2000 YZ426 problems. Need your expert advice

I'm posting this for my friend who has a 2000 YZ 426 that is in immaculate shape might I add. We recently did a top end rebuild 2 rides ago swapping the piston and rings (We didn't swap the valves due to perfect tollerance). Anyhow, he rode it around with the break-in oil nice and easy and she ran like a champ. Earlier today we went riding for the 2nd time since the rebuild and noticed she was backfiring when blipping the throttle. Ok we thought. She probably needs to be rejetted. We continued riding and besides the slight backfire under deceleration everything seemed normal until we both noticed a horrible ticking noise coming from what sounded like the left side of the top end. He shut her off quick! Well, our curiosity got the best of us and he started her up again to see if what we heard wasn't a figure of our imagination. Yep!!! A really loud ticking sound. When we got back to his house you guessed it. We started it again to get the opinions of other friends who weren't there riding. This time NO TICKING! The engine was cold at this time. It died, so he tried to fire her back up but was unable to. He couldn't kick it through the entire stroke. The kickstarter would only go 3/4 through the stroke before coming to a hault. He's never had a problem starting his bike. Heck.........He's never had any problems with his bike before. When we did the top end rebuild, we went step-by-step through the owners manual for the installation. We tore it back down and inspected valves/Cams/Piston/timing chain. Everything still cycles like butter and looks great. Could it be that infamous CB Key I've been reading up on here, or maybe the clutch basket? We didn't tear it down that far. I'm a 2 smoke guy myself and don't know much about 4 strokes. Your'e knowledge is greatly appreciated.

Thanks, Jeff

Whats the CB key?

Whats the CB key?

could it be the woodruff key?

Sorry. I should have been more descriptive. The Counter balancer key near the clutch. I hear those will cause a hellacious noise when loose.

any suggestions guys?

check the clutch, but if the noise is at the top left of the motor I would suspect it is a valve issue. I would say do a compression check, but if you cannot kick it over then tear the top end down again.

Alright more info on the bike.......I took the head cover off and removed the timing chain tensioner, after i removed the timing chain tensioner I noticed that the timing chain never loosened up. It stayed as tight as it was with the tensioner on. I then cycled the kick starter and heard a small grinding noise. I stopped and looked around to see if I could see where the noise was coming from but I saw nothing. I took the cam gear covers off and wiggled the gears and the timing chain went slack. I removed the gears and cycled the crank and everything was buttery smooth...cycled kickstarter and everything perfect. Took right side case cover off, clutch basket off, main drive gear and counterbalance gear off and everything perfect. Drained oil and no metal at all. Wondering if timing chain jumped momentarily off of lower gear and then back on. I see nothing wrong with bottom end, head, cyclinder, piston and rings, wrist pin, and clutch. How do I test tensioner to see if it is wearing. It seems to be fine when I cycle the tensioner...HELP!

I dont know of anyway to test the tensioner and I recall the manual states to check for smooth function and replace if it binds or catches. I replaced the chain tensioner as well as the timing chain when I rebuilt my 2000 for piece of mind to avoid these situations. Cause they do suck!!!!

Incorrect timing, a faulty chain tensioner or loose/worn timing chain are what I would be looking for. I would inspect the cam gears, the timing chain gear on the crank. If those show no abnormal wear then I'd replace the timing chain and tensioner and reassemble the top end accordingly. Triple check the timing!

Did you use OEM piston/rings? stock compression? Could the ticking have been piston slap in in the bore?

Wiseco piston and rings on stock compression. Double and triple checked everything you listed....think I will put it all back together and see what happens

I'm using a wiseco also and am very pleased.

You mentioned the chain would not loosen after removing the tensioner and the grinding noise when cranking. It's possible the chain jumped teeth at the crank and got bound up on the guide. I'd replace the timing chain at the very least. Has it ever been replaced?

Lay it side-by-side with a new one and see elongated it has become.

The counter balancer drive key has to be really tight in the key way on the crank and the gear. If its not it'll make one hell of a noise. The stock one is 5mm wide but too short. I ended up making one that was about 40% longer and a press fit into the crank. It was a gentle drive with a mallet to get the gear on, but after that I never had another problem with it. If you can push the CB drive gear on really easy and rotate it all, its going to fail and make noise sooner rather than later.

The wiseco pistons are a little louder than stock as they run a little looser clearence...could that be what you were hearing? It does get louder as the bike warms up. On the other hand, I had a similar experience that turned out to be a loose primary drive nut, whic allowed the cb gear and pri drive gear to wear the splines onthe crank. The noise was caused by all the slop...my new crank and gears should be here this week...

Alright think I figured it out. Putting head back on today and got to timing chain tensioner...noticed that when I wound it up to insert into head that it stuck fully wound up(meaning tensioner would let all slack out of timing chain in this position) I also noticed that when I put in in and let go of screwdriver that it didnt tighten timing chain with out a little help from the screwdriver. Im thinking this might be the reason for stalling out and making racket. Good thing I shut down bike when I heard it. It would also have something to do with kickstarter not going all the way down because timing chain had to much slack and was binding. WHATCH THINK???

Pull the oil filter and check for metal in the oil. You might want to pull the head and check the cylinder walls. It's possible you didn't get one of the wrist pin clips in right (they were brand new ones, weren't they?) and had one of them disengage. If it's ticking, and that's the source, the cylinder is already destroyed.

Another possibility if the noise does not resurface, is that it was a stray piece of carbon or something else that was temporarily caught at the edge of the combustion chamber.

The tensioner is supposed to work like that. It will hold itself retracted when it's manually backed all the way out to make it easy to remove and install. You're supposed to nudge it in a little once the timing is set so that it will run the chain up. I'm not certain that it would have held in that position with the engine running or that it would have stayed in time for more than a couple of minutes with no tension, either.

Is it possible that your timing chain has stretched past its limits? I saw that happen to an 01 426. The gut had just replaced the cam's with Hot cams but used the old timing chain and shortly after the cam timing jumped. When he attempted to start it after that it would do what your saying, when you would kick it over it would stop about 3/4 of the way through the stroke. Did you check the cam timing before you disassembled it after the problem arose?

Already pulled the head and the cylinder..checked timing before disassembly and timing was perfect...Cylinder walls are perfect, Already pulled oil filter and it is perfectly clean. Ok so tensioner is supposed to click back and hold but why when I release it does it need a little nudge to fully tighten chain. If chain is bad how hard is it to change...I know I have to pull flywheel and then what...also shop manual never mentions that tensioner is supposed to stay all the way retracted, it actually says to hold it retracted until bolts are tight and then release. If it supposed to stay retracted then why does is tell you to hold it with a screwdriver? Everything in the bike is perfect...No damage and did not jump timing. I have had everything out of the bike including clutch basket and both case covers... &%$#@!?

06 KX450 will clear your problem right up! :thumbsup:

I know you say the noise was coming from the top end/left side of the engine - but if it is binding up at all - that year is notorious for the poor design in crank and drive gear assembly. It does use a woodruff key to hold the drive gear onto the crank. If you still have any doubt in the engines intergrity after you get it back together this time - I would tear it down immidealty and check the gear that comes off the crank as well as the oil pump, counter balance, etc. CVH

Ok everyone....I FIGURED IT OUT! Timing chain is kinking during rotation. Took timing chain out and looked at it closely. Will kink in numerous spots when looked at closely. 32 dollar part...Not bad. The crank is in great shape and as far as the poor crank design...that is the first time I have ever heard anyone say that in th 6 years of owning this bad ass bike. Thank you everyone for your help!


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