1978/1981 Evinrude 115hp Lower Unit water flow for Speedometer?

[atktom]

I am not understanding how those two holes work. I do not have speedometer, but I do have a replacement lower unit for my original 1981 lower unit which did not have these holes. Currently the bottom hole is stopped up with crust. I ran a small drill bit by hand turning it and got about 3/4 of inch of crust out. but quit at that point cause I not sure what I am doing. The top hole goes way in but when I try to vacuum it is seems stopped up. However, when I run it on the ear muffs water comes out that hole and hits the transom of my boat. So I am assuming that when running something opens up and lets water come thru. I do not know what year the lower unit is so I can find no documentation on the water flow thru it. One video said that it is pressure related from the bottom hole to send a vacuum thru the upper hole to the speedometer. I just got thru servicing the lower unit, new seals (upper seals were leaking), water pump, and shift rod O ring. Pressure/Vacuum test held 15 pounds both ways. What I would like to know besides how this works can I just JB weld the two holes and not worry about how the water works. There is no sending unit in the upper hole, just an open hole. Appreciate anyone who can set me straight. Thanks in advance.

 

[flyingscott]

Put up a pic of these holes. More than likely they are drain holes and the plugged one needs to be cleared. Not a good idea to plug those up. A speedometer hole will be a single hole on the leading edge of the lower. Speedometers do not work off of vacuum they work off of pressure from one hole.

 

[F_R]

Agreed, I believe you are looking at drain holes. Do not plug them!!!

 

[atktom]

Okay here are the pics requested. I just noticed the square hole on the mid case right above the round hole on the lower gearcase. So maybe the water was coming out that square hole? Anyway the upper round hole and the lower round hole are on the lower gear case. Do I need to do anything with those two lower holes as definitely the bottom one is stopped up. The upper round hole does not seem to be stopped up but will create a vacuum so don't know if that is suppose to be open or not. When I had the shift rod cover off I noticed a large round pin in a hole where the upper round hole on the outside leads to which I think is sealing it off.

 

[racerone]

I looked at 2 newer gearcases today with that hole in the same location.---Also an 81 gearcase that does not have that hole.------That is the feed for speedometer pressure.-----Did not bother to look at any more gearcases.

 

[F_R]

The square hole is a drain---found on all of them. Pressure from driving through the water enters the lower round hole (called a pitot). From there it goes to the upper round hole with a hose leading to the speedometer. The speedometer is just a glorified water pressure gage, looking at the pitot. Faster you go, the higher the pressure.