Big Twin Lower Unit Reseal Question

[raglover]

I am chasing a pesky leak in my 1956 30 OMC. Cannot find an outward leak under pressure but get questionable results under vacuum. I have resealed but still leaking. No leaks from lower end I can find but thinking it is in my shaft seals.

I am going to go back in it and want to double stack the seals on the drive shaft. (Currently running one) Question is what two part numbers are best for this?

Marine engine calls out 313284. Are these thin enough to stack back to back?

Next, can you double stack the seals on the prop shaft? Thinking not asi do not recall enough clearance in the gear head cap. I bottomed the seal in it.

Thanks,

Allen

[ede]

Allen, The 313284 seal measures .316 thick. Don’t believe you can stack two of those seals in the housing (bearing head) or in the housing for the drive shaft. As for a thinner seal, I think you will need to go to a bearing/seal house. Is the prop shaft grooved? As you know, there aren’t many places for a leak to occur. Ed

[fleetwin]

These gearcases are a royal pain to seal properly. I think I am hearing you say that when you pressure test, no leaks are evident, is this correct? While pressure testing, are you rotating the shafts, and pulling the shift rod up and down? It is really helpful to submerge the gearcase completely in a trash can full of water while pressure testing to pinpoint the leak/area.
Like Ed says, these shafts are often grooved, but may not show leakage unless you rotate the shafts while pulling in/out on them.
Using a vacuum tester on single seal systems can cause confusion, because you don’t have the outer facing seal, and the vacuum tester might overcome the single seal. I don’t think you will be able to use two seals on these gearcases.
Try pressure testing again in a bucket of water while rotating/pulling the shafts and pulling up/down on the shift rod, I think the problem area will show up.

[frankr]

Don’t use very much air pressure to test. Too much forces the seal lips against the shaft, giving the false impression that they are OK. And have the case drained of oil for testing.

[bill-mcnamara]

And what is the approx. recommended pressure for the pressure test?

[frankr]

Grabbing a service manual at random, it says 16-18 psi.

[1957evinrude]

Good to know 16-18. Okay wow I was only putting about 6 pounds.

[Casey Lynn]

On those old gearcases I normally use no more than 5psi and usually a bit less.
Now…..on your original post you have mentioned shaft seals more than once but you have not mentioned the shift shaft O-ring as part of your re-seal.
Sometimes we get ahead of ourselves around here without asking the basic questions.
Have you changed out the shift shaft O-ring? If not, that is pretty much the main offender as far as a leak goes. Needs to be changed. You can verify with soap and water and a bit of pressure.

[frankr]

Actually, I was sort of surprised that it said 16-18 pounds. I, too, use around 5 PSI.

[dan-in-tn]

I too you 5lbs for beginning checks, but before I finish I do run the pressure up to 15lbs to check spaghetti seal joint and gasket under the water pump on small engines. I don’t even put the water pump on just bolt down the plate so I can see if it leaks. If it holds everything at 15lbs it won’t leak.

Dan in TN

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