Purpose of horizontal hole on right side of head?

8 replies to this topic
  • batmobil

Posted November 30, 2011 - 02:07 PM


Anybody know the purpose of the horizontal hole on right side of head on the 426? Is it to be blinded? I have bought a bike in pieces so I don't know what to do with it. On the Yamaha service manual there seams to be a bolt with a washer or gasket, but I can't find it on any part diagrams....


  • GCannon

Posted November 30, 2011 - 05:21 PM


Center = spark plug hole drain
Forward = the Decompression arm retaining bolt

  • YamaJet

Posted November 30, 2011 - 05:48 PM


What he said ^^
Or is it the oil pressure check bolt? A pic would be nice.

  • batmobil

Posted December 01, 2011 - 12:12 PM


Thanks, guys. Spark plug drain hole sounds likely. The hole is in the center. Have seen from pictures of other bikes that there aren't any bolts in the hole.

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

Posted December 01, 2011 - 01:07 PM


Posted Image

  • batmobil

Posted December 02, 2011 - 05:49 AM


That's the one. Thanks!

  • zlathim

Posted December 02, 2011 - 08:05 AM


You're welcome. How is the rebuilding process going? People around here love to see pictures of projects...

  • batmobil

Posted December 03, 2011 - 12:35 AM


It is going quite well. The engine is all back together, but still on the counter topp. I am stripping the carb at the moment. Going to clean it. The subframe is tilted back to access the airfilter box. It is full of piston debris. Needs a new handle bar. Will start the assembly this Sunday, I think.

  • garyweliver

Posted February 08, 2012 - 12:19 PM


I have a 1999 WR 400 and when it runs for a while I have water that comes out this hole and it starts to overheat. I changed my water pump and seals and new head and base gaskets plus didn't see any cracks in the combustion chamber (between valve seats, etc.) of the head but didn't take out the valves and check in the valve pockets anybody have any ideas?


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.