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Low Power in Continental or Lycoming aircraft engine. Loss of manifold pressure. Low RPM. Loss of power
Related problem: Engine will not turn static rpm.
Note: Low power can be
subjective since there's no one instrument that we can use to measure power
on the airplane. With fixed wing aircraft a pilot won't notice a 5 horsepower
loss in cruise. Five horsepower is noticeable during single engine climb
on a twin. If a constant speed propeller airplane won't reach red-line
rpm in cruise then the governor is holding back the propeller and your
problem is not low power. At cruise speeds the engine will turn the propeller
past red-line even with low power because of the low propeller loading.
Altitude related manifold pressure problems are usually caused by leaks in
the intake and exhaust system. Loss of manifold pressure in climb on
turbocharged engines is caused by leaks or the butterfly valve in the wastegate
is not closing completely.
1. Poor combustion. Check compression.
2. Leaks in induction system. Induction leaks cause poor idle and/or
poor engine acceleration. Check induction hoses. On Lycoming engines with
the short tubes swaged into the oil sump, check the tubes for tightness.
Loose tubes need to be re-swaged. On Lycoming engines that use ring seals
to seal the induction tube into the oil sump, check the ring seal for integrity.
Ring seals can be inspected with a flashlight by looking into the intake
tube housing bore. New seals are easiest installed by lubricating the seal
and the housing bore before pushing the tube with the new seal into the
bore. Do not use rubber sealants. Sealants don't compress into the bore
and therefore don't exert tension against the bore. As soon as vibration
breaks the sealant from the surfaces then the joint leaks.
3. Improper fuel flow. Check and clean screens. The August 1974 General
Aviation Inspection Aids wrote of an incident of low power caused by an
ant that had entered the injector line while it was removed for maintenance.
Check for ants!
4. Restriction in air inlet or manifold. Check carburetor air box for
protruding gasket. Check air filter. Inspect air duct for evidence of hose
collapsing. Check security of alternate air door. Check air filter for
plugging.
5. Alternate air door leaking allowing heated air to enter carburetor.
6. Throttle lever not properly adjusted. Check for full travel.
7. Broken baffles in muffler. If section of baffle is loose in muffler,
engine may operate satisfactory at times and may be low on power at other
times. This indicates baffle is moving around in muffler, blocking exhaust
gases sometimes and out of the way at other times. Strike muffler with
rubber mallet and listen for rattle in muffler. Inspect muffler per the
manufacturer's maintenance manual.
8. Prop out of adjustment (low pitch).
9. Governor linkage not adjusted properly. Adjust for full travel.
10. Crankshaft to camshaft timing off. Note: It is easy to assemble
the Lycoming O-320H2AD with the internal engine timing 1 tooth off.
This condition may be checked
by first disconnecting starter. Remove top spark plugs and rocker box cover
on #2 cylinder. Turn engine to TDC on compression stroke #1 cylinder. Engine
timing is checked by first observing the number two cylinder valve rocker
arms. Both valves should be closed or nearly closed. Move the propeller
slightly in one direction. Rocker arm motion should be seen as one valve
starts to open. STOP. Now rotate the engine back to the original position
with the #1 at TDC.. Now move the propeller slightly in the direction
opposite from the first movement. Rocker arm motion should again be seen
as the other valve starts to open. If the two valves started to open as
described with only a small amount of engine movement in each direction,
the engine timing is correct. If movement in either direction exceeds twenty
degrees of engine rotation before motion of the rocker arm occurs, the
crankshaft to camshaft timing is not correct and the engine was assembled
incorrectly.
11. Camshaft lobes flattened. Remove camshaft followers and inspect
condition or examine oil filter for metal.
12. Incorrect carburetor.
13. Incorrect propeller.
14. (Turbocharged engines) Controllers out of adjustment. Variable
absolute controller is adjusted by turning adjustment screw at cam end
of controller counter-clockwise to increase boost, and clockwise to decrease
boost. Controllers are set to obtain a specific MP and no compensation
for density and temperature is necessary. Required MP settings are found
in Operator's Manual. Adjust for full throttle setting only. Density controllers
compensate for temperature and pressure. Differential pressure controllers
are set to maintain 6" (Lycoming) differential between deck and MP.
