235 Low Compression from Sitting ?

[54blackhornet]

What are my options for a 235 that has sat idle for about 10 years? The 1950 GMC 250 ran fine when parked by the OR, but when I went to start it nothing. It has good spark but will not even begin to fire. I believe it has some valves stuck open ? Without pulling the head any suggestions on freeing up the valve train ? I was thinking of filling up thr cyls with some diesel-marvel mystrem oil

[OrrieG]

You can check for sticky valves by pulling the valve cover. I assume you have already dumped some oil or mmo down the spark holes and checked compression? I also assume the previous owner told you it was running like a top when parked? Did you clean up the gas tank, lines, etc. to make sure it is getting good clean fuel?

Recently I read a post somewhere about a guy that bought a car that had been sitting for 20 e years. He pulled the plugs and filled the chambers with MMO then pulled the carb and completely filled the rest of the engine with it (wonder how gallons that took). Let is set for a couple weeks while he went through the gas tank, brakes, etc. then drained it our and hand cranked the engine over a couple of time. Filled it up with oil, clean gas and it started right up, smoked for a while then ran fine.

Once you get it started it will take a while for the seals to seal back up, rings to seal, etc. When I got my 64 it was pretty loose for the first month and couple of hundred miles from sitting. It then tightened right up and I drove it another 48K to 130K before it needed rebuilt.

[54blackhornet]

Thanks Orrie for your reply ! I guess this must be a pretty boring subject ha ?
I was thinking of filling up the cyl's with a mixture of oil & diesel and just soak everything real well but others say it is a waste of time and that i should just pull the head and be done with it. Come on guy's a little feedback on this would be interesting

[OrrieG]

ATF works good for cleaning and loosing things up too, inside of auto transmissions are newer gummed up. If you can get it to turn by hand then there is a good chance it will run. Some times you need to rock it back and forth to get the rings to release.

[Fred T]

Unless multiple valves are stuck it should run. Time to check the basics of fuel and ignition.

Start with fuel. What kind of shape it the gas tank in? Did you drain the stale gas out? Are the spark plugs wet with gasoline? When you pump the throttle is there spray of gas inside? Are you getting fuel to the carb? Check by disconnecting the fuel line at the carb, putting the line in a container. Crank the engine and watch for fuel to come out of the tube. If none, you have either a plugged fuel line or broken pump.

If that doesn't get her started check the ignition system. . Spark at the plugs at the right time.

[54blackhornet]

Fred I bypassed the fuel tank and ran a new line to a small tank.
Spark is good at plugs, rebuilt starter, new battery. put a small amount of fuel in car to help.........nothing, that is why i feel it is a compression problem ? has sat for a longggggggggggggggg time.

[Fred T]

Usually these old engines will still run. I have been able to make the 235 run on two cylinders. It wouldn't pull anything, but it would start. That is why I am saying it is probably not just low compression.

To do a quick compression check remove the spark plugs. Spin the engine using the starter, while placing your thumb over (not in) each plug hole. There should be enough pressure to pop your thumb off the hole. What you are checking is the pressure difference between the cylinders. It's not accurate, but gives you a handle on things. A compression tester is better, but not everyone has one in their toolbox. Even if there are two cylinders that are low, it should still start. If most or all of the cylinders are low the issue is probably stuck rings, which is when the Marvel Oil is used. On a six, where the piston face is parallel to the pavement, about 2 tablespoons in each cylinder is all that is needed.

Before installing the plugs, a quick timing check. Turn the engine over by hand with your thumb over the #1 hole. When the pressure pushes your thumb off the hole, the rotor should be pointing at the #1 cylinder.

When you put the plugs back in, check the firing order. 1-5-3-6-2-4. 15 is too young, 36 is too old, 24 is just right. The number one connection on the distributor is the closest to the number one cylinder.

[OrrieG]

1-5-3-6-2-4. 15 is too young, 36 is too old, 24 is just right

BBOMN!!!

I used to remember my phone number the same way. The numbers were (this is NOT it I am using numbers close for example) 4-34-65-36 which I called my pregant wife measurements.

Back on topic, I agree with Fred it is amazing how poor of condition those old engines can get and still run, I cut my teeth with my grandfather on 216 and 235 tow yard Chevys getting them to run for resell.

[54blackhornet]

Fred Orrie thanks a lot for the help ! What about the valves being stuck open or not sealing all the way ?

[dwcsr]

Originally Posted by 54blackhornet

Fred Orrie thanks a lot for the help ! What about the valves being stuck open or not sealing all the way ?

You would need to pull the head to fix that.