Sealing up lower unit

[LAndrus]

86 Force 50HP

Have to do some major transom and deck rebuilding so taking the opportunity to seal up my leaky lower unit, replace the water inlet tube, and water pump. Lower unit is taking on water somewhere so I pulled it apart to seal it up. Ordered Quicksilver part #25-841807 from Marine Engine.com. The part number is #41 on the following image, which is part #25-841807

My issue is the following, the part I received is an O ring.

My lower unit is not round nor does it have a round slot for the O ring.

How am I supposed to seal up an oblong lower unit with a round seal?

Help is welcome and appreciated.

ps: pictures were taken from my phone.

 

[foodfisher]

Re: Sealing up lower unit

Not so sure you need a seal there, but I've seen pictures of RTV oozing out of that area. that O-ring will take any shape you bend it to.

 

[LAndrus]

Re: Sealing up lower unit

So I've been thinking myself, but wanted to get a second opinion. RTV it is.

 

[Frank Acampora]

Re: Sealing up lower unit

NO! NO RTV! There is a special gasket that goes there. Its thickness is calibrated to maintain correct gear lash between the pinion and forward gear. I have one so give me a day to get into the garage and I will give you the correct Mercury number. If you don't want to wait, that same gasket was used on Chrysler 35, 45, 50, and 55 engines in addition to early Force 50s. Contact Franz at franzmarine@aol and he will sell you the correct part.

 

[Nordin]

Re: Sealing up lower unit

You can make that gasket from gasketmaterial sheet. The thickness should be 010. As Frank says it sets the lash between froward and revers gear.

 

[Frank Acampora]

Re: Sealing up lower unit

Looking at that gearcase again, you have a couple of rather deep cuts in the sealing surface. No matter what gasket you end up using coat both sides in gasket varnish. RTV would be the second choice.