TOPIC: 64 650 prop seals, what the ??

I decided to get started on testing my lower unit for seal leaks. I had noticed that after the last day at the lake the prop shaft seal seemed to be actually dripping gear oil. When I pulled the prop, I found this. The inner shaft seal has come out flush or a little raised from the outer edge of the retainer. The outer seal was actually pushed out of the retainer and was seated on the forward thrust hub! Has anyone seen this before? Now, this seal set was in place when I got the motor and in several test runs the seals never wandered. I'm using the same thrust hub that came with my old prop, but I've added a new prop (direct replacement). Also, I notice the rubber on the new prop looks a little like it's squeezed out at one side, at the forward end of the hub. Might just be normal as the new prop and hub break in, I don't know. But mainly I'm stumped by the shaft seals coming loose like that. Merc experts, what do you think?

The shoulder on that propshaft shouldn't be flush with the seals, in fact you can see aluminum shavings where the thrust hub has been rubbing on the propshaft bearing carrier.

Doesn't seem to be a lot of internal threads showing on the gearcase, I'm wondering if this lower unit has been apart and they didn't screw the gearcase cover on tight enough (150 ft-lbs if I recall correctly).

I'm also wondering if this lower unit shifts OK.

Another issue you'd find if the bearing carrier wasn't in far enough, would be a ton of end play in the propshaft. You'll have some normally, but if it's too much you'll have troubles in reverse more than forward gear.

Sure looks to me like the prop hub, riding in too close to the seal, caught it and drug it out.

I'm thinkin' I'd be very inclined to pull the bearing carrier out and inspect everything. There may be another reason why the carrier isn't in as far as it should be.

You'll need the special gearcase cover tool or make a suitable tool to undo the threaded cover (normal, right-hand threads).

If this motor has been run pretty much only in fresh water, it should come apart OK. Otherwise, it'll require a lot of heat on the gearcase (think: Torch!) to break things free.

HTH & let us know what you find out.........ed

Proper seals are equipped with metal housings.

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These appear to be aftermarket " junk " and may have popped out due to pressure.

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A gearbox on an outboard develops pressure when operated !

Joe Poole contacted me and also mentioned that the seals look like aftermarket. I mic'd one and it had the same O.D. as a Merc seal, 1.692", but it's rubber coated metal instead of the seat surface being metal. Hey, maybe this is good news in disguise...If the lower unit is building up enough pressure to blow out the cheapo prop shaft seals, maybe that's an indication that the other seals are holding pressure. Joe also mentioned the possibility of a hairline crack in the carrier allowing the seals to un-seat.

Ed, I can't detect any end play and very little side play at the propshaft and the lower unit shifts fine. What looks like aluminum shavings in the prop shaft pic is more of a trick of the camera/strobe light. Instead of metal chips, that's just a "clean area" on the carrier.

Looks like I'll be ordering up the correct tool for removing the carrier and I'll have all your advice handy when I remove it. I sure appreciate all the info.

Oh and one more thing, I understand the seals go in back-to-back but it looks like the last person installed these two seals stacked, with the closed face of both facing rearward (spring side forward) on both. Could be that the prior mechanic was even more shade-tree than I am...?

Yup sounds like the last guy had no clue. You're correct the seals go in in opposite directions. The inner one lip facing in & the outer facing out. Having both the same direction is most likely why it leaked. You'll also need a special driver to install the new seals & don't forget the new O-ring for around the carrier. After you replace the prop seals pressure test again to be sure the others don't leak.

Hope I'm not boring you guys with all this. I really do appreciate the knowledge you share on the forum. Here's my update, good, bad, and ugly.

Ed, on second look, I can detect some end play by pushing in on the shaft. Feels firmly spring loaded. End play is a hair more than 1/16" , guesstimate 5/64".

Tim, I was wrong on the seal orientation, he had them back to back after all, with lips facing away from each other. No excuses for my error, I got confused on the orientation of the forward thrust washer when in place.

The inner seal, that was still in the cavity but out all the way flush with the retainer: I went ahead and pried it out with a small screwdriver. It popped right out easily. The spring that holds tension on the lips was partially off the seal and looking at the rubber part, I think it was that way for quite a while. So that seal wasn't doing anything. See lower photo, that's how the seal looked when I popped it out.

Now, looking down in the recess, I measured the depth to where the inner seal would seat, and when both are in place I'd say there would still be a full seal's thickness between the outer seal and the outer surface of the retainer. I can't see any way they could have drifted that far out unless they were too loose in the cavity and pressure pushed them out. I think the thrust hub would normally never come near the outer seal surface.

The good news, the shaft surface where the seals will ride looks perfect. No corrosion or scratches there and almost no discernable wear at all from seals.

The ugly: With both seals now out and the shaft looking good, minimal side play on the shaft and maybe 1/16" end play when I push in against the spring on the shaft, I'm considering using a home made tool to drive in two new correct Mercury seals without pulling the carrier out. I'm thinking a length of heavy wall PVC pipe or other pipe would work. Granted, I won't get to replace the carrier o-ring that way, but I could at least do my pressure/vacuum tests at that point to see what if anything is still leaking. What say you? Will this kind of shade tree thinking get me banned from Mercdom for life?

