We know it has been in storage for years, know nothing about the history of it beyond that.

Soaked the cylinders in 2 stroke oils for a few days and tried a 2' breaker bar with no movement.
Changing the oil out for diesel next.

I've read that slow and easy wins the race and not to force it.

Any other thoughts on this?

hondale11

I have heard a 50/50 mix of ATF and acetone soaking for over 24 hours works well. Also aero kroil is awesome but it is expensive

I have that same engine. The water pumps in them are barely big enough to cool the 9.8. The 7.5 probably does better. If the water pump failed and it got hot and locked up, it may be toast. Keep trying the oil/solvent mix and a strap wrench around the flywheel in both directions. Maybe it'll break loose. The water passages in the engine block on mine were clogged with salt. I poured toilet bowl cleaner with 10% hydroflouric acid down the pee tube until I got it clear. It still runs hot, and I get wet steam out the pee tube, enough to live. Marineengine.com has great parts diagrams. Most of the parts you might need are still available. IslandJim

get some blast from parts store

boatman: I almost suggested Blaster. I have a can that has saved me numerous times. IslandJim

I have access to a strap wrench and will try a can of blaster tomorrow evening.
Thanks for the help to date. horndale

I have broken several lose by soaking them in ATF/Acetone mix for a week or so and then taking a piece of wood and tapping the top of the piston carefully until it just breaks lose. Then it is just a matter of back and forth via a strap wrench on the flywheel. Of course, you have to be careful not to break the piston!

Soaked it in diesel and Seafoam. Tapped gently on the pistons and used a strap wrench back and forth. Engine is free and has compression.
We'll do a compression check hopefully tonight and see what it looks like.

Thanks for all of the suggestions.

Soaked it in diesel and Seafoam. Tapped gently on the pistons and used a strap wrench back and forth. Engine is free and has compression.
We'll do a compression check hopefully tonight and see what it looks like.

Thanks for all of the suggestions.

Ok, Checked compression out and found the upper cylinder at 100 psi and the lower at 65 psi. The lower will leak down at this point.

Filled the cylinders with Marvel Mystery oil and will try working the engine a bit hopefully this evening.

Anything else we can do before eventually pulling the head?

horndale11