The Lycoming and Continental can be very forgiving.
We had an Continental 0-200 come in reported as a little low on power. The rocker shaft had sheared off the no 4 cylinder head completely.
Even stranger was an R22 that flew in for a 50 hr and was found to have zero compression on all cylinders when a differential compression test was carried out.
First we changed the tester as it was obviously faulty to achieve only the same result.
We then changed the engineer (me) as being incompetant.
Second engineer got exactly the same result.
We could hear air whistling in the exhaust so we removed it and examined the valves.
All four cylinders had the valves hanging low on the seats with the guides totally worn out.
What was happening was that under a slow rotation during test the valves failed to close. However under speed there was sufficient force to drive the valves back on to their seats. Have to say I did not believe the pilot when he said there were no unusual symptoms but nevertheless the aircraft flew in with the cylinders in that condition.