Obsolete Outboards

by Max Wawrzyniak - St Louis, Missouri - USA Bringing a 1956 Johnson 15 hp Back to Life Part II: Water pump Work

Part 1 - Part 3 - Part 4 - Part 5 - Part 6 - Part 7

Before we get started on the water pump, I would suggest a quick review of the old "Water pumps" column, If Chuckie is going to waste his bandwidth on that old stuff, we might as well make good use of it.

For whatever reason, the two outboards featured in the first two "Start to Finish" series were about the most difficult of the old OMC (Outboard Marine Corp., parent of Johnson, Evinrude, & Gale) engines to change water pump impellers in. The 5 1/2 hp required that the whole powerhead be removed, while the 25 required that one work through a small gap between the lower unit and the exhaust housing ("tower" housing") in order to disconnect the gearshift linkage so that the lower units could be removed.

Exhaust housing (AKA tower housing) and lower unit overview (click images to enlarge)

It is much easier to change the impeller in the '56 15 hp because this engine has a small access door on the side of the exhaust housing which allows one to disconnect the shift linkage easily. One loosens the two screws and removes the little panel, revealing a coupler connecting the shift rod coming-up from the lower unit and the shift rod coming down from the shift lever. The lower bolt of this coupler must be completely removed, as the bolt engages a groove in the lower portion of the shift shaft, and merely loosening the bolt will not free the lower shaft. If you drop the bolt down into the exhaust housing at this point, it is no big deal, as the bolt will fall out the bottom of the exhaust housing as the lower unit is removed. If you accidently drop the bolt when re-installing the lower unit, however, you will have to remove the lower unit in order to retrieve the bolt.

Once the shift shaft coupler is disconnected, the five bolts holding the lower unit on can be loosened and removed. Once these bolts are out, the lower unit may fall-off the engine, or it might require a bit of a tug if the shift shaft is hanging-up in the couple. If the lower unit requires more than a minor tug to free it, then something is not correct. It is a bad idea to carry the lower unit around by the vertical driveshaft; the shaft may slide out, dropping the lower unit on your foot.

Wrenched on lower unit mounting bolts

Once off the engine, note if the copper water tube came out with the lower unit or is still up in the engine. This tube conducts water from the water pump up to the powerhead, and if the tube is attached to the water pump, pull it lose from the pump housing and insert it up into it's hole up in the exhaust housing. It is impossible to re-install the lower unit with the tube attached to the pump; it must be first inserted into the exhaust housing. When re-installing the lower unit, you will need to guide that tube into it's socket on the pump housing as the lower unit is pushed up against the exhaust housing.

The tube is retained at both ends with "push" fit rubber grommets and it would not be a bad idea to replace these sealing grommets if there is any doubt as to their condition. The one on the pump housing is easy to pry-out and replace; the one up in the exhaust housing is much more difficult. I decided to risk reusing the old grommets on the 15.

The top of the pump housing is held on with three screws. One of these screws on the 15 came out with some resistance and covered with white powder, which was corroded aluminum. The long periods of submergence, evidenced by the appearance of the lower unit, had a detremental effect on the threads in the lower unit casting. Fortunetly, only one threaded screw hole showed signs of deterioration, and although it's threads where in poor shape, there appeared to be enough thread engagement to hold the pump housing on. Corroded or stripped threads on these aluminum castings are a farily common problem, and there where special tools available to make drilling and re-tapping (re-threading) water pump retaining holes a quick and easy job. Without these special "jigs," the job is a bit more difficult but not beyound the abilities of the careful obsolete outboarder.

A special jig (tool) for quickly repairing stripped or broken water pump housing screws. Although a more difficult job without the tool, the basic procedures for repairs are still the same.

After the three screws are removed, the pump housing can be slid up the driveshaft and removed. Note that there is no gasket or seal used underneath the pump housing. Also note that there appears to be no seal for the driveshaft in the pump housing. Actually, there is a "seal" of sorts for the driveshaft where it passes through the pump housing. It is a water seal; a cup which holds water acts as a shaft seal. The water that keeps this cup full comes through a tiny hole in the pump housing, and this tiny hole must not be plugged. Excess water merely overflows the cup and exits the motor through the exhaust outlet.

