top overhaul

top overhaul

The overhaul of cylinders, valves, and pistons of a reciprocating engine. The crankcase, in this case, is not opened, and the connecting rods are not removed from the crankshaft.
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A top overhaul is basically what it sounds like: Remove and overhaul or replace the "top end" of the engine: cylinders, pistons and valves.
5 times, and the minimum interval for top overhaul has been extended to 1.
The tops and insides of pistons that were changed during a 20,000-hour top overhaul showed only a lightly baked-on white caking of silicate.
Worse is that the top overhaul, replacement of all cylinders, is almost never necessary--a sick cylinder is not infectious--yet it is still done with alarming frequency.
Many owners who weren't flying lots--say, 250 or more hours a year--were going through at least one top overhaul on their way to TBO.
I did a top overhaul last year as my almost 1000-hour cylinders were using too much oil.
Most engines probably make it to their TBO with little more than oil changes and some spark plugs, or maybe a top overhaul, But a few engines roll over long before that.
If the airplane is going to be down anyway--like for a top overhaul or other lengthy work--getting your local prop shop to take a look is a good idea.
Even if I do a top overhaul halfway to TBO and replace the mags and vacuum pump twice, my operating costs through TBO will be less.
The shop recommends a complete top overhaul, perhaps surmising that if two jugs are bad, the rest can't be far behind.