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Thread: Popping sound.

  1. #1
    n40ff's Avatar
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    Popping sound.

    Don't know what's going on with the Spezio/O290? I've noticed an occasional "popping" sound, like someone lightly tapping on maybe the exhaust pipe(or something else) with a ball peen hammer, while taxing in for some time. Only a few times in a minute or two...... Today it was constant after leveling off in cruise. Seemed slightly worse when leaned. I turned around and went back, total flight only 5 minutes.

    Back round. Haven't managed to fly much, maybe a half hour once a week just to get the oil temp 180+ for 10-15 min. This flight only got oil up to 150F. I did a compression check and wasn't surprised they were only 64, 74, 64 and 7o/80. Was expecting one would be worse...... One mag. was missing slightly too, will check that out. I came home, hurting, sweating and riding bike wanted to get home before the sun went down, hate cold in my old age.

    Any ideas? Got me spooked, WILL cure it! Might be the mag? I admit since I've only flown it 10-15 hours/year while flying the AD2, I haven't had the mags off in a couple years....they are coming off(bitch w/9" mount) 24" Acroduster 2 mount had me spoiled. Oh well

    Thanks,

    Jack

    PS can someone give me details on the "rope trick" to hold valves so I can remove valve springs for inspection.
    Last edited by n40ff; 05-17-2019 at 08:39 AM.
    Thanks windy thanked for this post

  2. #2
    www.SkupTech.com mike mcs repair's Avatar
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    Intake leak. Probably at cylinder where intake tube attaches. Gasket will crack an sometimes blow out. Also the tubes coming out of sump can get loose on some models. Don’t remember what style yours would be. Also the rubber hoses. Also make sure carb is tight. Gasket good. Also check muffler core just to be safe not that I think that would cause the lean.


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  3. #3
    Rick Papp's Avatar
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    Also check your primer lines. A small leak can cause a cylinder to run rich also.
    Never stay level!!!!!
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  4. #4
    n40ff's Avatar
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    May be an exhaust leak, really managed to blow the blow proof gasket? But intakes are problematic. #3 is custom made to fit "whatever" sump was used in the 'G" conversion and doesn't line-up exactly but don't think it was leaking? I'm going to do the annual a month early and IRAN the engine. Thanks
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  5. #5
    wireweinie's Avatar
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    The rope trick is no trick at all. Find a length of clean rope and position the piston at BDC with the plugs removed. Start feeding the rope into one spark plug hole until you get enough to put pressure on the valve faces, when you bring the piston towards TDC (compression stroke so both valves stay closed). When you remove the valve springs, the rope will hold the valves in place until you re install the springs/keepers.

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  6. #6
    txpacer's Avatar
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    The trick is getting the valves back in after you ream the guides. The more you do it, the easier it gets.

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    Could it be something else loose? At certain rpms our poorly mounted J3 compass can set up a real racket. Having only one ear, I had no idea where the noise was coming from. Grab the compass and it stops.

    Fix it? Nah - compass is useless. I never get out of the pattern.

    If it is intermittent, I would look somewhere other than the exhaust.

  8. #8
    skukum12's Avatar
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    My O320 was popping because it was lean. The intake tubes going into the sump get loose over time. Had an engine guy re-swage (correct term?) the tubes into the sump. Problem solved.
    "Always looking up"
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  9. #9
    skywagon8a's Avatar
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    Quote Originally Posted by Rick Papp View Post
    Also check your primer lines. A small leak can cause a cylinder to run rich also.
    A leaking primer can cause rich running.
    If the primer lines have a small leak with the primer locked, the engine will suck in air through the leak causing a lean mixture. Lean mixtures cause popping sounds.

    A loose clamp somewhere hitting on something (like the engine mount) will cause the same type of sounds. If it is a loose clamp, it is possible that it has been rotating slowly. Which could explain it at first being occasional then becoming more noticeable.

