Is my 305 locked?

[1969_CM2590D]

I have a 305E in my 1969 CM 2500. The truck's been laid up for a bit I got sick a few years ago and didn't really have the energy to work on it but now I want to rejuvenate it and get it going to do some work. I've been outside and I can get the engine to turn freely through about 90 degrees, but I then get some resistance. It's not hard it's actually kind of soft but I am wondering what might be stuck in the motor. Or is anything stuck in the motor? I don't want to get a battery and try to crank it for fear of busting or bending something. I'm about to put some Marvel Mystery Oil in the cylinders, and probably taking the valve covers off and spraying the valve train with PB Blaster. What does everybody think to get this motor to possibly get easily rotating again? It's kind of a prize truck since it's got virtually no rust and 41,000 miles. But it's been sitting idle for probably about 4 or five years. Thanks!

[Funky61]

Hi Dennis;
here's a great link on another thread with more tips...

https://6066gmcclub.com/showthread.php?t=51242

[1969_CM2590D]

Great and useful thread. Slow and steady will win the race on this I think as well as being gentle. I'm starting to suspect that I may have a stuck lifter, it's mechanical so it's possible something got a little rusty there. I'm going to squirt plenty of Blaster down the push rods and see what that does. I'm not in any hurry, and I skipped the Marvel Mystery Oil in the cylinders for now and put Blaster in. We'll see what progress happens but I don't think it's going to take too much to get this motor unstuck in time. The heads were extremely clean. I'll take pictures the next time I'm in there.

[George Bongert]

Greetings, Dennis!

It most likely is a valve that is stuck in the open position that is your problem. Continuing to crank the engine over in this case would result in a bent valve, and possible piston damage. It is also possible to have a valve stuck in the closed position, in which case continuing to crank the engine over would result in a bent pushrod. A sticking lifter is highly unlikely, since the lifters on these engines are in a well lubricated area.

[Ledslinger]

I took apart a flathead Ford motor once that had mice living in it. They took what looked like mattress stuffing and made a home in the lifter valley. The stuffing absorbed all of the oil which left the area prone to rushing. The lifters were stuck solid and i couldn't make the block usable. I'm wiser about impossible disassembly now and in hindsight, maybe it was possible. But 18 year old me couldn't do it.

If the valves are free, you might want to pull the intake and lifter valley cover to inspect before attempting to crank with the starter.

[James]

Originally Posted by George Bongert

Greetings, Dennis!

It most likely is a valve that is stuck in the open position that is your problem. Continuing to crank the engine over in this case would result in a bent valve, and possible piston damage. It is also possible to have a valve stuck in the closed position, in which case continuing to crank the engine over would result in a bent pushrod. A sticking lifter is highly unlikely, since the lifters on these engines are in a well lubricated area.

Our engine is a non-interference engine (with either valve fully open it will not touch the piston). If the engine had ever had old gas in it while the engine was running will cause the intake valve(s) to stick. I would pull the valve covers and the rocker arm assemblies. Then rotate the engine by hand. If it turn, then a valve job is in order. If you have the same problem then it something in the cylinder(s).

[BobBray]

If you don't have any stuck valves it may be some cylinder wall rust that is hanging up the rings. A little Mystery Oil in the cylinders and slowly turning the crank back and forth should free it up without causing any damage.

[George Bongert]

Originally Posted by James

Our engine is a non-interference engine (with either valve fully open it will not touch the piston). If the engine had ever had old gas in it while the engine was running will cause the intake valve(s) to stick. I would pull the valve covers and the rocker arm assemblies. Then rotate the engine by hand. If it turn, then a valve job is in order. If you have the same problem then it something in the cylinder(s).

Not all engines are non interference engines. If one is uncertain about their engine being non interference as opposed to an interference designed engine, it is better to err on the side of caution than to create more problems than there already are.