Yamaha ATV

YFZ450 - Exhaust Cam Retard INTENDED: YFZ450 | PERFORMED ON: YFZ450 | DIFFICULTY: 7/10 Yamaha ATV - YFZ450

INTRO: Retarding the exhaust cam sprocket one tooth on the timing chain, affectionately known as the "cam mod", has proven to boost power in the mid to upper range of the powerband on the YFZ450. This free modification can make starting easier too, especially if you've added a kickstarter. It's a fairly simple procedure which should only take about an hour. We recommend an increase in pilot jet size along with this (we used a 48-pilot), but as always, jet accordingly to your needs.

	STEP ONE: You'll first need to remove your gas tank. We'll assume you can do this without instructions. Once removed, you should clean the top of the engine and the above frame rails, along with all hoses and wires thoroughly. After that, go ahead and remove the two hoses attached to the top of the valve cover, without losing the clamps. Also remove the spark plug cap from the spark plug.
	STEP TWO: Now you can remove the two allen-head bolts located in the top of the valve cover, as seen in the photo. When both are removed, you can pull the valve cover off and set the rubber gasket back in the cover itself, as shown here. Now remove your spark plug with a spark plug socket.
	STEP THREE: Remove the two caps from the flywheel cover shown here, with a large flat-head screwdriver or something similar. Using a rachet with the correct size socket on the flywheel nut, turn the motor over slowly (make sure transmission is in neutral) in a counter-clockwise direction, until TDC (top dead center) is achieved. Do this by looking through the window on the flywheel cover until you see the timing mark on the flywheel itself. This can be hard to locate, so look at your exhaust and intake cam sprockets for verification. The marks on both sprockets should be in place like they are in this photo.
	STEP FOUR: It's time to remove the automatic timing chain tensioner, which is located on the backside of the cylinder. First loosen the 10mm center bolt, but do not remove. Then, remove the two 8mm bolts that hold it in place. This can be troublesome, as the bolt farther from you can be difficult to get to. Once you have both bolts removed, pull the entire assembly out of the motor. If the gasket is damaged, replace it.
	STEP FIVE: Using a magic marker, make a mark right below the cam sprocket tooth which is right beside the factory "B" marked tooth on the exhaust cam sprocket. Also make a mark on the timing chain itself, corresponding with the mark you made on the sprocket. Do the same with the intake cam sprocket. It doesn't matter which sprocket tooth you mark on this one, just as long as it's easily visibile, like here.
	STEP SIX: Remove the four exhaust cam journal bolts, shown in the photo. Use a criss-cross patern, loosening each one a little at a time. Place a clean rag inside the timing chain housing to prevent parts from falling into the motor. Once done, gently pull the cam journal cap off. Be careful, as there is a metal half-moon retainer that will fall out. Be sure to keep an eye on this as you lift the journal cap off. Place the half-moon retainer back into the journal cap, as shown here. Note the direction in which it sits carefully. Repeat this entire step with the intake cam.
	STEP SEVEN: Tie the timing chain up to the frame using string or a "Zip-tie", like we did here. This will prevent it from falling down into the motor. Take the exhaust cam itself and tilt it forward towards you while pulling the timing chain off the sprocket to gain as much slack as possible, so you can rotate the exhaust cam clockwise. This will be tricky, and you'll have to tilt the intake cam also a bit. Take your time until you have the exhaust cam rotated on the timing chain one tooth. When done right, the mark you made on the timing chain will now line up with the factory "B" mark on the sprocket, like shown in the photo. The marks made on the intake cam sprocket and timing chain should remain the same.
	STEP EIGHT: Detach the timing chain from the frame, and coat both cams thoroughly with motor oil, including the timing chain and sprockets. Insert the half-moon retainers on both cams (make sure they are seated in the proper direction), and re-install both cam journal caps with bolts. Using a torque wrench, slowly tighten each bolt a little at a time in a criss-cross pattern, to 7.5 ft/lbs each.
	STEP NINE: Remove the 10mm center bolt from the automatic timing chain tensioner. Inside the bolt hole is a flat-head screw that you need to turn clockwise. Use a very small screwdriver for this. While turning, the mechanism on the opposite side will be retracting in. When done, it will be fully compressed inside and will stay that way. Then, simply re-install the entire assembly back into the cylinder with the two 8mm bolts. Once that is complete, take your small flat-head screwdriver and turn the inside screw slightly, this time counter-clockwise. This will release the mechanism and tighten your timing chain, automatically. Insert center bolt and tighten.
	STEP TEN: Finally, turn your motor over again a few times like you did in Step 3. If everything looks fine and it turns smoothly, you can start putting everything back together. Re-install the two caps in your flywheel cover, and then your valve cover (with rubber gasket in place) using the two allen-head bolts. Attach the two hoses you removed in Step 1 along with your spark plug and spark plug cap. Throw your gas tank on, and you're ready to run!

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