06 YZ450F Engine Rebuild (Warped Head).. Help!


3 replies to this topic
  • Boston Mangler

Posted December 17, 2013 - 12:44 AM

#1

Hey Guys

 

I blew the head gasket on my 06 450 a few weeks ago out in the desert.. 

 

I limped it back to camp unsure what was wrong, and did some fairly extensive damage.

 

Pulled it all apart.  List of damage:
 

-Piston Chunked off a little
-Gouged cylinder wall, Cylinder Junk
-Exhaust cam is BLUE from massive heat.

-Head is warped, but not gouging anywhere, everything looks clean and nice

 

Got the bottom end redone, new rod, etc...  Got the new cylinder, piston, etc...

 

NOW...  The head..  These heads are FREAKING EXPENSIVE, even used..

 

This is just a dirtbike i use for the desert, and occasional putting around at the MX track, not my race bike.

I dont want any extra HP, or anything, and i want to run pump gas, etc....  I want this for reliability first and foremost, as we occasionally do 75+ mile rides!

 

Had one mechanic tell me he could shave it, and just use a a thicker gasket material to make up the difference.  Sounds pretty sketchy to me..  I have already spent a good chunk of $ on all new OEM parts, and i don't want to cut corners on the rebuild.

 

Same Mechanic told me he could possibly just shave the head, and bump up compression, but these head are very sensitive to that, and not much can be shaved, due to already tight tolerances.

 

Have searched high and low for a used head and coming up with nothing affordable..

 

Any ideas, options, or opinions guys??

 

Thanks a lot

Kevin



  • grayracer513

Posted December 17, 2013 - 11:18 AM

#2

You need to have the tech quantify how much the head is warped.  The service limit is .002", but you should be able to take .010-.012" off it without a problem. 

 

However, you could run into another problem if it got that hot; the head may have reached near melt temps in the area between the exhaust seats, and that may have put the seats too far out of round to refinish, meaning you'd need to replace them.  Then there's the matter of how straight/round the cam bores are.  A shop like EDCo. in Calif. that specializes in head repairs should look at this and evaluate the situation for you.  Otherwise, you're best off looking for a good used head to overhaul.



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  • NitrousR1

Posted December 17, 2013 - 04:50 PM

#3

I have milled one damaged head .010" and still had sufficient piston to valve clearance when measured with clay. We lost some volume from the combustion chamber but made up some from polishing the chamber.
Also any company that sells Yz head gaskets can make custom thickness gaskets to take up your lost volume if your worried about detonation on pump gas.

  • grayracer513

Posted December 17, 2013 - 08:25 PM

#4

I have milled one damaged head .010" and still had sufficient piston to valve clearance when measured with clay.

 

 

About what I figure would be safe.  I had to take a 426 as far as .008" once, but I was pretty sure it could have been cut more if necessary.  The 450 has a much more robust deck flange, too.  The most recent repair top end I did was crazy.  It had the head go through the scenario I mentioned above, where it almost dropped both exhaust valve seats, stretched a head bolt loose, and blew the gasket out, and yet, the head didn't warp beyond tolerances.  The cam didn't turn blue, though.  That's one I haven't seen.







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