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2006 KX250F new crank burnt up two top ends need help

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So its a really long story but i will start from scratch

 

So I acquired a 2006 KX250F in trade for a quad I had.  I usually ride a 2010 YZ450F but this bike needed a little tlc and I thought I have the time so I will fix the little stuff.  It needed fork seals and really just a good cleaning  The only reason I even traded was because the motor had been rebuilt very recently new crank piston all that good stuff.  I decided to check the valves I know these bikes are notorious for eating up valves and it wasnt running quite correct.  It had a 48 slow jet and the fuel screw was backed way out which richened it up to the point that it was very sluggish and not responsive.  

 

So while checking the valves which needed a shim job I noticed that the timing chain felt kind of chunky needed to be replaced.  I got a new chain and pulled the fly wheel and to my dismay i found over half the teeth of the brand new wiseco crank had been broken off.  Called the original owner and he ended up sending me 500 bucks which was good.  

 

So I bought a hot rods bottom end kit new bearings crank all that stuff.  Piston was brand new so I didnt worry about it.  Replaced crank everything turns and looks great.  I cleaned the carb because i figured it was just dirty.

 

I started the bike and it ran for maybe 15 min or so and this is what happened.  I think its a oil problem I recently took the oil pump apart and didnt see anything that would stop it from turning or pumping.  Although I haven't blown out the ports .  But the plug looked lean Im unsure if this is a lean condition or  a lack of oil problem.  I have a friend that does this for a living who had parts a used piston and cylinder with 2 hours on it that we installed and the same thing happened while trying to tune the carb.  Not as bad as the first one.  He had it running good though and the plug didn't look lean.  The first time it seized twice that is why it is so chowdered.  I dont know if someone can look at the pictures and tell if its fuel related or oil.  Thanks in advance.

KX2new.jpg

KXnew.jpg

KX3new.jpg

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What does the plug look like ?

 

Where you riding it hard when it happened ? 

 

Is the piston to barrel sizes in spec ?

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Well the first time it looked kind of lean.  The 2nd time it was normal colored.  No I i was not riding hard at all I didnt even have a helmet on. It was a low rpm up the road kind of a deal the crank is new so I didnt want to hammer on it yet.  The bike ran before the crank job it just was boggy like it was rich.  The piston had probably ten hours on it as well had been out and ridden so there was no reason to suspect that it needed to b e changed.  

 

The only reason I had to tear it apart was because the crank teeth.  The bike hadn't skipped timing or anything yet.  So I had no reason to suspect the piston.  

 

The 2nd piston and cylinder were a stock setup from a 06 KX250F and the ring gap and everything was checked.  This only had 2 hours on it was removed to do a big bore kit.  

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I checked my timing and piston to cylinder sizes were good both times.  Im speculating that it is lack of oil but there are a million piston diagnosis charts for 2 strokes but not 4.  I think it would be tough for a bike to be so lean that it would burn the piston down atleast on a 4 stroke and twice.  You would think it would just not run. 

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Also your cams cam caps what did they look like if it were an oil issue they would likely be shot that's the furthest place oil has to travel so if there fine I would say its not an oil issue

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So its a really long story but i will start from scratch

 

So I acquired a 2006 KX250F in trade for a quad I had.  I usually ride a 2010 YZ450F but this bike needed a little tlc and I thought I have the time so I will fix the little stuff.  It needed fork seals and really just a good cleaning  The only reason I even traded was because the motor had been rebuilt very recently new crank piston all that good stuff.  I decided to check the valves I know these bikes are notorious for eating up valves and it wasnt running quite correct.  It had a 48 slow jet and the fuel screw was backed way out which richened it up to the point that it was very sluggish and not responsive.  

 

So while checking the valves which needed a shim job I noticed that the timing chain felt kind of chunky needed to be replaced.  I got a new chain and pulled the fly wheel and to my dismay i found over half the teeth of the brand new wiseco crank had been broken off.  Called the original owner and he ended up sending me 500 bucks which was good.  

 

So I bought a hot rods bottom end kit new bearings crank all that stuff.  Piston was brand new so I didnt worry about it.  Replaced crank everything turns and looks great.  I cleaned the carb because i figured it was just dirty.

 

I started the bike and it ran for maybe 15 min or so and this is what happened.  I think its a oil problem I recently took the oil pump apart and didnt see anything that would stop it from turning or pumping.  Although I haven't blown out the ports .  But the plug looked lean Im unsure if this is a lean condition or  a lack of oil problem.  I have a friend that does this for a living who had parts a used piston and cylinder with 2 hours on it that we installed and the same thing happened while trying to tune the carb.  Not as bad as the first one.  He had it running good though and the plug didn't look lean.  The first time it seized twice that is why it is so chowdered.  I dont know if someone can look at the pictures and tell if its fuel related or oil.  Thanks in advance.

