I have recently picked up a 79 F250 4x4 with a 351M & C6 that has been sitting for around 5+ years. The carb caught fire and eventually burned the cab up. I am attempting to see if I can get the motor freed up again. I have tried different fluids to help break it free, mainly ATF and acetone mix. I have now removed the intake, heads and starter. I am spraying the pistons and cylinders down with PB Blaster now.

I am wondering how much force I can put on the crank bolt with a breaker bar before twisting it off or making it impossible to get back off. Right now I have tried a few times with a breaker bar and cheater bar (pipe) but not really pulled on it like crazy. Right now the bolt just seems to tighten up without moving anything. I have been soaking the engine for about 10 days so I'm about ready to try harder to get it to turn.

When pulling one head, it had a really bad old gas smell. From what I've been told the carb was leaking like maybe the float was stuck and that probably caused the fire in the first place. It may have had alot of fuel in a cylinder or two when it was parked.

Overall the engine is clean and the cylinders have light rust so I have not given up yet. Its no big loss if the engine is scrapped as I have a 460 to eventually go into the project.

 

This is the point I'd be pulling the engine. It could be that the rings are rust welded to the cylinder walls, and / or bearings are locked up on journals. Turn it upside down, and start pulling and inspecting rod caps & bearings. This is where you'll find specific cylinders that are locked up. Carefully push rods & pistons out. Inspect the other side of the bearings, the rod journals on the crankshaft, piston skirts, rings, and cylinder walls. Each time you push a rod & piston out, attempt to rotate the engine. Then pull the main caps, inspecting as you go, and then of course remove the crankshaft.

 

 

Gentlemen,

I am also in the midst of trying to get an engine unstuck. As mwallace70 has run into, the ATF and acetone etc. has done nothing. I know some older posts listed Evapo-Rust as a possibility. (The thinking being that if it a piston ring "rust weld" to the cylinder wall the Evapo-Rust might work through the mess.) Of course this assumes the product will work its way down to do some good. I suspect the stuff is just going to sit on top but I may try it.

Removing the rod bolts and trying to pull one piston asy out at a time (as ranger describes) has more logic. However, I ran into problems right away trying this. With the crank locked I could not get a good socket into position for most of the rod bolts. (I have a 1951 flathead V-8, you probably have better access with your 351.

If all else fails, we can always pour some CoCa-Cola in on top of the pistons ! Yes, I was watching "Lazy Car Dealer" (having run through all the other auto fix up offerings on Hulu) and they decided the acidity of the Coke might eat through the rust ! Unfortunately, they never came back and updated if there had been a break through? Maybe they are gearing up for trying a Seven-Seven next ?

 

That's when I'd consider myself as having three choices. Let it soak longer. Get destructive with piston removal. Or just scrap the engine.

Long ago, I watched my cousin use a hammer and chisel on a piston until it finally broke up enough to allow the rusted rings to release from the cylinder wall. But that was a 426 Hemi, and certainly worth the effort. Nowadays, I'd use a pneumatic hammer with a pointed tip.

Either way, mwallace70's engine needs pulling. If it's a seized piston, soak it or destroy it. If it's a spun bearing, you just take off as many rod caps as you can, and keep trying to rotate the crankshaft. Btw, if it is a spun bearing, you can usually spot it easily, by discoloration caused by extreme heat.

 

I've known of cases where kerosene poured in and allowed to sit for a few days worked. I think a peak from below to ascertain there are no bent rods or other effects from a past hydro lock episode might be worthwhile. I even know of a '70 Dodge truck 383 staying in truck, pan was dropped, and honing and new pistons and rings went in ... after knocking old ones up and out from below. I didn't do it, but I helped him.

 

My next course of action will be to remove the fuel pump and timing chain to see if the cam is free. Gonna drop the oil pan as well and take a look. At this point the motor is probably coming out of the truck.

 

Drop the oil pan first, so you don't risk bending it while removing the timing cover.

 

Ok thanks for the tip