"This winter, I replaced Hyperion's engine with a new Yanmar 2GM20 2-cylinder, 18HP diesel. The reason for the replacement is that the original Atomic Four had failed on me twice in uncomfortable circumstances.

Questions about replacement engines have come up in the Forum several times and I wanted to show people what is involved. The diesel itself was about $7500.00 Cdn. I did the complete installation myself, therefore I have no idea of the labour cost that would be involved. The swap, however, was a piece of cake for me. If you're not as mechanically inclined as I am, it might not be quite so simple, but note that this engine fits with no major modifications to the engine space and no glass work. The Yanmar 2GM20 even comes with a complete wiring harness that just plugs in, so the amount of work is minimal.

As far as making up the exhaust gooseneck, any competent welding shop can do it and I don't believe it would be all that expensive. Use Sch. 10 316 Stainless Steel material. The wall thickness is not that much.

At the same time as I changed the engine, I replaced the prop for a beautiful feathering prop made by Max-prop ($2200.00 Cdn. landed here). I had the prop manufacturer match the prop to the boat and the engine. Prop is 2 blades of 13" diameter set at 28 degrees of pitch [equivalent to 13"pitch]. I also increased the length of the shaft about an inch to give me proper clearance between the prop blade and the hull.

I replaced my tank with one I had made out of stainless steel to original dimensions. When I removed the 30-year-old tank, I could poke my finger through the bottom. Scared the daylights out of me.

There are a lot of people out there that would say I am crazy for spending the money on a 1971 Mk1 (I have spent more on improvements than I paid for the boat), but my wife and I love the performance of the boat and I have no intentions of ever selling it or moving up."

Thoughts on costs

Recently (Feb. 2008), a BC owner was quoted $7500 for a Yanmar and $5000 for the installation (at a $70/hr rate), which he found discouraging. However, while it might cost several thousand dollars of a mechanic's time to do the job, installation doesn't need to be done by a mechanic. Rather than abandon the thought of a new engine, it was suggested, he should do the work himself, as Ralph Ainslie did. There is nothing in an engine change that anyone who is reasonably competent with tools cannot do. My perception after watching some of the work being done on my boat and doing some of it myself (and saving quite a bit thereby), is that if you can confidently look after an engine (change oil and filters, winterize, etc.), you can swap one of these engines into the boat with the help of a friend.

There is one complication – the competing needs of getting the old engine out and the new one in, which is easily done with a club mast jack or even the boat's own boom and a block-&-tackle (in other words, on the water), versus the need to have the boat out of the water to replace the shaft (not obligatory but desirable, as you'll probably find the old one is quite worn and a new shaft can be a bit longer, allowing you to position the engine slightly farther forward); it's nice to replace the cutless bearing too. Also, you will have to resize the exhaust fitting on the transom. These competing needs could be dealt with through a bit of planning or – something sailors are good at – improvisation.

You can remove an A4 more easily by removing the wood cross-piece that supports the front of the engine cover. You will have much more room to work. Also, you can lift the engine straight out with a crane. You will need a #1 or #2 Robertson head screwdriver ( a variation is apparently sold in the US by Home Depot as a "square drive" screwdriver). There are three or four screws a side and then the cross-piece just lifts out. The engine is gearcase-heavy and will bind on the mounting bolts if you just try to lift it with the lifting eye on top of the block. Instead, drop a strop three or four feet from the lifting hook to the hoisting eye. Then, from the same hook, drop a block and tackle and make it fast at the rear of the gearcase; the block and tackle should make a slight dog-leg as it passes under the cockpit. With everything disconnected on the engine, tighten the block and tackle until the aft end of the engine rises. It's okay if it binds a little bit on the mounting bolts, but not too much. Raise the hook a bit until the front end of the engine binds a bit. Repeat until the engine is off the mounts and hanging free.

The Yanmar 2GM and 2YM engines are virtually a drop-in replacement. You don't touch the glass (see Ralph's comment above). The steel angles on top of the fibreglass or wood beds need to be changed, but anyone who can use a measuring tape and hold a hacksaw and a drill can do that.

• Steel: $30-$40
• New prop: $100 to $1000+
• New shaft: $500
• New cutless bearing $95
• Shaft seal $200 (nice but not essential)
• Muffler (Vetus): $200
• Hose: $200 (a guess - might be $300)
• Clean tank: need brass utility pump (non-sparking), one roll paper towel, 36" wooden dowel: $30 (if you have to buy the pump)
• New filter (Racor): $100
• Miscellaneous hose clamps: $40

If you have a steel tank you must replace it (see Ralph's comment above – original steel tanks are way past their best-by dates and so are some aluminum ones). If you have an aluminum tank, you're not off the hook; these can develop pinholes thanks to corrosion from within or, more commonly, from prolonged contact with wetness from the base on which they are mounted. You should lever it up and inspect the underside for corrosion before you start the engine replacement process, because the easiest time to get a tank out is through the engine bay. A replacement plastic tank will cost between $100 and $200.

Cleaning a tank is sometimes made out to be a big deal, but all you have to do is take the fuel sender off the top and you've got a hole large enough to insert a pump hose into the tank and, when the tank has been drained, to insert a dowel wrapped in paper towel – this will blot up any bits of crud on the tank bottom. You don't have to get every bit of the gas out. A diesel will easily tolerate a concentration of gas as high as a litre in the 50-litre tanks on a 27.