by Cory Carpenter
A 27-year-old outboard motor starts a newer, deeper life
|I bought Brushfire, my 1975 San Juan 24, from the Sea Scouts. Before I agreed to the deal the Sea Scouts offered to throw in an outboard as a sweetener. The motor they dug up for me was a 7 hp Eska of 1973 vintage, a two-cycle with an integral three-quart fuel tank.|
| It ran well enough once I did some research and discovered that
it wanted a 24:1 fuel-to-oil ratio, but I found that even with my 180 pounds
as far aft as possible, and Brushfire's scissors-style motor mount
at its lowest setting, the Eska's cavitation plate was barely below the surface.
The whole prop came out of the water with any kind of wave action and the
motor would race madly with a "www-AH, www-AH, www-AH" like a hydroplane running
My original intention was to use the Eska just long enough to get Brushfire about 3 1/2 miles down the Columbia River from the Sea Scouts' base near Lemon Island to a marina on Hayden Island. I figured I would return it to the Scouts and treat myself to a new long-shaft Honda four-stroke. Then I started checking prices ... and concluded that it wouldn't be such a bad thing to have an outboard from the same era as the boat!
|In the course of researching long-shaft outboards on the Web, I happened upon Bay Manufacturing of Milan, Ohio, which makes shaft-length conversion kits for Mariner, Mercury, OMC, and Yamaha outboard motors, but not for 27-year-old Eskas. Looking at the pictures on their Web page caused me to wonder what it would take to do my own long-shaft conversion.|
My Eska is a model 1747-C. It uses a Power Products/Tecumseh recoil-start, two-cycle, air-cooled power head much like a lawnmower engine's except that the exhaust port is on the bottom of the cylinder rather than the side. I've seen discussions on the Web that indicate this motor was also sold under the Sears Gamefisher and Ted Williams trademarks. It has a spring clutch to engage the driveshaft, providing neutral and drive gears. (Mine was frozen with rust, and the motor had to be started in drive. Soaking the clutch in kerosene for a week or so helped free it up.) For reverse, you swing the motor all the way around and, while hanging precariously over the transom, hope you remember which direction to twist the throttle. In drive, a small pump provides cooling water to the exhaust manifold/adapter plate that mounts the engine to the lower unit of the motor.
| I obtained a service manual from Certified Parts Corporation,
which purchased the Outboard Motor and Trolling Motor divisions of Eska in
1988 and still provides most parts for these units. Some study of the exploded
diagrams in the manual showed that given the proper tools it would be fairly
straightforward to construct a shaft extension. Conveniently, the housing
containing the propeller shaft, gears, and water pump separates from the main
section of the column just above the cavitation plate. The cooling-water tube
merely connects to the pump with a friction fit into an O-ring, while the
top end of the driveshaft fits into the clutch on the engine's output shaft
in much the same way, torque being transmitted by splines. Because of this
simple design, all I needed to do was add length to the cooling-water tube,
fabricate a new driveshaft, and build an extension fairing, a shell that would
conform to the cross-section of the column where it joined the gear housing.
I decided that an additional length of six inches would be about right.
For the best corrosion resistance and electrolytic compatibility with the rest of the motor, the new parts should have been fabricated from aluminum and stainless steel. Because I wasn't willing to go to the trouble and expense of obtaining the ideal materials, because my MIG welder won't handle aluminum wire reliably, and since this project was in the nature of an experiment anyway, I used mild-steel stock that was lying around my garage for the major components of the extension.
The long driveshaft
|Extending the column
Reassured that this whole exercise might actually work, I tackled the extension fairing for the column. What I had available was 14-gauge sheet steel, (approximately .075 inch thick). I quickly determined that the curve at the leading edge of the column fairs back into a straight line, so I could match it with just five sections of material as shown at right: two curved for each side of the leading edge, two straight for the trailing edges, and one flat piece for the back edge.
|I first obtained the outline of the required section by clamping a sheet of heavy paper between the column and gear housing and tracing around the join. This also punched holes in the paper, providing locations for the fasteners that connect the gear housing to the column. I translated the tracing of the fairing cross-section inward by the thickness of my sheet stock, then cut templates from 1/2-inch plywood. Laying the template on a flat surface, as shown in the top photo below, showed me where the trailing edge would begin. I marked this location, then wrapped a strip of paper around the curve to the tip of the profile, marking it to establish the length of sheet metal that I would need to bend in order to form each side of the leading edge. Later on, I used the templates to align the pieces of the extension fairing while welding.|
|From top: identifying the trailing edge, welding, and the HotCoat
||Creating the curved sections for the leading edge of the fairing involved
lots of hammering with the sheet metal supported against cylindrical objects
of various diameters, such as an empty propane-torch tank and a length of
2-inch iron pipe. I checked my progress frequently against the plywood templates.
