Yamaha o/b leak..Or is it?

[WindermereColvic]

Inherited this Yamaha o/b with the boat last year, not sure exactly what it is but a picture of the id plate is below. Tried it out the other day and noticed muddy, oily water coming out the front of the housing. Took the cowling off this afternoon and found a hole in the gasket between the bottom of the power head and the leg, but, it looks deliberate. The water only starts coming out when the engine has been running for about a minute, perhaps when the thermostat (if it has one) opens? Any ideas if its supposed to be there, and if not, what i can do about it. Thanks, Matt .

PS, bloomin thing has injured me, since runing it in the wheely bin my eyes are stinging, my ears are ringing, and my starter - pulling hand wont uncurl..Oh well

 

[steve28]

thats showing you the lower oil seal has failed.
Its an easy fix "IF" the bolts come out

Steve

 

[Lakesailor]

Even if some snap, it's not difficult to drill them out and re-tap the holes. You've nothing to lose.

 

[Cliveshep]

Not sure what oil seal you mean, the oil seal on the top of the drive shaft into lower unit and below the pump vanes? I believe that could be correct anyway and allowing oil to mix with pump water as water might force its way past the seal into the lower unit, but the water is not supposed to come out at the under side of the power head anyway, and that is where the picture shows the leak, and the oil seal will have no other direct bearing on that leak. It won't be a crankshaft oil seal because the engine wouldn't run anyway.

Any leak at the power head gasket will always be oily, this because a 2-stroke exhaust is oily. Water is pumped up a tube inside the leg, (with or without some gearbox oil) circulates around the engine block, and is ejected into the top of the leg from the engine block underside where it mixes with exhaust gases and is spat out below the anti-cavitation plate where propellor wash disperses it.

A small hole in the back or astern side of the leg is the tell tale, a little stream of water here, pressurised by the exhaust gases, indicates that the pump is working. It looks as though this motor has a leak under the power-head where it mates with the upper leg allowing water to escape there instead of below the anti-cav plate. Not bad in itself but messy and unsightly. You should be able to remove the 4 power head bolts and prize off the power head from the upper leg. This will reveal all. Separating the lower unit from the mid-section leg might be a little more taxing dependant on how much corrosion there is there on the 3 bolts. However, if you ever need to change the pump impellor sooner or later that is what you'll have to do.

 

[WindermereColvic]

Thanks to all so far. Ive not had chance to look properly yet, but ive always assumed that as this o/b has no gears, the impelor would be behind the prop. If the leak isn't damaging the engine, just leaving me with oily bilges in the tender, would it be a cardinal sin to put a blob of glue or some blue tack in the hole? Matt

 

[Cliveshep]

Well, it has still got gears hasn't it? Otherwise the vertical rotating shaft couldn't drive the prop through 90 degrees of axial change. It is usually the shaft from powerhead to lower unit with the bevel gears that contains the pump assembly just on top of the lower unit. You can get parts here (not cheap): http://www.buitenboord.com/look-yamaha-outboard-parts-c-272.html if nowhere in the UK.

I believe yours is the 2 hp 1979 onwards.

 

[leomagill]

Are the exhaust holes clear? The hole could be a deliberate design to stop excess pressure in the leg forcing water through the crankshaft oil seal, it will be a bit oily from the exhaust gasses being 2 stroke, blocking it could cause more expensive problems.
If a crankshaft seal goes on a 2 stroke they run like crap if at all.
Also on a leg pressure thing is the shaft length right for the use as that will increase the pressure in the leg if it runs too deep.

 

[steve28]

To clarify more clearly, i mean the oil seal in the bottom of the power head.

Common to fail and simple and cheap to replace so long as the bolts come out but as other poster says its easy to drill out the bolts unless someone has put stainless ones in.

It will start and run even better once done.


Steve

 

[Cliveshep]

I don't think so, the exhaust has the whole leg to go down and out via the exit port behind the prop. Short of sticking a potato up it it is not going to block and the exhaust pressure will not affect the crankshaft oil seal as it has the whole leg to expand into. It is more likely a bad seal between the leg and power head, possibly corrosion, possibly a defective gasket. They aren't supposed to leak there. Look at the pics, there's clearly no problem with exhaust, its blowing water all over the show!

 

[tross]

I don't think it is the lower crankcase oilseal. If my memory servers me right the drive shaft is housed within a stainless tube which enters the water pump at one end and a rubber seal at the power head end - so I don't think it is that as any oil would not exit where it isdoing so. Secondly - if it starts OK and idles then it is not the lower oil seal.

 

[gjh]

Hi it's been a long time but did this ever get resolved ? I've just rebuilt the same engine and have exactly the same issue ?? That gap is clearly supposed to be there above the gasket but at high rev's water comes out all over the carb and will make a mess under the cowling. If you do have any info would be really useful as I've spent hours racking my brains.
Ta Gary