Freak occurance or?

1 reply to this topic

Posted June 21, 2008 - 10:44 PM


I went to the track a couple weekends ago and while trying to kickstart my bike (03 YZ 450) there was an unusual amount of drag on the kickstarter. The bike started and ran for 5 seconds before dying. I thought something was wrong and pulled the spark plug. Even without the plug and no compression there was a lot of drag while kicking through. I started thinking the engine had seized. Went home and started tearing down the engine. Took off valve cover, cam caps and cams, everything looked good. Took off head and looked at cylinder walls. Perfect. Pulled off cylinder, piston was perfect. On to the clutch, nothing wrong. Took off oil filter cover and pulled oil filter out. Holy smokes, filter was full and I mean FULL of metal shavings. Pulled the side cover off and discovered the primary drive nut on the end of the crank had come loose and ground away at the inside of the side cover. Went online to order parts and started looking at the parts diagram only to discover that there is also a lock washer that goes behind the nut. Mine was GONE. I only found three small fragments of the washer with a magnet after flushing out the cases. It seems that the washer had disintegrated and allowed the nut to loosen until it hit the inside of the cover which was the cause of the drag. Luckily the only damage was to the side cover and the seal, washer and circlip where the end of the crankshaft fits into the side cover. The bike had never been apart so whoever assembled the engine must not of bent the washer tab enough to keep the nut from working loose. I didn't have a magnetic drain plug which would of told me a long time ago that something was wrong. I do now!!!

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted June 22, 2008 - 06:30 AM


While I agree that magnetic plugs are good (I have one in each bike), it wouldn't have done much here. The shavings were 99% aluminum from the case, and they accumulated over a very short span of time, once the nut hit the case (the crank turns forward, so contact with the case would immediately unscrew the nut), so there would have been no real advance warning.

Related Content


Yamaha YZ450F 2017 by Chris.GVS

Yamaha YZ450F 2017
  • * * * * *
  • 1 review
  • Last review by Tommyk_55
  • On January 15, 2017

James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

1998 yz400f will not idle. by trolley

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  32 replies

05 yz450f not fast enough by RedeyeYZ

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • Hot  38 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.