06 YZ450 Engine Noise (big surprise I know)

I recently bought a used 06 YZ 450 for a great price but it has been ridden hard (raced). I had to put a new cylinder and piston in (OEM), replaced the timing chain (OEM), clutch basket (GYTR), clutch boss (OEM) and clutches. It makes lots of noise at idle still, but it sounds like the majority of that is from the clutch/transmission since it quiets down when the clutch is pulled (engine still makes some noise though).

I have read lots and lots of posts about this and I know these things are really noisy, but there is a "clatter" in the mid-range under a load that I am still concerned with. The noise is pretty subtle but it is still there. So I am thinking four possibilities: 1) Crank bearing going bad 2) Piston slap 3) pre-ignition 4) I am just paranoid.

I took it out on a pretty good ride yesterday, 30+ miles of hot, dusty, rocky, steep stuff and the noise did not seem to get any louder. So the burning question is that once a crank bearing starts to go do you think it would be noticeably louder by the end of a hard ride?

I am on the bubble for doing the bottom end as a precaution or just ride it until it goes. Alot of the trails we ride would take two men and boy to push a broken bike out of so.....



Hi, is the skid plate stock? If not, take it off and run bike and see if the noise goes away. I replaced my stock plate with a Works Connection plate on my '06, and it changed the way the motor sounded so much I thought something was wrong. Turned out it was just the skid plate amplified everything.

It does have an after market glide plate, but the noise is there with or without it.

How long since you changed the cam chain? Have you checked the current cam chain stretch level? You get about 4 1/2 turns of adjustment from the tensioner from full retract to full extend, knowing this you can determine the current chain condition. My 06 was making some noise like you describe then jumped time, didn't turn out bad but it was time to rebuild my motor anyway.

I put a new OEM chain when I did the piston and cylinder.

Try running some race gas mixed to rule out pre ignition, ya never know. Personally I think being on the bubble to bottom end the bike or ride it until it goes is bad planning, have you any idea how much it costs when one of these motors goes boom? My bike made a distinct tick on decel before it shut off completely, that turned out to be a sloppy cam chain and big end rod bearing going south. I couldn't have gotten luckier, and I hope the same for you.

Yeah, I am with you on the bad planning thing. I am just not sure if I am just being paranoid or not, the previous owner had the top and bottom done in 2009 and says he has not put that many hours on it, but since the top was bad (scored cylinder) I am suspicious of the bottom.

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