Read the section in the Owner's Service Manual regarding cam removal.
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Yamaha Part Numbers: YZF cam = 5UL-12180-00, WRF cam = 5UM-12180-00
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Follow the steps in the manual for removing the cam, with the following pointers
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Remove gas tank with shrouds
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Do not remove radiator
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The carburetor can be left on but the job is easier if you remove it.
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Clean frame well and wrap it with plastic wrap to keep debris from falling into the head
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Remove spark plug. Check your spark plug tool. The pin connecting the two pieces is to long and scores the aluminum when you install/remove plug leaving chunks of aluminum just
waiting to fall into combustion chamber when plug comes out!!
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Check valve clearance. So far no one has reported having to re-shim! Click here for more info on valve
clearance
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The cam chain doesn’t have much play so you may have to take off both cams to provide enough room to install
new cam. After you take the cam chain tensioner off, you should have more than
enough slack in the chain to gently work the exhaust cam off the head. Work slowly.
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Install new cam with care. Work slowly! The cam will slide side to side in head until cam cover is in place so
be careful! Be sure to lube the cam liberally before installing. The manual
calls for assembly lube but a good coat of engine oil will do just fine. Also
some assembly lube products are not good for the clutch plates.
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Go real easy and don't force cam covers back on. A little at a time and they go on. They seem tight at first.
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Time cams as in manual (see below for more info). Also see the section regarding
cam timing. There is no "E" or "I" on new cam so make sure the lobes are
pointing forward and a little bit upward. There are two punch marks but only
one will be close when the lobs are properly positioned
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Check valve clearance. So far no one has reported having to re-shim!
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Install cam tensioner and test by spinning crankshaft.
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Don't worry when it doesn't line up after one spin. it has to line up every 2 spins (compression stroke)
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If it tests good close her up test starting. See the
starting drill.
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It would be a good idea to let it warm up and cool down once or twice before you ride it hard. The cam needs to "settle?" into the head/cam cover.
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Check your timing (count the links of the timing chain between the gears) before you take off the
original cam. Also, make sure you keep tension on the chain when you take off
the exhaust cam, so it stays on the bottom gear on the crank. Get a piece of
wire to hold the chain out of your way. |
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The spring loaded cam chain tensioner can be backed out with a small flatblade
screwdriver when you are putting it back together. |
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Also, make sure you check the specs on the valves before you take off the old
cam and then again when you put on the new cam. I think .07-.09 is spec, but
double check that with some other threads or call the service department at your
dealer to make sure. |
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Run the engine through a few revolutions with the kickstarter (or wrench on the crank) without trying to start it to
make sure everything moves smoothly and there are no strange noises. |
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The '03 YZF and '03 WRF cams are NOT
interchangeable per se. yes, they both fit into the head, but the result is a
different relationship between the lobes and the auto-compression release.
Although the bike will run properly, it will not start properly. 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. In other words...
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If you want auto-compression release AND YZF timing, you need a '03 YZF
cam |
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If you want auto-compression release AND WRF timing, you need a '03 WRF cam
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So you can't have both features (YZF timing and auto-decompression) with the WRF cam
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Apparently, WRF timing will work with the YZF cam, but it requires a slightly harder kick
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Removing the Manual Decompression Lever and Cable |
The decompression lever/cable/mechanism can be left on, but it is basically redundant with an 03
exhaust cam. There is a blanking plug installed on the 03 models (P/N: 90338-18064-00)
The plug costs ~$3.00. You can also just remove the lever and cable and leave
the mechanism in place on the head. When you remove the original seal, be aware
that there is a tension spring going around the inside lip of the seal. With a
small screwdriver (or other small tool) you can manipulate the spring out from
the inside the seal. This will allow you to pry the seal out & not cause too
much damage to anything. Simply replace the spring & you can reinstall the seal
in the event you feel the need for a manual decompression lever again.
Some members have reported "loosing" the decomp plug after doing the mod. This
leads to oil spewing out of the head. This would seemingly then also be a problem
on the 2003-2004 models but has not been reported. TT member Vibeguy is making
a trick aluminum plug that replaces the decomp shaft and is held in by the
retention screw. With this option there is no need to buy the blanking plug.
The decomp plug is available online at the TT store.
Buy VibeGuy's
Decomp Plug
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The stock cam = 10 oz.
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The '03 cam = 12.25 oz.
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Net gain here is 2.25 oz.
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The decompression lever = 2 oz.
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Cable / head bracket & bolt = 4.75 oz.
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Lever in head & spring = 1.75 oz.
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The seal as well as the plug for the lever in the head were about the same weight for both.
Net loss when removing the decompression lever = 8.5 oz.
Overall, there is 6.25 oz. less weight.
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ThumperTalk Archives (updated 09/08/03) |
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Listed here are what I consider the most helpful threads. There are more threads on this topic in the ThumperTalk archives. To find them,
search the YZ250F/WR250F forum. Suggested keywords:
autodecompression, autodecomp, E-cam, 03 cam 03 E-cam, decompression, decomp, camnow. |
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Here's a link to a nice write up with pictures from TT member AV:
AV's Site |
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Here's a link to a scanned version of the article from April 2003 Dirt Bike Magazine:
Here |
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