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Repowering with Diesel

July 2014 - About an hour into a trip where the wind conditions found us having to rely on the motor, our trusty Atomic Four engine that had served our vessel for 49 years started to make odd noises and lose power. After a few minutes, it became apparent that there was a serious problem developing, so we shut the engine down. Fortunately, we were heading home with some friends who towed us the few remaining miles to port.

After engaging some more friends who are well-versed with the vagaries of internal combustion engines, we arrived at the unwelcome conclusion that #3 cylinder was having issues with either a connecting rod or a connecting pin. At this point any more specificity would not have mattered, as the treatment for either is the same: Remove, rebuild, and replace.

Identifying Options

Option 1: Rebuild the Existing Motor

The most straightforward way to fix the engine would be to remove it from the boat, take it to a shop, and then overhaul it and replace any parts that looked to be broken or past their service life. There is lots of information available for the Atomic Four on the web and even more is available from Moyer Marine in Delaware. Since I was past the point of being a casual shopper, I started looking into what it would take to rebuild the engine myself.

Rebuild kits start around $4200, but this assumes that you can re-use many of the existing parts of the engine being serviced. In my case, I wasn’t so sure that this was a valid assumption, and I already knew that there were several “optional” components that had corroded to the point that they would need to be replaced. What made me most uncomfortable was that I would not know with any degree of certainty which parts would need to be replaced or refurbished prior to taking the engine apart and checking each one out. This could introduce all sorts of delays in the rebuilding process. Since we were at the beginning of the sailing season, the prospect of not having a motor at all for much of it was less than appealing.

Option 2: Swap for a Rebuilt Motor

A second option was to take advantage of Moyer’s trade-in program where one’s motor is swapped out with one that has been rebuilt by Moyer Marine. The “new” motor would come with some enhancements and would be guaranteed to run. While this option was certainly the most convenient and easiest to implement, the cost was relatively high (about $5000 after rebates for return of the non-running engine). In the end, I would still have a “vintage” motor and all of the issues that come with it.

Option 3: Replace with a New Diesel

For years I’ve pined after a diesel. Is it time? I had looked into this option about 10 years ago and found the cost of new diesels to be far in excess of what I could justify to replace a working engine. Now, however, there was some added justification since some major engine work was no longer optional.

I logged onto the Internet to see what diesel motors would qualify as replacements for an Atomic Four. Two were mentioned: Phasor and Beta Marine. Both are based on a Kubota tractor motor and are advertised as drop-in replacements for the A4. A dealer for Beta Marine engines was located within a reasonable distance, so I contacted him for a quote. An hour later I had a quote for $8100 for the 25 HP model. Mind you, this was just the engine. Some subsequent research suggested additional costs of $1500 to $2000 to convert and adapt the fuel, cooling and exhaust systems in the boat to be compatible with the new engine, making the total cost closer to $10,000.

Putting this into perspective, the cost of a new diesel motor would represent an investment of nearly half the market value of my Alberg 35. While a diesel does boost the market value of a boat a bit, one would be extremely lucky to recoup 20¢ on the Dollar.

Option 4: Replace with a Used Diesel

While chatting with the shop owner about the new diesel, I asked him if he was aware of any used Atomic Four’s or used diesels that might fit my boat. “Actually,” he said, “I do know of one!” Turns out he had a diesel with low hours that had been used as a trade-in on a recent transaction that would fit the Atomic Four engine bed with relatively minor modifications. Asking price was just under $4,000 . With the peripheral conversions that would be needed, the total was looking to be around $6,000. At this point, the conversation started to get interesting.

Comparing and Ranking the Options

With the options identified, a decision was now required. This involved looking at the problem from several different viewpoints. (Engineers reading this may recognize some techniques employed in Kepner-Tregoe analysis.)

Comparing the major features of each option:


Rebuild Existing Atomic 4

Swap for a Rebuilt Atomic 4

Replace with New Diesel

Replace with Used Diesel

Total Estimated Cost





Relative Time to Implement





Relative Effort to Implement





Fuel Type





Spare Parts Availability



Very High


Spare Parts Cost





Relative Risk


Moderately Low




The Pros and Cons

Rebuilding the existing motor is the most cost-effective option considered above. However, I’ve never rebuilt an engine myself before and it is likely that I wouldn’t have all of the tools necessary to complete the task properly, which would have an impact on the cost. This activity is also potentially time consuming, meaning that my boat would be unpowered for an extended period, possibly as long as 6-8 weeks. If the calendar said “October” on it, this would not be much of an issue, but since it’s early June…

For just a few hundred Dollars more, swapping the engine for one that has been professionally rebuilt is a really attractive option. All I need to do is send someone a wheelbarrow full of money, wait for an engine to show up, swap it for the one in my boat and then ship back the old motor. I have what is essentially a new engine that is guaranteed to fit into the existing mechanical space and will require no modifications to other boat systems. On the down side, I still have to deal with issues that are part and parcel of the Atomic Four. It’s a motor that hasn’t been manufactured in almost 35 years and there are very few places to get parts. Where parts are available, they are priced the way single-sourced, low-volume goods are priced (i.e., high). Then there is the issue of gasoline with its known risks and hazards. On the intangible side, is my long-standing wish for a diesel engine.

