Gearbox Pressure

[Taspiper]

I have noticed if I fill the gearbox to its correct level, then go out on the water, when I get back I find a fair amount of oil seeping along the prop shaft.
If I undo the filler plug oil spurts out under pressure and runs out for a considerable time. Obviously the water is mixing with the oil thus increasing the volume. Once I've let some out I then worry about how much is in there and drain and refill.
Gearbox is is reasonable condition in regards to bushes etc and holds pressure for quite a while. I'm using Penrite Transoil 140 specified by them for the seagull and other vintage gearboxes.

Should I not worry about this and just top up before a trip? Is it normal behavior?

[Ian Malcolm]

The water is usually cooler than the air temperature so the air inside the gearbox contracts and the gearbox sucks water in when you first immerse it. Pull it out and let it warm back up and the gearbox pressurises.

You can reduce the amount of oil loss if you replace the Seagull rubber 'sealing' washer behind the bush on the prop shaft (which only really keeps grit out) with a V seal that is a tight fit on the shaft with the lip running against the bearing face. You cant do much for the pinion bearing though or it wont get lubricated.

You will still need to check the level and change the oil (or at least freshen the mix) when you find that it has reached the top of the filler hole. (lay engine tank and prop down, remove plug, tip upright while covering hole with ball of thumb, ease thumb downwards to check level without letting much out.)

[Taspiper]

Thanks Ian,
I gather its pretty normal then.
When fishing I always leave the prop submerged for long periods maybe this adds to the amount of water.
Ill probably just use it, leave for a few days to settle/separate then check and top up.

[Ian Malcolm]

It will help if you can leave the engine tilted with the gearbox touching the water but not immersed right up to the propshaft for a few minutes when you first use it, so it can suck air while cooling down to the water temperature but the best improvement is from fitting a decent seal to the shaft. Google: V12A ring seal (not suitable for clutched, FNR and 102 models)
See these previous topics here:
viewtopic.php?p=1378#p1378
viewtopic.php?f=2&t=1806
viewtopic.php?f=5&t=2530#p16972

[Taspiper]

Thanks for the links Ian. I may look in to the V rings as every bit helps.

The first thread got me stuck back on mixture again. Although everything seems to be running right my plug is very clean with no signs of black or soot. This is with 10:1, no.3 needle running half a turn out in a M8j jet. I'm wondering if I leave it or try a little richer.
Out on the water.i can't seem to get first pull starts, usually two to three and wonder if it just needs a tad more fuel.
The throttle response isn't instant and seems to hesitate a small amount before Increasing speed.

Another thing I've noticed, from cold the engine will rev to its particular limit at full throttle for say one hundred meters then I hear it drop in revs slightly as it becomes hot, almost like its lost a hundred revs by knocking the throttle back which is what I first thought had happened. It still runs ok and evenly though. Maybe it's just a bit tighter when hot?