77 merc 20hp water intrusion

[cablebandit]

So i bought an old merc...77 20hp...got it running after cleaning the carb and replacing some wiring. When i went to drain the LU it was milky. I am going to order a water pump kit which seems to come with a seal or two. Where else do i need to look for water intrusion?

 

[oldman570]

Re: 77 merc 20hp water intrusion

The LU can be pressure tested, and soapy water in a spray bottle will tell just where all the leaks are. The test should be done with the LU off and before you replace the water pump. A lot of people never replace the fiber washers that are on the drain and vent screws, they should be replaced about every year or more if the LU lube is checked often. It only takes about 7LBs of pressure to test the LU and can save $$$ and time in the long run. JMO
Oldman570

 

[jbjennings]

Re: 77 merc 20hp water intrusion

The seals that come with the water pump do not keep water out of the lower unit. Shift shaft seal, drive shaft seals below the water pump, and prop shaft seals, along with the drain and vent screw washers as mentioned are the possible leak locations. The shift shaft seal is often the first to go on those.. Luckily, you've got a stainless shaft.
GOod luck,
JBJ

 

[cablebandit]

Re: 77 merc 20hp water intrusion

wow thanks for the quick responses! How exactly do you pressure test the lower unit?

 

[oldman570]

Re: 77 merc 20hp water intrusion

There is a tool made that is just for this application, but is rather costly for the average boat owner. The best way is to take the LU to a certified shop and have the rest done by them. I have made one for my usage by using a nylon bolt and a brake bleeder and a vacuum pump for bleeding automotive breaks. doing this you can both pressure test and vacuum test a LU and still use it for bleeding the brakes on your vehicle. It only takes around 5 to 7 LBs to find a leak that can cause trouble. JMO
Oldman570

 

[cablebandit]

Re: 77 merc 20hp water intrusion

well it looks like I am about to get some experience with a lower unit. oh the joys of picking up a project motor. Thanks for the replies

 

[cablebandit]

Re: 77 merc 20hp water intrusion

well i pulled out the shift shaft bushing and ordered the oil seal along with the 2 orings for the shift shaft as well as the washers for the oil fill/check screws.. it does look like it was leaking around the shift shaft so good call. the bearing for the driveshaft looks really good. If this doesn't fix the leak, I'll do the prop shaft stuff. This little thing is pretty darn easy to work on. While the lower unit is off, I'll also replace all the water pump gaskets/seals and impeller as my wp body looks good.

question...if you disconnect the hose to the pee hole fitting and blow thru it (reverse) should you only feel air coming from the copper tube that goes to the wp? I hear air going somewhere else as well when i plug the copper tube end with my finger

 

[cablebandit]

Re: 77 merc 20hp water intrusion

ok i replaced the shaft seal and the oring at the bottom of the bushing the shaft seal seats into. I also replaced all the seals in the waterpump and the impeller. Tomorrow I will fire her up and see if we have water flowing. I did find the pee hole fitting to be stopped up.

 

[oldman570]

Re: 77 merc 20hp water intrusion

Bugs have a way to find good places to build nest and the tell tail tube is one of them. I carry a piece of weed eater string on all my boats so I can run it up the tell tail to dislodge any obstructions that could be in the system up to the water jacket area. JMO
Oldman570

 

[cablebandit]

Re: 77 merc 20hp water intrusion

Bugs have a way to find good places to build nest and the tell tail tube is one of them. I carry a piece of weed eater string on all my boats so I can run it up the tell tail to dislodge any obstructions that could be in the system up to the water jacket area. JMO
Oldman570

Great idea! As I am new to boats AND outboards, I appreciate the tip. After i get it started, I will have to figure out how to adjust timing and get carb adjusted.