15. (Turbocharged engines) Damaged turbocharger impeller, binding or
tight wheels. Visually inspect wheels for damage and free rotation.
16. (Turbocharged engines) Kinked or restricted oil lines from engine
to actuator, and actuator to controller.
17. (Turbocharged engines) Wastegate out of adjustment or stuck open.
Lubricate ends of shaft with Mouse Milk.
18. (Turbocharged engines) Inlet orifice in actuator plugged.
19. (Turbocharged engines) Piston seal in wastegate actuator leaking.
Noted by excess oil coming out of drain.
20. (Turbocharged engines) Oil pressure to low to close wastegate.
Continental engines 30-60 psi limit.
21. Injector and controller linkage not adjusted properly (Lycoming
541 engines).
22. (Turbocharged engines) Variable pressure controller out of adjustment.
23. Inaccurate tachometer. Mechanical tachometers, such as the AC tachometers,
have a oil port in the rear. They never get oiled and over the years will
start to read slow.
24. Turbulence in air flow causing improper fuel metering.
25. Improper valve rocker clearance. This is important on solid tappet
engines (Lycoming O235).
26. Carburetor ice. Will be accompanied with drop in manifold pressure
on aircraft equipped with constant speed propellers and on fixed pitch airplanes
often a gradual loss of rpm and engine roughness
Carburetor Ice in Continental and Lycoming aircraft engines
27. Worn out spark plugs. Worn out spark plugs that fire but are weak
have been shown to reduce engine output by 5 horsepower in test conditions.
28. Air filter dislodged and stuck in intake system thereby cutting
off the air supply.
29. Heavy rain - paper air filter swelling.
30. Carburetor heat flapper valve in the air box partly open.
31. HA-6 carburetors- Float pin worn and out of one boss, preventing
the float needle from properly seating.
32. Loss of power and vibration suspect magneto problem. Switch from
both magnetos to the healthy magneto will regain power and smooth out engine.
33. Dirty or restriction in fuel nozzle. Will be accompanied by oily
spark plug.
34. Lycoming O235 refer to latest edition of Lycoming Service Instruction
1388 "Troubleshooting of the O235 Series Engine".
35. Exhaust pipe becoming disconnected in turbocharged engine. For
Beech Baron model 56TC serials TG-2 thru TG-94 and Duke models 60,A60,
and B60 serials P-4 thru P-596 comply with Lycoming Service Bulletin 479
or latest edition and refer to Beech Service Communiqué No.87 dated January,
1988.
36. Dragging valve.
37. Fuel siphoning into the cylinders past damaged "O" rings on the
primer plunger causing an overly rich mixture. 38. (Turbocharged engine)
Exhaust system leaks.
39. Plugged fuel vent creating vacuum in fuel tank.
40. Carburetor blockage in the channel at the base of the mixture metering
sleeve where fuel pick-up occurs for the fuel discharge nozzle. Will cause
the float to be unusually high.
41. Float stuck in carburetor
42. Continental "A", "C", and O200 engines - fuel flow
restriction caused by a clogged screen in fuel pump. Reference Continental
Service Bulletin M81-8R1.
43. Lycoming engine with mechanical (diaphragm style) fuel pump. Textron Lycoming
issued their Service Bulletin (SB) No. 548 determining that several lots of
diaphragm-type fuel pumps may have a potential for an internal failure. When an
internal failure occurs, the check valve seat separates from its shaft due to an
inadequate or improper assembly crimp. This allows the liberated parts to move
within the housing and may cause a blockage of fuel flow. This failure may not
be evident on the exterior of the pump, but it may result in a decrease or loss
of fuel flow and a corresponding decrease or loss of power. Textron Lycoming
estimates that approximately 1,252 fuel pumps were manufactured between
September 18, 2000 and February 18, 2001 with a potential to fail, but they can
not predict if or when the failure may occur.
44. Power interruptions in the IO-360-L2A engines used by the 172R were related
to a combination of over-rich operation and fuel system vapor formation during
prolonged ground operations in summer heat. Service Instruction #1498 states
that "vapor may form in the fuel system during ground operations when the
ambient temperature exceeds 85 degrees F," An alternative explanation is
that water is being trapped in the integral wing tank.
