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 Can too much gearbox oil cause oil leaks?

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PostSubject: Can too much gearbox oil cause oil leaks?   Wed Sep 27, 2017 9:08 pm

I have a new small oil leak, which seems to be coming from a few places where the gearbox case meets the engine. I recently changed my gearbox oil, so I wonder if overfilling could cause this? I didn't think it was possible to overfill, because the manual says to fill to the bottom of the inspection plug, and you can't add more than that without it coming out when the plug is off. However, it did take more than 500 ml so maybe it's supposed to be a bit below the bottom of the plug hole?

So the questions:

1. Should I remove oil to make it 500ml total put in?
2. Any chance this is the cause of the leak?
3. If YES to #2, would removing oil fix the leak or could there be some damage to gaskets or seals at this point?

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Pete Roper
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Wed Sep 27, 2017 10:59 pm

Nope . In your case it is almost certainly the rear main flange gasket leak issue. 2009 is right in the zone. Sorry.
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Wed Sep 27, 2017 11:01 pm

Argh! Does that mean taking the engine out of the frame and taking off the gearbox? Yikes!
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Wed Sep 27, 2017 11:38 pm

Take a smell and you will immediately know whether it's gearbox or engine oil. Gearbox oil smells like cats pissed on the bike. In both cases the engine has to be taken out of the frame. Nice exercise which noone really needs.


Last edited by 2highlander on Fri Sep 29, 2017 6:03 am; edited 1 time in total
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Thu Sep 28, 2017 2:50 am

Yup, any which way it's an engine out job. Thing is this doesn't take a month.

In the next week or two we're going to be puting the 1400 motor into Mark's bike. Sure there will be a couple of extra hours sourcing and fixing the leak on your bike and maybe a wait for parts but Michael and I would hang our heads in shame if it took us more than 2 days to complete an engine in/out and tune-up afterwards and as we were in there the swingarm and linkages would be re-greased just because.

GRiSO's are a joy to work on! Anyone who suggests that there is some sort of barmy 'Voodoo' involved needs their head felt!

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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Thu Sep 28, 2017 9:52 am

Pete Roper wrote:

GRiSO's are a joy to work on! Anyone who suggests that there is some sort of barmy 'Voodoo' involved needs their head felt!

I may be in need of a good head-feeling at this point. Just when I think it's all perfect, this bike hits me with something else. It's Voodoo, I tell you!

At least I can get the frame powder-coated black once it's all apart Smile

Can you point me to a how-to on how to fix that leak once and for all?
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Thu Sep 28, 2017 9:56 am

I found this thread, sounds like the right thing:

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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Thu Sep 28, 2017 10:06 am

Yup, I knew I'd covered it somewhere recently.

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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Thu Sep 28, 2017 11:19 am

I wish I lived in Australia right now so I could get you to service it for me, Pete. I don't trust any of the mechanics around here, so even though I barely know what I'm doing and have a good chance at messing something up, I'd rather know what's been done to it than let someone else hack it to bits.

So I'll probably live with the leak until I get the nerve to take the damn thing apart.
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Thu Sep 28, 2017 12:14 pm

First thing is to establish it is gear or engine oil as previously suggested. If it turns out to be gear oil there is a very slim possibility that it may of just leaked some up the clutch pushrod past the cone seals but in all honesty I think it very highly unlikely.

The other possibilities are, if it's gear oil, a damaged input shaft seal on the gearbox, (Also unlikely and as the gearbox isn't pressurised even if they do weep it is usually so minor that it will rarely drip.) or that it's engine oil.

If it's engine oil then the most likely cause on a 2009 is, as mentioned in the other thread, the flange, (Don't attempt removal without the proper puller!) but there is also the cap that carries the rear bearing that supports the timing idler shaft and the LH cylinder cam chain tensioner mounting bolt plug both of which are sealed with o-rings which of course have the potential to leak although I've never seen one do so!

As with all situations like this my tendency is, if I'm in that far, I'll check everything and replace anything that looks remotely dodgy! For the simple reason you don't want to be going in again any time soon. It's very easy to make false economies with something like this. Leaving it will also risk contaminating the clutch which would be another boring expense so I wouldn't leave it too long.

