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05 yz250f engine noise

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Hey guys, I was hoping someone can help me out. This is my first 4 stroke so I'm not real familiar with them. I have an 05 yz250f that makes a clattering (light knock) noise when it a constant throttle speed. When I accelerate the noise will go away. The bike is all stock, not sure on hours although the original tires were just replaced.... So I assume since it is so clean and had the original tires still on it from factory that it has fairly low hours. If anyone has any ideas about the clatter/ knock or where I can start to diagnose that would be greatly appreciated.

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I would bet good money it's your drive chain slapping.

Chain is brand new and correctly tightened. I've been riding for many years, but only 2 strokes. The sound I'm hearing is similar to 2 stroke piston slap. Could that be it? Valves, cam chain or something along those lines?

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Chain is brand new and correctly tightened. I've been riding for many years, but only 2 strokes. The sound I'm hearing is similar to 2 stroke piston slap. Could that be it? Valves, cam chain or something along those lines?

The sound is also there (slightly) at an idol as well....

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It's the four stroke power delivery. Old chain or not, and properly adjusted, at constant RPM it slaps. Single cylinder thumper has major torque reversal between combustion cycles

 

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It's the four stroke power delivery. Old chain or not, and properly adjusted, at constant RPM it slaps. Single cylinder thumper has major torque reversal between combustion cycles
 

So the sound I'm hearing just is normal although it just started making it? I have had this bike for about a year and up until recently it didn't make the sound I'm hearing. I realize there are many more moving parts in comparison to a 2T .

And I am well aware of chain slap. That's not the sound I'm hearing unfortunately.

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Rev it while not moving, if you hear it then worry. If not I bet it's the chain. It'll mess with your head. How many hours on the bike?

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Rev it while not moving, if you hear it then worry. If not I bet it's the chain. It'll mess with your head. How many hours on the bike?


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I hear it slightly when revving and holding it constant... I was hoping it was only the cam chain or something. I really have no idea what kind of hours are on the bike... I know the owner who bought it new, the bike wasn't rode hard nor was it ride a lot. It actually sat since 2008... So I would imagine it's only at 50-60 hrs



I hear it slightly when revving and holding it constant... I was hoping it was only the cam chain or something. I really have no idea what kind of hours are on the bike... I know the owner who bought it new, the bike wasn't rode hard nor was it ride a lot. It actually sat since 2008... So I would imagine it's only at 50-60 hrs

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They are generally noisy up top, the tensioner is very easy to check but I really doubt that would be the issue. I doubt it's valves either since they get tighter with age, not looser.

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Are you sure the sound wasn't always there and now you are noticing? If I listened to mine hard enough I could drive myself crazy!

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Are you sure the sound wasn't always there and now you are noticing? If I listened to mine hard enough I could drive myself crazy!

It's a possibility... I'll fire it up tomorrow and give it a good once over again. The bike runs flawlessly and starts on 2nd kick so I doubt it's valves either.

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It's a possibility... I'll fire it up tomorrow and give it a good once over again. The bike runs flawlessly and starts on 2nd kick so I doubt it's valves either.


If you want to check the tensioner, just take the valve cover off and see if the chain is tight. 30 minute job

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If you want to check the tensioner, just take the valve cover off and see if the chain is tight. 30 minute job

Chain is tight. Looks like the tensioner is about out of adjustment tho. How much play is the chain supposed to have when tight?

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Chain is tight. Looks like the tensioner is about out of adjustment tho. How much play is the chain supposed to have when tight?

Next to none should be difficult to move.

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Its 05, and its YZ.  The book says change piston at 50 hrs for best performance (racing).  Does your bike have over 100 hrs of run time?  Probably.  These engines are close tolerance meaning, very small clearances.  Lots of moving parts in the top end.

They normally run and have a stumble or burble at partial throttle under light load riding, but will clean out when you get on the throttle.  During that type of running, they are noisy.

I've rebuilt several along the way. The noise comes from: loose piston, loose piston pin, loose buckets, worn cam chain and sliders, worn crank and rod/bearings.  My personal 03 had a knock, and turned out the piston pin, piston, and buckets were all loose and had movement.  New piston will be within spec in the cylinder if the cylinder has good plating.  You can't determine that until you put a new piston into that cylinder and measure with a feeler gauge.  If its over spec, replace or cylinder or have it re-plated.  Put a new piston pin into the rod small end and see if it rocks a little up and down or sideways.  ANY play at all is wear, and a new rod will have no play with a new piston pin.  A new piston pin in an old piston will have play, seen it.  Up and down movement of the rod on the crank will cause a lot of noise.  Buckets will also make a lot of noise if they are slightly loose.  

When you add all the little movements up in a running engine, they are additive and accumulate into a lot of noise.  Rebuild that engine, and you'd be surprised at how much noise you will eliminate.  Piston slap, loose piston pin, loose rod, loose buckets, worn cam chain....... not saying your engine needs a rebuild because diagnosing engines from long distance is impossible.  But if you start with a fresh rebuild, you have a know quantity.

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Not the first time I have heard of the piston pin being the source of noise in these engines.  Grubby1, post a video so we can hear!

Edited by 0macman0

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