07 yz450 noises

Hi everyone,

Just got my first ever 4 stroke a week ago, an 07 yz450f. Just wondering if anybody could help with a few things, first is I've put about 4-5hrs on it since I got it and on my last ride it started to make a knocking noise that got louder till I stopped the bike and walked home, it hadn't lost power though, I let it cool off kicked it, started fine, and the noise is still there but louder? I pulled the tensioner out and it's fine. I was thinking might be cam chain is stuffed? If so what does that sound like? Second is the idle began to rise by itself pretty much the same time as the knocking sound started? The sound gets louder under throttle too? The bike has perfect oil colour and no metal shavings, new oil filter, clean air filter, freshly packed muffler as well, I did forget to change the spark plug though, not sure if a plug could make that happen but? Is it time to take it to my local yami guy? I'm new to 4 bangers but love it!


In the first place, NEVER remove the cam chain tensioner until you have put the engine somewhere near TDC on the compression stroke.  Pop that thing out in the wrong position and the engine will jump time.


Second, YZ450's are noisy.  Very noisy.  Compare with another one.


Your idle mixture probably needs to be adjusted to correct the idle speed shift.  Read:



I think you miss-read... The idle got higher the same time as the knock started, I know they are loud 'rattley' bikes.

This started about 4 hours into riding it, and it has gotten louder?

I will take that onboard about the tensioner, I don't have a manual and just learning about 4t bikes.

Ah ok that's good to know I was thinking if the rings are buggered it could cause the idle to rise somehow. Thanks for the manual download link : )

I will put in a new plug today and play with the idle circuit a bit as well.

There are mechanical conditions that will do it, but none that are noisy that I can think of.  Tight intake valves are one.  When they get too tight, say around .02mm (.001", roughly) clearance, they can leak enough combustion pressure back into the intake port to cause the engine to run leaner while it's at 3000 RPM than it does at idle speeds, and that holds the idle up for a time.  That's a classic "hanging idle", and valves aren't the only thing that will cause it. 


Broken rings on a "slipper skirt" piston, one with minimal skirts like those used in the YZF, will almost always cause a lot of "piston slap".  The rings are a big part of what stabilizes the piston, what with barely any skirt.  Piston slap occurs when the the piston and connecting rod go across TDC.  The thrust angle on the rod reverses, and the piston jumps from one side of the bore to the other.  If it is too loose, or rocks too much because of bad rings, it will make an excessively loud knock, or "clank" sound in the process.  Piston slap gets worse under a load, and diminishes as you accelerate.  Piston/ring problems relate to a hanging idle only in that both are general wear conditions, and can occur at the same time.


Now I'll correct what I said in the first place, that there isn't a condition that would cause a high idle that has an associated noise; there are two. There is a very limited chance this can happen, though because the conditions need to be just right.  If an intake valve were to be bent, or hang open because of carbon, just enough to diddle with the mixture, either condition would increase the clearance, probably enough to be heard.  The other is a broken valve spring, uncommon in YZF's but possible nevertheless.

Unreal thanks heaps I will rip it down tonight then and check the valve clearance and piston/rings. I hope it's just the tight valves and not worn rings, which would be a top end rebuild. Thanks again I now have heaps more to go on.

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