Yanmar 2GM20F

How did I go about rebuilding the inboard engine on a sailboat and why?

The answer is quite simple, considering that the engine is from 1987 and probably nothing more was invested in it in its entire history than changing the oil, I decided to invest some money and effort while the engine was still running, despite the engine's operation. The engine was leaving traces of oil in large places, the seals and oil seals were already very bad, and the exhaust mixing elbow was also heavily rusted. Of course, I did not start the project as a complete beginner, since many years ago I completed my first education as a vehicle repairman - a car mechanic. I did not have anything more than theoretical knowledge and the mandatory practice. When the decision was made to rebuild the engine, I first looked for relevant literature, studied it a bit and found that these engines have been more or less the same for decades, so there was no hot water to be found. When I searched various websites about the motorcycle, I found everything I needed, as the literature is quite easily accessible with just a little effort. So I found the appropriate instructions and also the part numbers for the entire engine. I found out that there are several models of 2GM20 engines and that I have the type 2GM20F, which means that my engine has a closed freshwater cooling system. The engine in question is a 2-cylinder diesel engine and has a maximum of 18 horsepower at 3600 rpm, a working volume of 635 cc, and the engine weighs about 110 kg. Interestingly, Yanmar engines have the same cylinder diameter regardless of the number of cylinders, so you only need the right number of pistons, bearings, connecting rods, valves,...

I drove to the sea with a pallet in the trunk, tied the sailboat to the side of the pier and got to work. First, I tore up the stairs and disconnected the electrical wiring, cables and all the pipes, then I disconnected the shaft and engine mounts. I lifted everything up from the inside using the boom, so that the engine was hanging in the air. I then turned the boom to the side towards the pier, where I lowered the engine onto a pallet and later placed it in the trunk of the car.

Since I didn't know how to go about it at the very beginning, I sent an inquiry to some service centers and found out that the repair would cost me around €1,500, which, together with the new parts that I would have to replace (mixing elbow, engine mounts, bearings, seals, oil seals, etc.), would add another €1,000 or more. I decided to tackle the project myself, so I looked up the appropriate article codes in the catalog and ordered them from all over the world, where I found the cheapest parts. When searching for parts, I found that individual parts were not available as originals (bearings, rings), except for certain parts for which there are replacement "fake" ones, such as engine mounts, seals and mixing elbow. I ordered everything together and of course waited a month for all the parts to arrive. In the meantime, I started dismantling the engine, preparing it and cleaning it. Because I wanted the engine to be repaired with high quality and to be safe for continued operation, I sent some elements to experts. So I sent the alternator for electricity production to a car electrician, who checked its operation, measured the current and replaced the sliding brushes. I sent the cylinder head and high-pressure fuel pump, along with the valves, to a specialist, who correctly adjusted the fuel injection nozzles, adjusted the valve seats and aligned the cylinder head. I did the rest myself, and according to the instructions, installed the new parts correctly. I borrowed a certain tool from a mechanic friend that I did not have, namely one of these tools is a torque wrench, which is used to properly tighten screws, and I also needed a micrometer for measuring.

Yanmar is a very simple engine, for which you can get all the necessary information, so I didn't have any major problems when assembling it. The Yanmar 2GM20F does not have a timing belt but works via gear transmissions, and the markings for just setting the ignition and the like are already marked. Since the said engine has a closed cooling system, it also has two water pumps, namely one is built into the engine which also has a thermostat and which mixes the water throughout the closed engine system itself. The second pump is for salt water, which pumps salt water through a pipe from the sea via an impeller, and pushes it further into the heat exchanger, where it mixes with fresh water. The engine pump also has 2 additional pipes that travel further to the water heater - boiler. While the engine is running, we get hot water in the boiler for washing and showering. Since the original control panel does not have a counter for the number of engine revolutions and the water temperature, it only has an audible alarm, I decided to upgrade everything and bought a tachometer and a heat sensor and a digital water temperature meter. I decided to measure the water digitally because conventional analog meters show a minimum-maximum scale and it is actually difficult to know what the actual water temperature is, but now I know very precisely. The water temperature also tells me whether the engine is overheating, whether it is due to a bad impeller, a clogged water filter, or whether the problem is even a malfunctioning thermostat.

I assembled the engine, protected the individual parts and painted them with the appropriate temperature-resistant paint so that the engine looked like new, not just in terms of operation. When I had everything assembled, the moment of truth came, whether I had assembled the engine correctly and well. Since I had to improvise starting the engine, I poured water into a large container for cooling and connected the exhaust pipe to it, as well as the pipe that was supposed to pump salt water. I poured oil into a bottle and improvised a tank. Since I didn't get an alternator from the service, I installed a replacement test one that I happened to have at home. I connected the tachometer and temperature gauge. Before starting, I used a hand fuel pump to bleed the fuel supply system, connected the battery and started the engine. The engine ran, the water circulated and satisfaction was inevitable. I then reassembled everything back into the sailboat and replaced the engine mounts.

Instructions, catalog numbers:

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