06 YZ, Seems to make more engine noise than my 05

I know that the Yamaha engines are noisy. The question is are the 06 models much more noisy than the 05's? My o6 starts and runs great but at an idle it makes way more noise. If I didn't know better I would say it had a rod knock. However it goes away if you give it just a little throttle. It doesn't seem to make a difference weather it's in gear with the clutch pulled, neutral, or neutral with clutch pulled. I was told it had around 30 hrs. time on it. However I guess there is no real way of knowing... But from the looks of the bike I would say it hasn't been ridden a whole lot, very clean under the engine as well as under the tank around the engine and up around the top shock bolt. Hopefully I'm just being paranoid.


Compare it to another one. The aluminum frame tends to attenuate the engine noise better than the steel did. Most of it is generated by the transmission being slapped around at an idle by the big thumper, and some more is because of the primary gears banging back and forth. If you have an aftermarket skid plate, that usually makes it louder yet. Do compare your to others, though. There's a small chance it really has something wrong with it.

if the problem was the rod, wouldn't make more knocking on a slight acceleration?

Unfortunately I don't have another bike to compare it to. The sound I heard to me sounded like piston slap or a rod knock... My gut reaction was to disassemble and get a visual. The wrist pin looks good, the rod has no play that I can feel however the piston skirt seems to be slightly worn. If my measurements are correct there is .029 difference between the piston and bore size. The cylinder looks to be in good shape other than not much of a cross hatch pattern left. I guess so much for 30 hrs on the bike... so I will have the parts measured at the machine shop to confirm actual wear. The only other thing I saw was some bluing on the crank lobes where the pin is pressed in. Nothing on the connecting rod itself. That to suggests that heat might have been used in the assembly process of the crank, but I'm not that familiar with crank assembly procedures.

The blue color is normal. It's from the original assembly

Thanks Gray, I appreciate the info and the help.

Update, I put a new piston and rings in the bike. The noise I was hearing is gone. I used OEM parts, mainly because I wanted to compare dimensions. The piston that came out measured .022 smaller than the new one. I'm going guess that maybe I was hearing some piston slap...

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