What is this hole in my head about? 2005 WR450

I was putting my right side radiator back on and I saw this hole in the right side of the front of the head.  It is the one directly above the exhaust port that is nice and shiny on the inside.  What is the hole for and do I need to do something about it?  This bike was modified to remove all the California emmisions hardware before I bought it and I am thinking that is what it is about but I would like to know for certain.  I can't find it pictured clearly in my manual and I cannot find anything connected to the hole in the microfiche views.   Please Advise.





Edited by mgoodwin9

That's the weep hole. It lets water drain from the spark plug area rather than fill up with gunk.

Your bike isn't a 2005 model...  or at least if it is, someone has changed the cylinder head to one from a 2003-2004 bike.


The hole you see is for the optional manual compression release.   Normally there is a plug there but they are prone to

falling out on older bikes.    You can get the plug from Yamaha for a few bucks or an 18mm freeze plug should work also.


If you don't fix it you will have slow oil leak there.

That looks like a 426 motor with a 2003 450 head.


...black frame...?

DeepPurple is right. Ignore my earlier post. I could only see the obvious hole on the right side from the small screen on my phone. I guess I need one of those new phones with a big screen... And probably eye glasses to boot.

It makes sense now.  Somebody put a 2004 head (or engine) on the bike.  The VIN etched on the frame is for a 2005 model (frame was powder-coated black.  I had to remove coating to get to the VIN).  The 2004 fiche shows the alternate decompression kit (but the exhaust cam on the 2004 has the low-rev decompression pin, why both?).   I must have had a plug in the hole that fell out because it is clean and shiny in the hole.  So if things go well, I will pick up the plug at the yamaha shop and have everything back together tonight.  Thanks for the information.  Mike

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