Repowering an Older Alberg 30 with a Yanmar 2GM20

Some thoughts and considerations.

When Isa Lei's Atomic 4 died, I had to do some serious thinking about what I wanted to replace it with. My options were:

  1. Rebuild the Atomic 4.
  2. A rebuilt Atomic 4.
  3. A small diesel, either the Westerbeake M4-30, or the Yanmar 2GM20.

My first thoughts were to try to rebuild my Atomic 4, or put in a rebuilt one. The advantages to this choice are; it's a simple bolt in job (the old engine beds, prop, electric and fuel system remain), and I know the engine. The biggest disadvantage to this route is the long term cost. I didn't like the idea of paying several thousand dollars for a 20+ year old engine, knowing that it's life expectancy is limited, and it to will have to be replaced. For a quick replacement, or if you are planning to sell soon, a rebuilt engine is a reasonable choice. If you are keeping the boat, I'm not sure it is economically prudent.

The diesel route, while initially more expensive, has several advantages. To begin with the fuel is safer, the consumption less and more power is delivered to the water; or you will go further and faster, for less. However the biggest advantage is that you are starting out with a new engine. I plan to keep Isa Lei for quite a while, and by putting in a new engine, I know that I won't have to go through the process again, at least in the foreseeable future.

When converting to diesel, you will have to make some changes. First the old prop will have to be replaced. For a cruising boat this is an advantage, the new prop will be 3 bladed, and deliver more thrust, as well as having some serious backing ability. The fuel system can probably be modified to accept diesel. If your tank is either plastic, or aluminumized steel, all you have to do is clean it well and add a fuel return line. If it is galvanized steel, it will have to be replaced. The fuel filter should be replaced with a Racor filter, to insure better water removal. The old muffler will probably be OK, as will the shaft and stuffing box.

Once I made the diesel choice, I had to narrow the field. After conversations with the members of our "maintenance committee," I was down to two serious contenders; the Westerbeake M4-30 and the 2 cylinder Yanmar. Mike Lehman, Bob Leigh, Phil Beigel, Don Kadenoff, et al., had me almost convinced that the Yanmar was my best bet. When Bob Montgomery called and told me that Yanmar had an "End of Year Sale." There was no hesitation, and in January Bob and I loaded my new engine in the bed of my truck.

In making the selection between the Westerbeake and the Yanmar, several things have to be considered. First either engine will deliver more power to the prop than the Atomic 4, so horsepower isn't a major concern. The Westerbeake, being a four cylinder, will idle smoother than the Yanmar - in fact the two cylinder idle is where the nickname YamerHammer comes from.

It isn't bad, but noticeable. The Westerbeake will cost about 40% more than the Yanmar to buy (this makes the idle tolerable) but may be less expensive to install, since it is alleged to replace the Atomic 4, there may be less alteration required. In the newer boats (with a molded engine pan), the Westerbeake is the better choice, it's outside dimensions are closer to the Atomic 4, meaning less surgery. The Yanmar is too deep to fit the engine pan. On the older boats, there is no engine pan, so there is no restriction and either engine will fit.

Installing the Yanmar, or Westerbeake, in an older boat.

For both engines the technique is the same, I'm not going into specifics, but a general overview. Once you have removed the Atomic 4, you need to clean the 20+ years of crud from the engine room. Then you should remove all of the electric wiring that belonged to the engine, including the instrument panel, this wiring will be replaced once the new engine and control panel are installed. You also need to remove the shift and throttle cables, along with the shift assembly. These parts will also have to be replaced. Leave the muffler and shaft in place. You can reuse them. I put a hose clamp on the shaft to keep it in the boat, since Isa Lei was afloat at the time of the replacement. You will need to cut the old engine beds out, so that new ones can be made and installed. The "Z" brackets that Whitby used to support the Atomic 4 shouldn't be used for a diesel. The worked on the Atomic 4, but with a diesel you will have more torque and vibration. Additionally the flex mounts used with the new engine won't fit on Whitby's brackets. A "cut-off wheel" for masonry does a good job on removing the fiberglass beds. I left the forward 8 inches in place, as an anchor point and ground the after section smooth enough to glass in new beds. The new beds were cut from 4" x 6" pressure treated lumber and ground to fit the hull with a belt sander.

I made a template of the engine out of plywood, and bolted the new engine's mounts to the template. By placing the template, with the mounts, on the new engine beds, I could see how much had to be cut from the beds for a perfect fit. Once everything fit perfectly, I glassed the new beds to the hull and bolted them to the remaining sections of the original beds.

The Yanmar came complete, new mounts, instruments and drive flange, however because our hull is so narrow under the engine, I had to replace the after mounts with "Globe M5" mounts. I also put a "Globe Drive Saver" flexible coupling between the engine and the shaft. The dimensions of these parts were included in making the template.

Because of the weather we had this past winter, I finished the conversion about a month later than planned. The project was labor intensive, but not as difficult as I expected, however it is basically a single handed job. There isn't a lot that you can use an assistant for. There just isn't enough room to get two people on the job. The entire project was straight forward, and did not require an engineering degree. It was just slow, careful work, often in cramped spaces. Everything about the conversion was worth the effort and now I can sit back and enjoy, knowing that my trusty, rusty old Atomic 4 is helping keep the Commodore's engine going (he is collecting used Atomic 4's in a parts bank).

Installing a Yanmar in a newer boat.

Because of the differences in mount dimensions, and increased engine depth, with the Yanmar, you will have to remove the engine pan. The engine mounts just will not line up with the existing Atomic 4 engine beds. In that this requires major surgery, I would recommend that this conversion be done by the dealer that sells you the engine. A better solution would be to install the Westerbeake. It will go in without having to cut the molded engine pan out. Because of the extra labor involved with the actual installation of a Yanmar, I feel that it would be cost effective to install the more expensive, but easier to install Westerbeake.


Our engines are wearing out, the last Atomic 4 was made more than 20 years ago, and replacements are not cheap, however a good diesel can usually be found at a reasonable price. One way to get a good price is to shop the boat show. Know what you need, and work the dealers, like buying a car. Of course, we can't predict when an engine will have to be replaced, but a little prior planning may pay off.

For the older boats, the Yanmar 2GM20 seems to be a good bet, for the newer boats the Westerbeake M4-30. A rebuilt Atomic 4, or Gray can also be picked up fairly easily, however if you plan to keep the Alberg, I would question this choice.

The installation is very straightforward, but a lot of work, and a job that one should consider hiring out. Many of the shops that sell engines will often put together a package deal that is reasonable. I'm sure Bob and Mike Montgomery can help here. If you want to do the job yourself, it isn't a difficult job, however it will take a lot of careful work. One major advantage we have is our Alberg maintenance committee. They are able to answer almost any question, and find several other members have also done the job. We are available to help - don't hesitate to call on us.

Parts used on Isa Lei

  • Yanmar 2GM20
  • 13x13x7/8 Right Hand 3 Blade Prop
  • Teleflex Single Lever Control, with cables
  • 2 - Globe "M5" mounts
  • 1 - Globe Drivesaver
  • 2 - 4x6 3 foot long Pressure Treated boards
  • West Epoxy and Fiberglass Cloth
  • 2 - 3/8 SS Bolts, washers and nuts
  • Racor Filter
  • Copper Fuel Line 1/4 inch and misc. fittings
  • Misc. screws and small supplies.

(Editors note. Rumor has it that Tylenol and Ben-Gay should be in the required items list.)

Jim Davis
formerly Isa Lei, #240

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