V50/V35 Gear box seeps oil through top vent

[Skivo]

My V50ii (1980) is seeping oil during rides via the oil pressure relief valve. Curious about troubleshooting ideas. From what I have gathered, on these vintage machines the oil pressure relief system is a small spring-loaded device on top of the case, near where the engine case meets the transmission case. This is my first foray into Moto Guzzi.

This bike has been on the road only for a month or so now and I noticed oil is collecting on the top of the case after each ride. My thought is maybe the screen/oil strainer is partially clogged, causing an excess of pressure to build up? I have not dropped the pan. Hoping for some good troubleshooting ideas before I dig into that.



A bit of background on this machine...
The odometer is at 34,000 miles. Compression was in the 150-160 psi range back when I first began investigating this machine. I haven't checked it again since I got it running. Evidence of oil fouling on the plugs. With any luck, if I can restore the oil pressure to normal the oil fouling will be alleviated somewhat (is that too much wishful thinking?). It doesn't smoke and has decent compression but, like I said, the plugs do get oil fouled rather quickly. Makes me think the valve guides are leaking. It's probably time for a top-end rebuild, but I don't have the space for that or the time. For now I'm content to ride it around the neighborhood and clean the spark plugs every 50 miles ;-), if only I could get it to stop seeping oil... The machine is stock.

(I searched all the vintage small block threads before posting here; forgive me if I overlooked a better thread to attach this to.)

 

[Kevin.NZ]

Are you sure the plugs are oil fouled and not too rich a mixture, have you got the correct heat range plugs installed. When an oil pressure relief valve operates it doesn't dump oil externally and I'm sure high oil pressure wont cause the plugs to become fouled. An "O" ring in the relief may have perished. Are you able to measure the oil pressure by removing the relief valve an attaching an oil pressure gauge. Having to clean the plugs every 50 miles!! I'm sure you'd notice some "smoke" out the exhausts. Worn valve guides are evident on overrun, like going down a hill with the throttle shut, the engine vacuum will draw oil down the guides and when you open up the throttle you get a big puff of blue smoke out the back.

 

[Skivo]

Are you sure the plugs are oil fouled and not too rich a mixture, have you got the correct heat range plugs installed. When an oil pressure relief valve operates it doesn't dump oil externally and I'm sure high oil pressure wont cause the plugs to become fouled. An "O" ring in the relief may have perished. Are you able to measure the oil pressure by removing the relief valve an attaching an oil pressure gauge. Having to clean the plugs every 50 miles!! I'm sure you'd notice some "smoke" out the exhausts. Worn valve guides are evident on overrun, like going down a hill with the throttle shut, the engine vacuum will draw oil down the guides and when you open up the throttle you get a big puff of blue smoke out the back.

Thank you for your insight Kevin. The parts diagram for the oil pressure relief valve doesn't indicate any o-rings.



As far as running rich: The plugs are gummy, not sooty, and they smell like oil. I've tried various plugs from heat ranges between 6 - 8. I'm using the NGK B8ES now. None of the plugs in the manual are produced any longer and this is what Harper's suggests. The cross references I researched also led me to B8ES. I've also tried various octanes. Right now I'm running about 95 octane based on the average method used here in the States.

The Dellorto carb rebuild kits I got from Harpers, weren't as dialed in as I had hoped. I had to supplement with another set of o-rings when one set didn't fit right. Conceivably this could cause a rich situation. But the gummy/tacky condition of the plugs indicates oil fouled, wouldn't you say? Running rich results in a sooty carbon build-up, which seems different than what I'm experiencing.

 

[Kevin.NZ]

With the seep from the oil pressure valve, is the washer 23 in good condition, with regards to the oil fouling on the plugs, there are oil control rings on the pistons, but with such low miles and the problem happening in both cylinders i cant imagine they have both failed together. To confirm high oil pressure, put a gauge in there. What viscosity oil are you running, it might be "to thin" for your era of bike. You may need to up it to 20/50 or there abouts.

 

[john zibell]

Skivo, What you are calling an oil pressure valve isn't. It is simply a vent that is also the plunger assembly for the gearbox selector drum. I've seen these push oil on these and the big block 5 speeds when non synthetic oil is used and it blocks the spring causing pressure to build and not let air vent out or in. They may also push some oil when over filled. If you can get to it, clean the oil off the spring and put in the correct amount of synthetic gear oil. It won't block air passage through the spring to the vent. In fact, of some of the 5 speeds a line is attached that goes up through the frame so that if oil does climb through, it goes up the line and returns to the gearbox when it cools.

 

[Kevin.NZ]

Thanks for clearing that up John, he would have read zero engine oil pressure and the gearbox wouldn't work.

 

[Skivo]

Thank you for your insight Kevin. I didn't notice an o-ring in the parts diagram for the oil pressure relief valve. I will take a look at that.

