Gearbox woes; unexplained oil leak

[boscoe99]

Are you saying pump air into the gearcase to 10 PSI to verify that water can't get INTO the gearcase. All I am saying is that Yamaha says to pressurize the inside of the gear case to see if it will hold that internal pressure for X period of time. Well that's logical! This is a Yamaha we are talking about. What's logic got to do with it?
Why can't they reduce the air pressure inside the gearcase by 10 PSI to see if it leaks inwardly? They can. Apparently they don't want to. Who is "they" anyway?
Don't techs over there have "vacuum" pumps, like air conditioning trades people have? We got all sorts of new fancy test equipment here up over. We got pumps that can reduce the internal pressure down to near absolute zero pressure if the seals can stand up to the test.

If oil cannot go out at 10 psi then one would surmise that water can't get in at 10 psi. Given the positioning of the seals that is. Now does the oil heating up result is a higher pressure inside the gear case (relative to outside pressure) or does it ever go below outside ambient air pressure?

Zeno, do we need to splain to you how seals work? It is the Christmas season and this is the season of giving. We give and we give and oft times it is never enough.

[TownsendsFJR1300]

Agreed, the pressure test is to check for ANY LEAKS, to keep water out.. If air escapes/or doesn't hold a vacuum, you'll have water intrusion.

Its not like an internal combustion engine with the internal engine pressures changing when running (piston's going up and down) vs a LU, spinning gears-basically just atmospheric pressure to speak of.

For the testing, the unit must be empty of oil. Rotating the prop shaft and drive shaft while checking as well.

For the Sazuki I pictured above, a NEW unit is well over $2k. The boat / engine might be worth $3k.

While we didn't do any gear changes, everything had to be cleaned, prop shaft removed, a new carrier o-ring installed, which would have been the biggest issue.

The LU was on its SECOND WELD JOB. Between that, the original cracks, it was NOT the "roundist surface" to put a carrier o-ring up against.

That particular unit called for 15 PSI thru the oil fill hole, spray soapy water on all seals (o-ring too). It held 15 PSI just fine.

As for the OP, I strongly suspect either the mechanic missed something after the first rebuild, or something was not set right.

**BTW, there's TWO SEALS under the water pump that DO WEAR OUT, no matter how well you treat the engine. Per the dealer, due to my engines age, it was HIGHLY RECOMMENDED to change out the seals. Sure enough, the upper(outer) seal had a broken SS spring(no water intrusion). They should have been changed, if there were several years on it or if fully rebuilt.. Its sounds as if those weren't changed per what your mechanic told you...


If the mechanic has a small air compressor, he can test it. Its not difficult. I turned my second, 5 gallon compressor regulator down to 15 PSI, and double checked the output pressure with a digital tire gauge. Hooked it up to the filler port for a tight seal

[zenoahphobic]

Boscoe, I presume seals work by fish and water in creates energy for them to swim.
Seriously the presumption if something holds pressure therefore stops pressure getting in is fundamentally absurd. You would have come across numerous examples where seals let pressure pass one way and not the other .
Years ago when I was young and learning, I discovered that the majority of seals are only one way (I know you know that) and that there were double seals available but strangely not used where they should.
The notorious other expansion and contraction situation is with boat trailer bearings.
Of course the curse with lower units is that the oil does heat up and expands, through friction and hot exhaust going through there.
I guess your intimating that if the seal holds this pressure then the cooling contraction just brings back the pressure to ambient(but is that atmosphere pressure at sea level etc. or the pressure one foot below the water surface?
The reason I understand one way seals tend to be used, is that of ease of assembly and as to a small extent to allow it to slightly leak as a safeguard against severer pressures building up causing more catastrophic failure.
This why perhaps oil changes are recommended in LU.
Yeah don't mean to hassle its Xmas.
But this is the season where many a boat trailer can be found on the side of the road with bearing failure. Happened to me too before I learnt that seals only work one way!

[boscoe99]

If you were to install the seal shown below to resist pressure from high to low in the most effective way, how would you position it?

Will it be more effective if maximum pressure is on the right side or the left side of the seal?

If the seal is rated to withstand 10 psi positive pressure on the left side of the seal with 0 pressure on the right side, would it be able to withstand less, the same, or more pressure on the right side than on the left hand side?



