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PowerPlant

Recip Engines (Additional Q's by Jcarrig73)

QuestionAnswer
What is the most common connecting rod arrangement on Radial Engines? Master Rod on a single throw, with all other pistons connected to the master rod with link rods
What speed does the Camshaft rotate at, relative to the Crankshaft? 1/2 the speed of the crankshaft
What is the purpose of valve overlap? Helps scavenge pressure from the exhaust leaving the cylinder, helping to draw in the intake mixture
What are the types of piston rings in a recip engine? (3 Types) Compression, Oil-Control, Scraper (Wiper) rings
If the valve clearance is too much, what impact will it have on the valve? It will open late, and close early
If the valve clearance is too little, what impact will it have on the valve? It will open early, and close late
What are Main Bearings usually made of for Radial Engines? Steel-Backed, Lead-Alloy bearing inserts
What are Cam-ground pistons? Why are they used? Pistons that are slightly oval-shaped (longer parallel to wrist pin) When they expand with heat, they become perfectly round
Why are two valve springs used on each recip-engine valve? The different pitch and diameter of the springs causes them to vibrate at separate frequencies, which reduces valve float by making sure at least 1 spring is always exerting force on the valve
What do hydraulic valve lifters do for recip engines? They reduce wear on valve-train parts by eliminating the clearance from the valve-operating mechanism (no gap/impacting parts)
What material makes up most piston rings? Gray Cast-Iron
What is a Full-Floating Wrist Pin? The pin is not clamped to either the piston, or the rod.
What keeps Full-Floating Wrist Pins from scoring the cylinder? Soft Metal plugs
On what stroke does the exhaust valve open? Power Stroke
What is the definition of Compression Ratio for Recip Engines? Ratio: Volume of Cylinder with Piston @ BDC to Volume @ TDC
What is Detonation? What causes it? Uncontrolled, explosive combustion. It occurs under excessive heat and pressure (mixture reaches critical pressure/temp).
Why are compression checks done? Assess the seals between rings/cylinder walls, and the valves/valve seats
How can you tell how many throws a crankshaft has? (Horiz.-Opposed recips) The # of cylinders
Why are some exhaust valves filled with Metallic Sodium? Reduced valve temps. Sodium sloshes, transfers heat from valve head into valve stem, through the valve guide into the cylinder head
What is Hot Clearance used for? (Radial Engines) How does it differ from Cold Clearance? Hot clearance used for Valve Timing. Timing set for valves in Cylinder #1, then all valves adjusted to cold clearance.
How far (from TDC is the piston head when ignition occurs? ~30 degrees before TDC, on compression stroke
When does the intake valve begin to open? During the exhaust stroke
When reducing engine power with a constant speed prop, which is adjusted first? Throttle (Manifold Pressure), or Prop RPM? Throttle - When operating near BMEP, the throttle is reduced first, otherwise, high manifold pressures and low rpm cause damaging-high cylinder pressures
Radial engine master rod bearings are _ type bearings? Plain-Type bearings
Operating at high power settings before proper warm-up can cause what? Oil starvation of bearings, etc.
Why can aircraft cylinders NOT be oversized as much as automobile cylinders? The walls are relatively thin, and may be treated (nitrided, etc).
How is crankshaft run-out measured? Using a dial caliper, rotate for 1 complete revolution. Total Runout = Difference between Max and Min readings.
Why should Aluminum/Magnesium NOT be cleaned with Soap solutions? The soap will be impregnated in the surface, causes engine oil foaming and contamination
In a cold engine, will oil pressure be higher, or lower than normal? Higher
At what degree of crankshaft travel will piston-speed be the fastest? 90 degrees after TDC (Accelerates, then decelerates before it reaches the end of the stroke)
If engine misses in both L and R mag positions, most likely problem is: 1 or more Cold cylinders
After servicing, spark plugs should be reinstalled in what order? Next in firing order, and swapped Bottom to top (from where they were removed)
Increased water vapor (higher humidity) has what affect on a recip engine? Decreased engine power @ constant RPM /Manifold Pressure (water vapor 5/8 weight of dry air, less power produced)
The amount of energy released by burning fuel-air mixture is determined by the _ of both the fuel and air Weight (Water vapor is 5/8 the weight of dry air, so less power produced)
How is valve stretch measured? Caliper to the stem diameter (thinner/smaller when stretched out), or radius gauge (between stem and the head)
What type of piston rings may be used in Nitrided, or Chrome-plated cylinders? Cast iron rings
Can chrome-plated piston rings be used in chrome/nitrided cylinders? No (they can be used in plain-steel cylinders
Increase in manifold pressure, with constant RPM causes the bearing load to _? Increase
The floating control thermostat regulates oil temp how? By controlling air flow through the oil cooler
If an overhead valve engine has too small valve clearances, what will most likely happen? The valves will not fully seat during start/warmup, since the clearance opens up as the cylinder head expands.
Excessive valve clearance will reduce _ on recip engines? Valve Overlap
What is the best indication of worn valve guides? High oil consumption
Most likely cause of a Backfire at low rpm? Lean mixture
Does a dead cylinder show up on a magneto check? Why/Why not? No, because the cylinder is not firing on either magneto.
If an engine is running rough, manifold pressure is higher than normal at all rpms, and mag drop is normal, what is the likely cause? Dead cylinder: throttle is higher to obtain the same rpm, leading to higher manifold pressures. Mag check won't show, since cylinder won't fire on either mag.
Why are mineral solvents used instead of water-mixed degreasers? Soap based residues cause oil contamination and foaming, and may corrode aluminum/magnesium parts
At how many revolutions of the crankshaft does each cylinder fire? Every other revolution of the crankshaft (Engine will have to turn 2x as fast to obtain a set # of firings per minute)
Most likely cause of detonation? Using fuel with too LOW an octane rating (Octane rating is measure of detonation resistance)
What does the Octane Rating of a fuel describe? The measure of detonation resistance
Engine Crankshaft runout is usually only performed when? At Engine Overhaul, or after any "Sudden Stoppage" event.
