TOPIC: Resealing L/U, Use RTV?

Finally got the seals, and getting around to resealing the L/U on my '76 25hp. I actually switched parts with a '75 25hp. I noticed on both of the L/U's that RTV was used on the spaghetti seal. Is this correct or just a stop-gap by someone along the way? Also this is my first time resealing a L/U, anything else I should know? I was able to get the upper seal extracted, but the lower, closest to the prop is still giving me fits... Thanks.

There are better sealers than RTV avaiable.

---

Do not overlook the shift rod O-ring seal in there.-Major cause of oil leakage that one.

OMC specifies their own brand of gasket sealer, think it's called Bombardier Gasket Sealer now. Mercury sells their "Sealer 1000". Both of which are roughly equivalent to "Perfect Seal #4".

But what I've always used is Permatex No. 3 Aviation-Type non-hardening gasket dressing.

You can get it in pretty much any auto parts store, in a small bottle with a brush-in-cap. Spread a thin coating on the surfaces and it'll seal just fine.

If you want to go Really Fancy, use a sparing coating of OMC Gel-Seal anaerobic sealer. It only hardens in the areas that are squished together, so it's ideal for metal-to-metal type of sealing applications.

Loctite/Permatex 518 is another good anaerobic sealer and many auto parts stores carry the stuff. I've used it to seal crankcase halves, amongst other things, and it works great.

You must scrupulously clean/degrease the gasket surfaces before using this type of sealer. Loctite sells a spray primer that cleans very well and promotes a faster/stronger seal.

But in reality, the good ol' Permatex No. 3 will seal the lower unit just fine.

A good tip for removing that pesky propshaft seal, reassemble the seal carrier in the lower unit without the "guts" and temporarily install the lower half/skeg section with 4 screws or so.

This will hold the seal carrier firmly and you'll be able to pry out the seal. Be careful of what force you use when prying, the walls of the carrier are thin and you don't want to break them. Having the carrier bolted back up into the lower unit gives it tons of support, with no way to crush it (as you could if you cranked down on it in a vise).

HTH & G'luck.............ed

p.s. to get the shift rod bushing out, I've tapped the hole with a 5/16" fine-threaded tap. Then you can thread a long bolt into the bushing to be able to pull it. Works great if you don't have the special removal tool. The threads will not affect the function of the bushing or interfere with shift shaft operation, once it's all back together.

Gel seal is for crankcase halves. Use the OMC/BRP gasket sealing compound for everything else including coating bolt threads.

Part numbers:
4 ounce 508235
16 ounce 317201
spray 771093

Mercury has an equivenlant called Perfect Seal.

Don't buy the 16 ounce can unless you do lots of work, a little goes a long way & 4 ounces will last the average garage guy years.

Wow, lot's of good info, Thanks much. When I say RTV, I mean
that it had some type of sealer, not necessarily specifically 'RTV'. The prop shaft seal carrier looks like the edges are 'flattened over' the seal, is this common or severe...? I will have to see what I can find for those sealers...Thanks much...

jimandros wrote:

Gel seal is for crankcase halves. Use the OMC/BRP gasket sealing compound for everything else including coating bolt threads.

Part numbers:
4 ounce 508235
16 ounce 317201
spray 771093

Mercury has an equivenlant called Perfect Seal.

Don't buy the 16 ounce can unless you do lots of work, a little goes a long way & 4 ounces will last the average garage guy years.

I thought the BRP reccomended goop for older lower units was part number 776964, which should get you a tube of 3M Scotchgrip #847. If your 25hp is the 22ci "sportster" (souped up fastwin) this may apply. I'm sure someone on the AOMCI "as-a-member" forum can say for sure.

I seem to recall hearing that gel seal IS used on some more modern vintage lower units.