How Did Gearbox Oil Get Into the Fuel System?

Hello fellow riders,

I need some serious help. My beloved GRiSO has a real problem. In a previous post I shared a picture of what looked like fuel storage stabilizer overflowing through the fuel cap making a huge mess. Turns out it was actually gearbox oil. The bike suddenly wouldn't shift as I tested for a solution to the issue. In checking the gearbox oil level a ton of fuel/oil came out. So how in the world does gearbox oil get into the fuel system and come spewing out of the fuel cap? Last year a MG dealer re-threaded the gearbox drain plug. Could they have somehow drilled too far causing this? Here are pictures to show this mess. It's not letting me upload the last one where it shows a big puddle of the same mixture as what's coming out on top. 2 questions:

1. What could have caused this?
2. Say it was caused by the drilling and I then rode 4,000 km like that. It seemed to run fine. Could there be long term damage done?

I appreciate any advice thank you!

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Bizarre!

The only thing I can imagine is that somebody has connected the gearbox breather pipe which usually just goes up and loops up under the tank venting to atmosphere to the fuel tank breather and heat cycling has drawn fuel into the gearbox somehow.

Now I'm not really familiar with the US tank venting system with the carbon canister so I don't know where the various vent tubes run normally but my guess would be that the gearbox vent tube has been connected into the system in such a way that fuel got drawn into the gearbox when the bike was parked and cooled filling it completely and then when it heats up and expands it pushed the diluted oil out, back through the breather system and into the tank! How anybody could do that is quite frankly beyond me but my suggestion would be remove the tank, identify the gearbox breather and make sure it's venting to atmosphere and then re plumb the charcoal canister and vent valve correctly or delete the system and run both the fuel vent and cap drain down under the bike to atmosphere and cap the suction ports on the inlet manifolds.

That is some next level shaved ape rape. I hope there isn’t any permanent damage.

I reckon Pete has it dead right..... water from the tank filler area has flowed down the overflow into the gearbox breather.

As water is heavier than oil it has sunk to the bottom of the gearbox displacing the lighter oil upwards.

I expect that the hot engine expanded the water in the gearbox forcing the gearbox oil up out of the overflow.

Great Zot! The level of dumbfuckery of whomever did this is astounding!


After you've removed the tank to identify the gearbox breather, I would be deleting the canister system as Pete suggests. It's a potential source of air leaks.

I presume you'll be flushing the tank?

Yeah, tank off, drain, I'd remove the pump as well and swap the fuel filter and check the pressure relief valve. Then delete the canister, block off the suction ports and consign the whole system to the dustbin.

The two nipples on the back of the tank are the filler water drain and the tank vent. On 'Rest of world' models these simply have short rubber hoses that go to a 'T' piece and the other hose from there simply goes down under the bike and slots into the little wire 'Hose Holder' just inboard of the RH footrest hanger plate.

The gearbox vent tube can be seen coming off a nipple on top of the gearbox casing if you look through the bike just behind the throttle bodies. Follow it up and it should just loop over the top of the throttle bodies and poke downward on the LH side of the bike. Make sure it can't interfere with the throttle cam or cables on the top of the RH throttle body.

I'll nip up to the workshop a bit later and get some pics of some of this stuff off the black shitheap.

Was just over at Michael's shop while he was tuning Bart's new V11

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Very nice, apart from the pipe wrap and stupid airbox intake extensions.

And grabbed a shot of a gearbox with the breather still attached.

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I'll bet if you take your battery and it's rubber tray out and follow that hose up from the box you'll find it's been plugged into the evaporative canister system by some Rhodes Schollar.

You all rock! Thank you for the help, instructions and pictures! I love this bike and have taken good care of it and hate to see this happen. I worked on sportbikes following Haynes and service manuals but those had lots of YouTube videos or posts to reference for help. With the Guzzi this is the first time I'll be really working on it. So I appreciate all the pointers. I'm taking notes, reading up on the service manual and I'll likely ask some questions as I go along. So I appreciate this! Going at it tomorrow, good night from Canada!

PS I'll take it that the heli-coil job on the gearbox drain plug last year is a non-factor. Couldn't have led to this.

Wow!!! Completely stuck for words over here

Looks like someone figured "gee, that must connect... somewhere" with the gearbox vent, and had at it. Fortunately an easy fix, and the bike will run better with the evap system removed and things plumbed like the non-US/Canada machines (as a bonus, the nice little fittings we get on the throttle bodies make it easy for balancing them).

I believe Pete has mentioned that the gearbox bearings are sealed, with any luck you may be OK there.

Your bike is rollerised isn't it?

It's a 2012 but the serial number shows it having flat tappets. I don't recall if it was converted, probably not. I'll look into this and ask a previous owner. I wasn't up to speed on this problem. It has gotten somewhat noisier but I figured it's an Italian thing. It has 34,000 km. The last to work on it was this dealer early last season to fix that stripped gearbox plug and they adjusted the valves. I take it the tank would likely not have been taken off, means if the drain lines were misconnected it would have been done years earlier but that gearbox was fine before. Just trying to figure out when this could have happened. Gonna look more into it this weekend. Thanks for the help!

