YANMAR ENGINE REBUILD
Yanmar original, we understand – so we
guessed it must have been replaced at
some time. Unfortunately this failure
meant water had probably entered the
cylinder, so we removed the cylinder head
to check it out.
The first damage noted was to the
There was plenty of damage on the head around the exhaust port Internal anode was coated in a crust of exhaust carbon
The face of the cylinder head after it had been flatted Once stripped, the engine could be manhandled out of the boat
Blown head gasket resulted in water etching a pit into the face of the engine block – and
just look at the state of the badly pitted piston crownInner and outer sections of the old
exhaust elbow had separated
ABOUT THE BOATNorthern Light, a Hunter Horizon 26,
was bought by Barri Hopkins’s
daughter and son-in-law at the
Tollesbury Boat Show in October- After work to meet a surveyor’s
recommendations, she was
launched in early 2007 and sailed on
the Essex and Suffolk rivers. The
engine was always difficult to start,
but the problem was manageable.
Then in 2008, an opportunity arose
for the couple to work abroad for two
years and the boat was laid up in a
West Mersea yard with the
expectation of being re-launched two
years later. But nine years passed
before they returned to the UK...
piston, which apart from being heavily
carbonised, was also badly corroded,
almost certainly caused by salt water.Blown head gasket
The head gasket had also blown, causing
a small pit to be etched into the face of the
block. The cylinder head itself was flat,
though, showing no sign of burning and
required only flatting off on 100-grit wet
and dry on a dead flat surface.
Before investigating further we decided
to remove the engine from the boat. Since
no mechanical aids were available, the
engine – it weighs only 76kg – was
stripped of the alternator, starter motor
and gearbox and was manhandled out of
the boat. No mean feat for two guys
whose years totalled nearly 150!
Once home, closer examinationrevealed that the face of the exhaust port
was badly corroded, undoubtedly caused
by salt water seeping down between the
engine block and the gasket. Oddly, there
were two gaskets fitted.
The internal anode, which should have
been a greyish colour, was still largely
intact, but was covered in a crust of
carbon from the exhaust gasses which
had been blown into the water jacket. In
fact, this effect could prove to be a simple
indicator if head gasket problems are
suspected in a 1GM10.
The valves and seats showed only
minimal wear, as did the cylinder bore,
crankshaft journals and big-ends. We
reground in the valves, but the bearings
needed no attention.
While the head was off, we cleaned
inside the water jacket as best we could