1100 hours, something just isn't adding up (although the hours may not be real).
If you need a ridge reamer and new rings, then you likely will also need new pistons, and honing or boring the cylinders. A big top end job. I'm not saying that isn't the answer, but I wouldn't jump right to that conclusion.
If you go down that path, eventually you'll need to remove the head, and inspect the head, head gasket, valves, and cylinders.
On some vehicles, faults are also noted under the valve cover (tight tappets, bad valves, lifters, etc).
Agreed. Thinking likely ether-blown rings and possibly piston lands
Very low compression that improves with oil in cylinders means rings are bad and the repair involves pulling the head and pistons. Doesn't rule out a valves not closing problem or a head gasket blown out between both set of cylinders problem but does rule in a ring/piston problem -still need to pull the head.
Borescope can determine if cylinder walls are scored or pistons are obviously damaged -still need to pull the head
Leakdown test can determine how bad rings/possibly valves are -still need to pull the head.
Valve lash adjustment is probably worth testing first because if someone incompetent set it grossly off it's possible the valves are never closing during compression stroke. It's also possible but less likely that someone pulled the cam and didn't retime it to the crank correctly or it somehow skipped time causing valves to be open during compression stroke. Valve not closing problem with lash in ballpark -still need to pull the head.
Head gasket blown between all 3 cylinders -still need to pull the head.
So if the compression tests +/- oil are giving valid results and there's not a gross valve adjustment problem or gross crank/cam timing problem, the head needs to come off in my view regardless of the source of the problem.
Some quick and dirty tests here:
Put a socket on the crank bolt and manually turn the engine -do you feel much in the way of compression resistance? Do you feel air blowing out the crankcase breather (valve cover on)? This will help validate your compression tester results.
With the valve cover off, use the socket on the crank to turn the engine until a given valve is pressed down by the rocker arm to it's maximum travel, then make sure you can move/rattle the other rocker arm for that cylinder. Repeat for all 6 valves. This will determine if your valve lash is set in the ballpark or if it's grossly off.
Cam/crank relation timing can be ballpark tested by looking for a crank rotation period where both valves are closed (up and rockers rattle) and seeing if you can feel the top of the piston with a long screwdriver probe through the glow plug hole. This is unlikely though and I wouldn't think necessary unless it's obvious someone has recently taken the front cover off.
As mentioned above did you drain the oil and get metal shavings/chunks out?
