BMW oil seals

Give me some ideas people. My trusty BMW R45, which I am trying to get up together to sell, developed an oil leak from the clutch housing a few weeks back. I finally got around to taking it apart this afternoon to remedy this.

My first thought was that it was the input shaft seal on the gearbox as earlier this year I had to rebuild the gearbox following a selector failure. I've removed the gearbox from the bike and now had the thought that it could potentially be the crankshaft output seal. In which case, bugger.

I had hoped that the oil stain inside the clutch housing would make it obvious but it hasn't as there is oil all over the bottom of the clutch housing, although thankfully none on the clutch itself. Oil levels in both gearbox and engine were respectable enough so that doesn't really help with saying where the oil has leaked from. Replacing the gearbox seal is easy enough and I have a new seal lurking in the garage, but of course if it is the crankshaft seal that has failed then I'm looking at a great deal more work to get at it. Even getting the clutch off to take a peek is a PITA.

So is there a shortcut I can use to diagnose which seal has gone? Or shall I play by the rules that whatever I touched last is most likely to be duff and replace the gearbox seal and see what happens?

Spray some brake cleaner behind the clutch to wash the back of the engine casing off, give it a good clean round the bottom of the casing

then fire the engine up and let it run for a while, if its the crank seal you'll see fresh oil dribbling down the back of the casing.

if you dislike your neighbours you'll run it with the silencers off.

crust

Gearbox oil has a very distinctive smell. That's how an oil leak from one of my previous BMs was diagnosed. Apparently it's almost always the gearbox seal - been doing it for eons without BMW being able to remedy it.

Good thinking Batman, I've stuck the engine back in but been scuppered by a bulb going in the garage as darkness fell. I'm also all but out of brake cleaner so I've given up for today. Cheers.

Originally Posted by littleredrooster

Gearbox oil has a very distinctive smell. That's how an oil leak from one of my previous BMs was diagnosed. Apparently it's almost always the gearbox seal - been doing it for eons without BMW being able to remedy it.

If only I wasn't a touch bunged up I might be able to tell. I'll try what crust suggested tomorrow, if anything to ease my mind. And it won't take too long either, so all being well I can get it back together and running again and then onto ebay.

The fact that the clutch is still dry means the leak is from the other side of the flywheel I'm afraid, the biggest single fault with the airheads, the rear crank oil seal.

You may need a spacer tool to press it to the right depth.

When you split at the bell housing, remove the engine mounts and pull it forward as far as you can. Then remove the swinging arm pivots and move that and the transmission as far back as reasonable, it should give enough room and cut overall labour time by about half.

Does anyone remember what was wrong with the bike in the end?

As its still in pieces and was thinking of getting it back together on behalf of his wife.