Drop a valve on my '08 WR450F

4 replies to this topic
  • willy_fitz

Posted April 02, 2015 - 07:04 AM


While on a recent trip to Mexico the bike lost power and quit on the highway after we had left Real de Catorce.

After I got the bike home there was no option but to pull the motor out of my 08 WR450F and have a look inside....




Once I got the valve cover off and removed the cams my initial suspisions about a broken valve were confirmed....




Getting the cylinder head off confirmed my worst fears....




Cylinder head is not repairable and it also cracked the barrel...




I considered scrapping the bike at this point and buying a 500 EXC KTM because the KTM is one of the few dirt bikes we can get registered with a street plate in Ontario but I decided in the end to go ahead with the repairs.

Parts bill was a touch over $1500 in US dollars and I am waiting on the last Cylinder Head Assembly in North America to show up but as of this moment it looks like we will be able to resurrect Big Blue.


The Mexico trip was supposed to be a dual sport ride with mostly dirt and backcountry gravel roads. Unfortunately the weather was nasty for most of the trip and we mostly rode pavement. A number of the other riders were on BMW GS's and I flogged the WR450 trying to stay with them. I was operating outside of design parameters and paid the price. You can read the ride report over on ADV Rider here


I thought about a 480 kit but after some research I have decided to stay with the stock bore and stroke though I am planning on having the head blueprinted with a minor porting and polishing just to clean things up. 


I will be posting up as the rebuild progresses....


  • stevethe

Posted April 02, 2015 - 07:53 AM


Yea it can happen. I wonder how the crack in the cylinder occurred. Stainless valves would take a better beating but you need to use stiffer springs.

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  • willy_fitz

Posted April 02, 2015 - 01:30 PM


According to a reputable engine builder in my area the stainless valves are not recommended for most applications with the WR450. The required stiffer valve springs are harder on the valve seats leading to reduced reliability. I think the barrel cracked when pieces of the valve got jammed between the piston and the cylinder wall but there was not much scoring to support that theory.

I'm an old rider with an artifical knee and don't run the engine anywhere near redline so the reported advantages of stainless valves would not really be a factor. The bike had been extremely reliable up to this event so I am inclined to go with stock parts.

Edited by willy_fitz, April 02, 2015 - 01:33 PM.

  • Krannie McKranface

Posted April 02, 2015 - 04:55 PM


OEM head parts on the WR gets you 500+ hours no problem

Not sure why that would need changing.....

  • willy_fitz

Posted April 03, 2015 - 07:28 AM


- deleted post -

Edited by willy_fitz, April 03, 2015 - 07:31 AM.


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