Breva 750 leaking rear main bearing

[rossw]

It seems my B750 has developed a case of incontinence. The leak is coming from the clutch housing. Since the clutch housing isn't supposed to have oil in it, I have to assume that the leak is from either the gearbox front seal or the engine rear main bearing seal.

Either way, I see a gearbox removal and clutch replacement (might as well, while I'm in there) in my very near future.

Does anyone have the dimensions necessary to make a clutch centering tool? I have a lathe to make it on. If I need to remove the flywheel I guess I'll also need to make a locking tool for that. Tooth spacing?

Are there any parts that should also be replaced while I'm at it?

[Charlie J]

The clutch can be centred without a tool,eye and measuring will do it. As for the flywheel holder, pm me I could lend you the one I made if you want. I could also lend you my tools for undoing the clutch hub nut.

[rossw]

I'm still debating about whether to disassemble and rebuild the gearbox or not. It does have a bit of noise in first and fifth, but I'm hoping not to have to rebuild it this time around.

On the other hand, If I do it now, I won't have to disassemble the whole thing again when it really needs doing.

[Holt]

I'm still debating about whether to disassemble and rebuild the gearbox or not. It does have a bit of noise in first and fifth, but I'm hoping not to have to rebuild it this time around.

On the other hand, If I do it now, I won't have to disassemble the whole thing again when it really needs doing.

What do you mean by "a bit of noise" ?

I have at a very few occasions driven my Breva without wearing ear-plugs, and THATS a scaring experience. Considering the general flawlessness, I won't do it again. The not-wearing-ear-plugs, that is.

[rossw]

5th and first are obviously whining. Other gears whine a bit but not as much. First has been whining (more than other gears) for ages. 5th has begun to be noticeably louder than 4th only recently.

Now that I have established (probably) that the leak is coming from the gearbox, I'm thinking the noise should reduce again when I top it up.

When I remove the gearbox to fix the leak, how I proceed from there is going to depend a lot on what I find in the fluid that drains out. Last time there was very little in the way of wear metal, so I'm hoping I can get away without the rebuild if it's still reasonably clear this time.

[sign216]

If there's a lot of metal on the magnetic drain plug, can you post a pic? I'm all about the visual.

[NOLAGuzzi]

The clutch can be centred without a tool,eye and measuring will do it.

+1

I just left one mounting bolt to use as a shelf then put a large flat head screw driver in the ring gear to hold it steady while loosening the nuts.

Does your leak smell like gear oil or engine oil?

[rossw]

The clutch can be centred without a tool,eye and measuring will do it.

+1

I just left one mounting bolt to use as a shelf then put a large flat head screw driver in the ring gear to hold it steady while loosening the nuts.

Does your leak smell like gear oil or engine oil?

I've had a sniff It's more like gear oil, which would explain why 5th is noisier. I guess I should top it up then ...

I've stopped riding the bike regularly for now until I can get hold of a seal and a clutch plate (on order with Stein Dinze, but they appear to be out of stock). When I drain the gearbox I'll get a picture of the drain plug contents.

[rossw]

Well after a lot of stuffing around, I finally got dismantling to fix my gearbox leak.
Now I have arrived at the dreaded "Screw of doom" . It's true. There is no way to get a socket on this without removing the throttle bodies.

So off they come. Pity the torx bit required to separate them is the only size I don't have. Off to Jaycar then...

I haven't done a writeup of the process because there is already good information out there. Some observations though:

The lower frame rails have to come off. There is nothing holding up the engine without these. I found it is necessary to support the engine underneath AND the frame at the back.

Getting the fuel injectors out was easier than I expected. Getting the airbox rubbers off perhaps not so much.

When I put it all back together I'll be making sure the clamp screw for the rear drive boot is positioned where I can get at it with a screwdriver, not like before.

All the effort needed makes me glad I bought a new clutch plate. Hopefully it will be a LONG time before I need to do this again.

Special thanks to Charlie J. and Mario from Thunderbikes in WA.

[john zibell]

Don't separate the throttle bodies. Bring them off as a unit. It is easy to do. It is more trouble to separate them, putting it back together in the bike would be difficult.