Hi all,

My bike is leaking oil from behind the front sprocket cover somewhere.
On inspection it looks like the oil originates from the bottom of the oil seal on the output shaft.
just behind the front sprocket.

I've removed the sprocket and the cover plate that covers the face of the
oil seal.
Question is; How do remove the old oil seal and fit a new one?
I REALLY hope the answer isn't going to be to split the crank case.

If the only way to replace the outer output shaft oil seal is to split the crank case,
then I am just going to have to live with the leak until I get a second bike.
My bike is my only means of transport so I cannot have it off the road for weeks at a time.

I think to properly replace the seal you do have to split the cases, sorry. But thats just off my memory. Anyone with the manual?

What you might want to do as a temporary fix is to drain the oil, use a degreaser to clean the area around the seal real well and then put a coating of RTV on to ah... seal the seal.

Another thing to do would be to put an automotive PCV valve in the cylinder head breather tube. This one way valve will create a partial vacumm in the crankcase and reduce the pressure that was squeezing the oil out the seal.

good luck

There is a way to remove oil seals without splitting the cases, its a method I have used many times to replace seals in industrial motor-gearboxes but its tricky to pull off. If you are going to split the cases its worth trying it first.  You need to fix 2 small self-tapping screws into the seal 180 deg apart, drill a small pilot hole first. Then jiggle the seal out using pliers or cutters by pulling on each screw in turn.  If you are careful and gentle it can be done, but by adopting this method you destroy the seal and there is no turning back once started. Remember NOT to drive the screw in by more than about 5 mm or you risk damging the secondary seal and bearing thats behind the outter seal.

Ripping it out is the easy part.  

How do you propose to get the new one in place properly and un-mangled so that it will form a proper seal (which is the point of the exercise)?

Fitting it is the EASY part....... the seal will knock into place over the shaft, but you do need to use a suitable tool to drive it home squarely such as a tube. Put plenty of grease into the housing and over the shaft first and ensure that the lip on the inner diameter does not turn inside out. Yeah its tricky and difficult but when you have no option to split the cases its worth having a go.

I can vouch for sledge's method.  I use it every day.  To protect the seal when installing it wrap the spline with a couple turns of drafting mylar or similar thin plastic.  Tap into place with a large socket or section of pipe.

Make sure to lubricate the seal before installation, as well as the seal recess.

This all assumes that the trans output seal is accessible, and of a type to permit these methods.  I've never pulled one before.

Currently the leak is a few drops of oil per day,
If it gets worse I'll try removal using the self tapping screw method mentioned above.

For now I shall just live with a bike that marks it's teritory.

I don't believe you should have to split the cases to replace that seal.The idea of drilling  small holes in the old seal, and then screwing in one or two sheet matal screws should work. You cab then pry the seal out with a screwdriver or two.Another good way is, again, drill one or two small holes in the old seal. Then use a "slidehammer". Its a shaft with a tip on one end where you can attach a sheet metal screw (to screw into the hole you just drilled). The other end has a weight and a stop at the end. You screw the sheet metal screw into the drilled hole (with the sheet metal screw attached to the tip of the slide hammer), and then by tapping the weight on the slidehammer (by moving it from the end closeste to the seal and moving it away from the seal) the seal should come out.Don't use caveman-like force, or you might pull the screw out of the drilled hole-just tap steadily.Two holes may work better if the seal is stuborn.The two holes should be drilled 180 degrees apart so you can work back and forth-first one hoole then the other until you get it out.
   Then clean up the hole where the seal fits the best you can. Sometimes you can use the old seal as a driver to install the new one. Or a socket works well.Just check the fit of the socket and use one that isnt too small that might damage the rubber lip on the seal.Seals have a right way and a wrong way of installing too-be sure you install it the same way the old one came out and not backwards.Take soam care when installing. You want to drive it in place without getting the cocked.You could dab a small amount of grease around the inside of the rubber lip to help it slide over the output shaft.
  Maybe youy could do a google search of "slidehammer".Once you see the tool it will become clear how it works. You can bye these without spending a lot of money.

you have to split the cases, there are 2 seals in there and its a crush fit between the cases.  you might be able to fish out the first seal, you wont get the second one.

i had the same issue.  it turned out to be a bent transmission shaft.  the seals were fine, but when i looked at the sprocket there was a visible wobble when it rotated.  needless to say, i had to split the cases.  that was a fun job.

racers trick-take rag soaked in brake fluid place against seal overnight ,will swell seal and reduce oil leak-ive done this many times w/decent sucsess

do it correctly, dont use the tech cheater meathode.

