426 Timing Chain and Cam Replacement


5 replies to this topic
  • BASSic

Posted December 16, 2008 - 08:17 AM

#1

I have a 01 YZ426 and have had a 03 450 cam along with a timing chain sitting in my parts bin for a few months now. It's finally time to install them.

I have the service manual, but I'm wondering if the manual I have is correct. I recall hearing something about a different flywheel/rotor/stator design on the 2001 model. Do I need the special holding tool to remove the rotor, or is there an easy workaround? I'm not trying to cut any corners, but I'm just wondering if this tool is essential or if there's an easy do-it-yourself method. (I do have a flywheel puller)

When removing the flywheel and replacing the timing chain, do I just make sure I don't rotate the engine or the cams? I recall reading something about making sure the flywheel is installed so the timing marks align properly.

Is it best to do the chain first and then the cam swap, or is the order unimportant? Since I'm doing this work, how much extra work would it be to remove the cylinder and replace the rings? My bike is in excellent condition and has been well maintained throughout it's life, however I don't know exactly how many hours are on it. Rings aren't very expensive. On the other hand it runs great, with plenty of power and no smoke, so I'm not sure it's necessary.


I'm sure I would answer these questions once I get in there, however I'd like to utilize all the knowledge and past experience here and know any issues ahead of time so I'm prepared.

  • grayracer513

Posted December 16, 2008 - 09:44 AM

#2

The easy work around is an impact gun, either air or electric, with air being preferable. Failing that, put the bike in 5th gear, lay a hardwood board across the swingarm as near the rim as possible, and crank it loose.

The order you do the chain in is unimportant, but there's no sense in not doing the whole thing at the same time. This may help:

http://www.thumperta...405#post3150405

As far as manuals go, you can get the right one for yours if you need it:

http://www.yamaha-mo...ice/manuals.jsp
or,
http://www.yamahaown...ook.com.au/?r=0

Be sure you understand how to correctly time the 450 cam into your 426 head. The stock timing marks on the cam will not work. Read:

http://www.thumperta...078#post3706078
AND
http://www.thumperta...040#post5378040

Two guesses where all of that info was...
(hint: Common Threads)

  • BASSic

Posted December 26, 2008 - 03:07 PM

#3

The easy work around is an impact gun, either air or electric, with air being preferable. Failing that, put the bike in 5th gear, lay a hardwood board across the swingarm as near the rim as possible, and crank it loose.


Thanks for the board trick - it worked like a charm!


Be sure you understand how to correctly time the 450 cam into your 426 head. The stock timing marks on the cam will not work. Read:

http://www.thumperta...078#post3706078
AND
http://www.thumperta...040#post5378040

Two guesses where all of that info was...
(hint: Common Threads)


I know how to time the 450 cam in my 426 head; I've read that many times in the common threads (I wasn't asking that question here)


Now I'm stuck: I can't get the timing chain off the crankshaft sprocket. I loosened the two bolts for the rear chain guide, but that isn't helping. How can I get the chain off the lower sprocket?

edit: Thanks to some friendly advice here and a little bit of patience, I got it off without any problems.

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  • BASSic

Posted December 27, 2008 - 04:58 PM

#4

I finally finished the cam swap. Everything went well, and after everything was bolted back up it fired up on the first kick (and no decompression lever to deal with).

I have some questions now regarding the valve adjustment. Prior to removing the old cams I measured the valve clearance.

Here's what I got:

IN1: .102
IN2: .102
IN3: .076

EX1: .178
EX2: .178

I have one intake valve out of spec, and both exhaust valves. I installed the new 03 450 exhaust cam and torqued everything back up (using the suggested 75 ft-lb instead of the 86 that the manual says) then rechecked the clearances:

IN1: .127
IN2: .127
IN3: .102

EX1: .229
EX2: .254

What could have happened that caused me to get larger clearances on the intake cam (0.05mm on all three valves) after putting it back together? Is it because the buckets and shims are not fully seated yet (I took them off to get the numbers from the shims)? I measured just after assembling and didn't run the engine yet. Those clearances are all within spec right now.

I was expecting the exhaust clearances to be larger because of the different cam. They were tight before, and now with the new cam they're closer to spec, except for the one which is just outside the acceptable range.


After putting everything all back together, to my amazement it fired up on the first kick! There's a noticeable amount of valvetrain noise now; there's a distinctive ticking from the right side that wasn't present before. This is where the third intake valve is, the one that's tighter than the others. Perhaps I'm just being paranoid (I know the YZs have a noisy valvetrain) but it is definitely louder and more 'pingy' than it was before I did the swap. Any thoughts or comments? Is it normal to hear louder ticking after the 450 cam swap?


I don't miss the decompression lever at all. After three basic heat cycles and taking it easy on the bike I had a few minutes to play. Maybe I'm just crazy, but it feels like there's a noticeable increase in power especially bottom end.

  • grayracer513

Posted December 28, 2008 - 09:32 AM

#5

The base circle of the cam you installed is smaller than the original, giving you the extra clearance.

As for the noise, you can go back and verify that you've got it all together right, but it's more likely "heightened awareness" than any real problem.

  • BASSic

Posted December 28, 2008 - 02:48 PM

#6

The base circle of the cam you installed is smaller than the original, giving you the extra clearance.

As for the noise, you can go back and verify that you've got it all together right, but it's more likely "heightened awareness" than any real problem.


I was expecting larger clearance on the exhaust cam (the cam swap instructions in the 'common threads' told me so!) but why am I measuring larger clearance on the intake valves? Is it because I was measuring them without running the engine first? I'm thinking the shims and buckets weren't fully seated yet.

edit: I just realized that if the shims and buckets weren't fully seated, I would have measured smaller clearance.

I'm sure it's not heightened awareness; there was always valvetrain noise but now there's a distinct ticking.


I'll measure clearances again, but if everything is still within specifications I'll just run it and accept that it's noisier (and more powerful).





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