2004 yz450 head blown

[Han Brolo 760]

Attached I have some images from what seems to be a couple dropped valves, and a severely bent one from my 04 450. I'm looking for advice from people who have been through this before. There is a nick on my cylinder wall, my piston is trashed, and there is obvious and severe head damage. I'm very mechanically inclined, but am by no means a machinist. My questions are, can I over bore the cylinder a bit and put a larger piston/larger rings in there as a price effective option to salvage my top end? And what can I do to save my head, or what options do I have to replace it. I'm working on a modest military salary for a budget, so a new $1,100 head and a $700 top end to fix a $2200 bike aren't really viable options. I'm sorry if there are several other threads along these lines already, I'm just stuck riding a 125 until this beast is running again, so I'm understandably desperate. Thanks in advance for your help.

[grayracer513]

The cylinders are Nikasil plated aluminum, and can't be bored oversize for wear.  There's only one size piston available, anyway.  If the damage isn't too bad, the cylinder can be bored, replated, even welding up some deeper gouges before hand, and then honed back to size.  You can also send it off to have it bored out 3mm over and replated as a big bore kit, expanding the engine to 480cc or so.

 

The head is repairable, too.  Places like EDCo can recondition the head (fill the dings, reshape the chamber, replace the valve seats and guide that were damaged, and restore cam bores, if needed) for a whole lot less than replacing it with new. 

 

So that's the good news. The bad is that you probably should also replace the crank because there is a pretty good chance that the rod bearing was damaged enough by the impact that it will fail shortly after being put back in service.

[Han Brolo 760]

How much do you think ball park I'm looking at for all the head work? That's good to know about the crank, I didn't really consider the damage the impact would have on those bearings down there. I had a quote from a guy on eBay saying the head would run me about $850 with parts and labor. That seemed a bit high to me, but maybe I'm off base with that.