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Thread: Engine vibration after rebuild

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  1. Question Engine vibration after rebuild 
    #1
    Join Date
    11-27-2011
    Location
    Ft Davis, Texas, USA
    Posts
    3
    I have an Evolution .52 NX engine that got damaged in a crash. The crank shaft got slightly bent just behind the propeller and cooling fins on the cylinder head were damaged but apart from that there were just a few other minor bumps and bruises. I rebuilt the engine and replaced all parts with any sign of damage and I also replaced both crank shaft bearings. The only parts I did not replace were the engine casing, cylinder sleeve, piston, connecting rod and carburetor. My problem now is severe engine vibration at high revolutions. The propeller is balanced spot on and I ran the engine with and without a spinner just in case the new spinner is out of balance. I then removed the new crankshaft again and compared critical dimensions against the old one and I even weighed both crank shafts, they weigh exactly the same. Iím still wondering about the crank shaft which is unbalanced by design but I assume the piston and connecting rod would balance that out once connected, correct? Does anyone have advice on what to look for that can cause the vibration?
     

  2.  
    #2
    I'll assume you repaired the aircraft as far as you saw was needed. Unfortunately there can be hidden damage that doesn't show until you apply operational loads.
    Even if you replaced the aircraft, you can find issues in new ARFs that will drive you nuts. All it takes is the underpaid, overworked person on the assembly line not applying enough glue someplace.

    Check for loose engine mounting, firewall defects, cracked engine mount (nylon, wood beams or aluminum... doesn't matter)

    Some vibration is typical of a single cylinder engine. Anything that lets the engine move will appear to amplify the vibrations. This can seem to be worse at some rpm range than at others due to harmonics of how the engine is being allowed to move.

    Your engine might be fine. The description of how you went about repairing it should have covered all the common post-crash sources of unusual vibrations.
     

  3.  
    #3
    Join Date
    11-27-2011
    Location
    Ft Davis, Texas, USA
    Posts
    3
    No, the aircraft was a total write-off so I built a new aircraft which I now fly with an old OS46 engine. I don't want to put the Evolution 52 on my new airplane until I've solved the vibration issue. I ran the E52 on my test stand which is pretty stout so I don't expect the problem to be some resonance of the engine mounting but I'll confirm that over the weekend.
     

  4.  
    #4
    Join Date
    02-06-2011
    Location
    MN
    Posts
    4,995
    Sort of sounds to me like maybe the new crank isn't quite right. What do the sleve and piston look like?
     

  5.  
    #5
    Join Date
    11-27-2011
    Location
    Ft Davis, Texas, USA
    Posts
    3
    Couldn't see any obvious damage to the piston, sleeve or connecting rod. I'm also still suspicious of the new crank shaft. I think I'll bring it in to our workshop at work and check it out with better measurement equipment.
     

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