Pulling the Prop through by Hand

Discussion in 'Flight Following' started by Jaybird180, Feb 12, 2014.

  1. Jaybird180

    Jaybird180 Final Approach

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    I recall reading in Lycoming literature that I should pull the prop through the strokes by hand if the engine has set for an extended time and or the OAT is below 40F; this helps break up congealed oil and prevents dry starts.

    What is the proper (safe) way to do this?
     
  2. JHW

    JHW En-Route

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    doesn't do squat for starting that the first couple revs of the starter won't also accomplish. But it does let you feel a no-compression cylinder and hear any odd noises like loose baffling rubbing on a ring gear, etc. I pull the prop through each compression before almost every flight. Found lots of problems over the years before starting the engine before everyone is on board and settled in.

    as for how to do it, have the brakes set, chocks on, throttle idle, mixture off, mags off, fuel selector off, and always assume the engine could start. Really it's no extra work, that's how most people park the plane anyway.
     
  3. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    A Lycoming or Continental can be pulled through backwards to reduce the chances of the impulse firing.

    Don't do that with a 4 stroke Rotax.
     
  4. bnt83

    bnt83 Final Approach PoA Supporter

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    There is no way in heck I'm going to turn the oil pump backwards to: "helps break up congealed oil and prevents dry starts."
     
  5. Bill Jennings

    Bill Jennings Touchdown! Greaser! PoA Supporter

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    I''ve heard that rotating the engine backwards can damage/break the vanes on older vacuum pumps, as they've worn in the direction of engine rotation. True or not?
     
  6. Norman

    Norman En-Route Gone West

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    True; I've seen it happen.

    Pulling the prop thru is a carry-over from the days of round engines where there was a possibility of the bottom cylinders becoming hydraulic locked with oil.
     
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  7. Fearless Tower

    Fearless Tower Touchdown! Greaser!

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    Or a radial. That will ruin your day.
     
  8. bnt83

    bnt83 Final Approach PoA Supporter

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    How often does the prop bounce backwars after a failed start or at shutdown?
     
  9. Bill Jennings

    Bill Jennings Touchdown! Greaser! PoA Supporter

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    True it does, but still, I've heard turning the engine backwards can harm the vacuum pump. I guess that's just an old wives tale.
     
  10. Fearless Tower

    Fearless Tower Touchdown! Greaser!

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    Not sure about vacuum pumps, but in radials, rotating it backwards puts oil in the intake pipe and can cause an even worse liquid lock than if oil was trapped in the cylinder in the first place.
     
  11. Clark1961

    Clark1961 Touchdown! Greaser!

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    The AFM for the 'kota sez to pull it through at least six blades prior to start in sub 40* weather. Definitely a temperature bases recommendation, not an oil in cylinder thing.

    OTOH, the manual for the airwolf wet vac pump sez direction of rotation is unimportant when in terms of breaking vanes.
     
  12. Fearless Tower

    Fearless Tower Touchdown! Greaser!

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    How far backwards does it go ? Certainly not through a complete compression cycle.
     
  13. bnt83

    bnt83 Final Approach PoA Supporter

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    Ok then. Watch you mechs do timing and compression checks, in addition to 400-500 hours of bouncing backwards in normal service.

    I'm not saying it doesn't happen, but its not that likely. It seems to me if it breaks going backwards then it was probably on its last leg to begin with.
     
  14. Fearless Tower

    Fearless Tower Touchdown! Greaser!

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    Just to be clear, I'm only saying that you should never rotate a radial engine backwards. I don't have a position in flat engines.
     
  15. flyingron

    flyingron Touchdown! Greaser!

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    I don't know what you claim to have been reading, but Lycoming doesn't advocate anything of the sort currently. Lycoming's guidance is exactly what the first response was, there's nothing that pulling through by hand does that the starter will not do.

    Certainly pulling by hand does NOTHING WHATSOEVER for lubrication (and potentially may even be detrimental).
     
  16. JOhnH

    JOhnH Touchdown! Greaser! PoA Supporter

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    Interesting thread. On my trip from Florida to PHX in October we hit some really cold overnight weather. Starting the engine cold was a real problem and we had t have a couple of jump starts after draining the battery. On the way home, an A&P suggested we turn the prop 4 or 5 times prior to starting. I did and we had one of the easiest starts ever. I have been doing that ever since when it is cold or if the plan hasn't been started for a few weeks. We have not had a difficult start since I started doing this.

