Yanmar 1GM Rebuild

So the current challenge for me is to get a 1980’s Yanmar 1GM running.  I got this engine by helping a client remove it from his recently acquired 1930’s Dutch built wooden sailboat and the owner before him had really abused / neglected this quirky but popular little workhorse for a number of years.  For those that don’t know, the 1GM is a single cylinder diesel motor which can be found in a number of small sailboat in the US and abroad.  They have some known issues but overall they work well if you take care of them.  And taking care of this specific example is exactly what did NOT happen.  When my client had this boat shipped in it was with the hope of getting rid of this motor in favor of a nice electric setup and it was clear why.  The motor was caked in rust (Yanmar paint is known to fail fairly easily), did not run and it was clear that it lacked full compression.  We got the engine out no issue except for the siezed engine mount nuts which meant that the motor came out with the mounts still attached.  Now that I have broken the motor down here is the list of items wrong with the motor:

Failed paint – Yanmars have a thick metalic paint which seems particularly prone to fracture and rust.  Combined with the cast block and you don’t really have a recipie for an engine that will forgive lack of maintenence.  This will need to be cleaned up and repainted.

Thermostat completely siezed with rust – The thermostat was completely rusted and fouled with deposits such that there is no consideration that it might be saved.  Into the garbage it goes!

Clogged cooling channels – This is a common issue with the Yanmar GM line.  No real damage to be seen as a result of this but it sure is a pain to get all of the deposits out.  I did not find any rusted through parts of the head channels which was good since it does happen.

Carbon scale in the exhaust ports – Carbon scale essentially gets baked on to the inside of your engine and is more difficult to clean that getting burned cassarole off of a baking pan.  I used a chisel very carefully on the surface of the carbon to see if I could get it to fracture which most of it did.  Lastly a dremel tool with a sanding brush light enough to not damage the metal made quick work of the leftover carbon.  This is an issue that only gets progressively worse over time such that eventually the motor will have so much backpressure that it will not run.

Exhaust valve erosion and carbon buildup – Because the exhaust valve had been fouled with carbon it was allowing the explosions to blow past the partially open valve.  This sacrifices engine power but also causes a burned valve via hot gas erosion and fatigue.  A new exhaust valve is so cheap that I will most likely just get a new one but I am at least attemping to see if I can lap the seat with a nice silve edge all around the valve and seat contact seal.  Doubt it but it is fun to try.

Exhaust bend mounting face on the head is rusted and will not seal – This is the gasketed joint between the head exhaust outlet and the exhaust elbow.  It is held on by three bolts at basically 9, 12 and 3 o’clock while 6 o’clock is unsupported.  I have no idea why they did this as there is room for a 6 o’clock bolt but I digress.  At the 6 o’clock position there was a past water leak coming from the unsupported side which turned the seal face into a rusty mess.  This probably means that the head itself is done for by most standard but ultimately I am not interested in paying hundreds of dollars on a new head and am more interested in making the old one work for the challenge and engineering of it all.  In my mind there is no real reason why a thick sturdy pipe can’t be welded on in order to be rid of the pesky rusted seal face.  If it needs service in the future then it can be ground off and I am totally ok with this versus buying a new head.

Exhaust elbow – This is a famously pesky part on these engines, pretty much guarenteed to fail like clockwork every 4 years.  And at only $300 a pop from Yanmar (granted it is a double wall tube but I still think that is a lot).  I am planning to duplicate the same thing in a more durable setup and simply weld it straight to the head.  It pays to mention that in order to weld to a head you have to know what you are doing or you will certainly just crack it.  For those of you who own this engine it is advised that you remove the exhaust elbow every two years and really just consider replacing it.  Failure of the water and exhaust mixer causes water to spray backward into the head with often pretty disasterous results and it is best to just avoid this.  You can find quality aftermarket examples in stainless steel for about a hundred bucks.

Overall a fun project engine and one which I plan to get chugging for about a hundred bucks.  It won’t be perfect but the goal right now is to consider installing it in our 14 foot cocktail launch built in the 1940’s, no round the world cruises with this motor.  The launch currently has an air cooled gas flathead engine which is unbelievably loud and despite being a reliable engine this noise is something that I would like to get rid of even if it means dumping the Kohler engine.  I have looked into mufflers made for it but the engineer seems to only think this will take care of about 20 db of sound so we have only gone from 747 engine noise to only a race car engine noise level, yea!!!  With a small water cooled diesel the motor could be mounted inside a sound proof enclosure where the engine noise goes out through a water muffler and the mechanical noise gets taken care of by the insulated enclosure.  And maybe, just maybe, my cocktail guests will be able to take off the hearing protection and actually converse with each other!!  One can always hope.

Happy boating to all!!!

Eric…