Valve Adjustment on a 2002 YZ426F

I need to know how difficult it is to adjust the valves on my bike! I read the manual, and it talks about removing the cams and all kinds of crap. Is this really what I need to do? :)

Checking the valves is an easy 10 minute job. Adjusting the valves is a bit more involved and yes you do need to remove the cams. I wouldn't say it's hard though. Just be patient, take your time and follow the manual. I would say any average back yard mechanic should be able to handle it. Plan on a few hours your first time. If you run into trouble you've got TT, so no worries.

If your valves are out of spec then you do have to remove the cams but it's not too complicated and you shouldn't have to change shims very often. My 99 WR valves just went out of spec, first time since new.

To check the clearances you set the engine on TDC, remove the valve cover and slip feeler guages between the cam and the valve buckets. If you're out of spec then you have to remove the cam caps and cams. Record the clearances for each valve, you'll need that later to compare to the chart in the manual. There's only 4 bolts on the exhaust cam and 6 on the intake. Make sure you're at TDC when you loosen the caps because valve spring pressure can warp the cams if the valves aren't closed. There is a half circle bearing locator clip near the sprocket side under each cap. Make sure you don't let these fall into the engine. Best to stuff a rag down into the cam chain hole so nothing falls in. You must also back off the cam chain tensioner.

You remove the caps and sort of tilt the cams so the side with the sprocket tips down and then you can slip the cam chain off and lift the cam out. Tie the cam chain up with wire or a zip ty to keep tension on it and prevent it from falling down into the engine. Pull up the buckets and you'll see a small shim underneath with a number on it. Don't mix up the buckets. They can be different thicknesses and are color coded.

Compare the number and the clearance you recorded with the chart to see the new size shim required. Install the new shim, slip the bucket back over and then set the cam back into place. You'll have to play with the cam abit to get the chain on the sprocket and to set it to the proper position at TDC. Torque the caps back on, spin the engine over a few times to seat everything, and then recheck the clearances.

You've gotta be careful but it's not very difficult, just time consuming.

Check this page:

It's written for a 250F, so the clearances are wrong for your bike (yours is .10-.15mm intake, .20-.25mm exhaust), but the procedure is exactly the same. On the 426/450 the head stay actually does have to come off.

Use Motoman393's instructions and you can find the valve clearance numbers in the shop manual chapter 3-23...which you can also download from Motoman393

How to adjust the YZF Valves



You got it goin on mister! :)


You got it goin on mister! :)

Thanks for the compliment Rip. :p

I swapped some shims yesterday with the engine in the frame. The other pics I posted were during a rebuild and the engine was out.

I popped out both cams since I had to retorque the head and a bolt hides under each cam.

For a true time test, I removed all shims and buckets and then replaced everything, checked clearances and timing and was back to running in under 2 hours.

Pop off the tank and the top motor mount 14mm bolt through the head and 3 allen bolts with 12mm nuts at the frame. I wiped everything down and wrapped a rag around the frame to keep dirt from falling into the engine.

Pop off the cam chain tensioner at the back of the cylinder. Take the 10mm bolt out first since you have to remove it to wind up the tensioner when you reinstall it and it's hard to remove the bolt holding the tensioner in your hand.

Remove the 2 allen bolts from the valve cover and slide it out, being careful of the gasket and the rubber halfmoon things. It'll come out on either side, both require some contorting and neither side really seemed easier.

Take out the 2 plugs on the left side cover and set the engine roughly to TDC. It usually doesn't want to stay right on the mark but close is good for now.

Check you clearances with feeler guages and keep stuffing bigger or smaller ones in until you find the biggest one that'll fit. Sometimes even the proper size guage is hard to get in. The rule I use is - once the guage is in if I turn the engine over a bit and the cam pulls the feeler strip through while I'm holding it, then it's too tight, if it doesn't, then it's good. If they're in spec you're laughing, if not you've got a bit more work. Bigger clearances mean loose valves, noisier and less performance. Tight valves could cause a loss of compression and cause you to burn a valve. Small clearances are worse than big clearances.

