Follow-up botheration

[mylovelyhorse]

Darn, as I believe our American cousins say.

My final drive has leaked again. Guess I had damaged the seal holding surface on the cover plate.

If I get another one, 2nd hand & complete with its shims, can I fit it in place of the original without re-measuring for shims?

My alternative thought was to smooth down the seal bearing surface, apply a little araldite to any depression and then once dry smooth that down. That's worked on forks (not BMW) before.

 

[Paul G (BHT)]

Darn, as I believe our American cousins say.

My final drive has leaked again. Guess I had damaged the seal holding surface on the cover plate.

If I get another one, 2nd hand & complete with its shims, can I fit it in place of the original without re-measuring for shims?

My alternative thought was to smooth down the seal bearing surface, apply a little araldite to any depression and then once dry smooth that down. That's worked on forks (not BMW) before.

Take the back wheel off, dry all the oil off with a cloth and then re top up the diff with more oil.

Then start the engine and put it in top gear, with the back of the crown wheel (the bit you bolt the wheel to) spinning round look to see where the oil is coming from, you may need to hold the throttle open for a SHORT while (2,000 RPM) to get the oil to start showing.

You may be lucky and it may be coming from the ABS sensor where it pokes through the diff.

There again you may be unlucky and it may be coming from the damaged oil seal housing

 

[mylovelyhorse]

You may be lucky and it may be coming from the ABS sensor where it pokes through the diff.

Unlikely, it's a non-ABS bike

There again you may be unlucky and it may be coming from the damaged oil seal housing

More likely, I believe.

 

[MattW]

The seal housing has quite a large surface area - I'd have thought you'd have to be pretty brutal to damage it enough to cause a leak?

Are you sure it's not the lip of the seal that's leaking (is there a wear groove on the bevel unit counterface)?

 

[ciderman gs]

take the wheel off and completly degrease/clean the seal area then using talc dust the area whilst it is spinning or take it for a run then dust it and the talc will show where the leak is then you will be able to figure out the repair route. on the replacement cover issue if the shims come with the cover then the correct preload should be ok because the shims are there to cover machining variations on the crown wheel and cover. to check the height of the crown wheel you need some vernier calipers and some way of preloading it then the bmw manual to show you the calculations you need to do and the place to measure, it sounds more complicated than it. is hope you fix it

 

[mylovelyhorse]

<sigh>

Well, I whipped the wheel off and this is how it looks:

Took off the cover:

This is the bearing:

And the housing:

The crown wheel - I'm a little concerned by the scoring close to the top:

The damage I did last time to the seal bearing face on the cover:

&

Looks like I've shagged it :-(

Installation of the 2nd hand cover & shims will follow later. This cover has a seal already in it but I think I'll replace with a new one (I have one already).

Any thoughts on recovering this situation (that don't include stating the bleedin' obvious about me shagging up the original cover) would be much appreciated.

Cheers

 

[Stewart H]

I would repair that ding either with epoxy or some good bearing mount paste, then clean up the area where the seal runs with scotchbrite or similar.

Stewart

 

[MattW]

While the damage you inflicted to the cover looks bad, I'd be surprised if this actually caused a leak - there's a lot of pressure between the installed seal and the housing and a large contact area - could be worth a smear of gasket goo before installing the seal (although if you've already got a second hand cover then it you might as well change it).

I'd be more concerned about the wear grooves on the crown wheel counterface (where the seal lip bears) - although it's hard to tell from the pics if there are actually grooves or it's just polished.

If the seal already installed in your replacement cover looks ok, I'd try it before possibly trashing another new seal on a damaged crown wheel.

And you've learned an important lesson about removing seals - stay away from housing and sealing faces - drill it (or carefully knock a spike through the seal) and screw a self tapper in.

Edit - Stewart beat me to it - wot he says

 

[mylovelyhorse]

While the damage you inflicted to the cover looks bad, I'd be surprised if this actually caused a leak
[..]
could be worth a smear of gasket goo before installing the seal

Heartening to hear. I shall certainly be trying the goo option

I'd be more concerned about the wear grooves on the crown wheel counterface

I think there's wear. I'm going to give it a good going over with Scotchbrite today.

Does the seal lip need to be above, in or below the groove that looks machined into the crown wheel?

If the seal already installed in your replacement cover looks ok, I'd try it before possibly trashing another new seal on a damaged crown wheel.

A good point.

Hopefully current crown wheel will be good with new cover & shims that came with it.

Thanks for the advice & comments. Let's hope it goes well today

 

[Stewart H]

The groove you describe is a line of wear, the new seal should go on a "new" bit either shallower or deeper

Stewart

 

[MattW]

Hopefully current crown wheel will be good with new cover & shims that came with it.

Thanks for the advice & comments. Let's hope it goes well today

You need to have a read about shimming the crown wheel before attacking your FD. The shims are used to take account of manufacturing tolerances in the crown wheel, cover plate and bearing (they also apply a small amount of preload to the taper roller bearing. If the shims are incorrect you could end up either loading the big bearing too much and causing premature failure or having it too slack (probably with the same consequences).

This is outside my experience (I've only ever replaced the seal) - hopefully someone who's done it will be able to offer some guidance.

 

[Ed209]

Looking at the first pic it look like the leak is from the actual knife edge of the seal and not the damaged outer edge. Did you oil the lip of the seal when you put it together? Its easy to forget and can rub the knife edge away if its dry. just a thought.

 

[mylovelyhorse]

I agree it looks a lot like the lip was leaking. I did oil the lip but I suspect the rust etc on the crown wheel tore it as it went back together.

I'm going to use original cover & new seal and put it back together today - the polished crown wheel has been in the freezer overnight & later on I'll be putting the new seal in the cover (with a touch of bearing fit goo on it, just in case) and then re-assembling.

Thanks to all for their advice and assistance

 

[mylovelyhorse]

I'm going to use original cover & new seal and put it back together today

Which I've now done. Wheel's back on and no leaks so far. Ride time is later this afternoon.

Here's hoping..!