Troubleshooting the Engine

I’ve been working the past couple of weekends on troubleshooting the engine. When working on projects like this I find it very helpful to get advice from other sailors, and have been posting my progress on the Cruiser’s forum here:

Here are the highlights of what I’ve done so far:

Post 1

Looking for help troubleshooting my old raw-water cooled Yanmar 2GM. Here are the symptoms and circumstances so far:

– sailed to offshore island with a friend. Just outside of harbor went to start engine and starter burnt out in a puff of smoke.
– with zero wind could not sail into harbour. With prevailing current onshore needed to get engine started asap.
– flipped up decompression levers, attempted to start by hand cranking, in my haste *forgot to close raw water inlet*.
– after several valiant attempts to hand crank, no skin left on knuckles, and rocks approaching, dropped anchor to await a tow.
– no starter parts available on island. Dissasembled starter, cleaned brushes to no avail, starter was dead.
– after two days couldn’t wait any longer, rowed her out of harbour with the dinghy, sailed home.
– various obligations kept me busy through the ensuing winter. It was 8 months later when I finally installed a new starter and tried to start her again. During that time she sat as she was.

– after installing new starter she wouldn’t crank at all. Tried with hand crank and found she was seized.
– checked oil and found crankcase overfull. Oil flowed out of crankcase when dipstick removed.
– tapped on hand crank with large hammer. After a few taps she started to free up. Continued tapping through one revolution untiil she freed up enough to turn over normally.
– removed oil fill cap on rocker cover to observe rocker movement. Rockers moving as expected.
– tried starter, she cranked over fine.
– checked turning by hand crank with and without decompression levers up. Compression strong.
– bled fuel system completely. Certain no air in fuel lines.
– tried starting. Would not fire at all.
– pumped out oil and replaced several times with fresh until system clean.
– stored oil in glass bottles. After sitting oil separated to top revealing mayonnaise like substance in bottom centimeter of jars.
– pumped out fuel tank and lines of all fuel, replaced with fresh diesel, rebled system.
– tried starting several times, will not fire at all. Not one pop.

– Hand cranking with raw water intake open allowed water to enter cylinders.
– After sitting for 8 months water seeped down past rings and gathered in crankcase.
– Resulting corrosion resulted in at least one seized piston.
– Top end corrosion resulting in improper injector and/or valve operation leading to lack of combustion.


Post 2

– removed exhaust elbow to ensure no blockage. Elbow was clear (expected, as replaced last year).
– removed alternator belt for easier cranking.
– removed fuel line at injectors to ensure steady stream of fuel is reaching them (see video below Yanmar 2GM injector test part 1).
– removed #2 injector and installed upside down to check spray pattern. Spray pattern looks good, nice cylindrical shape, strong jet (see video below Yanmar 2GM injector test part 2).
– cleaned carbon with a toothbrush and reinstalled #2 injector.
– removed #1 injector and tested spray pattern. Not clean like #2, irregluar shape (see video below Yanmar 2GM injector test part 3).
– cleaned with toothbrush and reinstalled.
– reassembled and tried to start engine, still does not fire

*Note: removed injectors by first removing retaining bracket, then hand cranking engine. Engine compression forcibly ejected injectors (bounced off cabin roof!) indicating at least fair compression remains.

You can see the results of the above tests by watching the following videos:

Yanmar 2GM injector test part 1:
Yanmar 2GM injector test part 2:
Yanmar 2GM injector test part 3:


Post 3

– checked shop manual and found that cylinder head to top of combustion chamber clearance is 0.07 mm
– manual says to check clearance with a crush test by inserting 1.2 mm fuse wire (which I take to be a poor translation of soldering wire) into injector nozzle hole in combustion chamber and turning engine over slowly with hand crank
– purchased 1.2 mm soldering wire at hardware store
– removed injectors, inserted wire into cylinders as per the manual
– wire crushed down to an almost perfect 0.07 mm on each cylinder
– however, crush pattern was very pitted and wire came out black indicating corrosion inside cylinders
– to make sure, double checked crush test with fresh wire
– 2nd crush test also worked, crushing wire flat. Unfortunately in cylinder#2 the wire was crushed so flat I could not remove it back through the hole in combustion chamber. Attempting to pull it out with pliers caused it to break off, perfectly jammed in combustion chamber

So the good news is that the rods do not appear to be bent. The bad news is that the head now has to come off, if only to clear the wire. Most likely this was necessary anyway given the apparent corrosion inside cylinders.

Updated hypothesis:
– a small amount of water did get into cylinders
– the engine was not hydrolocked badly enough to bend a rod
– however engine sat too long with moisture inside causing corrosion of combustion chamber
– head needs to be removed, it and cylinders cleaned, and valves turned
– rings may also need replacing due to damage from cylinder wall corrosion

Post 4


– Decided to go ahead and pull off the head. Was quite easy, took almost exactly one hour to complete following shop manual.
– Soldering wire was bent in such a way it would never have pulled out (see pic below). Lesson learned, don’t use too much wire when attempting crush test. Easily removed wire with head off.
– Happy I did pull the head. There was a lot of carbon and corrosion, and the head gasket, although showing no signs of rupture yet, looked to be very old.
– Cleaned up #1 cylinder for comparison (see pic below)
– Checked pushrods. All are straight and true.
– Compressed valves slightly to check. Actually seem to seat quite cleanly.
– Large amount of carbon on piston heads, as well as pitting on #2. Need to clean and analyze properly next time.
– Analyzed cylinder walls. Both cylinders are very smooth with no sign of scoring.
– Performed leak test as a rough test of rings. Put both pistons at equal height, midway in cylinder. Poured 1/4 inch of oil into both cylinders. Turned engine by hand forward and backwards several times to work oil in, then let sit. After 5 hours oil had seeped past rings somewhat, but both cylinders still held oil (Note: it’s a hot day, temperature in boat was about 90 degrees, so oil was warm and viscous).

Although I haven’t purchased a compression test kit yet, the fact that the engine had enough compression to blast injectors out, oil seepage past rings is very slow indicating tight ring fit, no indication of head gasket rupture, and valves relatively clean within valve chamber, I think she just needs a good cleaning. Will purchase new head gasket, clean everything up, and reassemble. Debating whether to turn valves while she’s apart.

Pics for reference:

Head (with wire visible):…ew?usp=sharing

One side cleaned:…ew?usp=sharing

Leak test:…ew?usp=sharing

Here’s a video as well showing the condition of the cylinders and head:

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