I hate wheel bearings, seals and axles. Had an axle snap off the boat trailer while tooling up the road. The wheel/tire assembly with the hub went rolling past me. Trailer was dragging down the highway.

[zenoahphobic]

Withstand more pressure on the right side. But that is not the orientation of all the seals how your pressure testing.
Depends which pressure direction you're concerned about; keeping oil in (or grease) or water out. Most manufacturers a concerned about the former.
Granted if 10psi does not pass on the left side then Prima Facea given the application leakage either way should not occur.
Pressure from the left reduces the tension of the seal. Pressure from the right increases tension of seal on the shaft leading to greater distortion and wear that correspondingly make the seal less affective from pressure from the left.
It seems if the seal seat was wide enough that two seals facing opposite direction would be the best of both worlds.
But I have heard the belief that two seals don't give double sealing. I personally would not insert two seals, but rather a single double seal.

[TownsendsFJR1300]

Now wheel bearing seals, (boat trailers) their "life", is somewhat different.

Its not uncommon to drive some to the ramp and immediately back into the water. Hubs get warm as well as everything else inside.

Its best to let them cool down a bit before immersing in cold water.


**Just a side note, on my motorcycle trailer I built, I have the spring loaded grease cap for the outer bearing.

On the HUB's themselves, I measured where the race stopped and the seal sat. I removed the race and drilled a small hole in the hub. I tapped and inserted a grease fitting and re-installed everything. Now, I can grease both bearings KNOWING the inner bearing DID GET GREASE... Obviously, occasional inspection is still due but the MC trailer doesn't see water.

[99yam40]

Withstand more pressure on the right side. But that is not the orientation of all the seals how your pressure testing.
Depends which pressure direction you're concerned about; keeping oil in (or grease) or water out. Most manufacturers a concerned about the former.
Granted if 10psi does not pass on the left side then Prima Facea given the application leakage either way should not occur.
Pressure from the left reduces the tension of the seal. Pressure from the right increases tension of seal on the shaft leading to greater distortion and wear that correspondingly make the seal less affective from pressure from the left.
It seems if the seal seat was wide enough that two seals facing opposite direction would be the best of both worlds.
But I have heard the belief that two seals don't give double sealing. I personally would not insert two seals, but rather a single double seal.

being this thread is about Yamaha lower units I thought I would mention that the yamahas I have looked at have 2 seals both installed the same direction on drive shaft and prop shaft.
I thought they should have been one in opposite direction, but that is not the way yamaha desinded or showed how the are installed

[boscoe99]

being this thread is about Yamaha lower units I thought I would mention that the yamahas I have looked at have 2 seals both installed the same direction on drive shaft and prop shaft.
I thought they should have been one in opposite direction, but that is not the way yamaha desinded or showed how the are installed

Every Yam lower unit I have seen is as you describe. Both seals face outward.

I can only presume that Yamaha is more concerned with keeping water out than with keeping oil in. Not a bad objective. A bit of oil out, no harm no foul. A bit of water in, there might be big troubles.

Yamaha prescribes an internal pressure test only. Presumably to verify that the integrity of the seals is such that they will keep oil in. Now if the seals will keep oil in, it is presumed (based on the design and orientation) that they will do an even better job of keeping water out, given that they should be more effective at keeping stuff (water) from moving from right to left, than they will at keeping stuff (oil) from moving from left to right.

Now let me bring up a question. Rubber seals and such wear with the passage of use and time. Impellers for instance. Which, of course, are stated to be inspected and replaced on a periodic basis. Not so with the propeller shaft seals. Are the propeller shaft seals less important that the impeller is?

[TownsendsFJR1300]

Now let me bring up a question. Rubber seals and such wear with the passage of use and time. Impellers for instance. Which, of course, are stated to be inspected and replaced on a periodic basis. Not so with the propeller shaft seals. Are the propeller shaft seals less important that the impeller is?

As you know, the impeller will take a set especially if not used often.

A shaft seal is NOT nearly as susceptible (can harden up, etc), but not take a set.

