1998 YZ WR400F Getting no compression

2 replies to this topic
  • chevymcdude1976

Posted June 14, 2015 - 09:55 AM


I recently was blessed with a 98' YZ WR400F  and have been sinking money in it since I have got this bike. I bought a new timing chain/guides, new spark plug, hot start, shifter lever and, some other parts.However I have all the new parts in the bike and it is in the correct time, but did not put the hot start on yet. My problem is,there is no compression, the pedal goes clear to the floor, can be pushed with your hand. I have been told by several people and different shops, numerous things it could be. I just now bought a new jug ( cylinder) and it comes with a piston. I need to know why and what would make my bike not get any compression. If someone can help, your input is much needed.

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  • WRF-Rowdy

Posted June 14, 2015 - 10:32 AM


piston rings, cylinder head gasket, bent valve(s), broken valve seats, foreign object on valve seat, spark plug missing ;)


If the kickstart lever ideed does move the piston, and you are shure cam timing is correct,

that's about all I can think of.

Edited by WRF-Rowdy, June 14, 2015 - 10:33 AM.

  • WRistheWay

Posted June 14, 2015 - 01:56 PM


Did you happen to mix up the valve shims/buckets and close up the clearance causing a valve to not seat?? or perhaps the decompression mechanism is hanging open??


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