Still trying to decide what I have with our 47 Cub at our local railroad museum. I checked the compression on each cylinder this morning, cranking it with a 12 V battery. I have one cylinder at 75psi, two at 50 psi that goes up 10 if I put a little oil in the cylinder and one that reads 0 and goes up to 25psi when I put oil in the cylinder. My 1st question is what should I get for readings and second is the change I'm seeing normal when I add some oil or is it a sign the rings are bad. Valves are all moving so a stuck valve isn't the problem.
- Thread starter Charlie M
- Start date
Janicholson
Well-known Member
Great question.
If the tractor has been sitting for more than a year or so the valves may have pieces of rust or flakes of trash material under them. I would suggest that the engine should be pulled in a parking lot at 4-5 mph in road gear for at least 1/4 mile before condeming anything. Cubs often have difficulty building oil pressure after sitting due to the pump being in the block casting, and above the oil level. I would pressurize the oiling oiling system with a pump oil can, and a small rubber hose to connect it into the oil gallery at the filter housing (1/8" pipe plug, probably hex key) If it shows oil pressure all is well. After pulling it then check the pressure, if as bad then, it will need to have the head pulled off, and looked at for possible burnt valves and bblown head gasket. The rings may be stuck causing the 50# numbers. If the Zero psi cylinder comes back to 50 or above, I would get it started before tearing it down. Jim
If the tractor has been sitting for more than a year or so the valves may have pieces of rust or flakes of trash material under them. I would suggest that the engine should be pulled in a parking lot at 4-5 mph in road gear for at least 1/4 mile before condeming anything. Cubs often have difficulty building oil pressure after sitting due to the pump being in the block casting, and above the oil level. I would pressurize the oiling oiling system with a pump oil can, and a small rubber hose to connect it into the oil gallery at the filter housing (1/8" pipe plug, probably hex key) If it shows oil pressure all is well. After pulling it then check the pressure, if as bad then, it will need to have the head pulled off, and looked at for possible burnt valves and bblown head gasket. The rings may be stuck causing the 50# numbers. If the Zero psi cylinder comes back to 50 or above, I would get it started before tearing it down. Jim
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