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2009 kx 250f - valve dropped, hit piston

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I'm relatively new to four strokes, looking for some advice.  My kx 250f died last week, I took it apart and it looks like a valve dropped and hit the piston.  The picture shows the broken valve.  The piston is also scarred up. 

What I need to know is what is necessary for the rebuild?  I figure I will need to send the head off for new seats, new valves etc.  What work will I need done exactly?  Any recommendations here?  I heard that fast heads was good. 

Also, I am worried that the bottom end components may be damaged when the piston hit.  How can I check this?

 

Thanks for any advice!

 

G

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Welcome to the forum gregosta!

Once the cylinder is off you can check the big rod end bearing for play, but other than that It's gonna be hard to check the lower end without disassembling it I think. Maybe some of the other guru's here will chime in with a method unknown to me, but I am doubting that you hurt the lower end. This is not to say that you dont have other issues with the lower end that need attention, because that's possible too.

If that valve head didn't get loose inside the cylinder you may have gotten lucky and not damaged it. If that's the case then send the head out to be repaired and order a new piston and rings.

If the cams are good you might just get away with the head repair, and a new piston and rings. Prolly put in a new cam chain too while your there.

Good luck!

Edited by Trfsrfr
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As far as the head, it might be cheaper to simply replace it with a new one. contact BigBoreThumpers and FastHeads for a pricing quote for a complete head. Then send them your cams so they can 'pre-shim' the valves for you (one less step, unless you have a shim kit). New cam chain and tensioner too (as Trfsrf astutely noted)

If the piston is gouged at all, it will have to be replaced as well as the rings, wrist pin, circlips. If the gouge is severe, you may want to replace the crank and main bearings as well. During this time, you'll want to inspect the cylinder for damage and excessive wear. If it needs to be redone, a place like Millennium Tech and square you away.

 

Your bottom line is (assuming you do all the labor yourself) is a minimum of about $600 and a maximum of about $1,400

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So I just finished completely rebuilding my kx250f that I bought with a dropped valve and man you are lucky it hasn't done more damage than it did

Anyway, your best bet is to send it off for new seats and valves and to buy a piston kit and gaskets. Oh and make sure the cylinder is good and give it a hone

As for the bottom end. Once your cylinder and piston is off check for any play in the rod. Bit of side to side play is fine as long as its nothing crazy, any up and down play and the bottom end is gone. Also check the rod to see if it's straight.

It doesn't look like a bad hit though 1 valve seat and some new valves all round and the rest should just be basic rebuild stuff

Good luck!


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