Overheated exhaust cam


5 replies to this topic
  • jasonlion54

Posted April 19, 2011 - 09:32 PM

#1

So I ran my 2008 YZ450F without water for a day or two (:thumbsup::cheers: I know :bonk::thumbsup:).

I took the motor apart and the exhaust cam shows some significant heat discoloration where it rides against the aluminum of the head. The camshaft has a bluish color to it centered around the cam journal but the discoloration does extend into both cam lobes.

My question is do I need to replace the exhaust cam? A friend of mine suggested that whatever heat tempering process was done at the factory has been ruined and the cam will soon fail. Basically, he says that the heat has weakened the metal. Is he right?

  • grayracer513

Posted April 20, 2011 - 06:05 AM

#2

Have you had the cam caps off to inspect the bearing surfaces? Let's have a look at that first.

  • jasonlion54

Posted April 20, 2011 - 06:51 AM

#3

Yes, the aluminum surface that the cam rides on also shows some discoloration, but not very much. It is still completely smooth to the touch, and the cam still spins smoothly and freely when bolted down. As far as the actual cam bearing (next to the gear part of the cam), it does not appear to have been affected by the heat at all.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted April 20, 2011 - 08:36 AM

#4

Is the discoloration yellow and/or blue, or is it more like a blackening from something burning on the metal surface?

If your cam journals look good, then your oil came through for you, although if it got that hot, my concern would be for the condition of the cylinder wall and piston.

If the discoloration is blackish, it's a matter of oil "burning" or oxidizing on the cam. Polish that off the shaft journals with oil and fine scotch-brite or steel wool, or "crocus cloth" (emery cloth with a grit of 1000 or finer). Don't use abrasives on the cam lobes.

If the discoloration on the steel of the cam is blue, it might have slightly degraded the metal, but it's not likely to have been hot enough to do that without causing some significant damage to the head that you would have been able to see.

Check your camshaft clearances in the saddles with Plasti-Gage, and run it if it checks out. Have a look at the cams now and then to see how they're doing.

  • jasonlion54

Posted April 20, 2011 - 06:34 PM

#5

Thanks a ton for the help, Grey.

The piston and cylinder are being replaced, so no worries there. The discoloration is blue.

What clearances should I be looking at with a plastigage?

  • grayracer513

Posted April 20, 2011 - 08:15 PM

#6

Camshaft to head. See page 4-17 of the manual for the procedure. Specs are .0011 to .0026"





Related Content

Forums
Photo

James Stewart back on a YZ450F by YamaLink


Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies
Forums
Photo

Snake pit oct 30th by The Anvil


Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies
Forums
Photo

Michigan Motocross Tires by 288yz450


Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply
Reviews

Yamaha YZ450F 2017 by Chris.GVS


Yamaha YZ450F 2017
  • - - - - -
  • 0 reviews
Forums
Photo

yz250x vs 450 4t comparisons (preferably desert riding) needed by JakeNorthrupYZ450F


Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • 9 replies
 
x

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.