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DIRTTRACKER0

450 noise/shifting thanks nephew (not!!)

13 posts in this topic

my nephew brought his 03 yz450f over for me to work on? had a high pitch rattle in the top end (at any rpm) and stated rachet type noise (liking chatter/popping out of forth gear). i tore it down first thing i found was the piston was broke off on one side where the clip holds the wrist pin in??

after further inspection i found the cranshaft black and blue around the rod bearing, showing signs that it was about to sieze at anytime ( although it ran and idled perferect) i split the cases, inspected all of the trans gears and shift forks (found the broken peice from the piston in the lower end) but all the gears and shift forks appear to be in good condition! i know where the noise was coming from (piston broken), i have never seen a piston break in this way any ideas as what could of caused this?? i am concerned about the trans popping in and out of 4th gear. is this common, have you heard of this or am i missing something in the trans. maybe the broken peice was going through the trans causing it to pop out, but i cannot see any witness marks in the gears indicating that is what happened?? any info or from you experience would be appreciated.

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well i just rebuilt my buddys bike...

the crank/rod looked blueish on his bike aswell i think this is normal

but as for the 4th gear thing

it starts out mellow and barely poppin out of gear but it gets worse

look at shift forks for signs of wear... but replace the 3rd and 4th gear pinions regardless... that is what failed on my friends bike and had the same symptoms

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I was told the blueing of the crank is done at the factory and is normal. Mine looked the same way and I left it there as there were no clearance or bearing issues. I can't help on the 4th gear. Never had that go wrong but please post what you find.

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The crank is normal. The color is from the manufacturing process.

The piston is not. You say the circlip groove is broken out, or it's cracked in line with the axis of the wrist pin bore?

The trans is jumping out because the locking lugs, or dogs, on the sides of the pair that engages 4th are worn. They are made with a slight undercut, or dovetail, so that the load holds them engaged. If this wears over the other way just the slightest amount, the load will force them apart instead. The repeated action of popping out and being forced back in has also bent that shift fork, and you'll see a wear mark in the center of the fork. Replace both gears and the fork.

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The crank is normal. The color is from the manufacturing process.

The piston is not. You say the circlip groove is broken out, or it's cracked in line with the axis of the wrist pin bore?

The trans is jumping out because the locking lugs, or dogs, on the sides of the pair that engages 4th are worn. They are made with a slight undercut, or dovetail, so that the load holds them engaged. If this wears over the other way just the slightest amount, the load will force them apart instead. The repeated action of popping out and being forced back in has also bent that shift fork, and you'll see a wear mark in the center of the fork. Replace both gears and the fork.

is it just me or does gray here know everything there is to know about yamahas. :eek:

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Gray is a bike encylopedia that types.

I like that description !!!!!!!!!!!

+1:ride:

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Gray is a bike encylopedia that types.

yeah basically. he's probably banned from all bike shops for showing up all of their staff, etc. :worthy:

EDIT: ok i fonally found the pic.

kids.JPG

thats basically what the mechanics look like when gray walks in when someone asks about a bike in front of him. :p

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yeah basically. he's probably banned from all bike shops for showing up all of their staff, etc. :worthy:

EDIT: ok i fonally found the pic.

kids.JPG

thats basically what the mechanics look like when gray walks in when someone asks about a bike in front of him. :p

Too funny!!!! ( and most likely 110% truth, too!!:worthy: ):lol: :lol: :lol:

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totally stealing that pic...love it

<img src=http://www.xylicon.com/misc/kids.JPG>

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The crank is normal. The color is from the manufacturing process.

The piston is not. You say the circlip groove is broken out, or it's cracked in line with the axis of the wrist pin bore?

The trans is jumping out because the locking lugs, or dogs, on the sides of the pair that engages 4th are worn. They are made with a slight undercut, or dovetail, so that the load holds them engaged. If this wears over the other way just the slightest amount, the load will force them apart instead. The repeated action of popping out and being forced back in has also bent that shift fork, and you'll see a wear mark in the center of the fork. Replace both gears and the fork.

first i would like to thank everyone for the information.

the piston has a broken off peice approx 3/4 of an inch at the end where the c-clip is installed ( i will try to get a pic to post). i was planning on replacing the crank/brgs anyway while the cases are split, as it is the original crank 4 yrs old. i will inspect the shift fork and gear for the wear you described but will replace them anyway. when i pulled the clutch apart, i checked all of the plates and disc they are well within the service limits, however all of the steel plates show signs of getting hot or bluish color is this normal like the crank?? i apoligize for my lack of knowledge on this motor, but i have done mainly 450 honda 's:worthy: as my son has been racing them for several years. SORRY TO USE THE "H" WORD HERE!! thanks again.

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I can't recall having ever seen any piston break in the way you described. Odd.

Your main worry with the clutch plates now that you know their thickness is OK is whether they are flat. The color is not built in, but it's not unusual, either, and if the plates are OK except for that, just rough them up a little with some 280-320 grit. The bluing won't hurt anything.

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