03 YZ450F Tranny Possibly Blown, due to broken sprocket??

 Ok, so I went to Glamis this weekend, had a lot of fun on my new
purchase, a 2003 Yamaha YZ450F. I love the bike it has soo much power,
i can do what i want with it. Ok the story is, I was riding around all
day iin the dunes and up and down the hill (oldsmobile that is), the
bike hauls A$$. Well came back to camp, and rested for a couple of
hours, then went out for a putt around with that kids, and was going
up a hill when i heard: clank. clank. clank, then it it SNAP!!!!, I
looked down and my chain was off, so i was like oh ok chain was not
adjusted right ok, then i looked and my sprocket was just hanging
there. Well i broke all 4 of the six bolts that hold the sprocket to
the hub, and the hub itslef, so im in for a new chain, new sprockets
and a new hub. Well i came home and started to assess my problem, well
i cant seem to get it into nuetral, I started it and it ran with the
bike in gear, ran fine. But it wont go out of gear. Has anyone had
this problem? Thanks
garrett

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Hmmm. How new was this bike for you? Did you get it at a dealer? How many miles
were on it? How many miles did you put on it?

My guess is that "all 4 of the six bolts" weren't tightened properly by whoever
attached that sprocket. If they're properly torqued down, then the torque is
transferred smoothly. But if they're loose, the result is constant banging on
the hub. And that will break things.

As for the transmission problem, I dunno. All kinds of things can mess up a
motorcycle transmission and cause that sort of problem.

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message

much power,

around all

is), the

couple of

was going

SNAP!!!!, I

was not

hanging

sprocket to

sprockets

problem, well

with the

anyone had

The rear wheel should have just slid in the dirt if the
transmission locked up and caused the problem..... and not
done any damage to the chain or especially the hub.   So in
light of that it seems like the hub bolts were loose or
weak... and it finally broke loose.

If the transmission was bad it seems like you would hear it
when you start the bike.

If its not noisy but won't shift you may have bent the
transmission shifting forks (inside the transmission) when the
rear sprocket fell apart. thats a guess.



Pull the oil drain plugs and inspect for metal shards...any
shards and you are looking at problems, any chunks of metal
and the transmission is probably gone...if there is just a
fine metal powder on the plug its normal.

That will be your best indicator.

Fixing the motor will be expensive.
Try to find a surplus motor on ebay... thats going to be
cheaper than fixing the one you have probably.  If there are
no chunks of metal or shards and you are good mechanically,
you might be able to take the motor apart yourself and sort
out the gear/shifting fork problem... thats a bit tricky
though.


Phil Scott



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Gbikerider760 wrote:

Check the parts diagrams at www.partsfish.com and see if the star wheel
on the shifter drum is accessible by just removing the clutch cover.
Sometimes you have to pull the clutch off just to see the star wheel if
it's under the clutch cover...

The shifter shaft usually goes through the crankcase from the left
side, comes all the way through to a ratcheting mechanism on the end of
the shifter drum. Sometimes the shifter shaft gets bent when you crash
and the tranny won't shift...

Sometimes the ratching mechanism screws up and it can't rotate the
shifter drum which moves the shifter forks sideways to slide the gears
in and out of engagement.

Sometimes the star wheel is a part that bolts onto the end of the
shifter drum, sometimes the star wheel is machined right onto the
shifter drum. If the star wheel is part of the shifter drum, it may be
inside the tranny where you can't get at it without splitting the
cases...

You can usually get at a ball and spring detent mechanism. It's usually
underneath the engine and there's a plug that looks like an extra oil
drain plug that you have to take out, and then the spring and ball are
in that hole...

The ball and spring push against the star wheel, holding the tranny in
whatever gear you shifted into. Sometimes the spring and ball will
stick.

Sometimes it's not a spring and ball, it's an arm with a roller that
rides against the star wheel and holds the bike in gear. An arm with a
roller would usualy be behind the clutch cover...

If you can't find the problem by messing around with the ratcheting
mechanism and the star wheel, the next thing is to pull the engine out
of the frame and split the cases to see what's wrong with the shifter
forks and the gears themselves.

Good luck, and don't run over any deaf lizards at Glamis ;-)

 

Before you go taking a lot of stuff apart, try grabbing the
countershaft sprocket with your hand (while the engine's NOT running)
and try to turn it clockwise and counterclockwise, while
working the shift lever up and down...

A motorcycle transmission doesn't shift gears by engaging and
disengaging geeth TEETH, the gears that slide, slide SIDEWAYS and they
have big square blocks called DOGS. The dogs slip into SLOTS on the
sides of the gears next to them in order to shift gears. If a dog is
jammed into a slot, it made just take a firm turn of the countershaft
sprocket while working the shift lever up or down to
get the dog unstuck...

Maybe you should wear a glove when you grab the countershaft sprocket
and start tweaking it...