Re: unseizing an engine

Paul D /
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First make sure it's not the bearings or something else that is seized. If the piston is seized, I would try Marvel Mystery oil and let it soak overnight and then try moving the piston or tapping it with a wood rod and a hammer. Marvel is good for breaking up rust and grime.

Aluminum expands and contracts about twice the rate of cast iron. Spraying the piston with freeze mist may help it contract away from the cylinder, especially if its cast iron or has a cast iron liner.

If the cylinder is cast iron, heating both the piston and cylinder might make it stick more, since aluminum expands at twice the rate of cast iron. Heating the cylinder and trying to move the piston before the piston heats up and expands will help loosen it.

Cooling both the piston and a cast iron cylinder will help, since the aluminum will contract at a higher rate. This is also the reason why an engine sometimes seizes and then unseizes after it has been given a chance to cool down.

A solution of sodium hydroxide (NaOH) etches aluminum readily but does not etch cast iron or chrome or nickel plating very well. Aluminum doesn't like bases and is etched readily by them. Some brands of drain cleaner are mostly sodium hydroxide and will etch aluminum. NaOH is also a good way to preferentially etch smeared aluminum off a cylinder without damaging the cylinder.

HCl (hydrochloric, muriatic acid) also etches aluminum, but it etches cast iron at a comparable rate.

Paul

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