after a few high speed runs around the dirt roads, i jumped a large double at my friends track. in mid air the bike started to ratle really loud, and after 5 seconds or so it stopped, but i still hear a loud clicking and low ratteling that i originally thought was fromt he valve area. so i checked the valves and everything is just fine there. After that i fired it up again for a seocnd and after reading about the primary gear coming loose, i realized that it is more prominent ont he clutch side in front of the clutch basket. do you think this is the problem? someone please let me know their opinion before i rip open my side cover. any info you have would help. thanks alot.


Check the timing. My 426 once jumped timing. If this is the case the tensioner could be bad.

It's not the primary gear as you've called it but rather the counterbalancer gear. The problem of the loose gear was cured for 01's by a splined shaft rather than a keyed shaft.


Couldn't have happened to a nicer racist. Why don't you call Bubba's mechanic, he might give you some tips??? :)

maybe a shattered clutch plate?

listen vegas, cant u let it go?

I just broke one clutch plate the other day, it rattled a bit. I knew it was a plate because the noise changed when I pulled in the clutch lever and the bike ran fine otherwise. If it's really noisy, maybe you have more than one broken plate? If you don't want to drain the oil, just lay the bike over on it's side, and pull the clutch to check it. Good luck.

PMK is right on this one. The counterbalancer shaft/gear has a key setup that can wiggle out of place. Only 2000 426 have this problem, since they went to a splined shaft for 2001. We just fixed this on a friends bike (no cost) just labor! You can just flip the key around, pop the counterbalancer gear back in and off you go, good as new! Well almost.


[ June 30, 2002: Message edited by: Scooter426 ]

holy guacamole!

...and that's what's left of my bottom end. I had the exact same symptoms two weekends ago. Yes, the gear let go. And it took out my water pump and (Chopin's Death March in the background)

my crankshaft. splines are gone. I'm having to split the case.

as in the helicopters I fly, gears exploding while in the air usually results in catastrophe.

Thank the Lord I had enough speed going up the small double to clear it on the downslope, or I would have experienced a 30 mph, 250 pound mousetrap.

I implore all with the 2000 426 to pull the clutch and inspect that cranshaft spline and associated cog.

I really should have known...


The same thing happened to me when I was gettin' after it at the local track. I went back to the truck and checked my air pressure. Lo and behold! It was low in both tires and I was missin' some knobbies. After I increased the air pressure, the noise stopped! I guess the missing knobbies were hittin' my fender when they flew off...makin' a rattling noise. LOL!

Man, for somebody that's a racer and rides a "near" factory bike, you sure ask some of the oddest questions. I couldn't help it, I had to flame you on this one.

The Jack

Is the 2000 400 model the same? Hate to have this happen to me in the middle of the national forest!

To clarify, the 98, 99, and 00 series YZ's use a key (costs about $1.00) to drive the counterbalancer gear. The 01 and 02 YZ's use a splined crankshaft with a splined gear, there is no key. Most likely the WR's were changed in 01 also, check your manual and see if it shows a key or not.

There are several posts listed from awhile back about this.

I've seen guys split the cases to replace the crankshaft, only to find out it could have been fixed in 30 minutes with a new key.

If your cranshaft is damaged, a good upgrade is changing to a 01 cranshaft and gear.


I would change the spark plug.

Thanks, PMK, that info is handy as I will order the cranshaft and gear upgrade as you suggested...

hey, ripped apart my moter and the primary drive and cb drive gears WERE LOOSE!!!!!!!!! the nut was only on the shaft by about 3 more threads. also my clutch basket was mangled.

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