posted 12-08-2008 04:38 AM ET (US)        

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I've just noticed an oil leak in the gear case housing where the propeller is on my 1999 Mercury OptiMax 135-HP. [The cause of the leak is] definately not the screws for oil removal and filling. [The leak] is coming from behind the propeller where the visible seal is around the propeller shaft. Can this seal be replaced by just removing the prop, digging out the old seal and carefully knocking in a new one?
Or am I up for some major surgery ? Thanks

Jake.

posted 12-08-2008 08:45 AM ET (US)            

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Pressure test the gear case to establish if there is a leak.

If the leak is from the propeller shaft seal, you will likely have to tear down the gear case to replace the shaft seal. If the gear case has been used in saltwater and has never been apart since 1999, it may be a project to disassemble it.

posted 12-08-2008 08:54 AM ET (US)            

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This exploded view should give you an idea of what's in the gear case:

http://www.iboats.com/ Mercury_V150_V175_V200_Gearcase_Assembly_Exploded_View/dm/cart_id. 695214943--list_time.1228744381--session_id.838029061--view_id.272940

The retaining nut usually has a rather unique configuration, and often a special tool is required to remove it. This may affect your ability to perform this repair yourself.

posted 12-08-2008 09:04 AM ET (US)            

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Visit Mercury Parts Express website. Enter the serial number of your Mercury engine. It will show you an exploded view of the gear case.

Begin at:

http://www.mercurypartsexpress.com/us/index.php

On the lower left (after scrolling down) select MY ENGINE button.

posted 12-08-2008 07:14 PM ET (US)            

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Thank you for this information Jim,

I have just been told by our local outboard mechanic that you can carefully pry the seals out and put the new ones in without removing the bearing carrier and prop shaft.

I will give it a go this weekend and post back my results.

Jake.

posted 12-08-2008 07:36 PM ET (US)            

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Jake,

The most common cause of prop shaft seal failure is monofiliment which the prop easily picks up around the dock or launch ramp.

On two occasions When I removed the prop to check for mono around the shaft I found some. I was lucky and able to unwind it before it could damage the seal.

Butch

posted 12-09-2008 01:02 AM ET (US)            

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Jake--Thanks for the follow up.

I was studying that exploded view diagram. Usually in those views the order of the parts along the dashed line indicates the order of the assembly. The seals look like they are installed after the bearing carrier. I wondered if they were just a press-fit into place. From your comment it sounds like they may be like that.

posted 12-09-2008 06:16 PM ET (US)            

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Removed the 2 seals with a screwdriver in around 15 minutes without removing the propellor shaft or bearing carrier. Just the propeller was removed. The most difficult part is removing the bottom seals metal outer case as it has been loctited into the bearing carrier and is awkward to get to. But with a bit of patience and lots of care it came out.

The new seals just knock in easily with loctite on the outer case and teflon grease on the propeller shaft.

Hopefully this helps others if they have the same issue.

cheers
Jake