Lower Unit Leak

[miichael18]

I just got a 1976 20 HP mercury and i was looking it over checking everything. The lower unit was dry of lube and i filled it back up but noticed it leaks the fluid out slowly where the prop is. Are there seals in there that would cause it to leak? What do i need to do to fix this leak? i took the prop off and couldn't go any farther without a special tool, had a nut with 4 notches cut in it holding it all in there. I'm going to order a repair manual but was wanting to get some info on this before i start. Is the water pump also behind the prop? or is it in the shaft? going to replace it while I'm in there if its at the right place. any info be good

 

[miichael18]

Re: Lower Unit Leak

Also what Seals do i need? If i get a water pump kit does that include the lower unit seals or i have to buy them seperate? The lower unit gastket set is $66.75 for a 20hp mercury!

26-66303A1 Lower Unit Seal Kit fits 20 HP models 1966-1980. $66.75

 

[toddr5516]

Re: Lower Unit Leak

you problably can just get the prop shaft seal for 4.00 and solve that.the impeller(water pump) is located vertically above the lower unit.there should be 4 bolts that hold the lower unit to the mid section of the motor that is where the impeller is.Impeller is @ 15.00 to 30.00.
yes get a manual. im new but learning fast

 

[miichael18]

Re: Lower Unit Leak

do you drop the lower unit without taking the prop shaft out? or do i have to have a prop wrench to remove the nut behind the prop?


Theres a inner and outer prop shaft seal. should i get both? are there anything else i should change maybe bearings/etc.?

 

[Motor Boater Bill]

Re: Lower Unit Leak

I also have a 1976 20 hp Merc, and have torn down a couple of these lower units. You need to drop the lower unit first, then you can get to the water pump. Impeller is about $15, OEM. Get the manual before you go too far. You will need to find the hidden bolt under the anode plate, which is held on by an allen head bolt accessed through a hole above the silver anode plate. There is one nut above the prop, and another on the leading edge above the lower unit. Three nuts, not four bolts as stated above.

I made a tool to remove the cover nut--the ring with four notches. I did it by finding an iron plumbing fitting (a bell coupling worked just right, take measurements and go to the hardware store) that would fit inside the cover nut. Then I drilled four holes around the perimeter of the plumbing fitting and put in four bolts so that the bolt heads would engage the notches in the cover nut. I did a little fine tuning on the bolt heads with a dremmel tool so they fit well. You can add spacers and washers then a nut on the prop shaft to hold it all in place, and turn it with a large pipe wrench. Use lots of penetrating oil and heat with a propane torch if it is stuck.

You can also buy the tool from oldmercs.com.

The book says to pull the bearing carrier to replace the seals, but I have also read of people removing these seals by drilling the metal flange of the seal and threading in a screw to pull the seal. Haven't tried that myself but it is interesting. You wouldn't have to remove the cover nut if you did it that way.

You should also inspect the shaft for pitting or grooves that will damage the new seal.

 

[miichael18]

Re: Lower Unit Leak

So i need to buy just the inner and outer prop shaft seal? or should i just tear it down first then order my parts? I was just thinking there couldnt be many seals in there figured replace them all and put a new waterpump while im in there and i should be good to go.

 

[Motor Boater Bill]

Re: Lower Unit Leak

It's a good idea to replace all the seals, and you are right about the price, about $66. Sierra aftermarket kit may be a few bucks less. Definitely do the water pump. Tearing it down first is a good idea so you can inspect the shafts in case you have more serious problems--rusty drive shaft, for instance, which would require a sleeve to fix. If this has been in salt water you definitely need to look at the shafts before you start spending money on it. Here is a link to some pictures of some bad shafts, my cover nut tool, and a puller I made for a stuck bearing carrier.

http://s46.photobucket.com/albums/f141/MotorBoaterBill/?sc=1&multi=5

 

[Motor Boater Bill]

Re: Lower Unit Leak

Having given the worst case scenario, here's the best case--fishing line can get caught in the prop and cut up the propshaft seals, so that may be your only problem. If the shafts look good, you can replace just the propshaft seals, then pressure test the LU to determine if the other seals are good. But the propshaft seals are the most difficult to get to, so if you do those you might as well do the others also, and you should pull the water pump body to inspect the drive shaft anyway, so at that point you might as well do those seals.

By the way, consensus seems to be that the seal on top of the water pump doesn't do much, and some kits don't even include it.

 

[miichael18]

Re: Lower Unit Leak

I cant find the complete lower unit seal kit for my engine? On iboats it lists only from serial numbers 4709593 and up. Mine is serial number 4409457. Will this seal kit work anyway?
http://iboats.com/mall/partfinder/c....1/search_in_category.t/session_id.938924978/

Says from serial number 4709593 to 6443972?

 

[miichael18]

Re: Lower Unit Leak

Does the lower unit seal kit include the prop shaft seal? inner and outer?

 

[miichael18]

Re: Lower Unit Leak

bump

 

[tmcalavy]

Re: Lower Unit Leak

A LU seal kit should include all the ones you need.

 

[Motor Boater Bill]

Re: Lower Unit Leak

Try www.oldmercs.com, they have a lot of parts for your motor, including the LU seal kit.

 

[miichael18]

Re: Lower Unit Leak

Does it have to be the same serial number or will it work anyway? From oldmercs.com it says the 20hp seal kit fits 64-80 but everywhere else its diffrent. Cant find a kit for my engine with my serial #. Mine is a 1976 mercury 20hp model 200 serial #4409457

 

[Motor Boater Bill]

Re: Lower Unit Leak

Call Grubbs if you want to check, they really know these motors. Did you go to the page that list the parts for your motor? Go through the model directory to get there.