Vibey 426...any ideas?

Vibey 426...any ideas?

I was riding a hot, loose, sandy trail on Saturday and my '01 YZ 426suddenly developed a bad vibration in the engine for no aparrent reason. I did not feel any significant loss of power, it starts fine and does not kill, it does not sound any different either--just this deep, intense vibration. I quit riding for fear of doing some damage. If it were a car w/a flywheel it felt like it was oblonged and something spinning very fast out of balance. it is in the engine,because it vibrated when idling.

I looked for any previous postings on this topic and I only found a reference to a counterbalancer adjustment on some thread for a 650. Does this 426 have a counter balance? Would that randomly go 'out' of adjustment and cause this type of vibration?

Does anyone have an idea of what may be causing this vibration?

Vibey 426...any ideas?

I was riding a hot, loose, sandy trail on Saturday and my '01 YZ 426suddenly developed a bad vibration in the engine for no aparrent reason. I did not feel any significant loss of power, it starts fine and does not kill, it does not sound any different either--just this deep, intense vibration. I quit riding for fear of doing some damage. If it were a car w/a flywheel it felt like it was oblonged and something spinning very fast out of balance. it is in the engine,because it vibrated when idling.

I looked for any previous postings on this topic and I only found a reference to a counterbalancer adjustment on some thread for a 650. Does this 426 have a counter balance? Would that randomly go 'out' of adjustment and cause this type of vibration?

Does anyone have an idea of what may be causing this vibration?

Sounds like maybe a big end rod bearing or a main bearing. Is there anything odd in the oil filter?

I had a WR400 that did the same thing.......I didn't pay attention to it and rode it another few minutes, then, boom!! The connecting rod split (lengthwise) and then broke off, sending itself through the rear of the case, destroying the motor. Piston was fine, but the vibration I was getting was the splitting of the connecting rod right before breaking in half. I would check this out!!!

The 426 does have a balance shaft. The shaft and gear are splined, not keyed, so a failure there isn't too likely unless the nut worked loose and the splines are loosening up. That should be accompanied by a noise, though. Does it vibe with the clutch in, out or both? Idle or not? In neutral or only in gear?

I would definately pull the clutch cover, flywheel cover, and top end and look until I found the culprit before I rode again!

It sounds pretty serious--I could really mess things up if i keep riding it. It vibrates both with the clutch in and at idle. Both in neutral, and in gear. I will pull the oil filter and check out that suggestion, and then pull the clutch cover and dig in to see what i can see. I take it that metal in the oil filter would suggest the bearing problem?

Someone else suggested that it may be a cracked ring? still providing good compression, but cracked enough to be vibrating. It sounds like it could be ANYthing in there. I am not sure that my untrained eye will even be able to spot a problem. I could recognize a split connecting rod, or cracked ring, but I don't know how to tell if the bearings are bad.

more info needed

approx hrs on the bike?

When was last top end done?

did you check oil filter yet?

It's got 350-400 hours on it. it's been ridden pretty hard in 8-10 endurance desert races and/or WORCS races. I have been really good about changing oil after every 5-6 rides and before every race. The top end has never been rebuilt. I will check the oil filter when i get home tonight.

It's got 350-400 hours on it. it's been ridden pretty hard in 8-10 endurance desert races and/or WORCS races. I have been really good about changing oil after every 5-6 rides and before every race. The top end has never been rebuilt. I will check the oil filter when i get home tonight.

All the signs are there, bud......time for a rebuild. Pay a little now, or a LOT later......either way, you are going to have to open this up and since you are going to do that, replace EVERYTHING wearable that you can.....

maybe a loose motor mount........:thumbsup:

Any update on what happened with this bike? I'm curious... the suspense is killing me!

Yeah--you are probably right--i should just go through the whole thing. Are you thinking bearings, rods, pistons, cam, valves...anything else? While i am in there, it would be nice to do the retrofit kick start that eliminates the decompression kick drill. THAT would almost be worth it just to do that alone!

So far it is just sitting. I hate to admit it...but I am a bit intimidated to tear into it. I have replaced the water pump before, but i don't know about valve adjustments, piston clearances...etc. I am not even sure if i have the right tools. Then when i do get in there--how do i know when i have fixed the problem? it could be something i don't even replace!

THAT WOULD BE AWESOME!!! I will check that!

While i am in there, it would be nice to do the retrofit kick start that eliminates the decompression kick drill.

No kick start modification needed. All you need is an exhaust cam from a 03 YZ450 (part 5TA-12180-00-00 if I'm not mistaken) and that'll do the auto decompression. While you're in there, be sure to check and adjust the valves if necessary, and it probably wouldn't hurt to replace the timing chain (another $30).

That's on my to-do list (if it gets too cold to ride... hasn't happened yet!)

These bikes aren't too intimidating. If you have a service manual and you know how to use a wrench you won't have any problems. It does help to have a garage/basement or some other work area that's warm and clean.

No kick start modification needed. All you need is an exhaust cam from a 03 YZ450 (part 5TA-12180-00-00 if I'm not mistaken)
You're not mistaken.

If you use the YZ450 cam, be aware that the timing must be done by a special procedure. Not hard to do at all, but important.

definatly worth the 450 cams but do the intake and the exhaust cams. and leave the decomp lever dont replace with the plug they just pop out..

its probly a loose motor mount, thats happened on my old yz250

definatly worth the 450 cams but do the intake and the exhaust cams. and leave the decomp lever dont replace with the plug they just pop out..
These don't pop out:

http://shop.thumpertalk.com/Decompression_Plug_p/qmr-03dpb.htm

Neither will an 18mm steel or brass cup plug from an auto parts store, but they're a little trickier to get installed right. The decomp shaft will just get in the way of future valve adjustments.

It's got 350-400 hours on it. it's been ridden pretty hard in 8-10 endurance desert races and/or WORCS races. I have been really good about changing oil after every 5-6 rides and before every race. The top end has never been rebuilt. I will check the oil filter when i get home tonight.

Getting in late on the post but the above says it all. How many other bikes would go this long without ever rebuilding the top end? Not many. Yep it is time...XR reliability with YZ performance... Can't be beat.

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