Yz400f Top End Overhaul??

5 replies to this topic
  • 98Thumpin400f

Posted January 26, 2006 - 06:16 PM


During a YZ400F top end overhaul has anybody noticed a clunking noise while spinning the engine back and forth past TDC by hand? Does the piston rod tend to have a little bit of play from side to side? The reason I am asking is because I had some weird engine noises before the tear down and I am trying to pinpoint the problem. Thanks for any input. :thumbsup:

  • 642MX

Posted January 26, 2006 - 06:24 PM


The rod should slide from side to side on the crank somewhat, but it shouldn't clunk.

  • 98Thumpin400f

Posted January 26, 2006 - 06:35 PM


The rod does not have any play up or down and the clunk sounds more like it is coming from down in the bottom like around the balance shaft. It only does it at tdc not at bdc could it be a small amount of lash between the crank and the balance shaft?

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  • jrcgaf364

Posted January 27, 2006 - 03:05 AM


maybe take a closer look at the bearings around the balencer shaft, and your main bearing, check the teeth on your primary drive gear, balencer gear...well all of them. maybe there is a chipped tooth or something. could just be time to replace your crankshaft also.

  • tom nolan

Posted January 27, 2006 - 03:11 PM


I changed my crank and my noise went away. I Had a pulsing sound when the throttle was cracked about a 1/4. Make sure the oil feed seal is installed properly, that's the one on the right side case, if not, the crank big end bearing doesn't get proper oiling. Have you noticed any small pieces of metal in the filter, if so, it's that big end bearing on the crank. You can take the crank to a shop and they can put a new rod and rod end bearing to save some bucks. Good luck

  • 98Thumpin400f

Posted January 27, 2006 - 06:12 PM


I think I have found the biggest of my problems. Today I was cleaning some of my parts up and found a piece of a metal shaft stuck to the magnet on the inside of my flywheel. I took it with me to pick up some parts from the dealer and asked a tech if he might know what it was he said he thought it could possibly be the tip of my water pump shaft so when I got home I pulled the right side cover and found that the shaft was very new looking. The piece of metal looked just like the tip of my shaft. It appears that the guy I bought the bike from broke it and just put a new shaft in and never got the old piece out. :thumbsup: So just in case anybody ever runs into this it is a straight shot through the balance shaft to the the flywheel side of the engine. If your water pump tip ever is to break off it will go right to the opposite side of the engine. It also makes some pretty weird and obvious rattling noises. Thank you to everybody for the input.

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