Re: 1953 Johnson 25hp Restoration: Lower Unit
Hey tmcalavy. Thanks for the compliment.
To answer your question about the water pick up, the water pick up is integrated at the seam, where the lower unit bolts to the motor leg. From the top view, the lower unit connection is shaped like a tear drop and the water passages run along the perimeter, behind the water pump housing. The tube is mounted inside the motor leg, from the bottom (where the lower unit mounts) and runs along the inside the rear rib of the motor leg and to the powerhead. There is still a copper tube, but it runs along the very back, instead of coming straight down. There really isn't any advantage or disadvantage for it being this way, but I think it may be more expensive to build, so Johnson and Evinrude redesigned the water pump housing to take the tube in 1955. That was a year that major changes were made in the RD/Big Twins. The one thing about the older design, like the '54 and older, there are possibilities of problems with water flow, at the seam, if they are not sealed properly. These models were built with a gasket, to go at the seam, but these were often destroyed, when someone removes the lower unit. If the lower unit ever had to be pryed from the leg, then there was a high risk of destroying this water passage by tweeking it out of shape. If you were lucky enough to pull the lower unit off without hassle, then it was still neccessary to apply sealer to the lower unit, when you re-installed it, so you wouldn't have water blow out there.
So, as you know, in 1955, when the big motors were redesigned, they eliminated a lot of little headaches like this and made things so much simpler. The timer and throttle linkage on these is another major improvement they made on this model too. No more cables.
It's a cool old motor though and I believe it is very restorable. It seems quite responsive. Just from squirting gas in the carb, it fired right off, so I think it'll work out great. I'm strippin 'er down and renewing stuff, so I'll see what it looked like, new.
