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My 250SXF rebuild saga...

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I took in a 06 250SXF basket case.  The crank had seized, but the PO did not “push” it and thankfully the cylinder was fine.  The needle bearing in the connecting rod was bad.  So I ordered a new Pro-X crank, crank bearing, piston & rings, and a complete gasket set. 

 

I installed the new crank, bearing, seals, gaskets, piston etc.  I put the head on and started install the cams, the timing chain was really tight.  In fact it was so tight I couldn't get the  exhaust cam into place…  So after much fuss I removed the gear, put the exhaust cam in place, and then re-installed the cam gear.  The tight chain still had me puzzled.  I finished installing the upper cam carrier and when I tightened the bolts, something dropped and now I had proper slack in the timing chain.  (I should have known something was up…  but I didn't check)

 

Put the rest of the bike together, and it was hard to start…  I bump started it and she ran fine…  I did this several times each time having bump starting it…  When we were still breaking it in, (we had maybe 15 min of run time on it when my son heard tink, tink, tank…  and the engine died…  hmmm  I tried bump starting it again…  and it seized.

 

So back in I go… pull valve cover, quick glance, all is well.  Pull timing chain, and cams, still nothing.  Look closer, I see parts of a valve keeper lying next to a valve.  Some of the bolts on the lower cam carrier are loose… hmmm.  Pull head… oh chit… it dropped a valve and part of its lying on top of the piston.  Well that’s why it seized… part of the valve lying on the piston was beating the crap out of the underside of the head and the top of the piston…  thankfully no damage to the cylinder…  At least one thing didn't get damaged.

 

Well we need some new parts… a new Vertex piston and a used head.  The original head was damaged and a used one was purchased because of the cost to repair the other was too high. With the head on the work bench I installed the cams and cam carriers so I can shim the valves.  I was able to shim the valves to the mid point of the specs. 

 

I cleaned all the parts, and started reassembly.  Piston and rings, the cylinder, the head, and then the bottom cam carrier were installed.  This is when I realized where I made a mistake the 1st time.  I don’t think the bottom cam carrier was completely down over the locating dowel.  When I tightened the bolts of the upper cam carrier, the bottom carrier dropped into place.  Yes it was my mechanical error that caused the failure. 

 

This time I know the bottom carrier is in place, installed cams and yes I have enough slack to get the cam into place as per the manual.  I finished re-installing everything and try to start it, kick, kick, kick nothing.  By this time, I’m tired…  All I want to hear is the engine come to life.  Since I live on a hill I decided to bump start it.  At best the back wheel made a ¼ of a rotation and she roared to life.  I ride it back to the garage and it dies… kick, kick, kick… nothing. I’m tired and will look at it later..

 

A few days later it hit me… Hey dummy put some fuel in the tank…  DUH!!!  Add some fuel, kick 4 times and she fires…  She sits there idling perfectly…

 

This was an expensive lesson… the head and 2nd piston cost an additional $600.  But I've got no one to blame other than me.  I can honestly say I know this bike inside and out… Now to finish a few more heat cycles, and then get it dirty.

 

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Edited by eprovenzano

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WOW, lots of work and expense. 

 

One of my friends had a similar issue with his 07' and blew it up 3 times before he caught the assembly issue. 

 

Glad you got it running and now know what not to do for the future! :)

 

P.S. you're not the only one who's tried to start a bike with no fuel after maintenance! HAHAHA 

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wow! a good story and an honest mistake that was owned up to! you dont see that on here ever!!

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It's been a learning (expensive) experience. I'm a two stroke guy and this bike was for my son. While I was rebuilding it I picked up a 01 380 EXC. He has since taken over my old 300. He loves the 300... The wife said since you've done so much work to the 250F why don't you keep it as a spare. Yea she's a keeper

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Sadly a keeper for life most likely. Older bikes just aren't worth selling as I found out when I tried to sell my 144 few years back. Man the low balls were hurtful. :(

But yea it has value to you and it will give you years of fun! ;)

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