possible seized pistion on a yz 426

20 replies to this topic
  • yz426f rider125

Posted September 28, 2011 - 06:16 PM


so i was out riding today and i killed my bikes iginition and tried to re start it but i cant get the motor to roll over and i put all my weight (im a pretty big boy) on it with the decompression lever pulled in and it wont budge please help!!

  • pscook

Posted September 28, 2011 - 06:46 PM


Could be several things. Seized piston, seized big end of the rod, jammed cam chain, lots of things. You won't know until you at least pull the head and look for proof. Another possibility is a jammed kickstart gear. That's a simple inspection (compared to a seized anything else), so pull the clutch cover and check out the kick gear.

Good luck, and post up if you need any help or find anything cool in there.

  • yz426f rider125

Posted September 30, 2011 - 11:46 AM


should i cpmpletly drain the oil and what exactly is it that i am looking for when i pull the clutch cover off?

  • nathanpa01

Posted October 02, 2011 - 05:07 AM


Yes, drain the oil. Remove the cover, then with your hand, try to work the kick starter. Watch the kickstart gear.

  • yz426f rider125

Posted October 02, 2011 - 11:12 AM


Ok i pulled off the clutch cover but i can't see the kick start gear, do i need to completely remove the clutch and the side case or just the clutch? Thanks for your help so far !!!!!!

  • pscook

Posted October 03, 2011 - 05:19 PM


Did you pull the clutch cover or the right case cover? If you don't have coolant everywhere you didn't pull the correct cover, you need to take off the big one. Remove the kick lever and the water pump hoses, then the multitude of bolts. The gears are slightly behind the clutch, up and to the left (as you are facing the clutch basket). Check for loose or binding parts, but watch the spring loaded bits.

I bought my 426 "seized," kick start didn't move or anything. Pulled the head off, loosened the piston, and then wobbled the crank around a bit to see if it turned. When I worked my way back to the kicker, it freed up after a little working back and forth, real easy to get moving. I bored the cylinder and rebuilt the head and went on my merry way. About 10 hours later, maybe less, the crank completely seized up.

Moral of the story? It could be as simple as the kick gear is stuck, or it could be as bad as a completely trashed engine. It's best to pull everything apart and check it out. Gaskets are cheap piece of mind for looking at everything and making sure it's all well and good. Unfortunately, I don't know of an easy way to check the rod bearings, because you can have good end play and bad bearings. But, you should pull the head and cylinder for piece of mind.

  • ZéPovinho

Posted October 04, 2011 - 11:54 AM


a seized crank is a comon issue on these bikes

  • yz426f rider125

Posted October 04, 2011 - 03:18 PM


i took the clutch cover off and the right side crank case but i dont have a impact wrench or even the right size socket to take the clutch basket off. Is their any way to take the clutch out with out the use of a impact wrench. Also where can you find both gaskets i looked on like 3 sites and couldn't find any

  • grayracer513

Posted October 04, 2011 - 05:34 PM


TT OEM Parts will have both gaskets. To remove the nut without an impact, do this: Put the bike in fifth gear. Lay a good sturdy board across the swing arm through the spokes as close to the rim as possible. Remove the nut by turning it counterclockwise.

  • yz426f rider125

Posted October 07, 2011 - 01:48 PM


Alright i took the clutch assembly completly out the kickstart gears look to be in great shape. I could turn and move the gears freely.So I put the outer most part of the clutch back on not the basket and now i cannot move the kick starter at all. What should I proced to do from here on out? Can't thank you guys enough on the advice.

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  • pscook

Posted October 07, 2011 - 02:37 PM


Have you removed the sparkplug? You might be fighting compression right now. Pull the plug, and if you still can't crank it over you will have to pull the cylinder head. Don't order any gaskets until you are sure that you will be repairing the bike, it would be a shame to spend money on parts that you aren't going to install.

  • grayracer513

Posted October 07, 2011 - 02:49 PM


The outermost part IS the basket. Try turning the crank with a wrench.

  • yz426f rider125

Posted October 08, 2011 - 07:49 AM


Still the kick start wont budge. How much is a top end rebuild going to cost if I rebuild it myshelf?

  • grayracer513

Posted October 08, 2011 - 08:18 AM


Never mind the kick starter, can you turn the crank forward in two full circles with a wrench or not?

  • yz426f rider125

Posted October 08, 2011 - 09:52 AM


yes I can do two full revloutions with the crank,
but it has one spot where it is harder to turn then very easy to turn dont know if thats a problem or not.

Edited by yz426f rider125, October 08, 2011 - 06:12 PM.

  • grayracer513

Posted October 09, 2011 - 07:19 PM


One spot per revolution, or one every two?

  • yz426f rider125

Posted October 10, 2011 - 08:01 AM


just one spot in every revloution

  • atomic_banana

Posted October 10, 2011 - 08:07 AM


my 03 yz 250f had the same problem it felt seized. the cam chain was just jammed. scored the bike for 1100 with no real issue lol then 4 hours later the piston actually seized.. ebay and $500 later i have a new cylinder kit and some other parts. good bike for 1600 lol. check your cam chain..

  • grayracer513

Posted October 10, 2011 - 08:16 AM


just one spot in every revloution

This, with the crank disconnected from the engine, tells you that some part of the main rotating/reciprocating assembly (crank, rod, piston) is being interfered with mechanically. There may be a problem with a bearing, or something laying on top of the piston, something around the stator, etc. Your next step should be to open the engine up from the top down, checking everything as you go; valve clearance, cam timing, etc., until you locate the cause.

You have the spark plug removed or the compression release pulled while turning, yes?

  • yz426f rider125

Posted October 10, 2011 - 09:22 AM


Yes i do have the spark plug removed. Whats a ball park estimate for a rebuild if it is done by myshelf?

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