If it isn't rollerised it has to be, and the sooner the better. 34,000KM is really stretching the friendship with a set of flatties and the longer it is left the greater the risk of terminal damage. Pulling the left hand cambox takes fifteen minutes, you don't even have to take the tank off. It would be a real shame to see a Tenni lost due to delay. The fact it was getting noisier means the tappets are done. Re-setting the valve lash is not a fix, not even a temporary one.

Checking if it is rollerised is critical & easy. just pop the wings off, undo the plug covers, lever the plug caps up and take off the rocker covers. This string has pictures to help you see the difference [You must be registered and logged in to see this link.]

Plus don't forget getting all H2O out of the gearbox before the sliding and rolling surfaces corrode. I would do at least 2 gearbox oil changes - running it to get it hot first.

Damn what a nightmare Good luck with your GRiSO, hope it will be fine soon and no real damage has been done.

(and ps. make sure after you sort out this issue, you do the rollerisation. I was skeptical, had it done anyway, and I was only just in time at 20.000km. You don't want to know how the tappets of my bike looked )

I've gotten to the fuel quick release to take the tank off. Got the rear of it raised a bit. Watched some YouTube videos, read some posts.. Standing to the left of the bike I'm using one hand to reach it and wiggle it a bit while pulling. No luck so far. Is it just a question of wiggling it carefully? The quick release mechanism doesn't have to be pulled in before pulling on the whole thing? I've broken things in the past so being extra careful. Would appreciate any tips to help get this thing off. BTW the drain on the right side of the tank was not connected. Haven't followed the left one yet where it leads. Can't wait to see underneath. Thanks!

Got it woohoo!!! Never been so happy to take something off that looked easy to break. Just by wiggling carefully and pulling.

Glad it came off so easily - on mine it is easier to take of the injectors and thread them out still attached to the tank

You nailed it! The vent line that was connected to the rear left side of the fuel tank was indeed connected to the gearbox. Unbelievable! It's all thanks to this community I've been able to find the cause of this mess. And I learned about rollerisation. It's now a priority and I'm on it. Looks like it wasn't done but I'll check to make sure in the coming days. Thank you all! May still have some questions but for now it's good progress.

I strongly recommend you don't start the bike again until you know for certain if it has been rollerised. If it hasn't? Don't start it again until it has been. Yes, it really is that important.

If your bike is a 2011 it will require an 'A' kit most likely but if you take a photo of the inside of the rocker cover when you are checking the tappets I can tell you for certain.

When removing the rocker cover to check you will need to remove the spark plug cap and HT lead. DO NOT try and pull them off from the top, you will damage them. Use a long, thin screwdriver inserted through the cooling tunnel in the head just above the exhaust manifold to lever the caps off the plugs from below.

Checking which type of tappets the bike has takes ten minutes. It's ten minutes that may save your engine.

To underscore the urgency of the tappet problem, here are pics of what mine looked like at only 6k miles. The worn centers are evidence of the failed “diamond like coating”. Small bits of that coating and the underlying metal have been circulating in your engine. It’s as bad as it sounds. Switch to rollers now and you have a fantastic and very durable engine. Leave it much longer and the engine will be ruined.

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Before removing the fuel connector:
- disconnect the electrical leads to the tank;
- crank over a few times, won't start but the pressure will be minimised, therefore it won't;

then remove the quick connect fitting - easy peasy

Here it is. Those are flat aren't they? I don't know what to look for yet, can you tell from these pictures their conditions and possible damage up to now? Let me know if you want another angle or different lighting. The bike won't be restarted until the conversion is done. I just hope it's not too late.

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Regrettably your bike still has the original flat followers.

Had it serviced through 3 established MG dealers and this issue had never been brought up. I also didn't take the time to learn about it although who the heck considers engine problems in the first thousand KMs. 34,000 is nothing. Sick to my stomach right now. I want to find out what the possible damage is. Never worked in an engine before, I have the service manual. Will wait to hear for advice on where to go from here. Tappets aside there's a lot of work to be done to clean up the original issue. Want to asses if it's likely to be ok in the long run before I proceed. Thanks everyone!

While waiting for advice based on the above my brain is in top gear. I got this crazy idea as a backup. The logical thing to do here I take it is to assess any possible damage and hopefully it should be ok in the long run and I can do the conversion. But if that isn't clear or it's too late. What if I kept it as it is and be a GRiSO lab rat to see how long I can get out of it. If the engine ever goes kapput I could buy say a 2016 for about double the cost of the tappet conversion. Throw the tank and fairings on the newer bike and voila, my Tenni lives on. I have a propensity for crazy ideas so feel free to tell me that's stupid. That backup idea would only make sense if there isn't a safety risk to proceed such as engine seizure.