4 HP Evinrude 2 stroke Outboard with Frozen Pistons

toivoJuly 5, 2009

I recently purchased a 1969 4 HP 2 stroke Evinrude Outboard that has not been run for 18 years. During this time the pistons have become stuck and I am not able to turn the engine over. Does anyone have a suggestion on how to free up this engine without tearing it apart? If I tear it apart will tapping the top of the pistons unstick them? The model of this outboard is an Evinrude 4906B

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If the pistons are badly stuck, the rings are likely corroded and need replacing. However, you can try the following:

Remove the head and orient the engine with the bore vertical. Put about a two table spoons of penetrating oil around the edges of the pistons. Allow the oil to soak in for 4 hr or more and then try to unstick the pistons. Apply a piece of wood against the piston top and tap with a hammer. A rubber mallet is a good choice. Tap both pistons, and then try to move turn the crankshaft. Work cautiously because it is easy to damage the port area. If the crank is stopped in the top dead center or bottom center, the crank will not turn by forcing the pistons. In that event, try rocking the crank back and forth.

With an engine that has not moved in 18 years and the pistons stuck in the bores, a disassembly is indicated to thoroughly clean the bores and assess what needs replacing. A broken ring poking out into a port can damage the port and make the cylinder useless.

    Bookmark   March 25, 2010 at 3:08AM
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And after you've done all that, try reading the forum heading.

Not that it matters...nothing else happening here.

    Bookmark   March 25, 2010 at 11:16PM
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