Continuing the restoration: Rebuilding the lower.....is this a good idea?

[mark in new jersey]

The restoration is moving forward. My machining issues on the shaft have been resolved, so it's time to rebuild the lower.

I really don't have the means to do a meaningful pressure test; I have no means of doing a vacuum test at all......so I was contemplating this:

Complete rebuild, seals, sealant, everything, but no oil and not reconnected to the exhaust tube.....then once everything's dry & closed up, I'll simply submerse the entire lower into a deep garbage can full of water. By doing so, it will be immersed deeper than it will ever be when on a boat, so the hydrostatic pressure will be more than it will ever see in actual service.

I'll leave it there a day or 2, then open the lower fill screw. If it's dry, then everything's good. If water comes out, then I have an issue & will need to seek a pro who can determine the leak's location.

Is that a plan, or just a dumb idea? It seems ok to my engineering mind, but you guys know way, way, way more about engines than I ever will!

Thoughts?

 

[freddyray21]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

not really a good test as the driveshaft is not turning. Get yourself a screw in lower unit lube filler. They have a plastic hose attached. Screw it in and hook up a bicycle pump with a good gauge to it. Fix it so the line does not leak. Then pump about 5-7 lbs of air in the lower unit and watch the gauge. If it stays put no leaks it if goes down you have a leak. If you have a leak put it in water with air in it and the bubbles will tell you where the leak is at.

 

[mark in new jersey]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

good idea.

That said, with a static pressure test like that, the shaft still isn't turning, so is there really any gain?

 

[HighTrim]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

I have personally never pressure tested any of my OWN lower units. If I find they are leaking by cracking the drain screw after a run and finding water exit, I simply re seal. If I have a gearcase pulled completely apart I find it silly to change the shift rod seal but not the prop shaft seal. But that is just my own personal opinion.

I have pressure tested a gearcase for someone else. I simply submerged it into water and spun the prop by putting a drill on the driveshaft on slow. Do not over pressurize, that is actually cheating and will not give you the results you would expect. I rigged up a pressure tester with a lower unit oil pump line/fitting onto a bike pump as mentioned.

 

[freddyray21]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

good idea.

That said, with a static pressure test like that, the shaft still isn't turning, so is there really any gain?

yes there is. Your method does not take into account any real pressure. It is simply will water stay out under no pressure. By pressurizing the lower it will tell you if the seals are really sealing.

 

[1946Zephyr]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

These seem to leak, while shafts are turning, so your air bubbles will likely come from the upper gear case seal, shift rod seal or prop seal. These three seals are the one that have moving parts running on them.

 

[mark in new jersey]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

yes there is. Your method does not take into account any real pressure. It is simply will water stay out under no pressure. By pressurizing the lower it will tell you if the seals are really sealing.

How is 3 to 4 feet (my deepest garbage can) "no pressure"?

3-1/2' of water represents about 7.8PSI above ambient atmospheric pressure, which is a.) more than anyone here is suggesting with a tire pump, and b.) more than the unit will see in actual service.

Moreover, we don't want to keep pressure in (which is what a bike pump would do), we want to keep external pressure out.

I'm failing to see how my test theory doesn't work....

I agree that spinning the shaft will be meaningful, and I can incorporate that into the test......

What am I missing?

 

[Mas]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

If I'm reading you right...gearcase pressure is also created by the slight heating and then cooling of the gear case oil due to the friction of the gears during operation. As the oil cools, it contracts creating a slightly lower pressure inside the gearcase thus being able to draw in water to compensate.

Mas

 

[wilde1j]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

How is 3 to 4 feet (my deepest garbage can) "no pressure"?

3-1/2' of water represents about 7.8PSI above ambient atmospheric pressure, which is a.) more than anyone here is suggesting with a tire pump, and b.) more than the unit will see in actual service.

Moreover, we don't want to keep pressure in (which is what a bike pump would do), we want to keep external pressure out.

I'm failing to see how my test theory doesn't work....

I agree that spinning the shaft will be meaningful, and I can incorporate that into the test......

What am I missing?

First, 42" H2O is NOT 7.8 psi or even close, it's 1.5 psig. Lower units, at least larger ones may be pressurized up to 15 psig, and no more or the seals may be blown. Your garbage can is not an adequate test for LU integrity, unless it's 25' or more tall. A brake bleeder may be used for vacuum testing and a bicycle pump is fine for producing pressure. In either case, the LU should hold some vacuum or pressure for 30 to 45 minutes and its good to rotate the drive shaft and move the shift rod during the test. Gear oil should always be drained before the testing is done. Don't bother, unless you're doing the testing in a reasonable way.

FYI: 28" H2O ~ 1 psig

 

[mark in new jersey]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

yeah...my math error smacked me in the head this morning at breakfast....

 

[AlTn]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

if you want to assemble a pressure/vacuum tester, Fatzbullet posted this suggestion..mityvac mv8255 with the fittings and hose from a lubrimatic gear oil hand pump <wallyworld has them around here>

 

[Solittle]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

Mark - Maybe I missed something - -Why are you rebuilding this?

 

[1946Zephyr]

Re: Continuing the restoration: Rebuilding the lower.....is this a good idea?

Well, the motor is almost 60 years old. It's not a bad idea at this point. With a motor this age, what seals appear to be good today, may not be good tomorrow. It is however still a good useable motor and rebuilding the lower unit and replacing all the consumable items on it, is a good piece of mind and he won't have to work on it again, for many years. The '53 Super Fastwin was one of the best motors ever built. I would take one of these, over a modern day 15. If a guy gets a decent looking one and gives it the complete service, he'll have a good reliable motor for decades.