2020 KX250F Loses power

AZIMM84
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AZIMM84
Hello all trying to diagnose an issue with my 2020 KX250, I have had zero problems with it, and on the face of a jump the other day it lost all power and died....

Let it cool down and it started right up, I noticed it got super hot quick, and then the motor dragged down again and lost power...

Pulled the valve cover and saw the intake cam off a tooth fixed it, replaced timing tensioner got it running again,

few laps around the yard seemed normal then once it got hot it lost all power like something was dragging it down.... looking for ideas before I pull it apart..

it seemed physically harder to kick, could be in my head though??
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walent215
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walent215 6/10/2022 5:32pm
6/10/2022 5:32pm
Sounds like oil starved and trying to seize
Getting hot and jumping tome is no bueno
Oil level good?
Oil smell burnt ?
Coolant level good?
AZIMM84
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AZIMM84 6/10/2022 6:06pm
6/10/2022 6:06pm
I started it with one valve cover bolt out, was a fountain within a second gas great pressure. no burn smell, coolant is fine
walent215
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walent215 6/10/2022 7:12pm
6/10/2022 7:12pm
I’d be focusing on the items you mentioned then
Cams
Tensioner
Chain
Guides
Pull valve cover asap and look at lobes
Chain for kinking etc
Did you replace tensioner with new one ?
Did you install tensioner collapsed ?
Cam gear may have slipped also
AZIMM84
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AZIMM84 6/11/2022 2:40pm
6/11/2022 2:40pm
I put on a manual tensioner, cam lobes are smooth as butter, chain has no kinks and moves free. I guess I am going to pull the head?

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RGaede
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RGaede 6/11/2022 4:06pm
6/11/2022 4:06pm
Have you pulled the cam caps and checked the journals? Ive seen the aluminum cam cap permanently stuck to a cam before. Typically that's where it'll start to lock up first, and can actually cause the can gear to spin on the cam.
AZIMM84
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AZIMM84 6/11/2022 5:30pm
6/11/2022 5:30pm
cam caps looked brand new
Hcallz5
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Hcallz5 6/11/2022 6:21pm
6/11/2022 6:21pm
Tensioner too tight? I put one on my 350 and I was a bit paranoid about getting the tension correct.
AZIMM84
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AZIMM84 6/11/2022 8:38pm
6/11/2022 8:38pm
It did the same thing before I replaced tensioner, so no
willbilly
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willbilly 6/15/2022 3:11pm
6/15/2022 3:11pm
I would drain the oil and look for metal. Pull off case covers and look for rubbing/binding. Move on to top end. Check for crank binding. Finally split cases if nothing found previously. Definitely would not start it again. Good luck and please let us know what you find.
AZIMM84
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AZIMM84 7/22/2022 10:35pm
7/22/2022 10:35pm
Finally an update, the rod had zero play on the crank, so I am guessing soon as it got hot it starts to seize....

Anyways after a TOUGH search for a new crank and rod. The engine is fully rebuilt. Discovered it has a ported head on it as well. Got it together tonight and it purrs!!

60 hours on the bike how did a crank go bad already? I ended up putting all new bearings in it etc. These four strokes have me worried now after $1600 into it that quick.

Second is there anywhere I can send the old crank to have another rod put on it, for a backup?

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