seized engine

IMHO if you can't turn the engine with a big breaker bar on the crank then there is enough rust to cause damage to the rings and cylinder. Water will not pass a plug that is in a cylinder that has good operating pressure. Water is a much bigger molecule then air. Try the Tranny fuild and Acetone. Though you will have to get all that out of the oil before you try running it. Just be prepared for not such a great running engine after this.

I've had luck with using "Corrosion block" found in boat stores.

I've mixed up the acetone tans fluid combo and I am going to let that work this week.  I've pulled the starter and loosened the belt to eliminate Starter or water pump as culprit. I suspect it is the number 4 cylinder as it had standing water around the Sparkplug despite having a cover over the jeep.  I'll pull the head this weekend and see how bad the damage is probably will have to pull the pan.  Number 4 is on the combustion stroke at TDC so hopefully It won't take too much to tap out.  I'll also take the valve cover off and peak in there. Probably hone it put new rings and bearings in while I am there but that is a slippery slope lol.

Hey Racer490 !

Good luck this weekend.

So, the 490 sounds like a Husky motorcycle. I had a friend who bought one brand new back in the '70's and it was black with gold trim and rims.

   I have been soaking my head-nuts with WD-40 on occasion with the idea that eventually I will pull the head to inspect and possibly pull the engine and do a tear-down to have a "Looksie" at what condition my condition-is-in, the engine's condition. hahaha
   (don't ask my wife, cause she will tell you I am a 'lost-cause'). joking
   She is probably right. too many irons in the fire.

   Here is a video I think may work for freeing a stuck piston:

    https://www.youtube.com/watch?v=oQLiDM6Ixn0

   I am going to try this trick on a marine engine that sat out in the rain for how-many-years before I bought it for the heads. And I have had good luck soaking stuck pistons with marvel-mystery oil.

   Personally I would recommend pulling pistons in-frame after removing the oil pan to see how many piston rings are stuck in the grooves.
   ( I find this OFTEN when disassembling used engines ) The story I get from the sellers is "oh, I think it was 'recently' rebuilt". Yeah, Right, but a real good sales pitch.
   If the rings are scraping accumulated rust off of the cylinder walls, and the engine fires, the compression blows the rust-gook-stuff into the ring grooves plugging them further. That is my theory.
   But, engines are tough, and the other day I was looking at some main-bearings which came with some L134 parts I bought, and the babbit portion of the bearing was gone and the steel shell was almost worn-through. I wonder how many decades that engine was successfully operated (powered-by-Budweiser and Camel cigarettes) before it was finally torn-down for inspection because it had some 'peculiar' noises.   :)

   I am hoping you don't have to tear down your buddies engine.

   Len

An update.  I pulled the head and oil pan.  Pulled number 4 but still could not rotate engine so I knocked out number 3 and then engine rotated.  Maybe there was a head gasket issue between 3 and 4 That is a common problem with my Triumph Spitfire. I'll try to figure out how to post pictures and add some.  My plan is to hone the cylinders with my ball hone and put new rings and rod bearings in and button it up. the pistons are .50 over and rod bearings .50 over so only 1 rebuils left in this block without resleeving. 

after I pull the other 2 pistons I'm going to rotate the engine a few times, observe the valves and spray some oil on them.