2004 YZ450F bottom end noise. help please

Picked up a 04 yz450f. Like showroom new, all orginal. Looks like less than 20 hours, not even frame paint wear. It did puff a little black smoke when its cold, but then it went away. Did that couple times only when cold, minimal amount. Could be old gas.

It was running great, but now has developed a noise from the bottom end.

This noise gets better when the clutch is pulled in, but then it also makes a metal on metal noise every once in while. I took out the clutch plates, to see if it would go away. Ran in just for 5 secs after adding a ton of oil in it. The noise is still there. The clutch basket dosnet seem loose, had a little back and forth play, just hair.

The noise sounds likes it coming from behind the clutch basket. Its not aknock but more a constant thud. Like I said with the clutch engaged it was more quiet.

Every once in while it makes like a metal on metal noise just for a second. A big clue is that when it happened I was in the woods, and the bike would really grab out from a standstill.

(Kind of like when your chain slaps real hard.. ) Like when I went to let the clutch out, it smacked real hard, sounded like a chain slap but could have been internal.

This sounds bad I know. But all the gears work just fine.

Any idea, I dont want to run it till I fix it.

I ran once with just clutch plates out for 5 secs to see if maybe it was something there.

I was going to take the whole basket off and make look behind there.

Any idea?

I really hope the crank or rod are not bad.... But wouldnt the bike have blown up by now...

I rode it 15 mins home in the woods after it made this noise..... still fires right up

All I can say is that when riidng, it felt like a grab going from 0 mph and starting to let the clutch out, almost like the chain grabbed, or brakes were on, then it breakes free and was fine. Only did this like twice.

And the noise in contant, sound like behind the clutch, but could be coming from left and right side. Def more towards the bottom of the motor..

Pulling in clutch helps w noise, but still makes the metal on metal just for a SPLIT SEC when it happens.....

Any ideas??

Crank? main bearing? clutch bearing? Clutch basket? transmission?

This bike has like 20 hours on it

the yz's bottom end is very noisey if it sounds like this

your fine most of the yz's sound like that

Is it a squeeling noise or a loud tap like a hammer hitting metal?.

Its not squeeling.....

well, it could be your timing chain is getting not so good........, it could be your crank, can you get a video of this at all? would help ALOT!

there is so many noises bikes make, and they do make a slight knock like sound, but thats normal, so its hard to tell whats excess and stuff by typing,

so if you can get a vid or recording of the sound, that would help Greatly!

Check that the cam chain is good BEFORE starting the bike again. Probably not the source of your noise, just to be safe though....

Could be that the clutch damper springs on the rear side of the basket (inside the drive gear) are worn or a couple broken. These work harder in engines with lighter cranks and flywheels.

my buddys bike was making a growling sound because his bearing was going out. the thud sounds like it could be normal(i wouldnt write if off till i found out for sure though). i would try and find someone with the same bike and compare sounds lol. these bikes rev at a 1700-1900rpm(at least the 426's do) and going to make noises sound louder then if the bike reved lower. just a few things to think about.

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