Help with Death "Rattle"

[Davos]

hey guys, i know these motors are loud and noisy. (08 yz450f)

But i am having an issue only when the bike is

1. warm

2. in the lower third of throttle

3. when the clutch is released.

valves are all in spec and torqued to spec.

Cam chain has no kinks and is tight.

It is entirely possible that I am just listening really hard to my engine, because the first day riding i don't hear it, and ripping hard i never hear it. (Example: from almost stalling if i give it full throttle i dont hear it, but if i slowly increase rpms there are about 300 rpms in the range that produce the sound.) and its really scary when climbing hills, nearly stalling, and having to coax the bike between rocks to hear the death rattle.

I honestly dont want to ride anymore because im scared of toasting my motor.

Oil is changed every 5 hours, air filter every time i ride. oh yeah and the old girl has 67 hours.

Does anyone have any ideas? could the clutch or a loose magneto make these sounds?

Any help is much appreciated.

Thanks, David

[grayracer513]

Probably rear chain slap, but the sound of it. Nothing to worry about.

[426 NOOB]

Probably rear chain slap, but the sound of it. Nothing to worry about.

im with gray. Its chain slap.

[jratcliffe3]

Sounds like chain slap, may also be worth a listen to the thrust bearing on the clutch. Get a fairly big screwdriver with a plastic handle, start the bike and put the tip on the clutch casing, and put your ear against the end of the screwdriver. Then give the bike a little throttle and keep listening. This is a good way of pinpointing any engine noise if you know what to listen for.

[grayracer513]

What thrust bearing?

[Davos]

Ok, ill let it go then, i may go ahead and try the screwdriver on the clutch side of the motor. only problem is i never did this when the bike was new. so im not sure what is abnormal. And knowing these 450 singles, i might loose some hair listening close. They make noises all day that standard engines make when there about to explode or send a rod thru your fire wall.

[grayracer513]

The only thrust bearing in the whole engine is the one that lifts the pressure plate, and that one does nothing at idle. The engine typically has a slightly noisy cam drive train, and a lot of primary gear backlash, which will not be apparent at speed or under a load, but quite loud at idle. There is also a normal growling/rattling generated by the natural uneven idle speed of a single that disappears when the clutch is pulled in. Read:

https://www.thumpertalk.com/forum/showthread.php?p=5362282#post5362282

One thing that does bear inspection if you believe the noise is abnormal or excessive is the nut holding the primary gear onto the end of the crank. Every once in a while, one will loosen and start rattling.

[Aka.Goose]

After 67 hours, maybe the rings are going bad? Maybe a little piston slap going on?

[BlackT5]

The chain slap noise scares the shit out of me. I was something I really had to get used to coming from 2 strokes. Especially chugging is in low speed technical stuff. I had not ridden in about 2 months and forgot how bad it could be. I find that keeping the chain tension dialed in lessens the amount of noise.

[Davos]

If i check the rings i gotta take the cams and all that off, and pull the cyl head off and the like.

I got a question though, do i need a new head gasket? i see them for about 30 bucks, and thats steep just to check the rings. I mean if i am doing that, ill replace them while i am in there regardless.

[grayracer513]

Yes, and a base gasket. And be sure you read, understand, and follow the head bolt torque procedure.

[Valkrider15]

Yes, and a base gasket. And be sure you read, understand, and follow the head bolt torque procedure.

I'd even sugest re-reading, and having a friend read the head bolt torque procedure. Then read it again!! ? Don't ask me how I know

[Nizzle]

My bike had the same symptoms as yours. It wasn’t that loud and I could only hear the rattle off and on not all the time. So I tore the into my bike and found this…

It was caused by what gray was taking about...

One thing that does bear inspection if you believe the noise is abnormal or excessive is the nut holding the primary gear onto the end of the crank. Every once in a while, one will loosen and start rattling.