4th gear issue with the YZF

[binge]

Hi,

I made a thread about a month ago, regarding my YZF450's clutch slipping.
I assumed this was the problem, as when in 4th gear (top gear on that bike), it started to jump/jolt at around 3/4 through the rev range.

Only in 4th, which lead me to beleive it was probably the clutch, as in 4th, the bike has least torque, putting the most strain on the clutch.


Anyway, £100 later, and a performance clutch in place of the old clutch. I still have exactly the same problem.

Which now leads me to believe it's a problem with 4th gear it's self.



I'm really stumped here now guys, and was wondering if there are any other checks I can do, before splitting the bloody engine in half to get at that gearbox.




Ben

[Pete.]

Nope, it's jumping the dogs and has to come apart. If you ride it too much you'll hammer the crap out of the shift drum groove and need a new drum too I'm afraid.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[binge]

[Fortuna]

Had to replace 2nd gear on my R1 as it used to jump.
It's easy-ish to do if you are mechanically minded.
Drop engine, split cases and remove gearbox and disassemble.

[Pete.]

https://www.boats.net/images/diagrams/yamaha/ATV/2004/YFZ450S/IMAGES/TRANSMISSION.png

8 is the 4th gear pinion. Pinion just means the smaller gear in a pair. 7 is the 3rd gear pinion and can slide on the shaft whereas 8 can spin freely. 7 slides over to 8 until the lumps on the side of each (the dogs) engage then you are in 4th gear.

What happens is that the corners of the dogs round off so they will no longer stay in engagement - instead they push each other apart and 'jump'.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[binge]

I've done a bit of google research, and it seems to be quite common on these bikes.

I thought the idea of a 4 speed box was to create an "un-breakable" type gearbox. As I remember reading that the earlier 5 speedo 450's used to drop 5th gear a lot.
So making each gear slightly bigger, and taking a gear out of the box, made a stronger set up.


Anyway.

I've got two options:


Fit the MX wheels, and hopefully the major increase in torque, will eliminate this problem as it takes a lot of strain off the box.
If this sorts it, I'll be selling the bike, and selling the SM wheels separately.

If it doesn't fix the problem, then the engine has gotta come out.

I've also read that the result of a worn 4th gear, causes one of the selector forks to bend?

I'm more than capable of dropping the engine out. draining the oil, stripping the side covers off, clutch etc.

But as soon as it comes to splitting the cases, I'd rather let somebody professional do it. I've only ever tried to split cases once, and couldnt get it back together. And that was on a 2 stroke.




Ben

[Wafer_Thin_Ham]

[binge]

[Pete.]

Don't waste your time swapping wheels it will still jump the dogs. If you want to drop the engine out and get what you can off it I'll crack it open for you and take a gander.
Might be able to salvage the gear even.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[binge]

[Pete.]

Yeah I could do with the oil pumps.

Rip it out and get it over here. My workshop is half tidy for once. Only half mind
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[binge]

[Fortuna]

If I can replace an R1 gearbox you can replace yours.

[binge]

[Pete.]

Just spent a couple of hours repairing the 4th gear dogs on Binge's bike, and I put a couple of degreees undercut on them too.

First I made a hub to mount a 5" grinding wheel on my cheapo compound miter saw, then I dressed it to run true with my home-made diamond dressing tool:

https://peterrimmer.myby.co.uk/images/gearboxcut01.jpg

Then I made a jig to hold the gear for grinding:

https://peterrimmer.myby.co.uk/images/gearboxcut02.jpg

Lined the gear up with the grinder visually, then fine-adjusted it so that stroking the side of the dog scratched it right across the width:

https://peterrimmer.myby.co.uk/images/gearboxcut03.jpg

Next I made an adjustable stop to index each of the teeth so they were cut the same amount, then I ground each dog with an undercut by tilting the saw over a couple of degrees:

https://peterrimmer.myby.co.uk/images/gearboxcut04.jpg

The fit-up turned out very good - better than I was expecting:

https://peterrimmer.myby.co.uk/images/gearboxcut05.jpg
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[ms51ves3]

Awesome!

[MickC]

Nice job Pete
____________________
XX XXXx
Previous: CG125,XS250 (converted to 400),Z250A, GPZ550, Norton Commando, XS500, 78 Laverda Jota, GPZ1100,Harris bonneville, XV750 (mono shock),TR1

[binge]

Massive thanks to Pete!
He's sorted my bike right out, and saved me a lot of money.

Serious kudos! His mechanical knowledge puts many to shame.

[P.]

[Fortuna]

How much do you charge for that?
Do you undercut both mating gears faces?
Would you do it as a preventative? (even new gears will wear eventually again).
Why did I not know about you when my R1 gearbox went?

I'll shut up now.

[Pete.]