If you've gotta change shims here's what you do. Write down the clearances you measured because you need them to use the shim chart in the manual.

Make sure you're back close to TDC (you don't have to be pinpoint on, as long as the cam lobes aren't starting to open the valves) stuff a rag down into the cam chain space to keep things from falling in, and remove the cam cap bolts in a criss cross pattern, just cracking them all first and then completely loosening and removing. If you take off a cam cap while the valves are open the spring pressure could warp the cam or damage the cap.

Once you get the bolts out give the cap a little wiggle while pulling up. There are 2 dowels locating each cap so it won't move sideways,pull straight up. There is also a bearing locater clip under each cap near the sprocket side. It's got a bit of spring tension and may pop out when you lift the caps so be careful it doesn't go flying.

With the cam tensioner off there should be enough slack in the chain to remove either one or both cams fairly easily. If you do both at the same time you get a bit more slack in the chain. I did mine one at a time as a test, and my chain is 4 hours old, and there was enough slack to do it. To get the cam out you tilt the cam with the sprocket down, then slide the cam towards the cam chain until the ball bearing race slips out of its pocket and then move the cam towards the other cam creating slack. There's not lots of slack but you will get enough to slip the chain off with your fingers.

Have a wire or zipty ready to keep tension on the chain so it doesn't fall into the hole or get loose on the crankshaft sprocket and skip a link which is a headache to fix.

Once the cam is out you can see the buckets. You should be able to grab them with pliers (I wrapped tape around the pliers for a better grip and to prevent scratches) and slide them straight out. My shims always stick to the underside of the bucket so tip it upright as soon as you clear the hole and have a look for the shim. If it's not there it's sitting in it's pocket on top of the valve. I had a hard time getting my buckets out the first time. Ridges had formed at the cam bearing surfaces and I had to carefully scrape them away with a razor knife before the buckets would come out. The ridges probably formed from starting in extreme cold when the oil is sludge and not lubricating well, you may not have to worry about this.

Keep the buckets and shims in order and make sure that the buckets go back in the original positions. They can be different thicknesses and if you put a thick bucket in a skinny spot you'll be tight on clearance. The shims are numbered, factory shims can be any number, the ones you buy from the dealer go in increments of .05 mm. The chart also goes by increments of .05mm and tells you to round up. If your factory shim is a .166 or 169 then you consider it a .170. The chart is pretty straightforward. You find the clearance you measured on the left side, then look for the shim size that was in the bike and where the 2 intersect in the chart is the shim size you must install.

Switch the shims and lube as per manual. I just pour a bit of oil over the valve and shim and then slip on the bucket. This might scare you a bit at first since the engine will suck the extra oil past the valves and burn it up for a few minutes.

Now you're ready to pop thecam back in. Check TDC, set the cam so the marks line up with the head surface and then slip on the chain in the reverse of how you got it off. I don't try to get the timing dead on when I first slip on the chain. Set the cam in place and see how the timing looks. It may be off since you have to roll the cam in place. I turn it 1 link at a time in the direction it needs to go. Tilt it for slack, slip one link and then set it back and have a look. This only takes a few minutes and is easy to do. When you get it in the right spot lube it up and then pop in the bearing clip and pop the cap on and torque. I don't have a 3/8 drive 8mm socket so I can't get to some of the bolts with my torque wrench with 1/4 drive adapter. I torque the ones I can and tighten the others with a ratchet so they feel as close to the others as I can get. I am going to order a 3/8 drive 8mm socket some day.

When you get everything torqued down spin the engine by hand a few times and then recheck the clearances. Hopefully they're good now and you can bolt everything back together and get riding. :)

thx for the write up's... :) im gonna do this to my wr426 when i get it home and have been doing as much reading as possible to get prepared for the masacre ahead of me.. :) thx for the help fellas... i will also be using the YZ timing when i get her all back together...

Thanks Gentleman, :) for all the good info, I now feel more confident tackling it on my own. Peace!

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