As far as running rich: The plugs are gummy, not sooty, and they smell like oil. I've tried various plugs from heat ranges between 6 - 8. I'm using the NGK B8ES now. None of the plugs in the manual are produced any longer and this is what Harper's suggests. The cross references I researched also led me to B8ES. I've also tried various octanes. Right now I'm running about 95 octane based on the average method used here in the States.

The Dellorto carb rebuild kits I got from Harpers, weren't as dialed in as I had hoped. I had to supplement with another set of o-rings when one set didn't fit right. Conceivably this could cause a rich situation. But the gummy/tacky condition of the plugs indicates oil fouled, wouldn't you say? Running rich results in a sooty carbon build-up, which seems different than what I'm experiencing.

With the seep from the oil pressure valve, is the washer 23 in good condition, with regards to the oil fouling on the plugs, there are oil control rings on the pistons, but with such low miles and the problem happening in both cylinders i cant imagine they have both failed together. To confirm high oil pressure, put a gauge in there. What viscosity oil are you running, it might be "to thin" for your era of bike. You may need to up it to 20/50 or there abouts.

Skivo, What you are calling an oil pressure valve isn't. It is simply a vent that is also the plunger assembly for the gearbox selector drum. I've seen these push oil on these and the big block 5 speeds when non synthetic oil is used and it blocks the spring causing pressure to build and not let air vent out or in. They may also push some oil when over filled. If you can get to it, clean the oil off the spring and put in the correct amount of synthetic gear oil. It won't block air passage through the spring to the vent. In fact, of some of the 5 speeds a line is attached that goes up through the frame so that if oil does climb through, it goes up the line and returns to the gearbox when it cools.

Thank you for that explanation John. I can confirm it is not a 1-way valve and is, in fact, just an open "vent/port". I think this also confirms that I've been burning engine oil (as opposed to it leaking out the top of the case). I recently added about 1/3 of a quart after ~300 miles.

I'm using an 80-90 weight gear oil. It is not synthetic. The shop manual calls for 90wt. In 1980 would a synthetic have been specified? It is possible I had slightly overfilled, but given the side location of the filler plug it's not really possible to add much excess "overfill" in the gear case--it would just run out the side.

I cleaned the spring/pin/vent prior to my last ride. I did leak oil again. I was not able to inspect the hole without first removing the carb/airbox...

I will confirm the proper fill level, or underfill now, as it were, and consider switching to a synthetic. I had wondered about extending the vent up past the airbox. Thank you for your great insight! I learn something new every day

UPDATE: The gear box level was slightly below the fill level. So the gear box continues to "vent" oil despite a slightly underfilled condition.

 

[john zibell]

Your gearbox calls for one liter of oil. The manuals says 140, but I believe that to be a misprint as the rear drive does need 140 weight oil So, just put in 1 quart (946cc) of 75W90 full synthetic gear oil in the gearbox, and 160cc of 85W140 synthetic in the rear drive. Also these engines will seek their own oil level. So long as you are between full and add you are OK. Don't keep topping up as she will just blow out the excess.

 

[Skivo]

So the bottom line is probably that I put too much gear oil in the gear box. User error strikes again. Here I was treating it like a Chevy differential... Thank you for the guidance all! (My shop manual does say 90wt)

 

[john zibell]

So the bottom line is probably that I put too much gear oil in the gear box. User error strikes again. Here I was treating it like a Chevy differential... Thank you for the guidance all! (My shop manual does say 90wt)

Yes, Guzzi manuals are very inconsistent. I was looking at a British owner's manual for the oil weights. Their technical writers are very lazy and copy material a great deal even if it is incorrect.

 

[Kevin.NZ]

So whats causing the plugs to foul up?

 

[Skivo]

So whats causing the plugs to foul up?

I'm perplexed. Like I said, it doesn't smoke but the plugs are oil fouled and it is using oil. I suppose it would be good to do another compression test now that I've got it running and I can test it with a warm engine and circulated oil. Some oil is being lost through various case joints/seams, but that doesn't explain the oil fouled plugs. One cylinder does seem to be worse than the other. Aside from a rebuild, any ideas for testing and troubleshooting are welcomed.

If, like you say, I would notice worn valve guides in a puff of smoke from the tailpipes after going downhill at idle, then that's likely not my problem. With my generally leaky case, is it possible failing head gaskets are allowing oil to enter the combustion chamber? Does the piston stroke go down that far?

 

[john zibell]

is it possible failing head gaskets are allowing oil to enter the combustion chamber? Does the piston stroke go down that far?

I hope the piston stays below the head gasket. If it didn't you would have a real problem. A leak down test will tell you if you have a ring or valve issue.

 

[Skivo]

I hope the piston stays below the head gasket. If it didn't you would have a real problem. A leak down test will tell you if you have a ring or valve issue.

So if the leak down test doesn't turn up any issues, it's plausible I have a head or cylinder gasket issue. How difficult will it be to obtain new valve guides for this bike which is 40 years old?

