Welcome to PriusChat

We'd love to have you join our community and participate in the conversation! Sign up for FREE today.

Sign Up
  1. TGB4 2014 Prius Convention Hotel Discounts are ending this week. Click for more information. All Access registration with personalized items ends Sept 1. Register now!

Baffler

Discussion in 'Fred's House of Pancakes' started by airportkid, Apr 2, 2012.

Social Buttons

  1. airportkid

    airportkid Will Fly For Food

    Joined:
    Sep 2, 2005
    Messages:
    2,165
    Likes Received:
    538
    Location:
    San Francisco Bay Area CA
    Your Vehicle Year:
    2005 Prius
    Weak compression on two cylinders, more than 20 years of elapsed time and a bottom spark plug drowing in oil were enough to make us write a check to ECI for 4 brand new cylinders for the O-200 on our Cessna, which I just finished installing last week (I'm an A&P so do all my own maintenance). Also installed are 8 brand new iridium spark plugs, and the cylinders looked so good I drove all the way to Redding to have the rocker box covers chromed at a shop our magneto guru said was the best on the west coast. It looks like a damn gleaming Harley Davidson on its slender mounts, yet no one will ever see it except us when the cowling comes off for oil changes & inspections. Pure vanity.

    Anyway, the test run was a bust. #3 doesn't fire. Totally dead. With dual magnetos an ignition problem was extremely unlikely and tests proved the cylinder IS getting spark at both plugs.

    I had to put in oversize pushrods to bring the dry lash clearances into spec. and thought there might have been a problem somewhere between the cam and the rocker arms but all that rube goldberg chain of lifter machinery checks out perfectly. Turning the engine by hand shows the valves opening and closing as expected - no sign of stickiness. And it holds 75/80 psi at TDC - about perfect for an unbroken-in cylinder, so there's no ring or valve leak issue.

    Ran it with the #3 rocker box cover off to see if a valve was floating but the engine shakes so badly with #3 dead you can't tell.

    Lastly I pulled the induction piping from the spider to the cylinder port to see if some bit of packing had got left inadvertantly inside something, but all is clear, right down to the back of the valve face.

    There's absolutely no reason in the world why that cylinder shouldn't fire, but it will not. It's getting mixture, it's getting spark; the laws of physics say it should combust, but all it is is bust.

    (We know it's dead because it's cold to the touch after running, and its CHT & EGT never light up the analyzer).

    My AI and I are totally flummoxed, as is every other curious soul who dropped into the hangar to check our progress.

    But perhaps there's someone sitting down for a few of Fred's pancakes who might have an insight we haven't had yet. Fred's pancakes are famous for inspiring improbable leaps of imagination.

    I look forward to any wisdom that may be forthcoming.
  2. ETC(SS)

    ETC(SS) Aspiring Hypocommuter.

    Joined:
    Oct 28, 2010
    Messages:
    2,790
    Likes Received:
    1,286
    Location:
    Redneck Riviera (Gulf South)
    Your Vehicle Year:
    2010 Prius
    Model:
    II
  3. hyo silver

    hyo silver Awaaaaay

    Joined:
    Mar 2, 2005
    Messages:
    15,147
    Likes Received:
    1,381
    Location:
    off into the sunset
    Your Vehicle Year:
    2004 Prius
    Model:
    N/A


    Yes there is. We just don't know what it is yet. ;)

    You did say it was getting mixture, so that takes care of the air and fuel part. And it's getting spark, so that's 3 out of 3. This may seem like a stupid idea, but is it getting all 3 at the same time? How's the firing order?

    Another wild and crazy idea - well, that IS what you asked for - can you run the engine without the exhaust pipes to verify what's coming out of cylinder three? Yes, it's gonna be hella loud, but if you don't see any flash, or if the exhaust valve spits out something other than gas - or nothing at all - that will tell you something.
  4. dustoff003

    dustoff003 Blizzard Brigade #003

    Joined:
    Dec 27, 2010
    Messages:
    1,339
    Likes Received:
    324
    Location:
    Waianae, HI (Oahu)
    Your Vehicle Year:
    2011 Prius
    Model:
    Five
    I am a non A&P aircraft mechanic I work for the military. I don't have much experience with reciprocating engines. You said that with the rocker cover off and engine running you could not tell if the valve train for #3 was operating. How's about pulling all the plugs and turning it over by hand to observe the operation?