A new diesel motor would definitely be classed as the “best, cost-is-no-object” option. It addresses all of the shortcomings of the gasoline-fueled Atomic Four while providing the ability to purchase a motor with a “drop in replacement” footprint. While there would be a fair amount of effort involved to convert other parts of the boat to accommodate the change in fuel, these upgrades would add value to the vessel and the motor would come with a 5-year warranty. In addition, cruising range of the boat could be almost doubled due to the increased fuel efficiency inherent to diesels compared to vintage (low compression) gasoline motors. The down side is the fact that this would take not one, but two wheelbarrow loads of money to implement and the increase in value of the boat would be nowhere near enough to offset the investment required.

If a used motor with the appropriate footprint could be found, this would have a very positive impact on the diesel option.

Fortunately, such an option exists. A Westerbeke 30B Three motor that had replaced an Atomic Four in a Tartan 34 just happened to be available. While the engine bed will have to be raised, the position of the rails would not need to be modified. With just over 400 hours, this motor was basically just broken in and sported an asking price of less than half that of a new diesel. In the end, the difference between a rebuilt Atomic Four and a “gently used” diesel motor was around $1,000. Looking at the various options this way, who wouldn’t go for a diesel motor for $1,000?

Out With The Old

Starting the Process: Removing the Old Engine

Because this project includes changing the type of fuel used, it is much more extensive than simply replacing the engine. Practically speaking, the entire mechanical space in the boat needs to be modified or adapted to the new power plant.

Before anything can be done, the old engine has to come out in order to make room not only for the new one, but also to gain access to a number of other things that will be replaced or overhauled. One advantage sported by the Alberg 35 is that it has relatively unobstructed engine access. (Note the word, “relatively.”)

Before anything serious can be done, the fuel tank needs to be emptied. This was done by sucking out the contents using a combination of hand pumps and a vacuum tank that you occasionally see used for changing engine oil. Both techniques were effective; the vacuum pump seemed to take a little longer, but required less physical effort than the hand pump. The stock fuel tank in the Alberg 35 holds 23 gallons of gasoline.

It took only a few hours to disconnect the Atomic Four from the boat. Attachments included the throttle cable, choke cable, shift cable, fuel line, the coupling to the prop shaft, a couple of hoses for cooling water, a heavy 12 VDC connection for the starter, a ground (DC return), and a handful of smaller electrical wires for the ignition and instrumentation. In my case, there was also a hard line connecting an oil pressure gauge.

Four bolts connect the Atomic Four to the engine bed. The Alberg 35 did not have any type of shock absorbing mounts. (Which might explain why the engine seemed to run so loud?) Once these were loosened, only gravity was holding the engine in place. To make the lift easier, some of the heavier peripherals, like the alternator and starter, were removed from the engine. Ignition wiring was also removed in order to minimize the chance of it becoming entangled during the lift.

The Atomic Four has a single lifting eye on top of the engine. A small chain hook fits into this nicely. The boom was used as a lifting point and 4:1 block and tackle were used to lift the engine. Step one was to slide the engine forward so it would clear the bridge deck during the lift out of the cabin. The casting has a nice, flat bottom, so the motor is reasonably stable when it is set down onto a surface.

We did our lift in three stages. We first lifted the motor to the height of the countertops in the galley and then rested it on a sturdy board while we adjusted the bock and tackle to make sure we had enough height to be able to get it over the sill of the companionway. The second phase of the lift then put us through the companionway where we pushed the load out onto the bridge deck. The third part of the lift then moved the engine from the bridge deck to the cockpit sole.

With the engine secured in the cockpit, we moved the boat to the slip used by the travel lift (the dock is much sturdier there) and then used the boom as a derrick to pick up the motor and set it into a pre-made cradle on a small pallet for transport home. After that, it was fairly easy to slide the pallet to the back of my van where four of us lifted the engine into the vehicle.

What proved to be much more difficult to remove was the fuel tank. While the hold-downs for the tank were straightforward to loosen and remove, the fittings for the fuel pickup, vent line, and especially the fill pipe, were nearly impossible to remove. The fill pipe turned out to be a solid bronze nipple connecting the deck fill plate to the top of the Monel tank. After failing to loosen this fitting, a sawz-all was eventually employed to convince it to separate. In the end, the nipple had to be cut free of the threads on the tank. Alas, even with the fittings removed, the tank did not fit through the cockpit locker opening, so some additional surgery was required to remove a lip in the opening through which we could then easily pass the tank. The good news is that the lip is easily glassed back in and will not result in cosmetic damage to the exterior of the boat.

Preparing For The New Motor

With the engine and tank removed, it’s time to begin prepping the space. With at least 25 years of grime in places, the mechanical space needed a good cleaning. With the boat back in her slip where shore power was available, the water heater was fired up and we used multiple loads of hot water and some dish soap to break down the grease and oil in the engine compartment. After scrubbing the worst of the dirt away, some time was spent cleaning up the wiring in the compartment.

A problem with the existing shaft coupling was that one of the Allen screws holding the coupler to the shaft had sheared off half way down in its socket. A good portion of an afternoon was spent drilling out the old set screw so that the coupler could be removed from the shaft. A couple of hose clamps were put on the shaft to prevent it from sliding out. Fortunately, the prop shaft cannot slide out completely, but it can shift enough to jam the rudder and prevent the boat from being steered.