IME, Yamaha motorcycle's (and seems marine), tend to have you replace parts much sooner than real life expectancy. IE, Yamaha has brake caliber SEAL replacement EVERY TWO YEARS. In real life, expect 4-5 years...

[DennisG01]

This is from a Mercruiser perspective, but for quite a while now they also only advocate a pressure test of the drive. They no longer spec doing vacuum testing since the seals they use now will fail a vacuum test every time.

[TownsendsFJR1300]

They no longer spec doing vacuum testing since the seals they use now will fail a vacuum test every time.

Very interesting!

[boscoe99]

As you know, the impeller will take a set especially if not used often.

A shaft seal is NOT nearly as susceptible (can harden up, etc), but not take a set.

IME, Yamaha motorcycle's (and seems marine), tend to have you replace parts much sooner than real life expectancy. IE, Yamaha has brake caliber SEAL replacement EVERY TWO YEARS. In real life, expect 4-5 years...

Is the impeller inspection requirement more due to it possibly taking a set or is it due to it wearing?

The vanes of the impeller flex. Even though they may be taking a set, does not the centrifugal force trying to throw the vanes off the hub of the impeller counteract any of whatever set may occur?

Should inspections and preventative maintenance actions be more conservative or less conservative? Should they vary depending upon the application of the part to be inspected?

Is the water pump system of an outboard motor more or less critical than the braking system on a motorbike?

[boscoe99]

This is from a Mercruiser perspective, but for quite a while now they also only advocate a pressure test of the drive. They no longer spec doing vacuum testing since the seals they use now will fail a vacuum test every time.

Yes, and their test is performed at 15 psi. For the Verado anyway.

I am trying to figure out why the vacuum (damn that word) test will fail. The Verado uses two propeller shaft seals. One facing inward and one facing outward. One might think that if the inner seal (facing inward) can withstand a 15 psi pressure differential that the outer seal (facing outward) could withstand a 15 psi pressure differential.

Boscoe must ponder his navel on this one.

[99yam40]

Every Yam lower unit I have seen is as you describe. Both seals face outward.

I can only presume that Yamaha is more concerned with keeping water out than with keeping oil in. Not a bad objective. A bit of oil out, no harm no foul. A bit of water in, there might be big troubles.

Yamaha prescribes an internal pressure test only. Presumably to verify that the integrity of the seals is such that they will keep oil in. Now if the seals will keep oil in, it is presumed (based on the design and orientation) that they will do an even better job of keeping water out, given that they should be more effective at keeping stuff (water) from moving from right to left, than they will at keeping stuff (oil) from moving from left to right.

Now let me bring up a question. Rubber seals and such wear with the passage of use and time. Impellers for instance. Which, of course, are stated to be inspected and replaced on a periodic basis. Not so with the propeller shaft seals. Are the propeller shaft seals less important that the impeller is?

IMHO The problem with the rubber water pump impellers is they do not pump clean water all of the time and are sometime started without water for lubrication.
And even clean water is not as good at lubricating the rubber as oil/grease

[TownsendsFJR1300]

Is the impeller inspection requirement more due to it possibly taking a set or is it due to it wearing? Depends on the operating conditions. My last one had a bit of a set. For S&G's, I tried tearing a vane, off. For the F150, it is damn near impossible to bust a piece off. Didn't appear worn at all but had some set (never an overheat). For me, If I'm in that deep, its getting a WP kit, period

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The vanes of the impeller flex. Even though they may be taking a set, does not the centrifugal force trying to throw the vanes off the hub of the impeller counteract any of whatever set may occur? There's not much room for the vanes to stretch out with centrifugal force. Try straightening out a vane that has a set by hand-AIN'T HAPPENING...
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Should inspections and preventative maintenance actions be more conservative or less conservative? Should they vary depending upon the application of the part to be inspected? I suppose that depends on the individual, his pocket book size and if he can find someone qualified to work on the machine.. For me, IE, I'm NOT re-building my brake caliper seals every TWO years- its plain NOT necessary...
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Is the water pump system of an outboard motor more or less critical than the braking system on a motorbike?

Well, if I'm running at 50MPH on my motorcycle, coming up on stopped traffic, I'd rather have brakes than a water pump failure. One I'll walk away from, the other I won't...