    An afterthought what cylinder was the bottom plug drowning in oil? We're all the new gaskets cut, punched, or stamped correctly?
  5. FL_Prius_Driver

    FL_Prius_Driver Senior Member

    Joined:
    Jun 17, 2007
    Messages:
    3,596
    Likes Received:
    908
    Location:
    Tampa Bay
    Your Vehicle Year:
    2001 Prius
    It seems that you were checking the exact right area ....... the valve(s) floating. All that it takes is for one to be unseated during the compression stroke. Something that might not show up on a slow hand crank.

    Let us know when you figure it out.
  6. amm0bob

    amm0bob Permanently Junior...

    Joined:
    May 29, 2008
    Messages:
    5,237
    Likes Received:
    2,098
    Location:
    The last place on earth to get cable, Sacramento
    Your Vehicle Year:
    2008 Prius
    Model:
    II
    Re: Baffler... my guess...

    exhaust valve failure...

    maybe the cam is over sized on the one lobe... or off time just before ignition...

    maybe the wrong sized pushrod...

    But you did say compression was good... so I don't think rings/seals are the culprit...
  7. daniel

    daniel Cat Lovers Against the Bomb

    Joined:
    Feb 25, 2004
    Messages:
    14,399
    Likes Received:
    1,496
    Location:
    Spokane, WA
    Your Vehicle Year:
    2004 Prius


    :pound:

    Get rid of that gas-burning engine and convert to electric. ;)
  8. airportkid

    airportkid Will Fly For Food

    Joined:
    Sep 2, 2005
    Messages:
    2,165
    Likes Received:
    538
    Location:
    San Francisco Bay Area CA
    Your Vehicle Year:
    2005 Prius


    Yeah, but feeding all those guinea pigs could get expensive:

  9. daniel

    daniel Cat Lovers Against the Bomb

    Joined:
    Feb 25, 2004
    Messages:
    14,399
    Likes Received:
    1,496
    Location:
    Spokane, WA
    Your Vehicle Year:
    2004 Prius
    Batteries, my friend. Batteries!
  10. airportkid

    airportkid Will Fly For Food

    Joined:
    Sep 2, 2005
    Messages:
    2,165
    Likes Received:
    538
    Location:
    San Francisco Bay Area CA
    Your Vehicle Year:
    2005 Prius
    Well, it's fixed. But how - that's still a mystery. All I did was pull things apart and put 'em back together and voila - all cylinders work beautifully. Not too comforting - what if whatever was awry recurs at 6,000 feet? Grrrr.
    I made two changes: removed a thin residue of old gasket I'd missed on the intake port elbow (which may have created a tiny leak but not enough to make the cylinder not work), and sprayed electrical contact cleaner on all the "cigarette" spark plug lead springs. We'd checked for spark beforehand, however, and got it so I'm not sure cleaning the leads made whatever change needed to be made.

    All I can do is hope something just needed to be poked or jostled and my disassembly/re-assembly did it.

    The test flight will be an hour of orbit just outside the pattern, so if the problem just recur the airport will be right there. Stay tuned.
  11. amm0bob

    amm0bob Permanently Junior...

    Joined:
    May 29, 2008
    Messages:
    5,237
    Likes Received:
    2,098
    Location:
    The last place on earth to get cable, Sacramento
    Your Vehicle Year:
    2008 Prius
    Model:
    II
  12. dustoff003

    dustoff003 Blizzard Brigade #003

    Joined:
    Dec 27, 2010
    Messages:
    1,339
    Likes Received:
    324
    Location:
    Waianae, HI (Oahu)
    Your Vehicle Year:
    2011 Prius
    Model:
    Five
    Good luck!


    Posted from my iPhone via the Tapatalk app.
  13. Rokeby

    Rokeby Member

    Joined:
    Jan 21, 2008
    Messages:
    3,006
    Likes Received:
    688
    Location:
    Ballamer, Merlin
    Your Vehicle Year:
    2008 Prius


    A clear case of what used to be called, and maybe still is, FM* in the military.

