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gearbox oil

Posted: Wed Oct 21, 2009 12:22 pm
by Pieter S
I have acquired a "vast" amount of Shell Omala 460 gear oil. (20 litres is a vast amount if you have only two Seagull gearboxes to feed.) A not too expert sounding person at Shell says she "thinks the viscosity is SAE 460". The oil pours freely but is definitely "stickier" than SAE 90. Will this be suitable for my Seagulls SJP 330 K5 and FP 724 MM3 ?

Re: gearbox oil

Posted: Thu Oct 22, 2009 6:35 am
by Waggles
Looking at the data sheet Omala 460 is probably overkill being a high grade industrial gear oil. Interestingly it states it has high water shedding properties allowing water to separate and be drained off, should be OK for Gulls then! It protects steel and bronze even in the presence of water, again sounds OK!

As for Viscosity it is ISO 460 which is equivalent to SAE 140 gear oil so should be OK

Re: gearbox oil

Posted: Thu Oct 22, 2009 3:37 pm
by Todd
I was given some Mobil 634 which probably has similar properties as your Shell oil. It is a synthetic and also has water shedding properties.

What I've found is that it doesn't readily mix with the water which leaks into the gearbox, but will be displaced by it. Clear water, being heavier, will accumulate in the bottom of the gearbox as the oil is forced out past the bushings. If one simply checks the oil level by removing the nylon plug, what he is seeing is merely the remaining oil which is floating on whatever amount of water has leaked in.

I'll gladly explain how I learned this for a beer and a crying towel.

Use the synthetics, but be willing to check often and drain off the water in the gearbox.


Re: gearbox oil

Posted: Thu Oct 22, 2009 6:29 pm
by Charles uk
Gear oil that doesn't emulsify is normally a NO NO for Seagull gearboxs.

As one of the previous posters correctly stated the last thing you want is a puddle of water in the bottom of your gearbox, corroding the teeth off your crownwheel.

The 140 grades of oil reccomended elsewhere on this site seem to emulsify rather well & prevent the gears corroding for several years, though it might be much safer to change the oil before putting away for the Winter.

Re: gearbox oil

Posted: Mon Oct 26, 2009 10:41 am
by Waggles
Interesting, and confusing.

Quite understand that the water should be drained off ( I should have laboured that a bit more ) but I am confused by the point that it 'protects steel and bronze even in the presence of water', any ideas how it can acheive such a feat if it just separates? ( or is it just advertising hype or applies to only tiny amounts of water rather then the deluge standard in gull boxes )

Re: gearbox oil

Posted: Tue Oct 27, 2009 4:42 am
by Todd
My laymans' understanding is this:

First, lubricating oils typically have properties which encourage them to cling to, for example, metal. Think of trying to clean an oily engine with nothing but a stream of water. Thus there's a thin, somewhat tenuous protective layer separating steel from water.

Secondly, the whirling gears will mix even synthetic oil with the trapped water, the difference being that when all the violence ceases, the standard 140 wt. will tend to hold the microscopic water molecules in suspension (the coffee milkshake effect) whereas the synthetic oils in question release the water bits which settle back down to rejoin in the bottom of the gearcase.

It's no secret British Seagull made a point of warning owners to use gear oil, and under no circumstances was there to be used anything that wouldn't pour. But I can't help but wonder when that admonishment was made, if had modern greases like Lubriplates 105 and 630AA been available, might not the designers have been more open to the use of grease.

I recently found two old motors, one a Seagull Featherweight, which had gearcases packed with a white lithium grease. In both cases, the gears were tight, clean and working perfectly. And, of course, the cases didn't leak. The primary concern originally was that the gears would dig out a hollow in the stiff grease, and then starve for lubrication. The new greases are formulated specifically for gear drives and are designed to flow into the geartrain. More a concern now might be whether or not the grease is fluid enough to work into the miniscule space between the propshaft and it's bushings. I can only say that when I pulled the endcap off the Featherweights' gearcase, the bushing and prop shaft both had a thin layer of grease on them and neither showed the slightest sign of wear.

Nor was there any water inside.

I'd cleaned out the grease and replaced it with 140 wt. and immediately noticed a return to a "normal", higher level of gear whine. Now, as someone who can never leave well enough alone, I'm tempted...

Here's an idea. Why don't one of you guys who have a bunch of "spare" lower units piled high in the corner of the shop, fill one with Lubriplate 105, bolt it to a runner, go abuse it for awhile, then report back your results. Settle the arguement for once and for all. All in the interest of science, you understand. I think it's a wonderful plan and in the interim, my motors will keep the 140 wt.


Re: gearbox oil

Posted: Tue Oct 27, 2009 10:02 am
by Waggles
I take it your previous bad experience trashed the box? my question was if the oil does cling and form a protective layer, what went wrong? even with water pooling in the bottom why wasn't that film sufficient bearing in mind it would be constantly replenished as the gears rotated? and as you say there would be an amount of emulsion caused during running too? Don't get me wrong am not trying to vindicate these water shedding oils, just trying to understand. Can see that the bearings would eventually be left high and dry ( wet? ) after a period and reliant on emulsion only but isn't that what normal oils give?

As for grease, thats really interesting, bear in mind the lack of noise could just be the acoustic dampening of the thick grease tho! I had always assumed that when you 'pack' an old type car wheel bearing with grease it is the heat from the bearing that 'melts' the grease in the dust cap and causes it to run into the bearing, wouldn't have thought the same heat would be avialable in a super cooled gull box? sounds like something was causing it to flow though, can you get more info on the grease? perhaps it is just that bit more fluid?

Re: gearbox oil

Posted: Wed Oct 28, 2009 3:49 pm
by Todd
Yes, I fell into the trap of merely looking for an adaquate oil level at the filler cap. Little did I know that eventually I was seeing only a thin layer of oil floating on top of a gearcase full of water. It was not enough.

The oil film is only a thin layer which provides some resistance to corrosion, and also provites a bit of protection during start-up - that brief period when there is metal-to-metal contact before the oil is picked up by the rotating parts. It's not enough to provide ongoing separation of metal parts in high pressure contact areas such as gear teeth. Hence the need for a continuous oil bath provided by the pool of lubricant in the bottom of the gearcase.

The benefit of grease may be, and I'm not yet convinced of this, but may be that it resists the dilution by water as the petro-based oils are prone to, and that it may resist being displaced by water as the synthetics are. The greater question for me is whether the bushings will be well served by the grease, and my answer to all these questions is only that, anecdotally, others have used a thin, flowing grease i.e. Lubriplate 105 successfully in Seagull boxes, and that the example which I examined myself seemed to be free of water with bushings well lubed. Hardly a scientific study.

Nor can I speak to the element of drag except to say that modern lubes, especially synthetics, are much more temperature-stable in that they resist becoming thicker as temps drop. But the grease definately ran quieter, probably, as you said, due to acoustic dampening and perhaps also to the greater cushioning effect of the thicker fluid.

Lubriplate info: ... index5.htm (scroll down to Lower Unit Lubricant) ... Series.pdf (Uses Lubriplate 630AA) ... Series.pdf