YZ426F 5TH Gear Problems...Pic Heavy

i just bought my 426, test rode it in town and didnt get to 5th gear, but it ran and rode great...

 

me and my buddy load up to ride, i took of just at a normal crusing pace, hit 5th gear and it acts as if the clutch is being pulled in and out while under acceleration in 5th only...

 

heres pics of my findings...seems like that shift fork is the culprit, but i wanted to get more opinions before i go buy parts...and also, can anyone tell me what crank/rod/piston i have...guy said it was rebuilt, crank shows signs of rod contact or something..also a pic of timing chain crank sprocket...also my middle intake valve looks different and says japan on it...is that oem?

 

and last i dont ride super hard or race,...mostly trails and gravel roads... but wheelies and WOT is there...any suggestions on durable parts?

 

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That's a very old motor.

Are you sure you want to pour money into it?

The OEM parts are the best available.

That's a very old motor.

Are you sure you want to pour money into it?

The OEM parts are the best available.

what makes it old?

what makes it old?

 

Years/Hours of use

Suspension design

Size and weight

Ergonomics

 

IMHO

The Yamaha bikes last a long time.

That's a good thing and a bad thing.

That means when you buy a used one, everything on the whole bike is worn out, because they don't typically fail at all, so they get ridden till they die, or close to it.

15 years is a long time for a dirtbike motor.

At probably 150 hours max you should change the piston (1/4 of that if you are racing mx with it). 

At 15 years that would mean it was only ridden 10 hours a year? Doubt it.  Probably triple that.

Years/Hours of use

Suspension design

Size and weight

Ergonomics

 

IMHO

The Yamaha bikes last a long time.

That's a good thing and a bad thing.

That means when you buy a used one, everything on the whole bike is worn out, because they don't typically fail at all, so they get ridden till they die, or close to it.

15 years is a long time for a dirtbike motor.

At probably 150 hours max you should change the piston (1/4 of that if you are racing mx with it). 

At 15 years that would mean it was only ridden 10 hours a year? Doubt it.  Probably triple that.

 

nothin a rebuild dont fix...im not worried on weight/suspension etc...i just need a decent reliable bike to have fun with..

im sure its out dated...plus my buddies bike is a 97 yz250...its not like we are out to race and compete

 

only reason i asked which rod an stuff i have is in case it was something good...i had planned on new crank/piston to begin with

Your 5th gear problem is the locking lugs and slots on the 3rd and 5th pinions (main shaft).  They are worn to the point where instead of holding in gear, they push away from each other under pressure.  The fork is bent as a result.

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Your 5th gear problem is the locking lugs and slots on the 3rd and 5th pinions (main shaft).  They are worn to the point where instead of holding in gear, they push away from each other under pressure.  The fork is bent as a result.

thanks a bunch, thats what i needed to know, thanks again!

 

so 15 and 19 is what i need correct? plus a shift fork

 

http://www.bikebandit.com/oem-parts/2001-yamaha-yz426f-yz426fn/o/m145769#sch114602

Edited by fastfiveoh

No, those are the 3rd and 5th "wheel" gears on the output shaft.  You need 3 and 6, the 5th and 3rd "pinions" on the main shaft, as well as any other gears showing that kind of wear, and the fork for the third pinion ("shift fork 2")

No, those are the 3rd and 5th "wheel" gears on the output shaft.  You need 3 and 6, the 5th and 3rd "pinions" on the main shaft, as well as any other gears showing that kind of wear, and the fork for the third pinion ("shift fork 2")

i was mixed up there, thanks again

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