    * F__king Magic :D

    Did you have any "extra" parts left over? :p
  14. daniel

    daniel Cat Lovers Against the Bomb

    Joined:
    Feb 25, 2004
    Messages:
    14,399
    Likes Received:
    1,496
    Location:
    Spokane, WA
    Your Vehicle Year:
    2004 Prius


    That's why having more than one engine is always comforting. ;)
  15. 2k1Toaster

    2k1Toaster HID Guru

    Joined:
    Feb 14, 2010
    Messages:
    3,933
    Likes Received:
    1,161
    Location:
    Rocky Mountains
    Your Vehicle Year:
    2006 Prius
    Model:
    Three


    Does present its own challenges though. Having 2 engines presumably mounted on wings instead of infront, if 1 dies, you have a really unbalanced force... That is a whole new can of worms!
  16. airportkid

    airportkid Will Fly For Food

    Joined:
    Sep 2, 2005
    Messages:
    2,165
    Likes Received:
    538
    Location:
    San Francisco Bay Area CA
    Your Vehicle Year:
    2005 Prius


    The jury is still out on that, but crash evidence so far tends to implicate multi-engine aircraft as more dangerous than single-engine aircraft for several reasons:

    > A dead engine makes the airplane significantly underpowered for its size & weight; its ceiling drops, its margin between max speed & stall shrinks, its handling may be more sluggish.

    > All multi-engine aircraft are more complex than single-engine aircraft by virtue of the additional engine(s) alone, but are also virtually always more complex by virtue of their increased efficiency systems: constant speed/feathering props, retractable gear, induction boost systems, fuel feed systems, which, under the stress of an emergency, are more prone to being mismanaged.

    > Most multi-engine aircraft have engines off centerline, recips most extremely with their engines out on the wings. A dead engine induces a serious yaw component that increases drag (and raises the stall speed) that if not properly compensated for can pull the airplane out of control. Cessna's Skymaster was designed to ameliorate the centerline thrust problems but introduced a new and unanticipated hazard: failure to realize an engine had quit, and inadvertantly flying the airplane beyond its diminished performance envelope because it didn't "feel" wrong until too late.

    > The most common time engines fail is right at takeoff; that's when they're at greatest stress: not yet at full operating temperatures yet putting out more power than will be commanded for the entire rest of the flight. That's the WORST time to suffer a sudden performance drop; the airplane is barely under aerodynamic control until established in the climb. It's a one-two punch of circumstance that has shredded many twins and their occupants, the pilot not able to quickly and correctly enough compensate for the abrupt aerodynamic decay and asymmetry and plunge right back into still immediately adjacent earth.

    > It's been said of many twins that all the surviving engine does is fly the airplane to the scene of the crash.


    You'll note that the vast majority of the commercial airline fleet is twin engine aircraft, NOT three or four engine aircraft, which a few decades ago were much more common. The trend is to REDUCE the number of powerplants, both making the airplane simpler to manage and less likely to break down. Within another decade I wouldn't be surprised to see 747s and the Airbus 380 retrofitted as twin engine aircraft, all in the pursuit of increased efficiencies as well as safety.

    The engineering ideal would be single-engine - but a lot of legal and popular prejudice would still have to be overcome long after it had been made feasible from an engineering standpoint.
    1 person likes this.
  17. amm0bob

    amm0bob Permanently Junior...

    Joined:
    May 29, 2008
    Messages:
    5,237
    Likes Received:
    2,098
    Location:
    The last place on earth to get cable, Sacramento
    Your Vehicle Year:
    2008 Prius
    Model:
    II


    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
    2 people like this.
  18. hyo silver

    hyo silver Awaaaaay

    Joined:
    Mar 2, 2005
    Messages:
    15,147
    Likes Received:
    1,381
    Location:
    off into the sunset
    Your Vehicle Year:
    2004 Prius
    Model:
    N/A


    Funny, isn't it, how often 'conventional wisdom' is just plain wrong?

    If sense were common, more people would have some. ;)
  19. 2k1Toaster

    2k1Toaster HID Guru

    Joined:
    Feb 14, 2010
    Messages:
    3,933
    Likes Received:
    1,161
    Location:
    Rocky Mountains
    Your Vehicle Year:
    2006 Prius
    Model:
    Three


    Those are cool planes! But other than the ones with the props in the front and back, you will be unbalanced with just one. Your yaw will go crazy.
  20. amm0bob

    amm0bob Permanently Junior...

    Joined:
    May 29, 2008
    Messages:
    5,237
    Likes Received:
    2,098
    Location:
    The last place on earth to get cable, Sacramento
    Your Vehicle Year:
    2008 Prius
    Model:
    II



    Can go crazy... but if you pay attention, and the weather isn't pissy, you can handle most all twins with one engine out... although I will say, I am not multi-engine certified, I have flown a Dutchess for about 45 hours...