ORIGINAL: jaka
Hi!
The only thing that will loosen up old castor oil gum inside the engine is heat! Alcohol or acetone won't do!
Agree heat is part of the solution. However, without a solvent, the engine will just stick again when it cools.
Warm the engine ...either with a propane torch or heat the engine in the oven.
Oven is much safer, with a torch it's tough to evenly heat the engine.
But! There is a but to this....The only thing that can't be fixed this way is the ballbearings!
They must be replaced by new ones if you are serious.
Maybe, maybe not. It's quite common for them to be ok, just gummed up by castor. Since the outboards are often stored on the boat, which puts the bearings up in the air, they usually have not been sitting in fuel and any alcohol would have evaporated quickly. The remaining castor does a good job of protecting the bearings from moisture.
When I put one of my outboards back in service this summer, after it had been sitting in storage for about 20 years, I removed the engine from the lower unit and disassembled the lower unit and cleaned it out good. I also removed the back plate and carb from the engine so I could take a good look inside. Once I had cleaned out the engine with alcohol, it was obvious the bearings were fine, so I did not change them.