    I would check the spark plugs before digging into the mag for the miss.
    N1PA
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  10. #10

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    Quote Originally Posted by n40ff View Post
    May be an exhaust leak, really managed to blow the blow proof gasket? But intakes are problematic. #3 is custom made to fit "whatever" sump was used in the 'G" conversion and doesn't line-up exactly but don't think it was leaking? I'm going to do the annual a month early and IRAN the engine. Thanks
    On an O200 when the intake elbow worked loose one edge of the gasket got sucked in. very hard to see. Wasn't found until stripping the cylinder to pull it off.
    You can't get there from here. You have to go over yonder and start from there.
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  11. #11
    n40ff's Avatar
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    Primer is another possible issue. I did notice it wasn't working as well as usual on the last flight. I recall the J5A I use to fly had issues before I started flying it. Carb. was rebuilt twice and it still ran rough. I noticed the primer wasn't working and "fixed" it with a dab of EZ Turn on the primer seal. I also broke an exhaust stud so that cylinder will have to come off. Oh well.

    Thanks Guys, you never fail to provide......

    Jack
    Last edited by n40ff; 05-18-2019 at 06:42 AM.
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  12. #12
    hotrod180's Avatar
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    Quote Originally Posted by txpacer View Post
    The trick is getting the valves back in after you ream the guides. The more you do it, the easier it gets.
    What I've done is to tie a piece of dental floss to the valve at the keeper groove.
    After pushing (drifting?) the valve out, use a hook of safety wire to pull the floss out of the spark plug hole so you can ream the guide.
    Then use the hook to fish the floss back up through the guide.
    Makes it a little easier to get the valve stem lined up and started.
    Cessna Skywagon-- accept no substitute!

  13. #13

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    A friend recently had a noise that sounded like two pieces of metal tapping. It was a broken engine mount tube, two pieces of metal tapping.
    Easy to overlook, but easy to fix.
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  14. #14
    n40ff's Avatar
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    Primer may be the issue. Been there/done that but overlooked it this time....... Worked almost 3 hours on the broken stud which is hard as glass. I've drilled and gotten them out several times but managed to break a drill off. Almost enough to try to weld a nut on but I don't want to screw it up so I'll take it to a shop to EDM it out. At least the cam looks good.


    Don't need the rope trick this time. I've been running a mix of auto/100LL plus MMO and hope to avoid valve issues.
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  15. #15
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by n40ff View Post
    ..but I don't want to screw it up so I'll take it to a shop to EDM it out.
    FYI for those who don't know what EDM is... some videos... MAYBE, just Maybe I'll get around to finishing my homemade one this year....

    videos explaining what EDM is and why you need it....







    more videos on his channel... https://www.youtube.com/user/JerrysBrokenTap

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    Quote Originally Posted by skukum12 View Post
    My O320 was popping because it was lean. The intake tubes going into the sump get loose over time. Had an engine guy re-swage (correct term?) the tubes into the sump. Problem solved.
    I have found that if I use a .4995" unpiloted reamer, I can pust the valve until it almost falls out and ream. There is never any build up at the inboard side of the valve so no real value in pushing the valve all the way out. Sometimes I can get the valves right back in, others have taken me an hour!

  17. #17
    n40ff's Avatar
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    Thanks for the EDM post. I know of it but have never had it done before. There are a couple shops with it near here.

  18. #18
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    Wrong-No EDM shops around here so did it the old way. Ordered a solid carbide drill that will bore through almost anything..It ate that broken drill like butter. Spent all day Fri. getting it back together having fixed everything I could think of. Nothing really obvious on induction side but doesn't take much.......New intake hoses really nice and much more pliable so should cure slight miss alignment on #3. Thought about robbing intake from my old O235 but it's back behind the AD2 and it was so windy I couldn't open my hangar doors to move stuff out and get engine hoist back there(I don't think the AD2 would do well on 108 HP) Too windy and too tired to try it out but looks like a great day today at least early on...Onward and upward.

    A friend called last night wanting help with broken stud on his PA22....Oh well

    Jack

    PS, on 2nd though I think the sump is different/odd on my O290 and the O235 tube wouldn't work anyway?

    Oh yea....local gas station was out of gas and my truck was running on fumes so I drove the 86 Z28 looking for EDM shop etc. Tues. It quit on me...$125 tow but at least have road service insurance. Of coarse it quit in the worst spot between here and Cumberland so I managed to piss off about 100 people... Narrow road, blind curve, RR yard on one side with retaining wall/ cliff/river on other side...I almost took a high dive. Cop showed-up and sat behind me in AC car while I directed traffic. I pissed him off too when I asked if he wanted me to have coffee delivered. He asked to see my DL and noticed my WV CCW(I was in Md.) He asked if I was carrying a gun and I think considered a search. I wasn't, am careful NOT to carry in Md. !!
    Last edited by n40ff; 05-25-2019 at 05:49 AM.

