Practical Boat Owner — January 2018

PRACTICAL

Boat owner Barri Hopkins shows how he and engineer Alan Cowper

resuscitated a seized motor without spending too much hard cash

T

his tale relates to an engine

widely found in small boats

and very often in Hunters

• this one in a Hunter 26.
  Although we’re dealing with a specific
  engine model, the Yanmar 1GM10, the
  principles will apply to most raw-water
  cooled marine engines.
  This engine in Northern Light had always
  been difficult to start, and after a period of
  10 years laid up it would, unsurprisingly,
  not even turn over.
  A recently retired engineering friend of
  mine, Alan Cowper, relished the challenge
  of getting the engine to run again, and so
  the pair of us started work.
  Having managed to free the valves by
  copious soaking in WD40 and then
  applying gentle persuasion with a
  soft-faced hammer, the next task was to
  free the piston.
  We removed the injector and sprayed in
  copious quantities of WD40. Vigorous
  rocking of the crankshaft via a 37mm
  socket and a long tommy bar began to
  produce a little movement. We then
  introduced engine oil into the cylinder and
  the injector was replaced. More rocking of
  the crankshaft caused ‘hydraulicing’ which
  slowly forced the oil down past the piston
  rings, thus lubricating the bore.
  Once the decompressed engine was
  able to be turned over smoothly, the old
  fuel was flushed out of the fuel line by
  providing a temporary feed to the primary
  fuel filter from a fresh can of diesel via a
  length of clean hose.

The Hunter 26 Northern Light

owned by Barri Hopkins’s

daughter and son-in-law

Cleaned up and with

a fresh coat of paint it

looks good as new

Rebuilding a seized

Yanmar 1GM10 engine

Motor seized on the inside and rusted on the outside

And after a good deal of cranking and

protest, the engine fired up once again –

and once it was going it ran reasonably

happily. But restarting was still as difficult

as ever.

Elbow trouble

The next step was to remove the exhaust

injector elbow, a well-known source of

trouble on the 1GM10. It is designed to

pass cooling water over an inner pipe

carrying the hot exhaust gasses, while

preventing water from entering the

cylinder. This one did neither – the weld

joining the two pipes had failed, and both

tubes had completely separated. The

elbow was of stainless steel – not a