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Author Topic:   Leaking lower unit - 100 Merc
Taylor posted 09-28-2001 05:58 PM ET (US)   Profile for Taylor   Send Email to Taylor  
I notice some oil dripping from the lower gearcase drain plug on my '88 Merc 100. (I leave the outboard in the down in the boathouse, if that matters... yes, its out of the water.)

I've tried getting the plug out to see what the problem is, and so far, its stuck. I think I need a bigger screwdriver. The plug looks a little the worse for wear to, folks have beat on it in the past and torn up the slot.

Is this something simple where I could just buy a new plug with a new O ring and swap them?

Can anyone recommend a good manual for this outboard. I'm tired of being stupid.

Dick posted 09-28-2001 08:18 PM ET (US)     Profile for Dick  Send Email to Dick     
Seloc makes a very good manual The number is 013-6.
Get a screwdriver that fits the drain plug, if it won't turn tap the end of the screwdriver lightly with a hammer as you try to turn it. Take it easy with the hammer. A new plug and gasket should solve the leak.
CarlRobert posted 09-28-2001 10:59 PM ET (US)     Profile for CarlRobert    
For some reason those plug screws have a very shallow slot. I had one freeze on an old Merc and I finally stripped the slot. If this happens in your case, you can drill a hole in the screw (make sure you tap/drill it exactly in the center), then use a left hand threaded back-out bit. It has reverse threads so when you screw it into the newly drilled hole and bottoms, it will exert force to loosen the stuck screw. Works very nicely and a new drain plug screw costs less than a buck.

Carl R

acseatsri posted 09-28-2001 11:10 PM ET (US)     Profile for acseatsri  Send Email to acseatsri     
Or you can try a center punch and try tapping it with a hammer to screw it out. Make sure you put it near the edge and don't hit too hard.
lhg posted 10-01-2001 05:35 PM ET (US)     Profile for lhg    
Lately Sears has been advertising, using the "this old House guy", a new tool for a power drill, about $20, that will back out ANY stripped/frozen screw (so they say) so that it doesn't have to be drilled out. Look into it for your problem.
From the pictures they were showing, sure seemed to work.
acseatsri posted 10-01-2001 05:59 PM ET (US)     Profile for acseatsri  Send Email to acseatsri     
The tool you're speaking of looks more suited to removing stripped Phillips head screws. Save your money. To get your plug out, use the punch and hammer if all else fails.
Taylor posted 10-05-2001 03:09 PM ET (US)     Profile for Taylor  Send Email to Taylor     
Got the plug out. Just took the right size screwdriver, as Dick suggested. (I also have the Seloc manual on order.)

The lube, which was fresh this summer, had a slightly milky quality, but still showed greenish, not the milkshake brown that I'd feared.

I've got a new plug, and fiber washer, as well as new washers for the upper vent plugs, and I've got some new gear lube and a nifty little pump, so its oil change time for my lower unit.

Wish me luck, and here's to the hope that the leak is just a bad gasket on the drain plug.

noswah posted 10-05-2001 06:20 PM ET (US)     Profile for noswah  Send Email to noswah     

You might try investing in an impact screwdriver. Anyone who has ever worked on Harleys knows that the heads of most screws will be stripped if an impact isn't used. All you do is fine the correct driver bit, insert it and hit it with a hammer. I would spray some Liquid Wrench first, then let it sit over night and try the impact.
Whalerdan posted 10-12-2001 04:27 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
Why don't you pressure test it? When I redid my seals the guy hooked up a bicycle pump with a gauge and put maybe 10 PSI or so on it. You could see it leaking down. If you do pressure test it you save more wear and tear on the gearbox from the water getting in. You could rig up a tester pretty easy or take it to a shop and have them do it real quick. I takes less than 60 seconds to do.

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