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V50/V35 Gear box seeps oil through top vent

Discussion in 'Small Block' started by Skivo, Feb 22, 2021 at 7:51 PM.

  1. Skivo

    Skivo Just got it firing!

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    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.

    IMG_1438.jpg

    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.)
     
  2. Kevin.NZ

    Kevin.NZ Cruisin' Guzzisti

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    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.
     
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  3. Skivo

    Skivo Just got it firing!

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

    IMG_1498.jpg

    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.
     
    Last edited: Feb 23, 2021 at 10:06 AM
  4. Kevin.NZ

    Kevin.NZ Cruisin' Guzzisti

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    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.
     
  5. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    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.
     
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  6. Kevin.NZ

    Kevin.NZ Cruisin' Guzzisti

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

    Skivo Just got it firing!

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    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.
     
    Last edited: Feb 24, 2021 at 11:53 AM
  8. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    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.
     
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  9. Skivo

    Skivo Just got it firing!

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    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)
     
  10. john zibell

    john zibell Moderator Staff Member GT di Razza Pura

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    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.
     
  11. Kevin.NZ

    Kevin.NZ Cruisin' Guzzisti

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    So whats causing the plugs to foul up?
     

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