An excessive valve clearance affects the valves how? Decreases the amount of time the valves are open.
The main purpose in setting proper valve timing and overlap is? To obtain the best volumetric efficiency, and lower ops temps. (If the mixture burns BEFORE the piston goes down, the walls won't overheat)
Hydraulic lifters, when the engine is NOT operating, should have a greater/lower clearance? Greater: When the lifters are flat, the gap opens up. When they are full, the gap is closed (during operation)
What is the purpose of choked/tapered cylinders? Provide a straight cylinder bore @ operating temps.
Master rod bearings (radial engines) are usually what kind of bearings? Plain bearings
Compression Ratio is the measure between_? Cylinder volume at BDC and TDC
What tool is used to measure crankshaft rotation in degrees? Timing disk
When operating with a fixed pitch prop/test club, a "Weak Engine" is indicated by what? Lower than normal static RPM @ full throttle operation
Reduced air density (on carbureted engines) reduces engine power by _ the mixture? Excessively Enriching the fuel/air mixture. (The air is less dense than SL, The fuel metered for the same VOLUME of air will be too rich.
In a constant speed prop, Manifold pressure is controlled with what? Throttle
14 CFR 43 Appendix D requires what to be performed during a 100hr/Annual? Compression check
Ideally, when should the combustion process be completed by? Just after TDC
If the intake valve were to open too early in the cycle, it could cause what? Backfire (burning exhaust gases enter the induction system and ignite the mixture.
The altitude at which a turbocharged engine can no longer maintain SL pressure is called what? Critical Altitude
On a radial engine with a floating cam ring, what must be done while adjusting the valves? You must depress the valves on the opposite side of the engine, which allows the cam ring to pull towards the bearing on the side being checked.
Engine with low oil pressure and high oil temp could indicate what? Leaking oil dilution valve
Why does an engine with more cylinders operate more smoothly? The power pulses are spaced more closely together
Fuel detonation characteristics, Design limitations, and the amount of Supercharging all effect the _ of the engine? Maximum Compression Ratio
On opposed-engines with hydraulic lifters, how is valve clearance adjusted? Replacing the Push-Rods
Which causes the least amount of rolling friction: Ball bearings, or Roller bearings? Ball Bearings
For compression ratios, the number is expressed as the Volume at _ to the volume at _. BDC to TDC. (Think the full amount of air, squeezed down to how little space)
Is the mixture for Best Power richer/leaner than Best Economy? Richer
For Radial engines, is operating valve clearance greater/smaller than Cold Clearance? Greater: the Cylinder head expands further than the rest of the cylinder, which opens up the gap.
Moveable counterweights on crankshafts help reduce what kind of vibrations? Torsional Vibrations
The thrust bearings in most Radial engines are what kind of bearings? Deep-Groove Ball Bearings (better for reducing friction, while carrying both thrust and radial loads).
Propeller reduction gears allow the engine rpm and power to increase, and have what effect on the prop? Allow the prop to remain at a lower, more efficient RPM
Pre-oiling is usually required during what kind of maintenance? Engine Overhaul/Installation
If the Hot clearance is used to set a cold engine, how will it affect the operation? The valves will open late and close early (shortens the time the valves are open, since the gap is greater).
High manifold pressure, High intake-temperature, and an overheated engine can all contribute to what? Increased tendency to detonate
A mixture leaner than the manual lean mixture of .060 can cause overheating where? The exhaust valve, since the leaner mixture will continue burning into the exhaust system.
To check for hydraulic lock, the engine should be turned 3-4 rotations in what direction of rotation? Normal direction of rotation
You should check for hydraulic lock if the engine has been shut down for more than _ minutes? 30 Minutes
As you increase in altitude (without a supercharger), will the Volume, or Density of the air decrease? How will it affect engine operation? The density of the air decreases, leading to a decrease in engine power.
In a dry-sump engine, how do you tell if the engine is pre-oiled sufficiently? When oil flows from the return line, or indicator port.
On Dyna-Focal engine mounts, the shock mounts point towards what? The Engines' Center of Gravity
How to you measure piston-ring end-gap clearance? With the ring in the cylinder, and use a feeler gauge to measure the gap between the ends.
The actual horsepower delivered to the propeller is called what? Brake Horsepower
What purpose does firing order serve in an opposed engine? Balance, and eliminating vibration as much as possible
If non-magnetic (non-ferrous) particles are found in the oil sump and filter, where are they most likely from? Could be from the plain-type bearings, or the pistons, since they are not magnetic. The cause should be investigated further.
Is a small induction air-leak more noticable at High or Low RPM? Low RPMs, because the relatively small amount of air coming in the intake is affected more by the additional air, which has a greater affect on the mixture.
Multiple valve springs are used in order to eliminate what? Why? Valve spring surge, or "Vibrations". The springs are different sizes to prevent both from vibrating at the same resonant frequencies.
When inspecting Engine Control Push/Pull rods, how do you check for proper thread engagement? Using the inspection hole. If you can pass a piece of safety-wire into the hole, then it may not be engaged far enough. Check the amount required.
If the oil pressure gauge fluctuates between 0 and Normal, what is the likely cause? Low oil supply. It drops to 0 when the pump draws air, and returns to normal when oil passes through.
When does valve overlap occur? End of the exhaust stroke, beginning of the intake stroke.
The horsepower developed in the cylinders is called what? Indicated Horsepower
When does Ignition normally occur in recip engines? Just before TDC on the Compression stroke
Created by: avandermey