426 blew up! help?

3 replies to this topic
  • idiot_on_426

Posted November 12, 2006 - 01:55 PM


hey, this weekend i was just riding my 2001 yz426 in fourth gear and all of the sudden my bike seized. so i go back to the house and rip it apart, and find that it didnt actually sieze, the valves blew up inside the engine and one even got lodged into the top of the piston, the entire top half of my engine is blown up into shreds and pieces. i really dont know why all of the sudden my bike does this. it has never had one problem in the 16 months i have had it. i change the oil and it had plenty when i drained it to take it apart. i had engine ice full to the top. i have checked the timing on it a while back and it was perfect. it has always started first or second kick, literally. now i am completely screwed because a big anual glamis trip is coming up in a month and i have no bike, and no money to fix it. can someone please give me a direction to go, for a college student!!

  • 02YZ426

Posted November 12, 2006 - 02:00 PM


Was the cam chain still in place? Sounds like it may have jumped a few teeth and the piston did in your valves. Your best bet is to search ebay.. I know there are a few sellers that make a living parting out bikes. I have seen some heads go for a good prices.

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  • sirthumpalot

Posted November 12, 2006 - 05:21 PM


As mentioned above, check the timing (if you still can). When 4-strokes get hours on them, the small cam sprocket (the one on the crank) is often the first to get worn and the chain can jump. Also the chain can get worn and loose. If it jumps one tooth it will probably run like junk. If it jumps a couple or more then the result can be a pile of parts, as you see now. If it's too late to double check the timing then have a look at the crank side cam sprocket. if it's very worn then that's likely the culprit.

  • idiot_on_426

Posted November 12, 2006 - 08:30 PM


yes this is what makes the most sense, but it showed no signs at all of performing bad, it ran great and then boom! and i have checked the timing a while back, but not recently because i know that the 426 is the least likely of all bikes to be missed timed. thanks i will look out for ebay.

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