Well norm; don't suppose it will get you banned but maybe spanked.
The pipe Idea should work OK . The inner seal needs to bottom in that cavity, then you"ll need to use a big washer between your pipe driver & the outer seal it should go in just flush with the end of the carrier, there should be a space between the 2 seals. Be sure to use a little permatex on the outside of the seals & liberally grease the lips before installing. I didn't notice in any of your pictures a little split washer that goes between the prop spacer & the prop shaft . It is necessary if you don't have it I probably could dig one up around here. The thing is roughly the same diameter as the small end of the spacer & .030 thick .
Tim

Glad you mentioned the space between the seals. I could have driven in the outer seal until it contacted the inner one, if you hadn't mentioned it.

You're right about the missing thrust washer. There was none in that area from the first time I pulled the prop to change it out. My Clymer Manual doesn't show it but describes the front piece as "thrust hub and washer". I have another manual that shows it in the blow-up picture and calls it a thrust washer. By split washer, you mean split like a lock washer, only thinner?

I did find a piece of 1-1/4", thick wall PVC (gray) pipe that very closely matches the seal O.D and I.D. the walls are 3/16 thick, enough to provide good support where it contacts the seal and large enough I.D. to clear the prop shaft. I screwed a regular iron 1-1/4" pipe nipple on the threaded end for a good hammer tapping surface.

This may or may not work, but if it doesn't I'm only out the cost of the seals and can still go further with dismantling and doing it the correct way. If the seals hold, I can proceed to pressure and vacuum testing the unit to see how everything else is doing.

Update: I installed my new Mercury prop shaft seals today. They went in like they should (not loose in the bore at all). My Shade Tree seal installer was up to the job.

I did a pressure/vacuum test with my Mity-Vac hand pump, rigged with a screw in-adapter from a gear oil fill pump. Disappointed at first, I was slowly losing pressure as well as vacuum. Rather than pull off the lower end, I first thought to check the Mity-Vac pump itself for leaks. Capped off the tube that attached to the fill fitting, and sure enough, I was slowly losing both pressure and vac through the pump! I re-ran the tests, but after pumping to 9 lbs pressure (and 6 lbs vac) I clamped off the tube that ran from the tee to the pump so the only open line ran from pump to gauge. I lost zero pressure or vacuum in 15 minute tests.

Thanks to Jim C, Ed, and Joe Poole for their advice on fixing and testing my gearcase. It's going to be over 90 degrees this week, time for the lake.

Looking at the seal pictures, I would grant you that the seals pinched on the propshaft on the way in, real easy to have that happen on this one. The prop shaft has a sharp edge shoulder that the thrust hub sits against, and it is a bugger for pinching seals as the carrier is pushed home. I build up this area with electrical tape, tapering down to the shaft like a cone to give the seals a ramp to ride up on. Once the carrier is installed you remove the tape and install the hub and washer. Pack the garter spring of the seals with grease to keep them in place as the carrier is installed as well, and use red Loctite on the metal edge of the seals when you install them.

Thanks for that. If I ever need to do this one again I'll use that electrical tape trick. Joe Poole also suggested red loctite on the outer edge so I used that. I lubed the seal lips real well and was careful on the install, and it looks like everything seated as it should. Since the non-mercury seals had uninstalled themselves, I did this seal job without removing the carrier. Before I installed the new seals, I cleaned the bore with some min spirits on a rag to remove any stray lubricants so the red loctite will have some grip. Just got done filling the bottom end with fresh lube and reinstalled the prop. I'm anxious for a test run.

Two minor questions I have, maybe you could fill me in. One, the manual I have shows the gear lube being pumped in while the motor is tilted up. Makes sense since it's harder to do with the motor in the down position. Is that the right way to do it? Two, and this is really dumb...The tilt lock...Should be disengaged while in forward, locked in reverse, and also locked in neutral, correct? I've had quite a few outboards but don't recall for sure. Seems like locking in neutral would help keep the motor from lifting if it was being started with the recoil starter. Not that I plan on doing that a lot.

Thanks

On the gear oil, you fill from the bottom until oil flows out the vent (upper) hole. This is the correct level in the gearcase, and the motor has to be lowered to its operating position to get the correct level.

Once full, you reinstall the vent plug, remove the oil supply and install the drain plug. With the vent plug installed first, you won't have a lot of oil gushing back out while you're trying to install the drain plug. That being said, I always have plenty of paper towels down, and have the drain plug all ready and positioned to install as soon as the oil supply is removed.

And it still makes a Stinky Mess! Yuk! One of the simplest things to do on an outboard but definitely not my favorite!

And yeah, the tilt lock is supposed to lock on the pin when in Neutral, too. Otherwise, if you were running at speed and the gearshift was quickly chopped to Neutral, drag on the lower end would cause the motor to kick up and possibly damage the motor and/or boat.

So, to raise the motor it must be in Fwd gear, and you also must leave the control lever in Fwd in order to properly set the motor back down on the tilt lock.

HTH........ed

Thanks again Ed.