    And as far as turning the prop backwards, I accidentally did that the first time I tried with no apparent damage (O-360)
     
  17. tehmightypirate

    tehmightypirate Line Up and Wait

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    From the Cessna 172 SP POH for cold weather operations:

    "When air temperatures are below 20°F (-6°C), use an external preheater and an external power source whenever possible to obtain positive starting and to reduce wear and abuse to the engine and electrical system. Preheat will thaw the oil trapped in the oil cooler, which probably will be congealed prior to starting in extremely cold temperatures.

    Prior to starting on cold mornings, it is advisable to turn the propeller manually through several engine compression cycles by hand to loosen the oil, so the engine cranks (motors) more easily and uses less battery power. When the propeller is turned manually, turn it in the opposite direction to normal engine rotation for greater safety. Opposite rotation disengages the magneto impulse couplings and prevents possible unwanted ignition."

    So, according to Cessna, it's the preheat that helps with the oil and wear and tear. Turning the prop only helps out the starter and battery.
     
  18. JasonM

    JasonM Pattern Altitude

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    FYI for those concerned about opposite rotation. This is directly from my Cessna T182T POH - Lycoming TIO-540

    [ Prior to starting on cold mornings, it is advisable to turn the
    propeller manually through several engine compression cycles by
    hand to loosen the oil, so the engine cranks (motors) more easily
    and uses less battery power. When the propeller is turned
    manually, turn it in the opposite direction to normal engine rotation
    for greater safety. Opposite rotation disengages the magneto
    impulse couplings and prevents possible unwanted ignition. ]
     
  19. Dan Thomas

    Dan Thomas Final Approach

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    Turning the prop backwards might bust the vacuum pump, but if it does, that pump was way beyond wear limits anyway and would have soon failed, maybe in flight and maybe in IMC. Consider yourself lucky if it fails on the ground.

    I have had engines kick back on start and turn backwards for several revolutions. It happens.

    Backwards can run oil backwards through the pumps. It doesn't hurt it and sure doesn't make much difference to oiling on startup unless you turned it backwards many blades and evacuated much of the system.

    On older small Continentals (65 thru 90 HP) the pumps tend to be weak and if they sit for a long time, some of them will not prime themselves. They leak the oil out past the pump cover and there's nothing but air in the pump and it won't lift the oil from the tank. I have a preoiler on mine to get the system all filled with oil and the pump all primed; it saves that engine.

    Dan
     
  20. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Yes Bill it is, turning a vac pump backwards move the vanes away from the walls of the pump. turning the pump forward makes the vanes move against the walls to make a tight seal.
     
  21. FastEddieB

    FastEddieB Final Approach

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    Interesting discussion.

    I was taught the "pull the prop through" routine in the beginning, but since have been presented pretty convincing arguments against.

    Much wear can occur when sliding unlubricated surfaces over one another.

    So, the best thing one can do is get the engine started so that the oil pump can provide pressure and keep the metal surfaces apart. Pulling the prop through by hand prevents that, while still dragging the surfaces against each other.

    And I'm having trouble with how rotating an engine slowly does anything to "loosen" up the oil - it seem like only heat will do that.

    As a data point, on my Sky Arrow I do pull the prop through one revolution during preflight - with my high mounted engine its the only way I can inspect the propeller blades. But my engine is also geared, so one revolution of the prop is much less at the crank.

    As a final caution, ROTAX 912 engines should not ever be rotated backwards more than a little - it sucks air into the system which is not a good thing and can lead to loss of oil circulation.
     
    Last edited: Feb 12, 2014
  22. PPC1052

    PPC1052 En-Route

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    My Cessna 177B (1976) POH instructs to pull the prop through a few cycles:

    Prior to starting on a cold morning, it is advisable to pull the propeller through several times by hand to 'break loose' or 'limber' the oil, thus conserving battery engery.

    This is an instruction that I have always ignored.
     
  23. Silvaire

    Silvaire En-Route

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    The carbon vanes in the vacuum pump are angled so in normal rotation they form a knife edge in that direction. So turning the prop backwards is kind of like stroking a cat backwards and if the pump is older and a bit worn the amount of vane that is still in the slot when it's extended into the void is less and yes, you can cause damage to it.

    But the pump is driven off the cam so, like the magnetos, turns at half speed so going back a little bit usually isn't going to cause a problem and going back a few turns usually isn't going to cause a problem either (especially with a newer pump) but the chances of something happening are obviously there so, being I have no really good reason for turning the prop backwards I generally try to avoid doing it as much as possible on airplanes that have carbon vaned dry pumps.

