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Thread: Rough O-200

  1. #11

    Join Date
    Jul 2011
    Location
    Oak Harbor Wa
    Posts
    384
    Quote Originally Posted by Eric Brown View Post
    Gentlemen.
    Here's what I have done so far. Visual check of induction system. Different spark plugs. Tried another O-200 carburetor. Removed both ignition leads from one cylinder at a time and ran engine below 1000 RPM to see if miss would disappear with the dead cylinder. Tried setting the idle mix very lean (1/4 turn). Tried very rich mix (3 turns). The miss is still present below 1200 RPM.

    Riddle me this. If the crank and cam gears were off by 1 tooth, would this create this problem ???? There were no index marks on my gears. I set them by feel of the #1 cylinder valve overlap per the OH manual.
    First of all, set the idle mixture by allowing the engine to run 3 minutes, then pull the mixture to idle cut off (full lean) and watch the tach, you should get a 10-to-50 RPM rise as the engine dies, above 50 lean it, below 10 enrichen it. after that leave it alone.

    Next, when you have no timing marks. you must inspect for them prior to teardown, If you don't have any place #1 cylinder at TDC by the crank flange and mark the gears.

    So that has not been done, we are now guessing where the gear goes.
    To dial in the cam gear, you need two dial indicators, set them up on the two rocker arms to both valves in #1 cylinder turn the crank and watch the opening and closing of each valve, When #1 cylinder is at TDC on the compression stroke, the two valves should be midway between touching there respective cams. Both should be fully closed.
    To change the gear mesh, remove the crank gear, and rotate the cam, then replace the crank gear.

    Now that we've been thru that, answer this, is this engine making full power, as in does it make rated RPM static. If it does the gears are correct.

    If you wish to send me the cam gear I will place the correct timing mark on it.

    PM me for the address if interested.
    Last edited by Tom Downey; 05-20-2017 at 12:17 AM.

  2. #12

    Join Date
    May 2012
    Posts
    51

    Update

    I've run the engine with the idle mixture very lean (1/2 turn) and very rich (3 turns).No change. I did the gear meshing procedure during assembly. No dial indicators. I used my fingers to feel. It always came out within 1/2 tooth.

    NEW SUFF. Removed entire induction system and inspected. Installed new intake elbow gaskets. No change. Ran on a cool morning. The missing was worse, especially on RH mag (top plugs). Cyls 2 & 4 were the hottest. 1 & 3 were the coolest (not by much). Engine still runs fine above 1300 RPM. Have not run engine above 1700 RPM. Still feels like one cyl. just cuts out.
    Am going to try an old ign. harness on RH mag.
    Last edited by Eric Brown; 05-24-2017 at 09:10 PM.

  3. #13

    Join Date
    May 2012
    Posts
    51
    GENTLEMEN;
    This one is "kicking my butt". No progress. I removed the RH Bendix mag and installed a Slick 4001 with it own harness. No change. It's not mags, harness, plugs, carb. primer, induction leakage, or idle mixture. The only thing left is sticking valves and these are new Millinium cyl. assemblies. Any additional ideas ?????

  4. #14

    Join Date
    Nov 2011
    Location
    KDCU
    Posts
    252
    I know this sounds too basic.....but are you positive you aren't experiencing carb ice? The O-200 on my Fokker replica will ice like crazy while taxiing for the first take-off of the day (the carb is still cold). It will run rough up to about 1200rpm until carb heat is applied.
    Sam Buchanan
    EAA Technical Counselor
    The RV Journal RV-6 build log
    Fokker D.VII build log

  5. #15

    Join Date
    Aug 2013
    Location
    Gwinn, Michigan
    Posts
    97
    I would go with possible carburetor problem and ask, was it overhauled by aviation carb overhaul shop or someone local ? I have seen some bad ones done by people who don t do it completely. Also, if it has new one piece venturii, was the "flash" left by manufacturing process cleaned off before installation ? Just listing some of the things I have seen over the years. Also, was new gasket installed between carb and intake mount ?

    Bill L

  6. #16

    Join Date
    Jul 2011
    Posts
    1,832
    Bill L. you may have missed it but Eric wrote that he had tried an entirely different carb on the engine and no improvement, same as he tried other plugs, other mag , other harness. etc.

  7. #17

    Join Date
    Jul 2011
    Posts
    1,832
    Eric, when you tried the new mag was it with an whole new cap and harness? Caps can have fine cracks.

    And since we are at the Ouiji board stage, are you sure the engine is missing and not just a vibration. I once in flight lost an entire cylinder on at 4 cylinder 0360 in a Mooney and it was definterly rough no doubt about . Turns outh the OH had not secured the valve guide right and it worked its way out of the head and hammered both plug gaps closed.

    I once had what I thought was a miss on cliimb out in my TSIO 520 in Bonanza, just a slight rough, could see it in the magnetice compass rocking. All gauges normal , but with a passenger and rougher terrain ahead I returned to the ariport and took an airline. Didnt get attacked by thugs on the ariline and had the equivalent of a checkup and tuneup on the plane the next 2 days. No problem found. Came back to fly home and still the same, a very slight vibration, worse with more rpm. Decieded it was not a miss but a vibration and took it to the shop. And a simple answer was found, where the deice boots on the prop went into the hub, a small piece of rubber had come off, hard to see, and just enough to slightly unbalance prop. So small that putting one tie wrap on the base of the prop made it smooth again.

    The hard part on yours is clearing at 1200? Try that phone number I gave, supposed to be an expert on this engine.

  8. #18

    Join Date
    May 2012
    Posts
    51
    Gentlemen, I think this will be my FINAL REPORT.
    Took cold compression checks. All 77/80. Confirmed correct crank to cam gear indexing thru the RH mag mount hole. Reinstalled RH Bendix mag. Swapped spark pugs top to bottom. No change. Don't believe it is a vibration. It's scatter miss. Da......... da ......da..da..da...................da .......da.da.......... Shakes the airplane. Put the cowling on it and took to full power. Turns a smooth 2425 RPM with a Sensenich 6948 prop. I'm going to use it this way and see if it may improve (spook theory) over time. Figure to have the airplane back together and flying within 30 days.

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