This is a simple write up for any year yamaha yfz450 quad to convert to yz450f cam timing.... also known as the "cam mod". No this will not hurt nor damage the motor in any way IF done correctly.
I know some people have heard that there could be some issues with doing the cam mod on an '06/'07 yfz450 so I have put this together to help some folks out. The cam timing is the same for all years yfz450. Yamaha has not made any changes from year to year.
Please wash your quad well. You do not want dirt or debris to fall into your newly exposed engine. That would take a fairly simple (with the right tools) job, and turn it into a nightmare!!
Remove your tank plastic/ and side panels.
Remove the gas tank.
Dissconnect the vent hoses/ air boot to carb boot/ spark plug/ carb. There is no need to remove your carb all the way just tie it out of the way.
Remove the top valve cover from motor.
I place all parts exactly how they came off into a clean box.
Remove the side cover plugs, and use a 17mm socket, and counter clockwise, rotate the crank to TDC on the combustion stroke. The combustion stroke is right after you see the intake valves move.... not the exhaust valves!! The cam lobes will be up and away from each other at a 45*.
Line up the mark in the top window with the center of the hole. You will see a I-I and then a I. Line it up with the last "I" as the first two is actually the range that the spark plug fires in. Here is a picture:
Now you need the factory service/ repair manual!!
Release the tension on the chain from inside the ACCT.You have to remove one bolt and copper washer, and then you can stick a small flat blade screw driver into the ACCT and turn it until it "clicks" in place. It is spring loaded so be carefull. By doing that this will retract the tension from the chain.
Remove the bolts that hold down the cam towers. Do this is 1/4" turns evenly across all the bolts in a criss cross pattern. This way it keeps the towers from warping as you remove them.
Be very carefull to not drop the 2 half moon clips down the motor. There is one for each cam.
Here is the underside of the cam tower.
I always place CLEAN rags into areas of the motor that is exposed that I do not need open. Take note of which side of the half moon clips faces the sprocket side and which faces the lobe side. There are two bolts that are longer then the rest. Do not mix them up!!
Mark the cams (both) with a marker or white out on the sprocket and the chain. This way you can see where you started at, and where you ended up at. Here is a marked stock yfz timed cam gears.
I had to remove both cams to be able to rotate just the exhaust cam. Some may not need to. It depends on how stretched your cam chain is.
I lay a long screw driver across the top of the head under tha cam chain in case I loose my grip on it so it doesn't fall into the exposed opening of the head.
Rotate your exhaust cam 1 tooth clockwise. Then replace the intake cam if you had to remove it to rotate the exhaust cam. ALWAYS keep tension on the exhaust side of the chain!! Chain slack goes to the intake side because that is where the ACCT is.
Here is a picture after the cam mod was done on a yfz450.
Please look at where the punch marks are on the gears before you start removing anything, as if you purchased your yfz used many have already done this mod.
Once you have the cam towers and half moon clips torq to spec (get a manual I convert foot pound to inch pound 7.2ft lb or "86.4 inch pound") turn the ACCT to place tension back on the chain! If your chain is sitting on top of the teeth and not where is is supposed to be, recheck that you have done everything correct. Slack goes to the ACCT side, never the exhaust side. Please do not count pins as the only way to do the cam mod. This is where people can get off track in doing the "mod". If you choose to count pins, mark the gears and chain, and please take note of the pin count before and after the "mod" only to show that it has been turned 1 tooth. Then replace the copper washer and end bolt. TQ to spec (7.2ft lb or 86.4 inch pound).
Now rotate the crank counter clockwise a few revalutions to make sure that nothing is wrong and that you have done this mod correctly. Recheck that your cam timing and punch marks are where they should be! Rotate again! As this is the part some people mess up.
Replace all that you have removed to do this mod back where it goes. Cam cover/ vacume hoses/ carb/ boot/ gas tank etc.
Rotate the crank by hand again counter clockwise.
Now if there is NO binding or "funny" noises, feel free to put in a new spark plug. Ha Ha. I bet you thought I'd say to fire it up
Rotate it again!! If there is no binding or anything hitting then you are good.
Now you can fire it up. If done correctly it will sound and feel just right.
This mod gives you an inrease in power in the mid to upper rpm range!! NOT in the lower rpm range!
I did notice that my motor does not run as hot and the fan does not come on with having the cam mod done. My fan used to come on all the time.
I hope that this write up gives some one the basic before hand knowledge to know what is involved. It is not a step by step. That is what the manual is for.
Some people have had to increase their pilot jet/ or needle clip postion. I did not.