    [​IMG]
     
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  24. 35B33

    35B33 Pre-Flight

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    1968 C-150 Pilots Manual p22 said, for cold weather, to pull the prop through while priming 8-10 times.
    http://www.elkgroveairport.org/c150.pdf

    I was working toward my commercial back then on some cold NY mornings. Obviously use proper hand propping procedures and treat the prop as if the engine will fire.

    I guess we could get a fish scale out and measure the initial force needed to start the prop moving and compare after pulling it through a few times. Multi grade oil may make this irrelevant.
     
  25. Bill Jennings

    Bill Jennings Touchdown! Greaser! PoA Supporter

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    So in this view the pump spins clockwise?
     
  26. MAKG1

    MAKG1 Touchdown! Greaser!

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    How are the cams driven on these engines?

    You don't turn a CSB backwards because it defeats the chain tensioner and slack in the chain can cause it to jump a tooth. It's less bad on a gear driven cam, and more bad on a belt driven cam.
     
  27. Tom-D

    Tom-D Taxi to Parking PoA Supporter

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    Yes, centrifugal force pushes the vanes out toward the cylinder walls, friction of the walls pushes the vanes back in their slot.
     
  28. Clark1961

    Clark1961 Touchdown! Greaser!

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    Question for folks: does oil that has been sheared recently have the same viscosity as oil that hasn't been sheared recently?
     
  29. 1600vw

    1600vw Pattern Altitude

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    I was told when hand propping a engine like an a-65 continental engine. That if you are using a wooden prop and no impulse couplers that this engine can start and run backwards.

    Is this correct.

    You guys really do amaze me with your knowledge.

    Tony

    P.S. Sorry if I went off topic a little. Back to regular programming.
     
  30. MAKG1

    MAKG1 Touchdown! Greaser!

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    Not necessarily, especially for multigrades.
     
  31. Clark1961

    Clark1961 Touchdown! Greaser!

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    From my perspective, recently sheared oil will not have the same viscosity as oil that has been static for "awhile". Our viscosity tests really don't examine the possible phenomena. We do know that static and dynamic viscosities are different but I don't have any data on a possible "recovery" time.
     
  32. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    An engine like an A-65 may kick and spin back a blade or two, but it won't run backwards. With it turning backwards the airflow is from the exhaust into the intakes so no fuel in the cylinders.

    The two stroke engines sometimes found on light aircraft, on the other hand, may run backwards just fine.
     
    Last edited: Feb 12, 2014
  33. poadeleted20

    poadeleted20 Deleted

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    First, Lycoming doesn't say that (Cessna does), and second, it only makes things worse (as Lycoming tells you in their publications).

    Preheat the engine and then start normally.
     
    Last edited: Feb 12, 2014
  34. Clark1961

    Clark1961 Touchdown! Greaser!

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    Turning an engine backwards somehow changes the valve timing so the intake is open on the upstroke? Hmmm...

    No argument on the two-strokers - ran a 6V71 Detroit backwards for a few seconds once...it didn't like it much.
     
  35. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser! PoA Supporter

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    Yes. Think about it.
     
  36. Clark1961

    Clark1961 Touchdown! Greaser!

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    Okay, it's an air pump running backwards. The Detroit really didn't like it though...
     
  37. docmirror

    docmirror Touchdown! Greaser!

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    I always prime then pull the prop through forward for 4 blades when under 40F. In fact, I pull it through as if I were weakly hand-propping to help get the mixture distributed in the jugs.

    Never had a problem cold starting. It saved my butt at Santa Fe two years ago. In fact, I had to hand-prop start my O-470 at Taos once. I don't recall anything in the POH about it, but it works for me.

    YMMV, do whatever you want with your plane.
     
  38. MAKG1

    MAKG1 Touchdown! Greaser!

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    You prime FIRST? Why?

    A loose p-lead can ruin your whole day.

    It makes a LOT more sense to do that with the fuel cut off.

    It's going to make no difference to the mixture. That's where preheat can do a lot of good. But frankly, at 40 deg F, evaporation of gasoline isn't a problem. Maybe at -40. Cranks are difficult in cold weather mainly because the battery produces less current.
     
  39. FastEddieB

    FastEddieB Final Approach

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    Does not priming also tend to wash off residual oil in the cylinder?

    May or may not, but I have that impression.

    BTW, how is it that our cars and motorcycles, even the air cooled ones, all seem to get along fine without being "pulled through"?
     
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  40. Norman

    Norman En-Route Gone West

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    Black magic. :yes: :D
     
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