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2006 kx250f weird noise

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Hi,

So.. I will tell what I think it is.but it may be not..

This is the sound it is making:

https://m.youtube.com/watch?v=17PXD_pfVHs

when I rebuilt the top end, it ran good , but I put 10w40 car oil instead of motorcycle oil and I ride 2 hours with it. I changed oil for motorcycle oil when i heard the sound coming on. But it did not go away

I have checked valve clearance again and theyre good. Ive taken out the spark plug and there was alot of wet black carbon on top of piston. It only ran for 2 hours. Did the car oil do that? Or is it normal.

You could be thinking it is the timing chain , but it is not loose ??

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Maybe do a quick check of the cam chain tensioner. Make sure it is clean and functioning proper. Reset it and reinstall. Other possibility is It could be the front cam chain guide is out of place from the rebuild.

I sincerely doubt the oil has anything to do with it. Now that you have fresh oil in it, take it for a ride.

Wet black carbon on the spark plug could be an oil leak from the head. Specifically intake valve stem seals.

When you say 2 hours from rebuild. What exactly was done in that rebuild. Please describe.

 

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7 minutes ago, FaceDeAce said:

Maybe do a quick check of the cam chain tensioner. Make sure it is clean and functioning proper. Reset it and reinstall.

It could be the front cam chain guide is out of place from the rebuild.

 

I sincerely doubt the oil has anything to do with it. Now that you have fresh oil in it, take it for a ride.

 

Wet black carbon on the spark plug could be an oil leak from the head. Specifically intake valve stem seals.

 

When you say 2 hours from rebuild. What exactly was done in that rebuild. Please describe.

I will reinstall the chain tensioner i didn't think about it.

I put a new piston&rings and gaskets i did not do anything to valves.

The spark plug is okay its just alot of black carbon almost sludge on top of piston

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You say a leak from intake valves. Could it be exhaust too?  I had to shim the right intake during rebuild

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You say a leak from intake valves. Could it be exhaust too?  I had to shim the right intake during rebuild

 

An exhaust valve leak would not get to the piston and spark plug as you describe. A leak at the exhaust valve goes straight into the exhaust pipe, it cannot be drawn into the cylinder. Only an intake valve stem seal would do that as the intake does get drawn into the cylinder.

 

Has it been smoking a-lot? Smoke out the exhaust?

 

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Just now, FaceDeAce said:

 


An exhaust valve leak would not get to the piston and spark plug as you describe. Only an intake valve stem seal would do that.

Has it been smoking a-lot? Smoke out the exhaust?

 

No smoke at all

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Not much of a leak then. Don’t worry about it.

 

There is no real harm done with a little leak. Only some carbonizing in the combustion chamber and exhaust valves. If the leak is bad enough it will start fouling plugs which you’ll notice because the bike will start running like shit, smoking alot, and the plug will be caked black.

 

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Probably worth double checking the timing too

seems to be a reoccurring theme on kxf’s that the exhaust cam is installed one tooth off which is enough for it to tap the piston a little 

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I guess you mean the tingley chain sound. As the other guys already said,  I'd def reset the tensioner and triple check the cam timing. Check the valve clearances again just because you can.

That louder chunky rattle sound would concern me.   Hope it's the piston clearance and not something worse.

Good 10x40 car oil wont cause any harm to the motor.  But might make the clutch feel too grabby or slip. I use diesel oil. Cheap in 10 or 20L containers.

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I took out and put back the chain tensioner, it didnt do anything. Maybe if I do the same with the camchain but that will be another time.

The sound is only there when engine is cold and fade when bottom gets hot about 15 minutes

I dont think it can make something happen and I hope it goes away next time I work on it 

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Be careful.  Any odd noise and the chance of a major failure increases a lot.

The timing chain, tensioner, sprockets and guides all need to be working properly.

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