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F.4.8) Engine Rebuild

A badly overheated engine whilst 12 miles from the marina resulted in having to trouble the RNLI...

The culprit was a piece of impeller that the previous owner had not tracked-down. It had jammed against the thermostat, impeding water flow and causing the cylinder head to overheat and the pistons to seize. Ironically, the blockage at the thermostat made the flow-from the tell-tale extremely voluminous, making this finger-in-the-air measure of cooling efficiency somewhat misleading.

Warning: This rebuild exposed me to a number of hazards, not least my wife discovering that I was doing this rebuild on the dining table. You have been warned.

The thermostat was not in good shape.
New and Old Thermostats (supplied with the seal upside-down!)

The expansion of the (aluminium alloy) pistons resulted in friction with the cylinder wall and removing quite a bit of material from the piston skirt.

Damaged piston.

The (much harder) cylinder walls came off much better, having only a few scratches. These are not deep enough to catch a fingernail or credit card so were judged 'acceptable'. The cylinders were re-honed to give a nice oil-retaining surface and a set of new pistons and piston rings were fitted (having first filed the exhaust ports so as not to catch the piston rings). The small ends of the piston rod are needle bearings and the needles were held in place with grease so that the piston pin could be fitted - no special tools here.

Honed Cylinder with Scratches.

Pistons and Crankshaft Oiled and Re-installed.

With Carb and Starter Installed onto Crankcase Cover

Exhaust Cover Back in Place

Flywheel Fitted (Nut yet to be tightened)

Recoil Starter in place