yz426 locking up repeatedly and metal shavings in oil?

7 replies to this topic
  • yz420f

Posted March 09, 2013 - 04:29 PM


Hi, my 2002 yanaha yz426 has a problem.. Wondering if you guys could help. I couldnt get it to start, then today, I got my bike to crank. Had to put new cylinder and rings on it. The old one was scarred up on one side and the plating was kinda... Rubbed off, i guess on the bottom of the cylinder. Anyway, it runs perfect for 10-30 seconds, then locks up. I turn the crank opposite way, unlock it, and it cranks right back up and locks again. I can always unlock it. no "ku klunk!" sound when it locks up. its real quit. as if you just hit a mute button. no smoke or anything. also has metal shavings in oil.. is this my crank bearings? bent rod? bent crank??

  • marv02

Posted March 09, 2013 - 04:37 PM


Remove the left side cover take a pair of vise grips on the crank nut and see if theres play ion the main crank bearings to see if the large end rod bearing went bad Pull the top end back off and take a look at the rod normaly the big end of the rod will be a diffrent color than normal check fro side play and up and down play.

Shaving in the oil is bad If you need a new trans let me know I have one I put a WR trans in myYZ 426.

  • usaf_yz426

Posted March 09, 2013 - 05:09 PM


I had the same issue a few years ago, and upon further inspection i had found that my crank bearings were smoked. How much effort is required to get the engine to kick over, are you having to put all yur weight on the kick starter to get it to spin?

  • grayracer513

Posted March 09, 2013 - 05:33 PM


Rod big end bearing.

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  • yz420f

Posted March 09, 2013 - 05:59 PM


Its hard to kick over at one point of the stroke. Hard enough that i cant walk on my left leg today... And the big end of the rod was metalic silver, the long rob part was an orange-red color...

Rod part**

  • yz420f

Posted March 10, 2013 - 08:27 AM


Update, i put vise grips on the flywheel nut and pulled back and forth and it has just a tiny bit of play

  • marv02

Posted March 10, 2013 - 09:28 AM


Theres going to be a little play at the crank nut but if lot play up and down or side to side or both it most likley the main bearings next check the rod bearings.

It's time to pull the top end back apart take you'r time and look at every thing in the top end as you take it back apart look at the cam [color="#000000"]journals in the head make sure there no [/color][color="#222222"]galling and look at the cam it self.[/color]

[color="#222222"]Take a good look at the Bore make sure the plating is still good, measure the bore and piston make sure there right and ring end gap.[/color]

[color="#222222"]When the Cylinder is off the easy way grab hold of the rod see if go's clunk side to side play and up and down play look for dicoloring on the big and small end of the rod it self most of the tme it a dead give away something has been over heated.[/color]

[color="#222222"]Splitting the botoom end not all that hard just take your time if you have a camara take pictures as you go a long and Use a OEM Yamaha manual you can down load one use it go step by step.[/color]

[color="#222222"]If there is metal shaving in the oil are ther steel or aluminum look at all the bearing I would change them all out my self look at the trans see if it any good shifter forks Ect.[/color]

  • yz420f

Posted March 10, 2013 - 10:32 PM


I guess im gonna havr to take ot apart again...when on the flywheel nut, there was no play up down left or tight. Just a tiny bit back and forth

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