Changing front sprocket..

I have developed an oil leak behind my front sprocket. I have purchased a new gasket and will attempt to put it in tonight. But as I'm sitting here at work, I realize I don't have a large enough socket to remove the bolt holding the sprocket on. Can anyone tell me what size that nut is? Also, is there anything tricky to removing the counter sproket and gasket?



99WR,WR timing,throttle stop removed,Twin Air filter,E-Series,carbon air box,Pro Tapers,lights removed,YZ tank,13 tooth sprocket,....Still can't ride worth a s@#t.

Umm, while your in there, I'd check for play in the bearing. The seal often goes after the bearing does. Bearing wear can be caused by a chain that's adjusted too tight, which pulls hard against the sprocket as the rear suspension compresses.

Thats exactly what I was going to suggest. Definatly check for slack in your chain. I ran mine too tight and my seal went out too. As did another guy I know. Bearings were fine though.


Darin from Missouri - 1999 WR 400F

I think my chain slack is ok, maybe even a touch loose, but I will definitely check the bearing. What should I be looking for?

In talking to a mechanic at a local shop, he said that the best way to get that gasket out was to lay the bike on its side and drill into the gasket using a small bit and pull it out. (After taking off the sprocket of course) Does this sound right?

that sprcket NUT on UK models is 32mm.


NO! Definatly do not drill into it! I wouldnt anyways.

After the sprocket is off all there is to taking the seal out is take the cover off (2 bolts) and get a small flathead screwdriver (with the bike on its side as you mentioned) and pry it out. No drilling is necessary. Drilling sounds dangerous to me.

And the sprocket nut is 32mm


Darin from Missouri - 1999 WR 400F

[This message has been edited by milkman2544 (edited 10-05-2000).]

The nut is definitely 32mm, I replaced mine last night and had to buy a new socket.!

What I really need to know is what do I torque this nut to? I put 60lb on it as the rear axle is 90lb. Any ideas?

Happy Roosting..

Graham is Sydney


I’ve never done this, and I hope I don’t guess wrong but I think the countershaft nut is 30 mm (I’m sitting here at work too or I would go look). I use an air-impact wrench so I’ve never had any problems but I remember reading here about a few folks having hell getting this nut loose. I know there is also a plate secured with a few bolts that holds the seal in the case.

Tips to hold shaft in place that I have seen are (both require chain to be on):

Have a buddy hold the rear brake on.

If you don’t have any friends place a tire iron (or something equally long and sturdy) across top of swingarm just inside rim, between spokes and under bead lock bolt. That way the wheel can’t rotate (counterclockwise) because the bead lock will contact the tire iron which is held in place by the swingarm. Does that make sense? I’ve never tried this either (I’m a big help, huh) but I would be wary of damaging the bead lock or letting tire iron slip and ruin a spoke.

You will also need a hammer and chisel (at least that is what I use) to unbend the lock washer tab that secures the nut. You should be able to reuse the washer a few times before replacing it. This nut should probably be torqued to spec when reinstalled, but I’ve ignored this rule many times in the past.

Hope this helps!

Ok, get this...

I finally get that stinkin nut off and replaced the trashed gasket behind the sprocket. No Leaks.... until I started the bike!! :) Now what?? I thought the gasket was going to solve the problem. Any suggestions?


99WR,WR timing,throttle stop removed,Uni filter,E-Series pipe,carbon air box,Pro Tapers,lights removed,YZ tank,13 tooth sprocket

Is the shaft damaged at all?

Hmmm, got me.? I don't think so.

Did you lube the seal up really good before installing it or did you put it in dry? I kind of treat all seals as I do when I put in fork seals.

I did put some grease on the outside of the gasket after it was installed. Not much, but a light coating. Maybe I don't have that thing seated all the way down..? I'll take it apart again tonight and take a look. I'll give it a touch more grease just in case and cross my fingers.

what milkman means scott, is

did you put a drop of oil on the lip of the seal/any on the shaft?

basically you will rip the fine lip of a new seal within 1 second if you didn't.

sorry to bring the bad news-hope i'm wrong.


If I remember right that seal isnt too cheap either. Thats why I wanted to install it only once and get it right the first time.

Good luck Scott and keep us posted.


Darin from Missouri - 1999 WR 400F

To All

Torque the countershaft sprockett to 50 to 55 ft-lbs max.


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