The pump impeller in the 15 was pretty much "toast." The fins retained their "curved' shape, whereas a good impeller will have "straight" fins. My opinion is that once one has gone this far, it would be dumb to reinstall the old impeller even if it looked "OK." Unless I KNOW that the impeller in an engine is good, I ALWAYS replace it. And I NEVER re-install an old impeller once it is out of the engine.

Underneath the impeller is a shiny metal "wear plate." If this wear plate shows signs of heavy scoring, if would not hurt to replace it. If the pump housing itself shows signs of heavy scoring, replacing that might be a good idea as well. So what constitutes "heavy scoring?" Beats me. I have replaced the wear plate in one or two of the engines that I have worked on over the years; I can't remember ever replacing a pump housing although I might have. A pump "rebuild kit" will always have the impeller and wear plate, and maybe the housing as well. Or you can buy just the impeller and/or wear plate seperately. I re-used the wear plate and housing in the 15.

Water will sometimes do weird things. For example, water will sometimes try to "climb" a spinning shaft. for this reason, there is an "O" ring in a groove around the splines at the top of the vertical driveshaft. You will need to remove this "O" ring in order to slide the pump housing and pump impeller on and off the driveshaft. If the "O" ring breaks, or if your engine is missing the "O" ring, you might run the lower unit by a good hardware store and see if they have an "O" ring which fits pretty well. The fit is not real critical. I will admit to occasionally not replacing a missing "O" ring. The risk is allowing water to get into the lower main bearing in the powerhead. It can happen but doesn't always happen; your choice.

Are we having fun yet?

Slide the new impeller down the driveshaft and be sure that the key way (notch) in the shaft hole of the impeller engages the little pin on the driveshaft. Slide the pump housing on the shaft. As you push the pump housing down onto the impeller, rotate the driveshaft in a clockwise (looking down) direction and the impeller blades (fins) will bend back, allowing the housing to drop down and seat on top of the wear plate. Make sure that the impeller stays engaged on the drive pin in the driveshaft. Install the three screws which secure the housing. I was very carefull to not over-tighten the one screw with bad threads. Replace the "O" ring at the top of the drive shaft. A very light coating of grease on the splines at the top of the driveshaft is a good idea: any more than a VERY light coat is NOT a good idea, as it can form a "hydraulic lock", preventing the splines from fully engaging.

Re-installing the lower unit might try your patience. Take your time. Have the motor vertical if possible, but high-enough off the ground so that you can get the lower unit under it. You need to get the driveshaft splines engaged with the splines in the crankshaft. Having someone slowly turn the flywheel (clockwise) might be of help. While doing this you also need to guide the water tube into it's grommet on top of the pump housing. Forget the shift shaft for the time being. Once you have the driveshaft/crankshaft engaged and the water tube in its grommet, install a few of the lower unit mouinting bolts but leave them slack so that the lower unit hangs with a little gap.

Looks like there may be a bit of water in that lower unit lube.

Use needle nose plies inserted though the shift shaft coupler door to move the lower end of the shift shaft up and down, while using the shift lever on the engine to move the upper half of the shift shaft up and down, as necessary in order for the lower shift shaft to engage the coupler on the upper shift shaft. Be sure the lower shift shaft is fully seated in the coupler and then re-install the lower bolt in the coupler. Install and tighten-up all mounting bolts and re-install the little cover over the access hole. Check the shift lever while slowly turning the propeller to see if the engine egages forward and reverse, and that the prop turns freely in neutral. Remember that either the prop or the flywheel must be turning when trying to shift the engine or the engagement "lugs" may not be aligned.

Removing the drain and vent plugs from the lower unit released a "milk shake" looking mess that indicated that there might be some water mixed-in with the lower unit lube; taking my own advice, I refilled the lower unit with Lubriplate #105 white grease. I really did not want to hassle with re-sealing this old, corroded lower unit.

... on to Part 3...

Happy Motor'n

click here for a list of Columns by Max Wawrzyniak

Email this page to a friend