I found that it worked best to create a curve that was tighter than what I
needed, then flatten it out progressively by hammering against the anvil surface
of a machinist's vise. (It took a while to form acceptable curves, but I got
Once I had all the pieces of the fairing worked to their proper lengths I ground a chamfer of about 45 degrees on the outside of each edge to be joined. This was to ensure good weld penetration of the entire thickness of the sheet metal, important because I wanted to build up a bead that I could later grind down flush with the outside surface of the extension fairing.
Assembling the pieces around my plywood templates, I tack-welded them together with a MIG welder, then removed the forms. I completed the welds a bit at a time, allowing them to cool between passes in order to minimize distortion of the sheet metal. I built each seam up into a nice, heavy bead as shown in the center photo at left.
Once the shell of the extension was welded together, I used an angle grinder to clean up the top and bottom edges, checking often with a framing square to make sure the surfaces were parallel with reference to the back edge of the fairing. I ground the edges until the height was uniform and slightly more than six inches, then did the final finish with a large mill file across the entire top and bottom edges of the shell to get the mating surfaces as straight and square as possible. The holes that allow water to drain from the column after the motor is hauled out were cut with a hacksaw and shaped with a file.
When I was satisfied with the fit of the shell against both the gear housing and the column I fabricated alignment tabs from 1/8-inch by 1-inch steel strap and welded them into the top and bottom of the fairing. These provide lateral rigidity as well as ensuring that the extension stays centered against the inside surfaces of the column and gear housing.
I fabricated mounting flanges from 1/8-inch by 1-inch strap to provide the connection points at the top and bottom of the fairing. I drilled the holes in them first, then lined them up with the holes in my templates and traced the outline that would become the edges to be welded to the inside of the fairing shell. As the drawing above shows, the flanges at the rear of the fairing are threaded for the mounting bolts. Here I cheated: Instead of spending a lot of time messing around with taps to thread holes in the flanges themselves (in which case they would have needed to be made of thicker material), I installed a nut and bolt on each flange with the nut on the inside face, then tack-welded the nuts to the flanges and removed the bolts. This provided for a strong connection in a situation in which it's impossible to get a wrench on the nut.
|The bottom flange at the leading edge is constructed in much the same way, but uses a section of threaded rod to mirror the stud on the leading edge of the column. The upper flange merely has a plain hole that the column stud passes through. It's secured by a nut and lockwasher from inside the extension fairing. (The original trailing-edge mounting bolt was frozen and I was forced to drill it out. I elected to install its replacement from the outside of the column, otherwise both top flanges would have had plain holes.)|
| Once the construction was complete, I ground the welds
down flush with the surface of the fairing, then polished the whole outside
surface with a 3M Scotch-Brite surface conditioning disc installed on an angle
grinder. This is the best way I've found so far to remove rust and mill scale
from steel components. It also left a very smooth, shiny surface, which was
important for the next step. Had I been thinking ahead, I would have polished
the inside surfaces of the fairing before welding it together. Since I hadn't
been, I did as much cleanup as I could afterward with wire brushes and a sand
blaster. Live and learn.
Don't try this at home, kids, without your mom's permission: fairing after coating and the finished result of the baking (done in a home oven).
Rust: While I hadn't noticed any signs of rust on the exterior of the extension assembly, it still concerned me that the whole thing is potentially susceptible to corrosion. I'm relieved to report that, after four months and about four-and-a-half hours of accumulated running time including two extended motor-only runs of an hour each, there was no sign of a problem when I disassembled the extension to take photos for this article. Note though that Brushfire sails in fresh water. I would definitely go to the expense of using inherently corrosion-resistant materials for saltwater operation, or if the motor were semi-permanently installed in an outboard well.
Sealing: The through-the-prop exhaust
system depends on a good seal between the mating surfaces of the column, the
extension fairing, and the gear housing. The walls of the column casting are
about 1/8-inch thick and the sealing surface of the gear housing is a nice
milled area that varies from 1/4-inch to about 1/2-inch wide. The walls of
the extension fairing are roughly 1/16-inch thick, providing only minimal
sealing area. Almost immediately after I put the converted motor into service
I noticed bubbles of exhaust gases forcing their way between these junctions.
The RTV silicone obviously wasn't enough. I later made gaskets from 1/32-inch
automotive-gasket material and bedded them in hardening-type gasket sealer.
These worked for a while, but they too eventually started leaking.
Drain holes: When I originally designed and built the extension I neglected to do anything about the original drain slots at the bottom of the column's leading edge. These slots are right at the waterline, and when I first tried the converted motor aboard Brushfire I noticed quite a bit of exhaust escaping from them. My remedy wasn't pretty, but it does work: I threaded stainless-steel sheetmetal screws into two scraps of wood about 1/8-inch thick and, with the extension fairing removed, filled the drain slots with thickened epoxy, using the wood on the inside of the column as backing. I tightened the screws down to hold the wooden backing blocks in place while the epoxy cured, then filed everything down flush with the mating surface of the column. With the extension reassembled the epoxy seals the original drain holes. (The screw heads are visible in the third photo below, just above the top of the extension fairing at the leading edge of the column.)
