Test 3 - Recip; repair, re-assembly, testing
⋆⋆⋆ List the steps for grinding valve seat
-First cut is the valve seat angle plus the amount needed for the interference angle (.5 - 1) -second cut uses a 15 degree stone, establishing the diameter of the seat. -third cut (normally only used on the intake) uses a 75 degree stone, cutting the bottom of the seat to establish the seat width.
⋆⋆⋆ Steps for reconditioning a cylinder?
-clean -inspection and dimensions, -replacing valve guides and seats (and grinding them) -honing cylinder walls -replacing rocker shaft bushings.
considerations and tests to be performed on hydraulic assemblies in tappet bodies?
-hydraulic assemblies should never be magnetized, it iwll prevent the check valve from seating. -assemble the plunger in the plunger body and quickly depress it with your finger. If it bounces back, the check valve is seating properly and it's good. If not, replace it.
🌠🌠🌠🌠🌠🌠🌠 How do you test a re-assembled engine?
-install in a test cell 🌠🌠🌠-connect to a DYNAMOMETER or fitted with a TEST CLUB (applies a specific load to the engine) -install air scoop to force cooling air through the fins -install a clean induction air filter and an exhaust system connected to the cylinders. 🌠🌠🌠-service with proper quantity of BREAK IN OIL -connect to a fuel system that provides adequate flow of the proper grade fuel. 🌠🌠🌠-ensure proper instruments are equipped and run through a TEST SCHEDULE (various rpms)
⋆⋆⋆ steps in crankcase re-assembly
-lube and install main bearing inserts -install crankshaft in the crankcase half -apply thin layer of non-hardening gasket compound to the mating surfaces of the crankcase halves and embed silk thread in the compound. -hold tappet bodies in place and place the other crankcase half over the one holding the crankshaft. -bolt and STEP TORQUE in the correct pattern.
⋆⋆⋆ steps in piston and ring re-assembly
-lube pistons, rings, and wrist pins -use the CORRECT RING EXPANDER, expand the rings and slip them into their grooves. -make sure the ring is facing the correct position. -Stagger the gap (2 rings = 180/180, 3 rings = 120/120/120; read the manual)
name the types of cylinder bores found in aircraft engines?
-plain steel -porous chrome-plated steel (spider web pattern of thousands of tiny cracks to hold oil for lube) -nitrided steel (treated with ammonia. has issues with rusting)
steps in crankshaft re-assembly
-sludge plugs installed -oil plug installed -expansion plug installed -any gears (if applicable) torqued place it vertically, lube it, and install the connecting rods (ensure it is facing the proper direction) -etc.
⋆⋆⋆ What do marking on cylinders identify?
-type of cylinder bore: identified either by a band of the proper color between the flange and lower fin, or by the outer tip of the cylinder head fins between the spark plug and the cylinder barrel. (chrome = oj; nitrided = blue, etc) -Spark plug reach: painted fin tips between the spark plug and the rocker box (long = yellow; short = grey or blue)
What procedures must be done when using a fixed-pitch prop vs a constant speed?
Constant-speed props require oil to be routed through the crankshaft to the prop/gov. Fixed-pitch props require a steel oil plug and an expansion plug to prevent oil traversing to the prop housing.
⋆⋆⋆ Who may perform repairs to a crankcase and crankshaft?
FAA certified repair stations
⋆⋆⋆ How do you remove the valve guides and seats from a cylinder?
Heat the cylinder to expand the head. Cool the valve guides and seats with a special water-injected tool so they will contract and can be removed. *same for re-installation except valve parts are chilled in dry ice
⋆⋆⋆ What type of fit exists between the valve face and seat?
Interference angle. A .5 degree - 1 degree difference in the angle of the valve and the seat must exist.
🌠🌠🌠🌠🌠🌠🌠 What will occur if a chrome-plated piston ring is installed on a cylinder with chrome-plated walls?
The rings will not seat and the engine will pump oil. -Always verify that the piston ring is compatible with the piston
What's a key factor of valve reconditioning?
The valve face and seat must be perfectly concentric.
⋆⋆⋆⋆⋆ After the valves and seats have been ground, what must be used before joining them and why?
Valve-lapping compound to abrade the surfaces to form a gas tight fit. After the lapping is completed, remove every trace of the compound. -A properly lapped valve will have a thin uniform grey band in the center of the ground face. the band is the actual sealing area between the valve and seat
Name some typical repairs done to a crankcase.
Welding cracks, line-boring worn camshaft bearings, repairing studs by going one size higher.
🌠🌠🌠🌠🌠🌠🌠 What should the test stand be equipped with?
accurately calibrated test instruments: -tachometer -oil pressure gauge -oil temperature gauge -cylinder head temperature gauge (installed on the cylinder specified by the manufacturer) -water manometer (measure pressure inside the crankcase) -voltmeter and ammeter
What are some repairs done to crankshafts / camshafts?
grinding (journal?) bearings that have worn out of round while preserving the original radius. -done by a faa approved repair station
What are sludge plugs?
metal spool-shaped plugs pressed into crankpin holes (path for oil to travel). Any sludge in the oil is slung out by centrifugal action and is trapped around the outside of the sludge plug. Replace at re-assembly and ensure it's properly seated to prevent oil leaks.
What must be done to the surface walls of plain steel and nitrided steel cylinders?
must be honed (AKA SURFACE ROUGHNESS) to a specified roughness with a special cylinder hone in order to hold lubricating oil. Depth of hones is measured by a profilometer (draws diamond patterns at 45 degree angles). It's measured in microinches RMS.
⋆⋆⋆What precautions must be taken when grinding valve faces(edges)
must not be ground so much that the edge becomes sharp or featheredged. Doing so may cause the edge to become so hot (incandescent) that it will cause pre-ignition and/or detonation. -grind it precisely to manufacturer's manual
What types of damage/defects should be looked out for on a camshaft and tappet bodies? what do they indicate?
pitting and/or spalling. spalling on tappet bodies is a sign of issues with the cam lobes. if any surface irregularities or feathering are spotted, replace the cam shaft. -ensure tappet bodies are kept iwth the same lobe on the camshaft when the engine is reassembled. If a new camshaft is installed, all tappet bodies must be replaced.
Steps in cylinder re-assembly
stuff
⋆⋆⋆ What is the most highly stressed component in an engine?
the crankshaft
What are dynamic dampers?
they're installed on a crankshaft to compensate for torsional vibration. If not properly installed, they can cause severe vibration and stresses.
⋆⋆⋆ What is the face angle of MOST intake and exhaust valves relative to the seat and why??
use a valve grinding machine. -Intake = 30 degrees relative to the seat - flatter angle to allow better flow of the fuel:air charge into the cylinder and to extend its life. -Exhaust = 45 degrees relative to the seat - steeper angle allows it to seat tighter and prevents carbon buildup on the seat