  19. #19

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    Quote Originally Posted by n40ff View Post
    Wrong-No EDM shops around here so did it the old way. Ordered a solid carbide drill that will bore through almost anything..It ate that broken drill like butter. Spent all day Fri. getting it back together having fixed everything I could think of. Nothing really obvious on induction side but doesn't take much.......New intake hoses really nice and much more pliable so should cure slight miss alignment on #3. Thought about robbing intake from my old O235 but it's back behind the AD2 and it was so windy I couldn't open my hangar doors to move stuff out and get engine hoist back there(I don't think the AD2 would do well on 108 HP) Too windy and too tired to try it out but looks like a great day today at least early on...Onward and upward.

    A friend called last night wanting help with broken stud on his PA22....Oh well

    Jack

    PS, on 2nd though I think the sump is different/odd on my O290 and the O235 tube wouldn't work anyway?

    Oh yea....local gas station was out of gas and my truck was running on fumes so I drove the 86 Z28 looking for EDM shop etc. Tues. It quit on me...$125 tow but at least have road service insurance. Of coarse it quit in the worst spot between here and Cumberland so I managed to piss off about 100 people... Narrow road, blind curve, RR yard on one side with retaining wall/ cliff/river on other side...I almost took a high dive. Cop showed-up and sat behind me in AC car while I directed traffic. I pissed him off too when I asked if he wanted me to have coffee delivered. He asked to see my DL and noticed my WV CCW(I was in Md.) He asked if I was carrying a gun and I think considered a search. I wasn't, am careful NOT to carry in Md. !!
    By all means, don’t carry in the communist republic of Maryland!


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  20. #20
    n40ff's Avatar
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    For sure. I live in WV and airport is in Md. so when spending so many days with the airplane I'm effectively disarmed. I call it the "Peoples Republic of Merryland"

    Anyway the airplane is fixed, no more popping. Question. How exactly does the lean mixture cause a pop? I assume only one cylinder is overly lean and maybe the other cylinders are somehow driving something?

    Thanks guys, as usual a ton of help

    Jack

  21. #21
    BC12D-4-85's Avatar
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    Quote Originally Posted by n40ff View Post
    ...How exactly does the lean mixture cause a pop?...Jack
    Easy explanation...note Post#42 here for an example of one: http://www.supercub.org/forum/showth...creature/page2

    WV is removed from the ocean but those of us nearer the sea know that lean mixtures are slow to burn. Poor ignition or timing can also cause incomplete combustion. When the exhaust valve opens unburned air and fuel are expelled. That's noisy! If there's a source of air and ignition nearby (hot exhaust gas for example) the explosion can be formidable. Any kid with a match knows that.

    Gary

  22. #22
    n40ff's Avatar
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    I spent 40 years near the ocean and the last 20 in WV......I much prefer WV! Thanks

  23. #23
    BC12D-4-85's Avatar
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    There's some off humor mixed in but basically lean is a slow burn and can finish it's job outside the cylinders and pop. Enjoy the Memorial Day weekend.

    Gary

  24. #24
    n40ff's Avatar
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    I understand Gary When I moved to WV my best friend sent me 1001 WV jokes. Many have a basis in fact, some were pretty nasty.

    Regards,

    Jack

    PS that post #42 in the other thread does require eye wash

  25. #25
    BC12D-4-85's Avatar
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    I like motorcycles Jack and WV would be a great place to scoot and tour (https://visitwv.com/trip-tools/). I've come across lean run pop and other magic when changing exhaust systems and adding engine controllers that adjust fuel and timing. Mess with the factory setups and expect to have to deal with air-fuel-ignition. Reversion flow of exhaust pressure waves is another mystery that can be hard to mask or control for benefit (https://www.hotrod.com/articles/effe...iciency-power/). An exhaust tuned for aircraft rpm can be a benefit waiting to happen.

    Gary

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