2009 KX250F Intake Cam and Journals

Brownie281
Edited Date/Time 6/28/2019 5:40am
Hey guys! Hoping to have someone with some more mechanical knowledge and skill point me in the correct direction here. I have torn down a friends 2009 KX250F and done a top end rebuild. New valves are installed and the cylinder head cleaned up, and in the process of torquing down the camshaft cap and cams to check valve clearances I have noticed the intake cam is more or less seized. With a fair amount of force it will move but certainly not freely as it should. The kids original complaint was that the bike seized in spring of last year while riding, and a few months later it was magically un-seized. I suppose a damaged cam/journal could explain why he may believe it was seized when that was not the case. I’ve torn the motor down and replaced the piston and inspected the crank and all is in working order. Again, upon re-assembly I was near the stage of checking valve clearances and have now noticed the intake cam is not seated correctly as it does not move freely at all. The bearing seems to be okay on the cam itself and rotates smoothly. My main question would be is it the camshaft that would be damaged or the cam journal on the cylinder head? If it’s the cylinder head it’s a kick in the ass after completely cleaning and installing new valves and springs but I’ll live. And if it is an issue with the cam journal being burnt up, it’s likely starving for oil? Does anyone have any info or insight If this was similar with kx’s of these years? Just appreciate any insight anyone may have. Hoping to have this reconciled and the kid riding soon!






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kb228
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kb228 6/25/2019 3:58am
6/25/2019 3:58am Edited Date/Time 6/25/2019 4:03am
I own the same bike. With a new head and cams, they were not stiff at all. The journals do look concerning to me. Try a liberal amount of assembly lube and see if they free up. Without feeling it im not 100% sure, but from the pics it looks like the head is damaged.

The head on my 2009 had a destroyed cam journal when i bought it. From what i could see it was from not tightening the cap bolts correctly and in order. no signs of oil starvation from a clogged filter or anything.
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Paul_Pitzonka
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Paul_Pitzonka 6/25/2019 10:17am
6/25/2019 10:17am
It’s common in almost every bike, I don’t think I’ve disassembled a modern 4 stroke( aside from a brand new one) and not seen some sort of minor damage on the cam journals... the damage shown here looks like it an excessive amount with the amount of aluminum remaining on the cam... if they don’t turn very easy (minimal resistance) then I would assume the heads damaged... You may be able to polish the cam journal, but the only way to correctly fix the head is to weld it and have it line bored back to spec.. (that’s never cost effective unless it’s a non-existent head)...
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colvin227
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colvin227 6/25/2019 1:26pm
6/25/2019 1:26pm
Cam and head journals are both junk.....sorry bro
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Brownie281 6/25/2019 2:31pm
6/25/2019 2:31pm
colvin227 wrote:
Cam and head journals are both junk.....sorry bro
I believe your correct at this point man, I’ve started to come to terms with it! Unfortunate but lesson learned. Will definitely inspect cams and journals in further detail in the future to avoid halfway assembling a head! Glad it’s caught now rather than later!

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Paw Paw 271
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Paw Paw 271 6/26/2019 9:55am
6/26/2019 9:55am
Looks like a tipical oil filter cover leak caused oil starvation and then self distructed.

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Sachmo831
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Sachmo831 6/28/2019 2:59am
6/28/2019 2:59am Edited Date/Time 6/28/2019 4:49am
A company called advanced machining saved a yz250f head with similar damage to the cam journal. The cap and head is welded then bored to size. The diameter tolerance is between 1 and 2 thousandths if I remember correctly. It doesn't take much for the cam to gall the aluminum journal without proper oil flow.

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kb228
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kb228 6/28/2019 4:23am
6/28/2019 4:23am
Sachmo831 wrote:
A company called advanced machining saved a yz250f head with similar damage to the cam journal. The cap and head is welded then bored to size...
A company called advanced machining saved a yz250f head with similar damage to the cam journal. The cap and head is welded then bored to size. The diameter tolerance is between 1 and 2 thousandths if I remember correctly. It doesn't take much for the cam to gall the aluminum journal without proper oil flow.

How much did this cost compared to buying a new head?
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Sachmo831
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Sachmo831 6/28/2019 4:47am
6/28/2019 4:47am
Sachmo831 wrote:
A company called advanced machining saved a yz250f head with similar damage to the cam journal. The cap and head is welded then bored to size...
A company called advanced machining saved a yz250f head with similar damage to the cam journal. The cap and head is welded then bored to size. The diameter tolerance is between 1 and 2 thousandths if I remember correctly. It doesn't take much for the cam to gall the aluminum journal without proper oil flow.

kb228 wrote:
How much did this cost compared to buying a new head?
It was for my brothers bike, I want to say he said it came out to $400 with new valves and the seats cut. It came back as basically a brand new head
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kb228
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kb228 6/28/2019 5:40am
6/28/2019 5:40am
Sachmo831 wrote:
A company called advanced machining saved a yz250f head with similar damage to the cam journal. The cap and head is welded then bored to size...
A company called advanced machining saved a yz250f head with similar damage to the cam journal. The cap and head is welded then bored to size. The diameter tolerance is between 1 and 2 thousandths if I remember correctly. It doesn't take much for the cam to gall the aluminum journal without proper oil flow.

kb228 wrote:
How much did this cost compared to buying a new head?
Sachmo831 wrote:
It was for my brothers bike, I want to say he said it came out to $400 with new valves and the seats cut. It came...
It was for my brothers bike, I want to say he said it came out to $400 with new valves and the seats cut. It came back as basically a brand new head
Thats not bad. A new head for this bike is $550 if i remember correctly. And thats without valves. SS valves from prox were $100/pair with springs. Good deal i guess.
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