The only good news about things like this is that as you go about fixing the principle issue you also get to do all those shitty little maintenance tasks you've been puting off like greasing the swingarm and linkage bearings and bleeding the clutch properly! The latter is well worth doing as my recently done GRiSO attests! I'd been slack and hadn't changed it for a year. Michael did it for me while swapping out my forks and steering head bearings and it's reduced the pull considerably. For some reason our CARC bikes are absolute bloody murder on clutch fluid. I copped an ear bashing of Mike about my slackness! Very Happy

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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Fri Sep 29, 2017 12:11 am

It might not be the rear main seal flange gasket! There is only a very slight hint of oil in some places where gearbox meet clutch housing, but that doesn't seem to have gone anywhere. I inspected more carefully and it looks like it's coming from the top of the flange above the sump, where it joins the bottom of the crankcase.

When I removed the sump I changed the sump gasket, and that seems to be ok. But I didn't remove the flange above the sump so I didn't change that gasket. Might it be required due to removing the sump and relieving most of the pressure on that gasket from those 18 bolts?

It's tempting to try tightening the bolts but I'm pretty sure I shouldn't go beyond the prescribed torque value.
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sat Sep 30, 2017 3:41 pm

Well, two things have come to light:
1) it can be very difficult to find out where an oil leak is originating from
2) denial is not just a river in Egypt.

I think I might be seeing what I am hoping to see. It’s possible the leak is coming from above and running along the groove where the upper sump flange meets the crankcase. So it might really be the rear main seal flange after all. Crying or Very sad

Any ideas for a low-cost flange pulling tool?
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sat Sep 30, 2017 3:47 pm

The factory tool is easy to replicate.
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 12:17 pm

Well lookee here... I was surprised to see this after a ride. I drained some engine oil since it was near the upper line, to see if that made a difference. I took it for a ride and came back to see this surprising leak from the crankshaft inspection plug. Maybe it is the gear oil after all?

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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 12:48 pm

Nah, that’s flywheel/ring gear inspection port. Could still be rear main.


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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 12:52 pm

Oh, right! Damn, that means the leak is getting worse, and possibly messing up the clutch!
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 12:58 pm

Yup, there's no way it's going to cure itself. You've gotta go in.

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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 1:02 pm

OK, I’m ready to take out the engine and take a look at the rear main seal/flange area. If that’s the leak, I’ll do the flange repair. I’m fairly confident about the gasket replacement with three bond, and using shorter bolts, but I’m still not clear what to do about small oil pipe that can leak. I’ve read different things about what to do there. I wonder if there is a document from Moto Guzzi detailing this service bulletin repair?
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 1:03 pm

I took a couple of pics on Friday. I'll post 'em up a bit later.

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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 1:08 pm

Awesome, thanks Pete!
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 1:57 pm

Rear flange with oil dowel and o-ring.

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Close up of the dowel and o-ring. Some people use an o-ring with a slightly larger cross section to assist with sealing.

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And a side elevation. This is the dowel that on some early models protrudes too far so it sits on the register in the crankcase preventing the o-ring from crushing down.

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Just filing it down by a mm or so will prevent it from bottoming on the register. Using the shorter bolts in the bottom two flange holes also ensures they clamp tightly. The leakers didn't have enough depth in the holes in the case for the 25mm bolts!

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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 2:28 pm

That is extremely helpful, thanks so much Pete! I always like to know what to expect before I start the job, now I think I have a good understanding. I hope this goes as successfully as the rollerization upgrade did.
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 3:10 pm

Do be very careful removing the flange. If you crack it its very likely you'll need to strip the motor to get it out.

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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 3:34 pm

Don't forget to share !Got Pics?

We all like a good re-build thread ! cheers
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PostSubject: Re: Can too much gearbox oil cause oil leaks?   Sun Oct 08, 2017 4:01 pm

For sure! I’ll start a new thread and document the whole thing from the beginning. This will be one of those “If I can do this, anyone can” type of projects, because the rollerizing job was already pushing the limits of my mechanical competence. So taking out the engine and stripping the frame is the most ambitious thing I’ve ever done. Can’t wait!
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