Certified engine crankshaft repair

Discussion in 'Firewall Forward / Props / Fuel system' started by pfarber, Oct 10, 2019.

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  1. Oct 10, 2019 #1

    pfarber

    pfarber

    pfarber

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    Does anyone have a list or know of what repairs are available to Lyc IO-360 crankshafts?

    I know cracks are thrown away.. that's the easy stuff.

    And Lyc forbids any sort of prop flange repairs, but what about crank straightening? Welding of journals back to spec etc.

    This is NOT an automotive question, just wondering what options a shop might present me if I showed up with a crank that had a defect or what experiences others have had.

    Thanks
     
  2. Oct 10, 2019 #2

    Turd Ferguson

    Turd Ferguson

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    It's usually limited to grinding and polishing. A seemingly good crank can be rejected during the NDT process as well.
     
  3. Oct 10, 2019 #3

    TFF

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    No welding. Some straightening but it’s more like trueing; it can’t be far out. Some shops will do a little more as long as you don’t want traceable paper saying it’s good. Call herehttp://www.aircraftspecialties.aero/crankshafts/
    Going on a homebuilt if you find a local shop who will weld on your crank and grind it, your prerogative. Mark the crank experimental and remove the engine data tag. I took my 0-290 crank to a local machine shop. I would not take it to just anyone. I took mine to someone I knew and I had worked for their dad’s machine shop as one of my first jobs. eBay tends to have a decent selection of slightly unairworthy cranks that would be just fine in a homebuilt.
     
  4. Oct 10, 2019 #4

    cheapracer

    cheapracer

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    Cranks can be straightened in presses with no great problem, suitably warmed first (not heated), and of course carefully crack tested later. It's quite common, and nothing special. Many would be shocked how not straight and out of index many stock cranks are.

    "Indexing" means that the journals are all in their correct place in terms of degrees apart from each other, and distance outwards from the crank's centerline. It takes a competent crank grinder who know's his stuff to get it right.

    As for welding for journal build up to be reground to size, Google 'Plasma Spraying Crankshafts'.
     
  5. Oct 10, 2019 #5

    TFF

    TFF

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    In the world of cranks, that is all true. In the world of aircraft cranks at an aircraft crank shop, not so true. Lycoming and Continental and whoever else sets the rules and they say pretty much no to anything. If you vary from that, you have to have your own process oked by the FAA. Machine and knowledge means nothing in aviation. Only paperwork.
     
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  6. Oct 10, 2019 #6

    Pops

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    Had a crank break in an Lyc 290. Vibration like you would not believe until I got the power off. Came back on the power and vibration got really bad starting about 1500/1700 rpm. I could hold altitude at 75 mph at that rpm ( stall speed was 68 mph) . Flew 7 miles to an airport. Just worried about losing the weight of the engine.
    DO NOT take any chances with a crank.
     
  7. Oct 11, 2019 #7

    Winginitt

    Winginitt

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    Has anyone actually thought about what it takes to bend a crankshaft in the first place? Not rebend and straighten.....just bend it badly enough to require straightening. Remember that the crankshaft is held in place by the main bearings and their supports. If its minor misalignment, simple grinding should bring it back to true. So what force caused this highly supported and constrained chunk of metal to bend so badly that grinding won't true it?
     
  8. Oct 11, 2019 #8

    TFF

    TFF

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    Sometimes the things twist from usage. The Lycoming and Continental cranks look like a big MG or Triumph crank the way the throws are connected. There is a lot of room to twist. Heat cycles and usage probably puts a couple of degrees in over time. They artificially age NASCAR parts by putting them in ovens and heat cycle them. Get them to twist then machine them. Prop stoppage may twist it some or not. Each one is its own problem.

    I was there the whole time when my crank was ground. I had it turned to .006. Most just want to go .010 which is easier as you don’t have to be as spot on setting it up. It takes a while to do it right. It took four hours to do it. Mine had a prop strike but flange is true and original prop is going back on. It was checked at a prop shop. I am keeping an eye on it and will do a dye pen every year.
     
  9. Oct 14, 2019 #9

    proppastie

    proppastie

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    Where it break? How could it still run
     
  10. Oct 14, 2019 #10

    proppastie

    proppastie

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    Were you able to get bearings? (stupid question )
     
  11. Oct 14, 2019 #11

    TFF

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    Yes. They make .003, .006, .010 undersized. .003 they actually polished down with a clamshell polisher not the belt polisher. .006 and .010 they grind. One stink of it is undersize bearings cost more than Standard by enough to make you think. I asked the head guy at Aircraft Specialties why. He said that the bearings were saving an expensive part so the parts makers were going to capitalize on it.
     
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  12. Oct 14, 2019 #12

    Winginitt

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    What's a clam shell polisher ?
     
  13. Oct 14, 2019 #13

    Pops

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    In the middle of the throw just forward of the center main bearing. Broke at an angle and the rear half of the crank turned almost 360 deg and hit the part of the throw that was attached to the forward half of the crank and turned the front half and prop. So I was flying on the rear 2 cylinders and the front cylinder were out of time and firing out the exhaust.
    Lots of noise and vibration. After landing and taxing to the ramp, I shut the engine down and just for the heck of it tried to restart, it did, on the rear 2 cylinders.
     
  14. Oct 14, 2019 #14

    Pops

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    Friend of mine did the .003 on his Lyc-360. Been about 10 years now and a lot of flying.
     
  15. Oct 14, 2019 #15

    TFF

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    About 4:11 into the video the guy uses a clamshell polisher.
    On my crankshaft, I measured it as Standard at the widest tolerance. All passed but at biggest gap. That gap was only .0005 off the close tolerance of the .003 undersize. I could probably have thrown the .003 bearings in and not known a difference. My crank had two problems one the just barely STD bearings and two some pitts on the journals from sitting many years. One or the other I could deal with but not both. My guy could not do a job he would be proud of at .003 but he knew he could do .006. At .003 they are starting with a just about perfect crank and can get more life out of it without going all out.
     
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  16. Oct 14, 2019 #16

    Turd Ferguson

    Turd Ferguson

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    Broke a crank is a TSIO 520 in a 402 and it kept running. Made a lot of mechanical noise but still ran. Could shut it off and restart it.
     
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  17. Oct 14, 2019 #17

    Pops

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    And I thought I was the only one that would try to restart an engine after all the noise and vibration. :)
    Could have been worse for you, could have been flying a 411.
     
  18. Oct 14, 2019 #18

    Pops

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    If you are a motor head, you will love the tour of the Lyc plant. I would like to go back a second time. You learn a lot.
    Just don't ask about the 320-HAD engine that was missing in the museum. I ask, they said they didn't make that engine. :)
     
  19. Oct 14, 2019 #19

    proppastie

    proppastie

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    I know several people love that engine.....
     
  20. Oct 15, 2019 #20

    Turd Ferguson

    Turd Ferguson

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    I owned one for several yrs. Best engine ever. Lycoming certified a full electronic ignition to retrofit on the engine since Bendix doesn't support the dual mag anymore. An alternator goes on the pad where the mag was so it will have a self contained source of power; the rest are essentially GM electronic ignition parts.
     

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