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Old 23-03-2011, 05:38   #1
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Outboard Driveshaft Scratches Cause Leak?

I am in the process of working on my 2002 15hp Mercury 2-stroke outboard. I'm replacing the water pump and the propeller shaft seals. When I took the driveshaft out, I noticed that it has some wear around where it passes through the water pump. It's hard to describe how worn it is, but you can feel it with your hand more easily than you can see it. The worn part has no deep gouges or scratches but is about an inch tall.

Will it be likely to leak here, even with new seals and a new water pump? I'd really rather not replace the $160 driveshaft if it's not yet necessary, but I don't have a way to do a pressure test on the unit to see if it's leaking after I get it back together. Should I just put the old shaft in and test it after a few weeks of operation for signs of water, or should I replace the shaft as a precaution?

Thanks for your suggestions!

Jack
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Old 23-03-2011, 06:34   #2
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Re: How scratched can outboard driveshaft be and not leak?

The wear you describe, if its "smooth" and "shiny" wear, and not rough and sharp, seems pretty normal for the dozen or more I've dealt with. A 2002 engine is not so old, likely doesn't need a shaft, but may be ready for a new pump housing.

I would just put it back together with a new impeller, and also a pump housing if the old one is cracked or _significantly_ worn. But the housing can look "bad" and still pump plenty of water to produce the tell-tale stream at the outlet tube. If it does that, the shaft wear is not a problem.

The bottom line for me is:
- Absolutely do replace the impeller every few years as parts of the rubber vanes that break off from an age-hardened impeller can clog coolant passages and cause major hotspots and engine failure.

- Other than that, replace the pump housing if it looks _very_ worn - some wear is OK, for me. I'd guess I replace housings on a average of every two or three impellers, or if they are cracked at all.

- Do coat all the bolt threads in that stinky, brown thick liquid gasket sealer you can buy at the OB parts supplier, so they won't seize due to electrolysis. A mechanic told me this once and after seeing how well it works I wish they were assembled that way at the factory (I've had a few bolts break off...).

- Given proper impeller replacement schedule, if the unit "pees" well from the outlet tube while its running, that's the single most important thing to note.

These guys will take very good care of you if you have detailed questions on outboard operation or repair:
http://www.marineengine.com/boat-forum/forumdisplay.php?966-Outboard-Motors-Forum

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Old 23-03-2011, 06:42   #3
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Re: How scratched can outboard driveshaft be and not leak?

Depends on where on the shaft.

If below the water pump and you can feel them with your finger nail replace the shaft. If the roughness is in the area where the shaft passes thru the upper part of the housing you maybe able to smooth it with abrasive paper. The important area is where the shaft passes thru the water pump base and seals. Ref #24 below
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Old 23-03-2011, 07:49   #4
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Re: How scratched can outboard driveshaft be and not leak?

I'm pretty sure the worn area is exactly the height and location of the two back-to-back seals inside the water pump base plate, where the shaft passes through. I'm assuming the friction from the seals themselves are the source of the wear. It is not rough or grooved, but very smooth. You probably could feel it with your fingernail as a very slight indentation on the shaft, as it decreases in diameter by a fraction of fraction of an inch.

The motor has always 'pissed' water beautifully, and has never showed signs of letting water in. (Except a very very slight milky look to the oil that I put in last fall. I think this is just from residual water or condensation inside the unit since I haven't used the motor since then. I just drained it to do the water pump job.)

Is pumping water well the biggest concern for this type of wear or is it letting water into the lower unit? Do I really want to smooth this out with sandpaper? That idea makes me a little nervous, as I wouldn't want to decrease the diameter of the shaft any more where it passes through the seals.

Thanks for the help so far!

Jack
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Old 23-03-2011, 08:01   #5
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Re: How scratched can outboard driveshaft be and not leak?

Jack, if it's just a fact that the shaft looks polished in the double seal area that's normal. That area normally will have no effect on water pump output but can let water into the gear case. If you are giong to replace the impeller anyway I would suggest a complete WP kit and new seals in the base.
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Old 23-03-2011, 08:12   #6
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Re: How scratched can outboard driveshaft be and not leak?

Yeah I am already in the process of doing the complete water pump, my only question is about the shaft wear. It does look polished, but it looks like it was polished to the point of actually making a slight indentation around the circumference of the shaft. If the seals squeeze in tight to the shaft, there probably won't be much of an issue here, but if the seals are rigid and there is a slight gap now, I would expect water to be able to get in.

Jack
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Old 23-03-2011, 08:21   #7
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Re: How scratched can outboard driveshaft be and not leak?

Quote:
Originally Posted by OrangeCrush View Post
...It is not rough or grooved, but very smooth. You probably could feel it with your fingernail as a very slight indentation on the shaft, as it decreases in diameter by a fraction of fraction of an inch.

Is pumping water well the biggest concern for this type of wear or is it letting water into the lower unit? Do I really want to smooth this out with sandpaper? ...
Smooth wear is normal and OK, even to the point of what appear to be slight grooves, .012" deep, or so (I'm not quoting a spec here, just looking a pair of digital calipers and guessing... For reference, a sheet of standard 20# printer paper is ~.003" thick.)

Barely detectable wear is nothing, considering the seals are flexible rubber and can compensate extensively.

Pumping water is the largest concern since not pumping water will ruin your engine from heat in seconds or minutes. BTW, running the engine 'dry' for even a few seconds without water to the pump, though it may not allow the engine to overheat, absolutely can ruin an impeller. I coat the impellers of inboards with silicone grease prior to installing to give it a slight lube advantage for the dry run as it sucks up the cooling water on the first start. OB foot should be in water (or muffs) prior to any cranking.

