1. Describe what efforts must be completed during an engine overhaul. Reference the correct FAR in your response: Disassemble, clean, inspect, test (FAR 43.2)
- a complete engine overhaul involves replacing piston rings, reboring or honning cylinder walls, replacing pistons (if the cylinders are rebored), replacing main and connecting rod bearings, regriding the crankshaft to restore the journals (if needed), and restoring the valves. Rebuilding parts like the starter, distributor, carburetor and alternator while the engine is being overhauled is common to ensure that the entire runs like new but isn't always necessary.
2. List the 4 strokes of the Otto cycle gasoline powered spark ignition engine in the table below. Provide a brief description and direction of the piston
- The Four-stroke cycle of a piston engine includes intake stroke, compression stroke, power stroke, and also exhaust stroke.
the intake valve opens the crankshaft rotates to move the piston from TDC to BDC as the volume in the cylinder increases, a vacuum is created that draws in a fuel/air mixture.
The intake valve closes the crankshaft rotates to move the piston from BDC to TDC as the volume in the cylinder decreases, the fuel/air mixture is compressed – pressure increases
both valves remain closed a spark from the spark plug ignites the compressed fuel/air mixture
Power stroke the valves are still closed the combustion process causes a rapid increase in temperature and pressure the pressure forces the piston down in the cylinder
Exhaust stroke as the piston reaches BDC, the exhaust valve opens the piston moves from BDC to TDC exhaust gasses are forced out of the passage created by the opened valve as the piston approaches TDC, the intake valve opens to begin the process again
3. You have just overhauled a Teledyne continental O-200A engine for your Cessna-150. Full power 2350 RPM. Torque measurement was 223.5 ft-lb. How much horsepower is the engine producing? lecture 2 slides 34
(2350 RPM x 223.5 ft-lb)/5252 = 100 BHP
4. What is a horsepower
- Horsepower is a measure of an engine’s ability to perform work over a period of time. work is measured in foot-pounds. The turning force of an engine along with the revolutions per minute (RPM) of that engine will determine the actual power output.
- Scottish scientist James Watt developed methods to compare steam engines to horses.
Power is a factor of (1) force, (2) distance moved, (3) tune required
Horse power: derived from James Watt’s studies of work performed by English workhorse
1lb weight lifted 1ft = 1ft lb of work
1000lb lifted 33ft = 33000ft lb of work
If this take 1min, then 1HP work was performed
1hp = 33000ft*lb/min of work
IHP and BHP
Indicated Horsepower: the total HP developed by the engine; heat energy coverting into mechanical energy
Brake Horsepower. The actual HP delivered to a propeller or other device. It is the IHP minus the friction HP (FHP); HP lost from friction of moving parts in engine and other accessories. BHP = IHP – FHP
IHP = plank / 33000
P = Mean Effective Pressure
5. What is valve overlap? Why engine designers set valve timing such that there is valve overlap?
- The angular distance through which both valves are open; it is also call a valve lap. Valve overlap is when the intake/exhaust valve open at the same time, earlier in intake, and later on exhaust, more fuel air = more power
6. Describe the importance of the octane