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. :dry:

 

[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 :whistle: ...

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" :angry: . 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.

 

[Holt]

A little late, as I can see, but for future exercises; I think it would be easier to demount the motor and entire drive line including the back wheel, as one unit.

 

[sign216]

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

That's what I have found too; take the throttle bodies off as a unit.

I agree RossW, that the airbox rubbers are hard to take off. I had to be more forceful with them than I liked.
Joe

 

[rossw]

A little late, as I can see, but for future exercises; I think it would be easier to demount the motor and entire drive line including the back wheel, as one unit.

I hear what you're saying. Undo the electrics, hoses and the top gearbox mounts and just lift off the whole top half of the bike.

A variation on the "crabbing" technique? I looked at that until I realised that a) once the bottom frame rails are gone there's nothing to crab against. and b) either way those throttle bodies have to come off, and thus far, it's proving to be the most difficult part.

I'll take your advice John and Sign216 and leave them assembled. I'm just having trouble getting the airbox rubbers off. There must be something I'm missing.

Perhaps Sign216, it's just a matter of more brute force then. I'll have another go tonight.

For those interested, the gearbox oil when I drained it was black with a metallic sheen, but no chunks sticking to the magnet.

Edit: The metallic sludge is most probably the moly additive I put in it to try and shut it up. It's the same stuff that goes in the rear drive. I just put the excess in the gearbox at the time of teh last oil change hoping it would help.

 

[sign216]

Ross,

Taking the TBs off as a single unit is definitely the right way. I started to separate them, and it was wrong.

The rubber boots were a bear. I heated them with a hair dryer, and sprayed lube, but in the end it was brute force with screwdrivers and other tools. I forced the boots open and around. I did "feed" a little of the boots into the airbox to give me room to work with, but it was really just manhandling the boots that got them off and on.

It was really rough on the boots but they could take it in the end. After I did it the first time, it became much easier, as I got a feel for "what to do" and "where to do it."

You think you are tearing things apart, but they can take it, and it's how to get the rubbers off/on.

Joe

 

[rossw]

Success!

Managed to push the rubbers into the airbox after a bit of a struggle. Once that was done the throttle bodies came out and I was able to access the "screw of death".

Now my gearbox is sitting on the floor. I'm away on business for the rest of the week, but Saturday is looking more promising than it was.

 

[gstallons]

those throttle bodies are bolted together for a VERY good reason... You don't need to find out why ?

 

[rossw]

those throttle bodies are bolted together for a VERY good reason... You don't need to find out why ?

It was no problem leaving them bolted together in the end. I guess that's why they use torx screws there.

 

[rossw]

OK, Now that the gearbox is off, I've removed the flywheel to clean off the contamination and replace the clutch plate. The clutch plate has plenty of meat on it, but I'm wasn't going to take the risk that it might be contaminated and bought a new one. I probably didn't need to, but I don't want to do this again for a while.

The friction surface of the flywheel and backing plate have wear that I've never seen before. It looks as though it's been getting hot from excessive slipping/riding. The pressure plate is similar.


There has been no sign (as far as I could tell) of roughness, sticking, slipping or any other clutch misbehaviour. The surface is smooth to the touch but the machining marks are worn down unevenly. It doesn't look right and I'd rather give it the bucket test than have to do all of this again.

What does everyone think?

 

[john zibell]

That is caused by the oil contamination. Just go over the surfaces with coarse sandpaper to score the surface and get to clean metal. It will be OK to use.

 

[rossw]

That is caused by the oil contamination. Just go over the surfaces with coarse sandpaper to score the surface and get to clean metal. It will be OK to use.

Thanks John, I'll do just that. Coarse sandpaper I can do.