I have been thinking of doing an engine swap for my well worn beast ('75 245 with 218,000 hard miles). Awhile back I checked comprsssion (without oil added) on the cuurent engine and found all cylinders 105 to 125 PSI.
Today I checked the comprssion on another engine that I own. This engine has sat unstarted for about 4-5 years. It turned over easy using the starter. With all plugs removed, I checked compression after 3 compression cycles without adding oil to the cylinders. Two cylinders checked 120 to 140 PSI, one read 90 PSI and one 60 PSI. After adding oil to each cylinder I retested. First two cylinder stayed about the same. Number 3 pumped to 110 PSI and number four pumped to 90 PSI.
My read on this is number 3 cylinder may have a burned valve and number 4 cylinder has bad or stuck rings and may also have bad valves. What is the impact of 4 to 5 years of no use? Will compression improve as this engine runs again? Do I have an engine worth swapping without repairs or can this engine be repaired? I have tools and facilities to do a full rebuild but what are the cost of parts likely to total?
What do you think??
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Beastdriver - '75 245 217K miles (Beast), '83 245 216K miles (Beauty),'87 244 DL 160K miles (Dodo)

Before beleiving your compression test, I would pre~pressurise the oil system...one lifter with air in it could do a lot to your readings.
A leakdown check will test your valve.

I have had some good luck with 'sat' engines, Recently got a 72 454 Chevy which sat for 10 years without moving, unknown if it was run at all, certainly not in years(rats had filled the driver seat and footwell). I pump-ed in some gas from a can, changed the points, and it fired on the 10th crank, and ran perfect, no smoke no knock, and the carb worked well! after we took the body to the dump, I drove the bare chassis around and did a few easy burnouts and obstacle climbs for laughs before recycling the frame for $12.

I would probably soak the cylinders in some ATF or penetrating oil to help free the rings, then run the motor gently for a bit. If it was good before, I think you should have a runner as long as storage conditions were good.

If the engine that sat is out, and it seems to be out of the car you want it in, I think I would refesh it...

have the head off and bench test the valves with keroscene in the combustion chambers looking for leaks..

Pull the pistons, have the ridge reamed and the bores honed, and install new rings, and perhaps new rod bearings. Inspect the oil pump...

The valves... The once that leak K-1 should come out and be inspected, and replaced and surfaced as needed...

A comp test on a stored engine is not exactly valid, and when that engine is cold worse yet. You have some decent reading however, andd running alone should improve them, but why not just know the engine has been made sound before you install it?
The gaskets will cost more than the valves and the rings combined probably.. Mac

IF the motor has set for over 2 years the compression test is not reliable. Your take on the problems may be accurate. You may want to at least pull the head to look at the valves and look over the cylinders. Doing this may save you a lot of time and frustration.

Good Luck
Brian
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86 240GL, 86 740GLE & others