Johnson 70hp lower unit question

im sure this question has been asked before, but i bought a 1975 johnson 70hp. the compression checks are spot on but the lower unit had water in the oil when i drained it. i plan to buy a water pump kit for it. when i took the existing water pump housing off it looked as if someone just used silicone to seal it instead of a gasket. could this be the cause of the water in the oil? or does water only get in through some other seal somewhere? i just need to know if the water pump kit COULD fix it or if i am looking in the wrong place for the leak. thanks

Re: Johnson 70hp lower unit question

Silicone should NOT be used anywhere on a outboard engine, BUT this would not be the cause of water entering the lower unit.

The usual cause of water entering the lower unit is either having fishing line becoming entangled in the propshaft seals, OR the top driveshaft bearing becoming worn slightly which would allow the driveshaft to wobble ever so slightly, but just enough to allow water to enter the unit via the seals in that housing, OR simply having no nylon, fiber, or O Ring type seal on the drain and oil lever screws (whatever seal might be required).

(Checking Gearcase For Leaks)
(J.Reeves)

Remove the large slotted drain/fill screw from the bottom of the gearcase and also the identical looking screw that will be located up near the cavitation plate in order to drain the gearlube.

After all of the lubricant has drained, install one of the slotted screws, whichever your preference might be.

Apply 7 to 12 pounds of air pressure to the open screw hole. Use a piece of rubber fuel line or something to create a tight air hose fit if you do not have a proper fitting.

If a leak exists, that pressure should allow you to locate the leak by sound and/or sight.

Re: Johnson 70hp lower unit question

What Joe said

Also, I don't think there is any kind of gasket between the impeller housing and floor.

Rgds

Re: Johnson 70hp lower unit question

could water get in through the prop hub? im just trying to figure out what to do if i still get water in there after replacing the crush gaskets on the drain and fill plugs on lower unit

Re: Johnson 70hp lower unit question

Do as Joe Reeves says and pressure test the Lower. You should be able to quickly isolate where the lower is leaking. You should also, however, replace all the seals if you are going to have the gearcase apart. I don't know what you mean by water getting in through the prop hub. As Joe says, you can get water through the prop shaft seal.

Rgds

Re: Johnson 70hp lower unit question

It's also possible that the large O Ring on the carrier assembly might be leaking. A Pressure tests would reveal that if it exists.

Re: Johnson 70hp lower unit question

any clue which seal kit to buy? iv looked and there are so many different ones for that motor. i dont have my title for the motor so i dont know whether its a large or small gear case.

Re: Johnson 70hp lower unit question

I have the same question...Not sure of which gearcase seal kit to buy, b/c I'm not sure if mine is a large or small gearcase (not really sure how to tell). The Model is a 70esl75b.

Would like to replace the seals why I am in there replacing water pump, as they are most likely the original seals, and I don't want to have to go back in at a later date and replace them.

Re: Johnson 70hp lower unit question

lehkyc, find your model number, it is on a plate attached to the motor, around the clamp area, it is a similar number what amishatc has.
Go to this web page http://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1975&hp=70, pick your model number, and then select your gear case (based on model number). It gives a part breakdown with numbers.
You are right about replacing all the seals.

Peter