Auxiliary engine maintenance - less glamorous than Rock Stars, but critically important

Aux Engine - Yanmar 2GM20F

To avoid running the main engine aboard MAYAN, which is a 130hp Mercedes Benz OM-352 bus engine, for prolonged periods at light load to cool the refrigeration and charge the batteries, MAYAN has an Yanmar 2GM20F 16hp auxiliary engine located in the port side of the engine room.  As is typical of most cruising boats that make relatively short trips, the auxiliary engine gets a lot more hours than the main engine.  We don't know exactly how many hours have been put on the auxiliary engine, but from the looks of things it's at least a thousand or more.

Rust under old muffler

The update to this engine started with the observation of pin-hole leaks in the side of the water-lift muffler.  Sadly, this muffler was constructed of what appears to be 304 stainless steel and, as is typical of this metal, it started to fail all along the welds.  The leaks had drained water on the wood cleats supporting the muffler, and as a result rot had set it.  The Yanmar 2GM20F is notorious for clogging up its exhaust mixing elbow, and our auxiliary engine was no exceptions.  Given we were going to be pulling off all the exhaust pipes anyway to replace the muffler, it made sense to strip off the mixing elbow and taking a look.  Sure enough, the exhaust hole was over half clogged with soot and chunks of rust.

Exhaust Mixing Elbow, the silver thing

A quick trip to the Bosun's Locker in Costa Mesa yielded a new mixing elbow, some new hose, a gasket and a new fiberglass water-lift muffler.  Some sailors are concerned about using fiberglass to build the muffler.  This concern is based on the scenario in which cooling water is blocked to the engine and prior to any other warning or alarm the hot exhaust melts (or worse ignites) the muffler.  We're not concerned about this primarily because the exhaust note of the Yanmar is quite noticeably different and louder when running dry.  We will certainly notice the bellowing.  The second failure scenario is that one can't hear the auxiliary engine running dry because the main engine is also running and masking the sound.  This shouldn't happen aboard MAYAN as some other engineering we're doing will make running both engines at once extremely rare.

While we were at work on the Yanmar, we also discovered the air filter was heavily clogged with dust and guck, so it was replaced.  Given the significant increase in air and exhaust flow, the Yanmar should run substantially better.

Top view of auxiliary engine

Of course, whenever one starts pulling on the "thread of a sweater" of one project.... it leads to others.  While we were pulling the muffler thread from the sweater of our project it became clear that it was completely impossible to access the muffler and the exhaust system (including the sea water through hull) due to the way in which the refrigeration compressor and water-maker pressure pump were installed.  This was unacceptable for any number of reasons, primarily because in the event of a hose failure it wasn't possible to get to the sea cock to turn off the flow of sea water.  In the picture to the right one can see the water-maker pump (black pump on the far right), which was mounted above the refrigeration compressor, which was mounted above the exhaust muffler, and all of this left only 5 inches of space to try and squeeze through to get to the sea cock.

Aux engine stripped down

We had been planning to change our refrigeration strategy anyway, so we took the opportunity to remove the old system, clearing away the compressor with its two belts, the condenser, dryer and head exchanger.  Of course, the removal of all this required the temporary removal of the high pressure pump for the water-maker.  We'll reinstall the water-maker pump when we prepare for a long trip that requires that device aboard.  In the mean time, we'll be able to easily and safely get at things.

Once again, as we pulled the thread of cleaning things up to make it easier and safer to access things, it became obvious that this was a great chance to get a coat of paint on the auxiliary engine.  Of course, while this wasn't in "the plan", it was painfully clear it needed doing.  In the picture to the right we've masked off all the non-Yanmar-gray bits and painted up the engine.  The painting process is a crazy dance of sticking one's head out the hatch to get a lung full of fresh air, going back into the engine room and painting until one needs more air, and repeating the process until the engine is well painted.  I suppose I could get a breather, but this works.

Finally, with the engine painted and the excess equipment moved aside, the high output alternator received new belts and was tensioned.

This project, which originally set out to fix a small leak in the muffler was scheduled as a one-day job.... well... like almost every project on a boat it ballooned into a four day set of interlocking projects.  While at each step of the way it was clear that the additional work both needed doing and would improve MAYAN, it illustrates just how difficult it is to "plan" projects on a boat, even for those who have been planing projects for years.