'04 450 overall impression / repair questions


I've been reading this forum for couple of months (even before I got the bike) and realised it's an endless well of knowledge.


I bought '04 yz450f 3 months ago. Bike pulls like crazy, I barely have strength to ride it longer than 1 hour :).


When I was purchasing it,the bike ran really well. It still does, but I've got couple of questions. I read a lot of topics concerning lots of usual and unusual things these bikes tend "to do" ;)


Just after I bought it, the engine was running really quietly and there was no any rattling noises I could notice. Just SUPER rhytmic bang sound, that the engine makes when the gas is exploding in it. I was impressed - 10 years old bike running like brand new.


The guy who was selling it told me that the last investment he made was the new piston. Bought it with 30hrs after replacement. 


After 10 hours of really soft riding the engine started to rattle. I was really worried about it, but I found lot of info here, that these bikes just do like this. (it wasn't very loud or making me think it's gonna blow - it just appeared and made me suspicious)


The idle rpm started to swing a little bit and sometimes (depends on the weather and if the bike is warmed enough) the rpms wouldnt go fully down just after reving the bike (it stays on something like 1/8 of throttle and when u rev it couple of times it goes down to idle)


Few days ago I decided to check valves clearances. all three intake were .15mm and the exhausts were .20mm.


The cam chain slack and tensioners eject level (60%)  made me suspicious. I decided to change the chain and the tensioner (i thought that the new one will work better, but it's the same way :D - the only difference is that the old tensioner has "1" casted on it and the new one has "3")

Should I stay with the old one?


The old chain wasn't stretched when I compared it to the new one. The only difference between those 2 is that the old one isn't bending smoothly, just like the new one does. (finally a good decision :D)


I took off the rear chain guide (thanks to Grayracer for the instructions :))


The main question is:

does this guide needs to be replaced? (look at the pic)

The surface where chain slips on is kind of wiped. The rubber thing that covers the guide is much thicker on side and the back of guide than on the "slipping surface". Actually I checked it with my tongue and teeth :D and it seems that its 3/4 thicker than the "slip surface" (anyway, there's still some "rubber" on it).


BTW: Can the floating rpms cause the rattle to appear? (it caused the engine to run not as EVENLY as it did on the beginning)


PS: I found this scar on the bottom of left crankcase, beside this rectangular passage. Will it proceed fast? It's a 1mm deep groove.









cam chain guide front.jpg

cam chain guide front2.jpg

cam chain guide bott2.jpg

cam chain guide rear.jpg

carter scar.jpg

Edited by sosycz

Could anyone tell if the chain guide is worn and has to be replaced?

you've already got it out in your hand might as well might save you another tear down and a headache later...also my 04 has this ghost rattle also just seems to come and go as it pleases but I also hammer on the thing 95% of the time..lol just keep changing your oil on time

I've ordered it yesterday, before you replied. 

BTW I dropped a valve lifter on the ground, it wasn't more than 1meter high. Could I damage it? I didn't check before, but after putting it back it turns a little bit harder that the second one, that wasn't moved.

Edited by sosycz

Depends on how it landed.  Could have bent the skirt if it came down on the bottom edge.

Depends on how it landed.  Could have bent the skirt if it came down on the bottom edge.

well, it might fall the way you've described. it turns when in it's place, the only difference is that i need to press it by my finger  with some little force to turn it around and avoid finger to slip on its edge. please tell me it doesn't need to be replaced....  :banghead:


ps no force needed to turn the second lifter.


ps2: is it that fragile?!

Edited by sosycz

Back after research. I guess my lifter didnt bent. I overreacted. Removed it from the head, used low-comp air to clean the head lifter spot, then put it back. it moves smother, almost no difference between the second exhaust lifter.


The only thing that concerns me are the marks on the top of the lifter. How did these micro little grooves appear and what does it mean. 


Don't want to constantly bother Grayracer for help. Is there anyone who could tell me if there's something wrong with my lifter/cam shaft, whatever made these grooves and are they serious thing?


I found out that these marks could be made with the decomp pin placed on the exhaust camshaft.

Anyway, a confirmation would be apreciated :D


Edited by sosycz

if it were mine and I could actually feel those grooves I would replace it....

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