Sandpaper can only make it worse, IMO. If it 'needs' sandpaper, I'd replace the shaft, since, as you point out, that can only remove material...

Monitoring the lower unit oil for milkiness is the next priority after pumping water - slight milkiness, as you point out, can be from condensation. More milkiness, and I'd replace the seals long before replacing the shaft, since new seals will 'grip' the shaft tighter and the rubber of the seal is likely to wear out hundreds, or thousands of times faster than the steel of the shaft.
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Old 23-03-2011, 08:46   #8
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Re: How scratched can outboard driveshaft be and not leak?

Just some thoughts

Quote:
Originally Posted by Whimsy View Post
Pumping water is the largest concern since not pumping water will ruin your engine from heat in seconds or minutes. BTW, running the engine 'dry' for even a few seconds without water to the pump, though it may not allow the engine to overheat, absolutely can ruin an impeller. ...........

I totally agree with the above, but would add that water in the gearcase can rapidly destroy the components.

Sandpaper can only make it worse, IMO. If it 'needs' sandpaper, I'd replace the shaft, since, as you point out, that can only remove material...

Never use sandpaper in a seal area. If the shaft was damaged at the top of the water pump housing you could smooth it with the paper as there are no seals there.

Monitoring the lower unit oil for milkiness is the next priority after pumping water - slight milkiness, as you point out, can be from condensation.

Better yet preasure check the gearcase at 3, 5, and 15 lbs.
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Old 23-03-2011, 09:01   #9
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Re: How scratched can outboard driveshaft be and not leak?

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Just some thoughts...Better yet preasure check the gearcase at 3, 5, and 15 lbs.
Excellent! Is it common for a shop to do this after a reseal or or more extensive work? What should the results be? <X psi decrease after Y seconds or minutes? Is this commonly speced in shop manuals or more of a generic test that could be done with a custom oil plug/air fitting?
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Old 23-03-2011, 09:21   #10
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Re: How scratched can outboard driveshaft be and not leak?

I don't have any access to a pressure pump, nor am I willing to buy one right now. Based on all your feedback, my plan is to keep the existing shaft, replace the water pump and related seals, replace the propeller shaft seals, and use the motor. After a few weeks of normal use I will drain the gearcase again and check the appearance of the oil. If it is too milky, I will consider pulling the water pump again and replacing the driveshaft.

One quick question I can't find an answer to in the repair manual. Do I put teflon lubricant in the splines at the bottom of the driveshaft or just at the top? I'm not sure if this is required since it is immersed in the lower unit oil anyway.

Thanks a lot... it's amazing how useful this forum is to me.
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Old 23-03-2011, 09:22   #11
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Re: How scratched can outboard driveshaft be and not leak?

Quote:
Originally Posted by Whimsy View Post
Excellent! Is it common for a shop to do this after a reseal or or more extensive work? What should the results be? <X psi decrease after Y seconds or minutes? Is this commonly speced in shop manuals or more of a generic test that could be done with a custom oil plug/air fitting?
This is common shop procedures and recommended by outboard/ sterndrive service manuals. The reason for the multiple PSI is that some leakages actually fix themselves with higher pressures. If the gearcase tested has either back to back or double lipped seals we will also vacuum check.

Most US manufactured units have a 3/8 nc thread at the drain point. An adaptor to the pressure source can be secured at a Marine Service center and additional adaptors for foreign made units (metric) can be added to that. DO NOT EXCEED 15 lbs. as you could actually blow the seals from their seats.
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Old 23-03-2011, 09:39   #12
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Re: How scratched can outboard driveshaft be and not leak?

Quote:
Originally Posted by OrangeCrush View Post
One quick question I can't find an answer to in the repair manual. Do I put teflon lubricant in the splines at the bottom of the driveshaft or just at the top? I'm not sure if this is required since it is immersed in the lower unit oil anyway.

Thanks a lot... it's amazing how useful this forum is to me.
Just the top. Put some lube on the seal lips to prevent damage as you pass the d/shaft thru them.

FWIW - you could probably jury rigg a dinghy pump to put at least a little pressure and soap the locations
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Old 23-03-2011, 10:16   #13
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Re: How scratched can outboard driveshaft be and not leak?

Thanks, knotnow.

One more question while I'm at it. The seloc manual says I need a special tool to change the back-to-back seals (#24) in the water pump base (#18) (sorry I don't have the book in front of me so I don't remember what they called it). I think this tool may just be to get the seals out without damaging the water pump. Since I am assembling a brand new water pump, do I really need such a tool? Can you elaborate on how these seals go in exactly? Does the loctite go on the curved outer surfaces of the seals, where it sits against the plastic water pump base? Do I put the seals in before passing the driveshaft through, the same way it came out?

Thanks again!

Jack
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Old 23-03-2011, 10:38   #14
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Re: How scratched can outboard driveshaft be and not leak?

I believe the tool in question is the seal installer. The seals go into the WP base, and as youíve said, back to back. Youíre pushing against the thin tin which can be easily damaged or bent. The tool supports the seals and sets them to the proper depth. Fortunately the seals go in quite easily with very little pressure needed if you havenít damaged the base removing the old ones. I have seen folks carefully use the back side of a socket successfully. Pay attention to the installed depth before you remove the old ones. Remember that polished area you originally mentioned? We want to make sure the new seals end up there. You need to install the seals in the base and the base into the gearcase before installing the d/shaft.
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Old 23-03-2011, 10:43   #15
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Re: How scratched can outboard driveshaft be and not leak?

O ya. The locktite is used around the outside of the new seals to glue them to the plastic.
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