 

[Kevin.NZ]

A failing head gasket "could " let oil into the combustion chamber, but both failing seems a bit of a long shot. What do you mean" does the piston stroke go down that far", I'm a bit confused. As I said it could be the old/wrong viscosity engine oil or worn oil control rings. Are you sure the mileage is correct at 34,000mls and not 134 or even 234,000mls. As John says , a leak down test will eliminate some problems.

 

[Skivo]

A failing head gasket "could " let oil into the combustion chamber, but both failing seems a bit of a long shot. What do you mean" does the piston stroke go down that far", I'm a bit confused. As I said it could be the old/wrong viscosity engine oil or worn oil control rings. Are you sure the mileage is correct at 34,000mls and not 134 or even 234,000mls. As John says , a leak down test will eliminate some problems.

I don't know for sure that the odo isn't 134,000 versus 34,000. It could have turned over, but this isn't really a highway machine and it previously sat for 10-15 years up until recently. It was dirty but pretty straight overall. I'm fairly certain it's just 34k.

Given the generally leaky condition of my case I leaning toward oil intrusion via the head gasket. The cylinder gasket also leaks but that wouldn't allow for intrusion into the combustion chamber. I'll see if my local shop will perform a leak down test for me to eliminate those other possibilities before I remove the heads. I'll circle back here after I know more. Thanks for the advice guys!

 

[john zibell]

So if the leak down test doesn't turn up any issues, it's plausible I have a head or cylinder gasket issue. How difficult will it be to obtain new valve guides for this bike which is 40 years old?

If the guides are worn, find a shop that inserts K-lines. http://www.sbintl.com/

 

[john zibell]

I don't know for sure that the odo isn't 134,000 versus 34,000. It could have turned over, but this isn't really a highway machine and it previously sat for 10-15 years up until recently. It was dirty but pretty straight overall. I'm fairly certain it's just 34k.

Given the generally leaky condition of my case I leaning toward oil intrusion via the head gasket. The cylinder gasket also leaks but that wouldn't allow for intrusion into the combustion chamber. I'll see if my local shop will perform a leak down test for me to eliminate those other possibilities before I remove the heads. I'll circle back here after I know more. Thanks for the advice guys!

If the head gasket has any kind of leak, you will lose compression. Also with the copper ring at the cylinder I doubt the head gasket is your issue.

 

[Skivo]

Compression was 158psi in the right cylinder and 151psi in the left when I initially tested back in 2019. In my notes from the test I wrote that the plug I first pulled from the right cylinder (the one with higher compression) had more oil fouling. The right side is still worse than left for oil fouling today, but both show signs of abnormal combustion. Have not retested compression since I got her running. The guy I bought the bike from had virtually no mechanical knowledge whatsoever, so who knows if he swapped the plugs at some point back when. He had the bike for 8 years and never got very far with it. Thankfully he didn't disassemble it

The cylinders got seriously flooded a few times before I rebuilt the carbs. It was so bad I had to change the oil after. How likely is it that this is just residual carbon burning off? It does seem to be less and less as I put more miles on her.

Another thought...I'm running ~ 95 octane (r+m)/2. Could that too high? Using 93 pump gas I've been adding Lucas octane booster which adds about 2 more octane. I talked with a guy who said his similar model always ran well with supreme straight from the pump; my shop manual says 100 octane (research octane), which translates to 93-95 octane (r+m)/2 by my estimate. Thoughts on octane for these older models?

 

[Skivo]

1. Synth oil for gearbox is an asking for a trouble - bearings won't survive much longer after such swap. I got such leak, but I never decided to find a reason. Yet... Had "good" oil in gearbox years ago and will not make this mistake again. Although - this has happened in V65 where roll bearings are used, while in V50 box you got ball ones. You may try, 50 miles is enough to see if this cures the problem, but not enough to mess up the bearings. Looking at my inners' pics I would blame viscosity indeed, as neighbouring big wheel throws oil onto selector shaft, filling up the gear-setting groves with oil...
2. In case of your heads I bet not the guides, but guide/stem seals. Job easy enough to do without head removal, you just need to keep piston in TDC. Do just inlet valves, don't be bothered with exhaust ones. Think well about the tool you gonna use to press new seals on the guide. It's easy to damage the seal if your approach is too agricultural. This probably won't help for seven seasons, as worn seal may(but not need)mean worn guide, but it helped in my case, ad I ride like that for years - old guides, new(-ish)seals.
3. Think what petrol was available back in '80s and try to use similar. Anything "better" is worse in fact: different combustion time = different advance setup needed. Counterintuitively, the higher octanes, the slower combustion.
Suerte!

Thanks for sharing that knowledge Adamigo. We certainly had higher octane fuel in the States back in the 80s, and a lot of fuel was still leaded too. The valve seal job looks like one I can do, once I find a source for the valve seals.