TOPIC: releasing stuck piston and rings

I just picked this 1960 evinrude lark 40 for $160. It is super clean and not banged up at all and i've been looking for this model for my boat (1960 Slickcraft) for quite awhile now so i bought it.

Unfortunately it will not turn over. Is there a recommended concoction to pour in the cylinders to release pistons and is there a recommended procedure? Or should i just take heads off and see what's going on?

I tried posting a pic but it didn't go through...here it is

I saw a thread on the aomcia forum with same issue and a reply suggested it could be the impeller? or at least thats the first place to check, as they can get hard and give the same problem or symptom with many years just setting. Your going to have to remove the lower unit anyway and will make it easier to free the motor if it is the pistons. I used Gumout carb spray many years ago to free really bad stuck hydrolic lifters to replace them in a V-8, just removed the push rods and sprayed a bit and let it soak for a couple days then started to work it loose with a magnetic pick-up tool and finally they came out then did a oil change. Just a thought? might be better ideas comm'n:)
link to the thread on aomcia; www.aomci.org/cgi-bin/yabb2/YaBB.pl?num=1371536674

Step # 1 is to remove the lower unit as it could be rusted solid.

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Remove bypass covers to see if it is in fact a ring problem or internal rust on crankshaft.

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If it is internal rust it may run again but will soon come to a dynamic halt.--There are precision bearings in there that can not tolerate water / rust !!

Pop the hood and grab flywheel with both hands. If flywheel moves even a little bit while turning back and forth the problem is in the lower unit. If flywheel is solid it's your upper end (power head) . If power head, spray both sea foam penetrating spray and penetrating oil liberaly in spark plug holes. Raise motor to as horizontal as possible and try rotating flywheel again in a couple days. If upon inspection when removing bypass covers you see any corrosion nothing short of tear down and rebuild will result in a reliable motor. Good luck. As far as lower unit, if power head is without issue and has good compression, then a rebuild of the lower unit involving impeller and all seals will be what is minimaly warranted. Does the prop spin when in neutral?

I had a mk 55 in about the same shape. in my case it wasent the lower unit, so I sprayed misc wd-40 and others into the cyl and it still wouldnt move, later I took my compression tester and removed the schrader valve out of the bottom and attached it to my compressor @ 90 psi. nothing.....then while talking to a friend it just started moving. I just kept moving it and adding more spray. It later started up and ran, I sold it to a friend that restores old mercs, he replaced the crnk brgs and honed the cyls, it is a running motor today!

Looks like i'll be doing a rebuild.
There is rust and corrosion in crankcase but extent is unknown until i get it further apart. It looks like i can still get most of the parts new which is a relief. I plan on replacing all bearings and piston rings. If crank is ok i'll reuse it, if not i'll replace it. Anything else i should replace while i got it apart?

You may be money ahead to find a powerhead or whole motor and swap some parts. There are a lot of them around and in my opinion they are almost bullet proof unless they were abused/neglected greatly.

Hey Paul, i just got a powerhead off ebay this morning. Complete with good compression for $30 plus $30 for shipping. I'll have to check actual compression when i get it.