Silicone to use for sealing leak between outboard upper an lower leg??

[JayT]

Hey,
Just replaced the impellor on my 99 70hp Johno an since it aint been done for years it certainly needed it! lucky i noticed really as I had broken a tooth an was slightly creating a blockage, only noticed cause the last 2 trips she didnt seem to be pumping the constant stream out the telltale like usual....
Anyways back to the heading, after sussing it out an a little trial an error my bro an I split the legs changed the impellor cleaned her all up inside an whacked her back together for a run with the muffs,
Oh mind you in splitting the legs we had too bash each side of the lower leg with a block of timber an hammer an in doin so slightly bent the wings on either side of the lower leg, leaving a visible 1mil gap in places where the legs join...
So kind off expecting the outcome, water pissed out the, say 100mil long,1mil gaps on either side thus creating water loss so that I still not getting my constant stream out the telltale....idiots for not sealing the leaks previously!!...
So in a long story whats the best silicone, sealant to use in between legs???

Cheers Thorpy

[spearking]

JayT, my old man runs 2 large prawn trawlers up in the gulf and has been using a silicon product called 'sikaflex' for the last 15 years. I now use this product for all my marine applications with great sucess. You can pick it up at any well stocked bunnings or other hardware store. It comes in black and white. Hope this helps

[JayT]

Cheers spearking, was thinking sikaflex an with the gap sealed do ya think this would correct the telltale flow? cause thats what I am hoping:)

[FNQCairns]

I am not sure exactly where around that joint on the leg you are speaking about.

So 2 options if it is coming from the internal cavity that houses the pump, pull the leg rough up the surfaces that are a problem and apply some of that epoxy aluminium 2 part filler (forget it's name someone might help) then when set file and shape to suit.

if from the exhaust portion do as above or just apply some marine sika, doesn't really matter if it leaks from here.

cheers fnq

[Spaniard_King]

There is no need to use any sealant between the gear case and the leg

[FNQCairns]

Gary he has bruised the mating surfaces trying to get them apart.

cheers fnq

[Spaniard_King]

FNQ,

The only purpose it would serve would be to stop a small amount of exhaust.. in some of the early V6 OMC engines they actually had a releived gearcase i.e there was a section where there was a gap in several spots where the gearcase did not seal against the leg.

Personally it.s not required

[FNQCairns]

yeah I agree overall, but what about the 1m gap? When some engines get old (and not so old) they rely on filling the internal driveshaft cavity partly with water as a help to force more flow up the tube.

But again I agree it shouldn't be a true problem just so long as when at speed the cavity can still hold a head of water, at slow speeds the surrounding water will help do it naturally.

cheers fnq

[Spaniard_King]

The gap will have nuthing to do with the water pump so cooling water wont be affected.

[FNQCairns]

yeah I suspect you are right Gary, not a nice thing to see on the muffs though, the head that gets built up in the leg can forced a good squirt out.

cheers fnq

[Spaniard_King]

Still struggling to see where this squirt is going to come from.. its unlikely he had damaged the 2 exhaust surfaces so the used cooling water and exhaust should still pass throught the gearcase and out the exhaust.

[FNQCairns]

It comes from the poor mating of the pump outlet and the water tube. At the ramp for example it's easy to pick the worst ones, as they may take a while to start pissing as it still had to fill a good head of water internally but around the pump.

cheers fnq

[Spaniard_King]

Have to say I have never come across that.. cant see there ever being a head of pressure as the shift shaft on just about all outboards is not sealed so anyexcess water would flow out the hole where the shift shaft protrudes, hence not needing to seal the gearcase to the leg

[FNQCairns]

Yeah it will if it get that high, My yam has a cast small gap in the leg mating surface, when on the muffs the water pours out of, it's not used water it's simply the escaped water from the pump outlet and all parts are new or was 2 years ago, modern engines may have a more solid connection here?

cheers fnq

[JayT]

Cheers Fella's,
Its the same as what FNQ is explaining Garry, it is along the mating surface of the legs roughly between the front an back of the leg down each side,
Now I know water does hold in there cause after I run the motor on the muffs an even when leaving the ramp I always trim the motor up to expell any water left in the lower leg, there is a small hole, at the back of the motor (meaning toward the boat) that is right on that same mating line where water looks like its supposed to leak out of an does, draining water from the leg i imagine,
Anyways have since backed all the bolts off an have applied a 2part epoxy resin in an around the mating surfaces especially the 100mil gaps an have tightened it all back up:)
So, just have to wait awhile an give her a test run an hopefully problem solved,
The main reason for the thread was that I was worried that because of this extra leaking would it effect water flow up an thru the engine like when the old impellor with broken tooth inside did or not, I am hoping that this will fix my problem an I will get back that constant stream again:)
Thanks again for ya replys,
Thorpy

[mercury'srising]

Hi Jayt, No sealant is required on lower leg mating surface, especially if you want to get it of again easily. More likely if you still have a weak flow from your telltale or pressure gauge then a piece of rubber from the old impeller has probably gone up the tube and into the powerhead causing a restriction somewhere. If you're lucky it may be lodged in the telltale outlet against the flow restrictor and may have been there for some time. Try poking a suitable piece of wire up the telltale outlet and also blow it through with air, but from the outside only. It may be just as easy to remove the tube and clean it out. Replacing the impeller every season start can work out cheap in the long run.
Hope this helps

MERCURY'S STILL RISING WHILE OTHERS FALL