Yamaha 30d upper oil seals or something else ?

[pstephens46]

Seals are oriented to keep water out moreso than to keep oil in. See parts book illustration below.

Yes, lots of folks think vacuum testing should be done. Yamaha is just not one of those that think so. Many know better than Yamaha.

Specs for the test are in the applicable service manual. See illustration below from a 30D SM.

If the pressure test fails then the seals or their mating surfaces should be inspected and/or replaced. Or some may say fuuckit, close enough for government work, I am going with what I got.

Isn't the innerweb wonderful? You make me chuckle over on THT. C4 indeed.

C-4 might just help in removing the stubborn propshaft carrier also. Heating and pushing at the same instant.

I wonder if a vacuum test could damage the seal?. Reversing the direction of the sealing material that may cause a nice leak once the motor is run in gear????

[TownsendsFJR1300]

Isn't the innerweb wonderful? You make me chuckle over on THT. C4 indeed.

Now what engine is that spec (pressure and 14PSI) for?

And why does it need to be in water if your checking to SEE IF IT HOLDS PRESSURE?? Isn't that what the gauge is for?

[walleye1]

Mercury is 14 psi, there seals are back to back. Yamaha are in the same direction facing out.

[boscoe99]

OP says he has a 30D model Yamaha. "When I removed the gear oil from my Yamaha 30 DEO 2-stroke engine it was milky"

Data is from a Yamaha 30D service manual.

Pressure gauge is to see if the pressure is being maintained or lost. Lower unit being in water would indicate where any leaks may be.

[zenoahphobic]

It's good to revisit this topic from time to time.

I wonder how many have used the pressure test that has failed after discovering milky oil first? I suspect this test is more often used to confirm sealing of new seals. But other things can be tested to confirm success of work done and are not done. So an unnecessary procedure?

Interestingly the Yamaha procedure has ********g pressures to be used for different models. Note their caution on the example above to not use too much pressure else the seals may leak air(?)

I wonder whether it is useful to use this pressure test to predict imminent seal failure? Not heard of this though.

Editor has reject the word derived from "different" ?..

[TownsendsFJR1300]

Apparently there is no set procedure (in general) from Yamaha.

What I posted was for the F150-Vacuum testing.


*Also, I understand a pressure test with a leak would bubble, (and narrow down the area), BUT the gauge would SHOW it's NOT holding pressure..

[rodbolt17]

why is it so hard to simply follow the procedure in the SM for the MODEL being serviced???????
as a tech all I need to do is follow the SM. the anganeer work has long been done.
you will find test pressures from 2.5PSI to 14.8, DEPENDING on the MODEL.

[gvp90000]

What i did.
Gear oil was milky ..
so first I removed the lower unit and I pressure test it (100kpa for 10seconds). Pressure could not go above 60kpa.
Then i put the lower unit in a can of water in order to find the leakage.
The first leakage was in the gear shift rod. I changed item 6 and the leakage was gone but I had a second leakage in the upper seals.
Changed items 25,26 and no leakage at 100kpa for 10 seconds.
Thank you all,

[zenoahphobic]

why is it so hard to simply follow the procedure in the SM for the MODEL being serviced???????
as a tech all I need to do is follow the SM. the anganeer work has long been done.
you will find test pressures from 2.5PSI to 14.8, DEPENDING on the MODEL.

I guess the variation between models is that seals have different sealing pressures depending upon their size and their material properties. So the test pressures are probably a compromise, to avoid air pushing past the weakest (but not necessarily faulty) seal.

Pressure testing can make sense if one considers that the lower unit is a sealed container, that in order for water to get in the oil needs to get out first, the water needs to displace what's already in the sealed container.

[pstephens46]

I find the physics interesting concerning seals. The orings on the ‘86 Space Shuttle holding back the might of the solid rocket engine....or the seals on my Seastar steering that supposedly operates at 1000 psi. How do they contain all this energy? They basically are just small rubber surfaces....

[zenoahphobic]

I find the physics interesting concerning seals. The orings on the ‘86 Space Shuttle holding back the might of the solid rocket engine....or the seals on my Seastar steering that supposedly operates at 1000 psi. How do they contain all this energy? They basically are just small rubber surfaces....

Matter, even rubber is extremely resistant to compression. We normally think water is incompressible but all liquids and solids tend to be.

High performance Two Stroke motorcycles KTM use just one 2 mm o ring as its head gasket!

It is easier to understand that the force on o rings is not as great as you might think. Pressure is weight over area. Weight is the mass of something being pulled by gravity. This is how we describe units of force. Now if we reduce the area that requires to be sealed, say use a very small o ring, the force also becomes less. The smaller the gap the stronger the seal. A larger o ring is actually weaker than a smaller one, because it has a larger surface area.

Its the same principle like whales cannot carry the weight of another, but an ant can carry 100 times it's own weight. I can't remember exactly but atmospheric pressure is about the weight of five elephants upon us - but we don't squash to nothing!

[yamster69]

I know this is a very old thread, but I have the same problem - and its the gearbox shifter boot seal which is leaking. (Item 6 in the pic above)

When you say "I changed item 6 and the leakage was gone" - how does this boot/seal come out / refit? Is it simply a case of pulling on the rubber, or pulling / removing on the entire shift rod - does it just pull out completely?

There isnt much room for fat fingers to get at just the rubber boot, I dont want to break anything, and I dont want to have to get the gearbox / carrier out if I dont have to. Also it doesnt tell you how to remove the shaft in the service manual. Thanks in advance.

[yamster69]

Its ok, ive figured it out. This is a 6j8 / 30d motor btw.

here is a white "clamp" at the bottom of the boot holding it in place, which in my case was jammed up with sand, gunk, milky gearbox oil. Once id prised around the edge gently the white clamp came up and out, and then the whole gear shift lever assembly just pulled straight up and out easily. The boot and clamp actually look in good condition once cleaned up, no tears, the rubber is quite supple, but its definitely not holding pressure so im gonna replace the clamp and the boot.