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Old 18 February 2019, 03:47   #1
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Yamaha F80, water in gearbox

Drained the gearbox for the annual service and found alot of water and the oil was black and gloopy. Is this a diy job to strip, clean, inspect, replace seals and reassemble?
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Old 18 February 2019, 06:24   #2
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Hi Swifty, just working on my yam gearbox also....The oil should be a golden colour so if that oil is only a year old i'd say there's something wearing inside as a result of the water getting in..
There are two screws on the leg side. I'd remove the remaining oil and with a gentle hand pump,pressurise the gear box to 15psi (?). Using bottle of soapy water you'll see the bubbles and hence the culprit leaking seal(s)
The lower output shaft seal is more difficult to work on, so I'd find the offending leak first. Was it used in fresh or salt water? how old? Hope this helps. Nik
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Old 18 February 2019, 06:57   #3
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+1 for a pressure test - I change our leg oil at the start and also mid-season, that way I feel you can get ahead of any issues, good luck!
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Old 18 February 2019, 10:26   #4
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What sometimes happens is that the prop hits something, and slightly bends the output shaft. This means that the seals cannot seal properly, letting in water.

Obviously don't know if that is the problem in this case; but I would suggesting seeing if the prop has any dings in it as a result of hitting something; and also checking the output shaft to ensure that it runs true. (I can't see all the blades of the prop from the photo.)
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Old 18 February 2019, 20:36   #5
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Since the gearbox needs to be worked on, would suggest to change both the drive shaft and prop shaft seal as well. Check both shaft to see if there is any scouring on the shaft where the seals comes in contact. Also do a run out test of the prop shaft with a micrometer to be safe.
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Old 19 February 2019, 01:05   #6
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Quote:
Originally Posted by matata View Post
Hi Swifty, just working on my yam gearbox also....The oil should be a golden colour...
If you're using SAE 80/90 Yamlube, its golden syrup stuff, but Quicksilver SAE 90 high performance gear oil looks like this (except emulsification of course).
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Old 19 February 2019, 05:04   #7
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The oil is very black is that exhaust contamination?
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Old 20 February 2019, 06:08   #8
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Here the most common cause of seals leaking is from fishing line getting around the prop then inside onto the shaft, where it can damage the seals.

My advice would be to find a decent mobile mechanic who could show you how to change the seals incase it happens again.

As the guys state, gearbox oil is like golden syrup, I replace mine every 100hrs where it looks the same clear golden colour on removal as the day I put it in. By the way 100hrs comes around four times per year on my engine.
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Old 21 February 2019, 03:36   #9
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Thanks for the comments. I have always changed the oil regularly and never seen this before.
I am going to attempt a pressure test first to identify where the original problem is. For cleaning out the gunk, I was going to flush with diesel to get as much crud out before filling with oil.
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Old 21 February 2019, 04:17   #10
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Bear in mind that a pressure test may not show the fault as the shaft seals are in pairs back to back, one to keep oil in the other water out
It might help you but it isnt definitive. a vacuum test may help to find leaks going inwards but again its not 100% as its a static test ,personally I'd replace all the seals in the box for peace of mind . Yamaha seals are just metric seals so relatively easy to source from a bearing stockist if the genuine items are extortionate prices or long lead time, just make sure they have stainless garter springs
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