45. Water ingestion into engine. Water trapped in integral wing tank.
46.On 07 November 1991, Schweizer issued MSB B-248, pertaining to compliance
with the Precision Airmotive Service Bulletin No. PRS-94 issued 21 September
1989, and states that, "there are persistent reports of low power and high
engine temperatures (cylinder head, oil, and EGT on new aircraft, and on
overhauled engine/servo combinations". It also states that, "failure
to comply with this Service Bulletin could result in engine failure, which may
lead to loss of control of the helicopter and subsequent injury or death".
47. Loose carburetor bowl attachment bolts allowing air to suck into carburetor.
48. Fuel leak from the engine driven fuel pump. Continental SB 01-1
49. Improper float level. Refer to FAA Special Airworthiness Information
Bulletin NM-02-47 September 30, 2002. and Precision Airmotive
Service Information Letter MS-4, Revision 1, dated July 18, 2002,
Installation Instruction E-954 Revision 2 dated June 18, 2002, and E-955
Revision 2, dated June 14, 2002 to expand and clarify these instructions.
50.Valve float caused by not enough dry tappet clearance, insufficient lifter
bleed-down, or heavy rocker arms (roller rocker arms). Occasionally occurs on
Continental 520 engines. On these engines if the lifter pumps up and holds the
valve open the rocker arm will strike the inside of the rocker cover causing a
crack. If you are using the "full flow lifter" (constant registration)
then check to see if you have the correct rocker arms installed. Also, replace
the lifters as they may have low bleed-down rates due to varnish build-up. Valve
float is more typically at higher rpm's and with cold oil as both of these
reduce the rate of lifter bleed-down.
51. Weak or broken valve spring.
52. Hot air from alternate air door or carburetor heat. As a rule-of-thumb
for every 10 degrees F. heat above the standard 59 degrees F. there is a 1%
power loss. At 100 degrees this adds up to 10% power loss. Tests at Lycoming
yielded a 15% power loss with the full application of carburetor heat.
53. Hydraulic lifter pumping up and holding the valve open.
Valves can leak if the hydraulic lifters pump-up. This may result in the
situation where the compression check is good, the engine starts to run OK but
then a cylinder drops-off or the engine becomes rough. This happens when the
hydraulic lifter pumps up and holds the valve open. An example of this happening
is on the A-75, A-64 engine installed in an aircraft that originally used an oil
cooler. Then the engine is removed and installed in an aircraft without an oil
cooler. Now the engine drops two cylinders and runs rough because two hydraulic
lifters on one side of the engine are pumping up and holding the valve open. The
reason its doing this is that the 22130 sleeve (oil restrictor) was not removed
from the crankcase. This oil restrictor diverts some of the oil thru the oil
cooler. If you remove the oil cooler and don't remove the restrictor then
pressure builds up on one side the the crankcase and the extra oil pressure
causes the hydraulic lifters on that side of the engine to pump up and hold the
valves open.
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Description of symptom
The major problem thou is low engine power.
I don't have experience with this engines performance prior to the
annual. It came out of a 12 year storage and the pilot who flew it
in stated it was low on power then. The mechanics say it isn't low on
power but I pointed out the engine doesn't approach static R.P.M. stated
by Continental with this engine and prop combination. In fact according
to the power absorption curve for this prop it is lucky to be producing
50 horsepower out of a 75 HP rated engine and prop. It flys but
just barely. When I tried to explain power absorption to the
A&Ps I was met with blank stares. I noticed the plugs and
exhaust are covered with black soot. The mechanics reset the carb
and now it drips fuel. It drips even worse in flight attitude
and I suspect this may be a contributing factor. Do you offer new
or rebuilt carburetors for this A75. Bigger and better would be
nicer if the engine would benefit from it.
I picked up 50 R.P.M. moving the
muffler inner perforated cylinder away from the discharge pipe which was
an apparent restriction. Now if I can find another 150 R.P.M. in static
I will be happy. Any information on carbs and suggestions would be
greatly appreciated.
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Solution
I found someone more qualified to work
on my J4,.... me. The problem was weak valve springs. 62 years of
heating and cooling caused these 54# springs to lose temper and drop
to 37#. The higher R.P.M. caused valve float and worked like a
governor. Pulls like it is advertised to do now. I am a happy
camper.
Thanks for your time.
Comment
Were the valve springs really 62 years
old!
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