Yamaha F80, water in gearbox

[Swifty]

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?

[matata]

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

[Fender]

+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!

[goearth]

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.)

[Eric]

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.

[spartacus]

Originally Posted by matata

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).

[jeffstevens763@g]

The oil is very black is that exhaust contamination?

[jonp]

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.

[Swifty]

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.

[beamishken]

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

[matata]

Do you remember what colour the oil was going in?. How many hours has it been in? Nik

[Swifty]

Thanks for all your comments.

So had a try with pressurising and the input shaft and prop shaft blew easily but there was no obvious signs of failure, shifter shaft held fine.

Have opened up the gearbox and washed out the emulsified oil and the trapped water (was sitting somewhere out of reach of the drain??). Inspecting the contents there's no sign of corrosion or damage. - pictures attached. Main shafts don't appear to have deep grooves where the seals run.

I am going to order new seals allround and water pump gaskets. Only dodgy looking bit is the water pump lower casing, but may clean up ok.

Anything else worth checking at this stage?

[spartacus]

Renew 'o' ring on dog clutch gear rod. Also 'o' ring under water pump above drive shaft bearing.

[A1an]

What is the history to the gearbox? How many hours on it? Were you the last person to service it?


Personally id have changed the prop shaft seal and put new washers on the fill/vent plugs and run it to see if water appeared again before tearing the whole gearbox apart.


I'm of the belief 'if it aint broke don't fix it'

[matata]

Hi Swifty, you've done a great job. I'm watching this with interest as we have a dribble of water in the oil in ours. Did you have diffs removing the output carrier or generally dismantling it due to corrosion etc??

[spartacus]

That water pump lower housing looks like Swiss cheese. If the surface has deteriorated to such an extent, it would be worth replacing. No point buying new waterpump gaskets if they're not seated properly. There's Yamaha parts diagrams on Boats.net. Easy to navigate with engine year. Think part is around £90 plus shipping.

While you're there check the sacrificial anodes on the engine to see they are doing their job, including the earth cables on the leg.

I've started using Salt Away at the end of the season. Granted it wouldn't stop water ingress on a failed seal, but think of the cooling passages, water jacket, thermostat.

[Swifty]

To answer your questions...

I have indeed ordered a new water pump housing at £81 along with all O rings and seals. Total is about £150 for parts.

The ring nut was a bugger to remove. I started by drifting it off but it started to flatten, it's made of alloy, so made a jig out of sheet steel and a couple of M8 bolts. Two of us using long prybars between the jig and the propshaft shifted it.
Hub carrier came out easily with a puller but I did have to make some extension arms for the puller to reach from the end of the prop shaft.

The engine is circa 1998 and total hours are unknown, but probably a couple of thousand. It's done 350 hours since the power head rebuild a few years ago. Gearbox was overhauled two years ago by Yam dealer as the gearshift was getting clonky. They had to drill the ring nut to remove it. I was very relieved when they reported all internals were in good condition.

I usually change engine & gear oil every year, spark plugs & impeller every three years. I didn't change oil last year due to the rebuild and low hours. With hindsight, I should have done it anyway and not trusted the dealer. We live and learn.

[jeffstevens763@g]

swifty any idea why the oil is black very interested because i've seen it before in a johnson 15 hp it smelt like exhaust fumes but wasn't sure it had the correct oil but this had no water ingress.

cheers jeff

[Swifty]

Originally Posted by jeffstevens763@g

swifty any idea why the oil is black...

cheers jeff

Nope, it didn't really smell of EP90 either! It had the consistancy of epoxy glue and the total volume of what came out was less than half the normal capacity. Maybe oil was being forced out when running hot and water sucked in as it cooled down.

I think I was lucky to uncover the problem before complete destruction.

[jeffstevens763@g]

Originally Posted by Swifty

Nope, it didn't really smell of EP90 either! It had the consistancy of epoxy glue and the total volume of what came out was less than half the normal capacity. Maybe oil was being forced out when running hot and water sucked in as it cooled down.

I think I was lucky to uncover the problem before complete destruction.

I remember in the old days when the cylinder head gasket went on the car you had a creamy residue in the rocker box but that was cream to white in colour