I changed that seal and I didn't have to split the cases.  You just have to get past the fear of commitment (that point where you destroy the old seal...).  

Use whatever method/tool is available that won't booger up the ID of the bore the seal sits in.  I bent up a screwdriver or something into a ghetto seal puller.  Get a new seal, clean up the area, goop some sealer on the outside edge of the seal and tap into place with the appropriate "seal driver".  I think my "seal driver" ended up being a combination of pieces of wood and/or a large socket.  It's been a few years since I did this and I've had no leaks.  In fact, after this seal stopped leaking, I found the shift selector shaft seal was leaking and after fixing that, the neutral switch shaft (not sure what it's called) seal was leaking.  I ended up replacing them all over a few year's time and have had no leaks since.  I might not have gotten all the seals (referencing JamesG?'s post about 2 seals?) but I got all the leaks!

I still think if you aren't going to do the job right, at least don't do it half assed. There is the potential to do some serious, can't-ride-the-bike-til-you-fix-it damage by jerking seals out of thier seats.

Either leave it be, or entomb it like I mentioned before.

James?
Your comments are contradicting. Firstly how can you expect to repair this seal by covering it in silicon? There is a moving shaft in the center, is this not going to tear any silicon off and break and bond the bond when it starts to rotate. Chances are the leak is where the shaft passes through the seal as this where there is movement and friction. Secondly you mention half-assed attempts at repair, well how would you describe your suggestion to repair with silicon!!
The decision to replace the seal has to be based on certain factors, such as cost, inconvenience ability to do the job yourself etc. When you have absolutlely no option left but to replace it then try to remove it in situ...if you manage to do it its a bonus..if you dont you have lost nothing.

Unless of course you bugger up the new seal attempting to pound it in, or worse still, score the seal surfaces of the shaft or cases, punch the inner seal or damage the bearing.  Lots of things could go wrong by doing it the wrong way.

My way might not be successful, but its nondestructive and at worse just won't help stop the leak.

James?
No one said it was easy,  least of all me. There are risks involved which have been highlighted and at least one other person has managed to do the job without a problem. Just because you dont agree with the method and are not confident enough to consider it yourself I dont think it fair to dismiss the suggestion. I personally wouldnt think twice about trying to change a seal in this way and neither would thousands of other competent Engineers and Mechanics, I have done it hundreds of times before although on industrial equipment not bikes, but there is no real difference in the application, all I see is a casing a shaft and a industry standard lip-seal. True to say that not everyone is capapable or confident enough to try it but the final decison rests with the individual who will base his judgement on certain criteria. I agree with you in that the job should be done correctly and with good engineering practise but sometimes the costs involved far outweigh the benefits.
Lets imagine you are quoted $600 by a mechanic to replace the seal but your bike is only worth $500 or the mechanic says its gonna cost $600 to remove, strip and rebuild the engine but there is a chance I can do it for $25. Which options would you take??

I am confident and competent enough not to consider doing it your way. I would pull the engine, split the cases, and replace the entire seal, myself.

The problem you don't see is that the person asking hasn't done something like this before and doesn't have the mechanical/engineering experiance to "fudge" it.  I think you are glossing over the dangers of it just because you "do it all the time".

Anyway, I'm not arguing that you *can't* replace the outer seal that way, just that he ought not to.
Just my opinion, which we are all entitled to. :mrgreen:

If you do it the correct way, this will give you the chance to check on the wear of the crank bearings, CB shaft bearings,Clutch plates, and shifter forks/gear dawgs.

James,
You have hit the nail on the head,

""the person asking hasn't done something like this before and doesn't have the mechanical/engineering experiance to "fudge" it.""

Yet you seem to assume he is able to strip the engine himself to replace the seal, or is in a position to pay someone else to do it. My view is if someone doesnt have the confidence or ability to replace the seal as described he certainly shouldnt attempt it by removal of the engine and splitting the cases which is expensive, time consuming and a by far riskier and more difficult procedure that in itself presents the possibilty of damaging many component parts.

How do you propose to get the new one in place properly and un-mangled so that it will form a proper seal (which is the point of the exercise)?

I would have guessed if you can strip and reasseamble a motorcycle engine yourself you would know how lip-seals are fitted.