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Old 22 August 2019, 09:54   #1
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New problem, gear oil.

New problem for the newbie.
I've recently fitted new prop. Now I have tightened it up but not went mental torque wise.
After being out last night as per usual I let the engine run in the wheelie bin to flush out.
And I noticed a lot of oil. Dipped finger in the water and was pretty sure it was fresh gear oil as engine had been checked over. Possibly topped up.
Decided to double check this morning and sure enough, it took oil usual procedure until oil comes out of top screw hole.
I've had the engine sitting all day, no leak, while it was sitting.
Put it back in wheelie bin, with fresh water, and sure enough they'res the oil again.
So deffo not coming from the fill hole bottom or top. I can only think it's coming from prop. But no signs of it coming from they're either. Removed prop to check. Still nothing.
Can't get hold of my engine guy. So any ideas?
I'm thinking some sort of seal is away.
Does pressure build in the lower unit that would cause this? So only leaks while running?
Glad I noticed as was planning a little jaunt today.
Any suggestions appreciated.

Sorry.this probably should have been in engine/prop section if admin would move.
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Old 22 August 2019, 10:06   #2
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If you are convinced this is gear oil and not oil residue from the exhaust the usual reason to go from the gearcase being OK one trip... and leaking the next... is fishing line drawn round behind the prop and into the oil seal.

When you topped up from the bottom so pushing a little of the existing oil out did it still look new or was it milky at all?
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Old 22 August 2019, 10:12   #3
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Thanks Fenlander quick response as always.
I have removed the prop and nothing they're, that I could see, possibly dragged it all the way in that I can't see it? It's deffo not the usual residue that's left in the bin after a flush. I can dip my finger in it and it's a thick film of oil left on my finger, with the noticeable smell of gear oil.

But on checking the gear oil again from the bottom top up screw they're is no water contamination in the oil. So looks like a 1 way thing . Oil coming out but no water getting in .
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Old 22 August 2019, 10:26   #4
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Ideally it need a gearbox pressure and vacuum test.

The pressure test on my Yamaha 15 2-stroke is about 14psi and only needs to hold for 10-20sec.
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Old 22 August 2019, 10:28   #5
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So do the gears within the lower unit just splash about in the oil like a wet sump, or does it in fact pressurise when in use?
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Old 22 August 2019, 10:30   #6
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Well that's spoiled the fun for later today. I'll get hold of the engine guy when I can see what his prognosis is.

Thanks again Fenlander. .
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Old 22 August 2019, 10:32   #7
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It's running in oil splash lubrication.
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Old 22 August 2019, 10:36   #8
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Ok brill I'll remove the prop again for a more detailed inspection, but if nothing they're which I'm sure they're isn't . I'll get it in and checked properly. .
Thanks again.
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Old 22 August 2019, 10:45   #9
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You can do a basic test if you have a bike pump with a gauge and can make up an adaptor with bike valve... bit of tube... and one of those yellow plastic tapers for inflating all sorts of things that comes with pretty well every pump. The taper will sort of screw into the gear level hole enough to get a temp seal. Inflate to 10-15psi and if there is a prop shaft seal leak you'll see it push the oil out.
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Old 22 August 2019, 10:49   #10
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When you fitted the prop, did you fit the thrust washer?
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