bought barn truck, need ideas

[looney]

Just bought 71 GMC been in barn since 83. Motor is seized but very little rust. Both cab corners a little rust, rockers ok, front corners of both floor pans have small holes. Interior great, I also have a 71 with a great running 307, the barn truck has a 350. Should I change motors. Truck with good motor is rusted bad all over, thought about parting. Ideals on any of above.

[WIDESIDE72]

I would work on seeing if I could get the 350 in the truck broken loose. How many milesmare on it? Is it a standard trans or auto? In the past my dad wand I have broken motors loose on tractors by pulling the plugs and spraying k&w knock 'er loose and or lb blaster in the cylinders. Let it sit a while then pull them with another tractor, work the clutch on the stuck tractor with iron gear. We had one that was still stuck, took heD off and used a 4x4 block and sledge. You actually might get lucky and not have to get so "mideivel" on it! Just try working it back and forth with a breAker bar and turning tool that won't back the balancer bolt out, or pull the balancer bolt and use a crank socket
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[WIDESIDE72]

Otherwise if the 350 won't budge, swap it for the 307. A running 307 bears a stuck 350 any day. IMO, 307's get a bad rap. They are plenty of motor for a driver. You only need more cubes if you are towing or want a lot of power ( and less fuel mileage) Now as far as which to spend money on on a rebuild, that's another story.
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[Xeen]

Im with Wideside on this one, if its numbers matching see if you can get it broke loose, because if its rebuildable the value of the truck just went way up.

[looney]

Thanks, Iwill try to get it broken loose. Will it need any overhaul if it breaks free or just tune up and run and go from there. It has 78k on truck

[blue 72 gmc 4x4]

Lets see some pics!!!

[looney]

I will get pics this evening.

[haysonj]

Originally Posted by looney

Thanks, Iwill try to get it broken loose. Will it need any overhaul if it breaks free or just tune up and run and go from there. It has 78k on truck

Even if you get it broke loose it will need to be tore down and looked at. Most likely the rings will be froze and they will never seal good.

[CC69Rat]

WD-40 just came out with some stuff too. Pull the plugs and spray it down in the cyls and let it sit. Turn the crank (or clutch it with a tractor) ..

[GASoline71]

I know cats have "unfrozen" engines and had decent luck without a rebuild. But they were extremely lucky. If it were me... I'd tear it down, and see what ya got to work with.

Gary

[prostreetC-10]

I know they are coming but I still had to add this!

[looney]

Pics of both trucks. The green one has motor locked.

[looney]

barn truck

[looney]

more

[mud.man.rj]

Looks like you have some work on both trucks, good thing is lots of spare parts to finish one. I would pull the 350, rings are struck for a reason and can't see it ever being a great engine, if you break a ring trying to start it then it will chewup the cylinder and need a rebore, but I guess if it isn't frozen too bad. Pretty much spray it down and wait at least a day and try it easily with a breaker bar on the crank bolt if it moves fairly easily then may have good luck with it but if not then pull it and tear it down and if not great with building engines just swap the 307, they are a good engine for normal use. Good luck.

[Rob H.]

Green one definately looks better, the rockers and floor in the barn truck look about like the ones I just cut out of my 72. Good luck with it, I wouldn't be afraid to put the 307 in it, I just recently blew up the 307 in mine but it was plenty strong for a driver and I have even pulled a 2000 Ford tractor with a tiller attached on my 16' foot trailer without any problems. I'm only about 45 mins from Mt. Sterling if you need anything give a shout.

[looney]

Thanks, I'm just getting into this with my son who will be going to college in a couple of years so I'm sure I'll need plenty of advice. Should I go ahead and order the cab corners. I guess you cut out old and weld in new, same for floor?

[CC69Rat]

You're not getting under that green truck are ya? Wow ..

[shawno72]

Originally Posted by CC69Rat

You're not getting under that green truck are ya? Wow ..

X2

[prostreetC-10]

At least out here, sometimes it's cheaper and a lot easier just to find a donor cab. Course we also done have the rust issues on the high desert.

[GASoline71]

Rust never sleeps...

Gary

[GeeMCeee]

First, check the oil and see if there is any in it, if there isn't, forget it. Next, check for coolant. If there is none, it could have been seriously overheated and seized that way..

Sometimes they just seize from sitting forever and those can be freed up using PB Blaster. Pull the plugs and dump it in there. Pull the valve covers and dump it across the valvetrain and down into the lifter gallery where it will also drain down onto the crankshaft partially. Let it soak for a couple days and with the plugs out, attempt to turn it over with the starter. Bump it a few times and see what happens. If that doesn't work, use a breaker bar at the crank. Be careful not to torque too hard and break off the end bolt in the crank..

If that doesn't work, automatics will engage if towed at a speed of about 35 mph. In neutral, tow the truck up to that speed then drop in in drive. It will be the big skid session or it will roll over the motor, one or the other.. Make sure the brakes are in operating order before attempting anything..

If you get it freed up, roll the engine over with the plugs out for a few seconds. Do this a few times at interval as not to overheat the starter and electrical wiring. Drain the oil and put in fresh, reinstall the plugs and valve covers and see if it will fire. If it does it will smoke heavily for a few minues but should clear up if the engine isn't worn out already...

Good luck..

BTW The 307 is a good engine. They were just famous for having soft camshafts that went flat prematurely. Once corrected, they will go many trouble free miles.. It will work equally fine in your 1/2 ton

[special-K]

It doesn't take a whole lot of typing to answer your question. Put the 307 in the green truck,save the 350,and depending on how far you decide to go,you can always rebuild the 350 and put back in. If you just want it to run,why put effort into an iffy engine when you have one you know runs good. And,307s tend to go longer than the 350s. Don't know why,they just do.

[GRX]

True about the cams. Think you'll find it's usually the center lobes which wipe first. GM plants had problems with the induction hardening process early on. The center of the cams didn't heat properly. Pontiac V-8's were especially susceptible to this since they have higher open spring pressures because of the factory double valve springs. Also ... one reason the 307 tend to last longer than 350's is because of the shorter stroke. Less angular pressure on the cylinder walls.

With that said, I'd be inclined to drop the 307 in there and save the original 350 for a rebuild. One the engines seizes like that you are hard pressed to get the rings properly freed in the piston grooves again. Depends on the amount of rust on the cylinder walls really. Let us know how it goes.
Best of luck!

[cdowns]

i'd pull the plugs on the engine then with an old fashioned squirt oilcan filled with ATF just start pumpin as much as you can get into the cylinders/// do that every day for a week or so// try BY HAND to turn the engine a bit at a time DO NOT TRY USING THE STARTER// slow and gentile a bit each way both clockwise counter clockwise just a bit at a time


if you try to overpower it with brute force you will probally break the rings

i've put over 50thousand miles on engine that i broke loose like that with no longterm effects that i could see