Oil leak behind front sprocket fixxed

[SoonerYFZ]

I had the oil seal behind the front sprocket changed at a local dealer (mine had been leaking for a while now) and I watched the mechanic change it out. I went ahead and had him change out the lock washer, collar, oil seal and the o-ring like the thread over at bluetraxx suggests.

93102-32480-00 Oil Seal (~$7)
93210-22298-00 O-Ring (~$4)
90387-2513F-00 Collar (~$11)
90215-21001-00 Lock Washer (~$3)

First off the main tool you might need that you may not already have is something that looks like a dental pick, this is pretty important to make the job easy. You will obviously have to take the chain guard and sprocket off... the screws that hold the guard on can be really difficult to loosen if they were torqued down at the factory. The mechanic used a impact driver (looks like a screw driver and you hit it with a hammer to loosen overly tight bolts) to remove the bolts on the guard. A tip to make the whole job easier is to jack up your quad under the frame so your swing arm hangs further down, this loosens up your chain and allows you to get the sprocket off and on alot easier.

You will need a really big flat head screw driver or a small crow bar/chisel to tap the bend down on the lock washer and then it takes a 27mm socket to remove the nut that holds the sprocket in place. The mechanic had access to air tools but if you don't you might have to sit on the quad and hold down the rear brake with your right foot while you break the nut free by pushing down on a breaker bar or ratchet with your left foot.

Pull the washer and sprocket off with the chain still on and once its free of the shaft take the sprocket out and set it aside. There is a metal plate that covers the oil seal, so you will need to remove the screws and pull the plate off. There is alot of grime and gunk behind there so you will want to clean it up.

Now is when the dental pick type tool comes in handy use it to pull the oil seal out from around the collar (be ready for a small amount of oil to leak out). Don't worry about tearing the seal up, thats one of the parts getting replaced. Once the seal is out use the pick to reach back behind the collar and pull it off... this is really the toughest part. The mechanic tried and failed with all kinds of pliers first, until he decided to use the pick to reach behind the collar... then it easily came out, the trick I believe he used is that there are a few indention type notches on the back side of the collar that allow you to get the pick in behind it so you might have to turn the shaft till you find one. You may decide to re-use the existing collar, if so you will definitely want to clean it up and make sure there isn't a speck of dirt on it. The last thing to remove is the o-ring that sits behind the collar in a groove on the shaft... the pick is good for that too.

The mechanic then cleaned up the shaft and used steel wool on it. He also mentioned that sometimes a sprocket, over time, will deform the tines a bit and that might make getting the collar off a bit tricky, although mine came off easy using that dental pick.

Once he had it all cleaned up he greased up the o-ring. He used a mixture and I can't quite remember what he said was in it but it had a purplish color I know he said it was half "moly" and something else... sure wish I could remember but I'm sure that regular lithium grease works fine. With the new o-ring greased he put that in place then slid on the new collar. He then smeared the same grease concoction all over the new oil seal then gently slid it around the collar. This is the part to be extra careful... you don't want to damage the oil seal. With the oil seal partially in, he took a flat head punch and a hammer and very gently tapped the oil seal in all the way around making sure to get it in even. With that done he put the metal plate back on, then the sprocket, the new lock washer (there are 3 bends on the lock washer, if you have never taken your front sprocket off you probably won't need a new one, I had taken mine off before so it was needed) and then the chain guard.

I think thats all there is to it... the mechanic finished up in just under 30 minutes. Maybe my 30 bucks for labor will help other people do it on their own... I know now that this is something thats likely to need replacing yearly depending on the conditions you ride in. I race in some pretty terrible conditions so lots of grunge gets in every little nook and cranny. Next time I will be able to do it on my own with no problems.

[BladeRunner]

Great write-up.

[YFZ909]

that seal ended my weekend early in glamis but it's fixed now. anyone know what causes it to blow out? i have heard from quite a few people about this problem

[burly50]

Can this be pinned?

[ndhennin]

I've had the same problem. For me, it's caused by the plastic flange on the inner side of the front sprocket. A small stone get caught between the motor and the plastic flange and it destroyed the seal. No more problems after taking off the plastic.
Oh, this plastic flange is there to reduce the noise of the chain going on the sprocket so no real use...

[jim417mx]

Can somebody post a pic ... what "plastic" do you take off? mine just started leaking the other day

[yfz450psycho]

are there any pics

[desertbound]

I did a write up on it on Tech a while ago. Here is the link with pics.

http://www.yfztech.com/forum/index.php?showtopic=1123

[lawmaster891]

yeah a t shirt got caught in my sprocket and ruined my ride today so i will be doing this

[Joester]

ahaha? the broken part isnt funny but a t-shirt? wth?

[cmat]

I had the same problem, one thing I figured out is you want to have the collar on before you install the oil seal. The taper on the collar helps from damaging the seal when you install it after the collar, the collar also helps you know it is not in crooked.

[lawmaster891]

QUOTE (Joester @ May 3 2009, 07:51 PM)

ahaha? the broken part isnt funny but a t-shirt? wth?[/b]

yeah i had a girl on the back and she was sitting on her shirt and i guess from all the bumps it kinda fell i guess.
the chick was like wheres my shirt, then we found it in the sprocket

[yamifan]

I'm glad I looked at this post. I somehow managed to catch my carb overflow tubes behind my front sprocket and saw what appeared to be oil all over the skid plate and back of the quad. I checked the oil tank and it was still full. I assumed that I just pinched the line enough to create too much vaccum pressure and when the tube finally tore off it just threw gas everywhere. But I will deffenitaley check this tomorrow.

[efleming]

i was trying to take my front sprocket nut off on my 2004 yfz 450 today to replace it and the thing wont even budge when i am turning it counter clockwise. i was wondering if i am turning it the right way or do i just need to put a little more muscle into it.

[yamifan]

QUOTE (efleming @ May 11 2010, 11:52 PM)

i was trying to take my front sprocket nut off on my 2004 yfz 450 today to replace it and the thing wont even budge when i am turning it counter clockwise. i was wondering if i am turning it the right way or do i just need to put a little more muscle into it.[/b]

More muscle. Find a way to lock the rear brake down. I sit on my quad and lock the brake down with my foot, then hold the breaker bar on with my left hand, and push down on it with my left foot. I look REALLY stupid doing it, but it works hahaha

[efleming]

QUOTE (yamifan @ May 12 2010, 02:44 AM)

More muscle. Find a way to lock the rear brake down. I sit on my quad and lock the brake down with my foot, then hold the breaker bar on with my left hand, and push down on it with my left foot. I look REALLY stupid doing it, but it works hahaha[/b]

haha thanks man i really appreciate it

[FaintReality]

So after a good half hour of trying to get the seal off, I decided to use a paint can opened (~$1 at Lowes) and it came off so easy... same for the collar. Best $1 spent and will save you lots of frustration. Just an FYI for anyone attempting this.

- Dave

[Hayter11]

I will be doing this on the weekend as well. What exactly is the lock washer that I have to bend in order to get the sprocket off? It looks to me like there is a washer just under the nut holding on the sprocket with a few bends in it is this it? do I bend it completely flat? thanks

[simthizzle]

ya thats it. Just take a flathead and bend it up and take an impact to get the sprocket off.

[Hayter11]

bend it up? I thought it neded to be flattened to take it off?