 

 

look at the oil pump.

There's  2 pumps. the outer is the trans pump and the inner is the engine top end.

Its easy to loose the 2 drive pins that engage the shaft with the gears.

on the attached fiche its part 92043. theres 2. one for each pump.

without those pins properly installed the oil pump gears dont spin.

 

you can verify the pump working by running the engine without the oil filter cover in place.

if the pump is working oil will flow out the filter area.

if oil doesn't flow your pump isn't working

 

 

I recently worked on a KX250F with this exact problem. here's some info.

 

https://www.facebook.com/photo.php?fbid=896876210393981&set=pcb.896886073726328&type=3&theater

oil pump.gif

Edited by nesc103y

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Well I figured it out my intake cam gear spun. I bought the big bore kit for it and was in the process of installing it this weekend and could not get the bike to time. That is when I noticed the lobes compared to the dots on the cam. I will post a pic soon thanks for the help. Kind of a weird one but I guess it happens.

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Hello guys!

I'm having a similar issue with a 2007.

I don't mean to thread-jack, hopefully my question doesn't bother anyone!

Working on this bike for a neighbor and trying to iron out the would-be issues.

My problem was an EXTREMELY loud valve train.

So, pulled the valve cover and noticed it was very dry/ no residual oil.

This motor "was just rebuilt" and actually does have great compression by feel, and nothing has been destroyed yet (cams/ buckets) Soon as the excess noise was noticed, it wasn't ridden.

While kicking the bike with the oil filter cover open, and filter removed, I could not get oil to pump up into the filter housing.

I have:

-Checked oil level (was full)

-Made sure oil filter wasn't in backwards

-Just pulled and inspected the oil pumps. All gears engage and both gear-pins are present.

I'm wondering what I should check next.

All that comes to mind now would be:

-Blocked oil passages?

-Clogged strainers?

-(Is it possible) improper gasket used someplace during the "rebuild" that could block the flow of oil?

Any help or ideas would be incredible, and appreciated!

I have no problem splitting the cases if need be, just picking brains ;)

Thanx a ton, guys!

Edited by moto_xmayhem21

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I heard of a someone using wrong head gasket that blocked hole to pump oil up to top it was a video on youtube

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Well I figured it out my intake cam gear spun. I bought the big bore kit for it and was in the process of installing it this weekend and could not get the bike to time. That is when I noticed the lobes compared to the dots on the cam. I will post a pic soon thanks for the help. Kind of a weird one but I guess it happens.

 

This is the result of no oil to the top end. it is not the cause.  if you reassemble it without finding the cause you are asking for more $$$ problems. .

Edited by nesc103y
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I agree your cam gear spinning should have nothing to do with u wrecking a piston unless the valves put holes in it which didn't happen

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I think its weird but the cam had spun so far that it was actually hitting the valves.  This just didnt happen all at once.  Over half the teeth were broken off the crankshaft I'm guessing the cam spun a bit then.  They had to back the fuel screw all the way out to get it to run with all the added air from the valves.  It clearly has been moving everytime we stick the piston to the cylinder because now its so far off that the valves hit the piston.  It has rotated almost 90 degrees.  I could be wrong but the way it moved when the piston was traveling up on the compression stroke the valves were still open causing a lean conditon.  Not to mention your timing would be way off.  It would be just like if you timed the bike wrong.  There is a reason why you have dots on the cams and also a mark on the crank.  Imagine if you timed the bike with the intake cam 90 degrees off.  Its amazing it even ran. 

 

I pulled the oil pumps apart they looked brand new and when I was installing the new cylinder I removed the timing chain and pumped the oil pump by hand using the kick starter.  Oil was going everywhere . The manual calls for 2.8 psi at 4000 rpm that isnt a lot of pressure. The oil travels from a port into the head studs and up.  I filled the bike with oil and pumped by hand a back blew the port to the nozzle on the piston oil went everywhere again.  

 

 So we will see thanks for your help.

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inconclusive. 

 

  Could have possibly spun when the crank suddenly stopped. 

 

 No out of time valves are going to caused a localized problem like the one in your pic. Out of time valves keep an engine  from starting.  If it is running and riding then the valves are in time, maybe not perfect time, but by no means way out of time.

 

  The pic I saw was a localized problem. . That piston was gnarly.   Were the rings gapped properly?  Both with the dimension of the cylinder, and spaced properly apart. 

 

  if the piston ring gap is too tight, when it warms up it will do what your pic shows.  Or if there is a piece of trash in the rings. 

 

  I don't think you have an oil pump problem. Nor really an oiling problem. 

 

  When the oil stops typically the first thing to go is the rod bearing, then the cams.  Both of those are still ok but the cylinder and piston are bad?  

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