01 yz426 timing chain question?

When is it time for a new one??

I heard its about the only thing that can go wrong in these engines.

Oil changed and valves cked often.

Looking for some preventive maintence ?

Thanks

my local yamaha dealer here in sweden said that they never seen a cam chain break ... and thats on all 400/426/450 they´ve sold ...

they´ve had two chains that were replaced wrong (the guys who changed them didnt screw the tensioner back in) and the chain broke fot that reason ..

They don't break often, but will elongate due to wear.

Timing chains are cheap items, and it would be wise to change them out when you service your valves.

You can see from the photos that a stretched chain is easy to identify. It simply won't fit just right in the teeth, and it is apparent when you try.

When it's off the bike, it will also kink up and not flex just right...similar to a hosed ring chain.

TC2.jpg

TC1.jpg

(photos courtesy of Treejumper)

dude you need to remove the cylinder to change the timing chain. so maybe change it when you do the top end instead of when you check valves.. :thumbsup:

It's true, they don't very often break, if ever, but the problem is in what the worn, over-length, or binding chain will do to the crank sprocket. The crank sprocket is integral with the left axle of the crank assembly, so when it gets worn by an old chain to the point of being unserviceable, the crank needs to be replaced. If it gets so bad that it starts letting the chain jump time, the results can be ugly, to say the least.

The cylinder does not need to be removed, and the whole thing takes less than two hours. The process of replacing it goes like this on all YZF's:

Start and run the bike for just long enough to clear the sump of oil. Remove the cam cover, ignition cover (no significant oil will be lost), flywheel (puller required, don't cheat), and stator plate (#27 Torx bit required). Remove the tensioner (see manual for unloading instructions) and the two bolts holding the bottom of the rear chain guide shoe. Rotate the bottom end of this part outward and remove it by pulling it down. (Note: if if doesn't want to come all the way out without a fight, just let it sit there.)

Remove at least one cam (probably both will be required) and rotate the chain off the crank as you did the rear guide.

In reassembling, you have a couple of options:

a) place to the chain over the crank and bolt the rear guide back in place. Reinstall the stator and flywheel, and depend on the front and rear guides to keep the chain from looping off the bottom of the crank sprocket as they are designed to while you time and assemble the top. Probably safe, but you always find yourself wondering if the chain is really on right.

:thumbsup: Remove the spark plug and use a screwdriver to find TDC, or eyeball it by lining up the flywheel key with the bore centerline and time and assemble the chain and cams with the whole run of chain visible. Foolproof, but be sure to double check the timing by pushing the flywheel and cover on by hand and using the real marks just before torquing everything all the way up. You don't want to have to take any more apart than necessary if you screw up.

I use option b myself.

Two mistakes commonly made are failing to torque the cam caps right, and timing the cams wrong because the cams weren't rolled back. Back the engine up to a few degrees before TDC, and then roll each cam back until the front run of chain is tight, and the slack is on the back side. Now, hold pressure against the rear guide shoe by pushing your finger through the tensioner hole and rotate the engine forward back to TDC. Then check the timing. Note that there's no point in worrying too much about the timing marks lining up perfectly. The marks simply are never going to be perfect. What you do is imagine the timing marks on in the same position on the next tooth, and see how that would look. If it makes it closer, move it. If not, it's OK.

Always carefully torque up the cam caps in three successively tighter steps. I use 75 in/lb instead of 86. 86 just seems too tight to me, and I believe Yamaha has reduced that value for the later models.

It's a pretty simple job. Remember to check your valve clearances before removing the cams in case any of them need correcting, as this will be the perfect time for that.

(#27 Torx bit required).

This may be different on the YZf's or the big bores but just for reference, the 2002 WR250f takes a T30 torx bit to remove the three bolts on the magneto, not T27.

Please let me know if it is different for certain models, I don't want to be leading anyone in the wrong direction. Thanks. :thumbsup:

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