Shaft alignment and vibration: I have no way to evaluate this, since there's so much incidental vibration when the motor's running. I'm reasonably confident that the driveshaft itself is true, since I could check that while I was machining it; I don't know how accurately it is aligned between the motor and gear housing but there's not a lot that I can think of to correct such a problem. (I try to ignore the possibility, apart from making sure I have fresh batteries in my hand-held VHF transceiver in case the gear housing should fall off in mid-river and I need to call for a tow.)
The nicest part of using the powdercoating process for this project was that the charged powder was attracted to and covered every surface of the fairing, inside and out, even the irregular surfaces of exposed welds. To avoid fouling the threads, I installed bolts in the threaded holes and masked off the trailing-edge stud with high-temperature fiberglass tape (also from Eastwood) before coating everything with the shade of powder I had on hand that came closest to matching the Eska's paint. The photos above show the fairing after coating and the finished powder-coated fairing was baked for 15 minutes at 400°F. I also powder-coated my new driveshaft after taping off the splines and the surfaces that would bear on the bushings and seals. (Any color would have done for the driveshaft; I happened to have black in the HotCoat gun at the time.)
|Extending the cooling-water tube
The final piece of the project was the extension for the cooling-water tube. In this case I actually had to break down and go to the hardware store to buy aluminum tubing that matched the 3/8-inch outside diameter of the water tube, as well as vinyl hose with a 3/8-inch inside diameter to join the extension to the original tube. (Since I was there anyway, I also purchased stainless-steel cap screws, nuts, and lockwashers.) I cut the ends of the new 6-inch extension to the same angle as the end of the original water tube so they would fit together flush, then smeared the outsides of the two aluminum pieces with RTV silicone and joined them with a length of vinyl tubing as shown in the first photo at right. (Epoxy might have been a better choice for this, but so far the RTV seems to be working fine.)
"Assembly is the reverse of removal"
From top: joining the cooling water tube, reassembling the gear housing and driveshaft, and the finished project.
After the RTV had cured, I refilled the gear housing with SAE 90 lubricant as specified in the Eska service manual and using the time-honored outboard-motor test stand, a sawhorse and a 55-gallon trash can full of water, fired up my good old motor. With the gear selector in "neutral" I was gratified to see that the clutch was now working properly: The propeller remained motionless while exhaust racketed from the relief port at the top of the column, sounding like a leafblower on steroids. Once the motor warmed up and the idle settled down, I cautiously moved the selector to "drive," and - it worked!
I've been very pleased with this conversion's performance aboard Brushfire. With the motor mount in its lowest position the entire extension is underwater, giving the propeller plenty of bite, and I can move forward in the boat without it becoming a menace to low-flying birds. The tip of the gear housing's fin is just barely in the water with the motor mount in the topmost position, and with the motor rocked forward in its tilt bracket everything is high and dry. One odd side effect of the extension is that with the motor idling and the gear selector in "neutral" the exhaust resonates inside the comparatively thin-walled extension fairing with a funny "bloop-bloop-bloop-bloop" note that puts me in mind of The Secret Life of Walter Mitty.
If you're one of the two or three unfortunate readers who doesn't have a well-equipped metalworking facility in your garage, you should be able to find a machine shop willing to fabricate all or part of a similar shaft extension "kit." Some research in my area turned up two shops that were capable of the job, one specializing in high-volume CNC production and not interested in one-off jobs; the other a gear-making business that estimated $225 just to make the driveshaft. Though I haven't had to take work to a machine shop for nearly two decades, I find it hard to believe that there's nothing left but specialists.
Certified Parts Corporation
The Eastwood Company
Sea Scouts Ship 601
| Fabricating the driveshaft obviously requires some
moderately specialized equipment, but the operations involved are straightforward
and shouldn't be too costly in terms of labor time. (It took me about six
hours all told, but 80 percent of that was in building a flycutter.) If you
don't have a welding outfit, any decent machine shop should be able to construct
the extension fairing as well. If you don't know of a shop already, talking
to a few old-timers around your marina should turn up someone who can do the
job. Anyone who can cope with simple hand tools can handle the fabrication
of the cooling-water tube extension and the final assembly.
I've noticed that even a reconditioned long-shaft outboard starts at $900; new ones are going for $1,500 or more. If you have an older motor available, this project could be cost-effective even if you have to farm out the actual fabrication work. (Not too long ago, I noticed a 7-hp Eska identical to mine offered for $350 at my local marine exchange. Now if I were to buy that and modify it I might be able to clear about $500. Hmmm ...)
|Cory's uncle taught him to sail when he was in high school. After 20 years, he's relearning those skills with the help of Brushfire, his 1975 San Juan 24. Most of his sailing is done as a singlehander on the Columbia River in Portland, Ore., but the right 30-something crewwoman could change all that|
Article taken from Good Old Boat Magazine: Volume 4, Number 6, November/December 2001. Reproduced with permission.
Mary Margaret's Art
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