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Thread: Cylinder replacement...... DANGER! DANGER!

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    Cylinder replacement...... DANGER! DANGER!

    I just read a popular aviation magazine article about replacing a cylinder/cylinders without a major or being on a stand, and it says that it is almost never done correctly, and it is mostly luck that a replaced cylinder doesn’t fail.

    Big question... Do you torque cylinder studs wet or dry?

    One thing the article didn’t cover is the percentage of failed replaced cylinders vs not replaced.

  2. #2
    wireweinie's Avatar
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    The torque is done wet or dry as spelled out in the maintenance manual.

    I think the author needs to come up here for a season or two and try to explain these claims. Apparently we are extremely lucky. Replacing a cylinder is just a maintenance item.

    Web
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    Quote Originally Posted by MoJo View Post
    I just read a popular aviation magazine article about replacing a cylinder/cylinders without a major or being on a stand, and it says that it is almost never done correctly, and it is mostly luck that a replaced cylinder doesn’t fail.

    Big question... Do you torque cylinder studs wet or dry?

    One thing the article didn’t cover is the percentage of failed replaced cylinders vs not replaced.
    Can you post a link this BS.
    Remember, These are the Good old Days!
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    Mike Busch? https://www.savvyaviation.com/wp-con...-be-afraid.pdf

    My last couple of cylinder repairs were for exhaust valves. After they were repaired we put them back on without honing and used the same rings. Worked great.
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    Richgj3's Avatar
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    It is Mike Busch. He’s been preaching this for years. He may have a point when it comes to the big Continental motors. It my short time in the Bonanza world there seem to be enough engine failures within 200 hours of cylinder replacement to get one thinking. I witnessed my ex partner top the engine in what’s now his Bonanza. He did it by the book and explained what mistakes are easy to make if someone is not educated or willing to learn.

    As far as small Continentals and all Lycomings , my opinion is Mr. Busch is over concerned.
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  6. #6

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    Sadly big Continentals have been plagued with bad cylinders for a long time so changing them and having subsequent failures may be attributed to bad cylinders. Once you get them fixed right they seem to work fine.
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    Richgj3's Avatar
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    The failures Mike Busch worries about are rods coming through the case due to improper torque and reuse of through stud nuts or even wrong nuts or one I personally saw, the special nuts installed upside down. That failure killed two people in a 210. Improper procedures can end up with a bearing spinning during or shortly after installation.

    I think when a competent mechanic does a top using proper new or serviceable parts and following the proper procedure, that would be a safe engine to fly.
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  8. #8
    wireweinie's Avatar
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    This article is a load of crap. He says not to blame the mechanic for cylinder failure then lists all the stuff the mechanic does/doesn't do that causes the failure. The long and short of this is that cylinder replacement is an unfortunate maintenance item. When the cylinder is determined to have 'failed', there are manufacturer's instructions on how to remove and then replace it. There are also manufacturer's instructions on how to determine if a replacement cylinder is serviceable (whether new or overhauled).

    If a cylinder fails due to engineering or metalurgical issues, this is not the fault of the mechanic or operator. If the cylinder fails due to not following the instructions in the manual, THAT is the fault of the mechanic. Items such as improper torque procedures or not replacing any mandatory replacement items is squarely the fault of the mechanic.

    Any one of us authorized to do maintenance (even you pilots are authorized certain maintenance items) take on the responsibility of performing all such operations correctly. We are even bound by regulation to use the correct manuals/information that is available. While we may raise issue with what may seem to be improper maintenance instructions, we must rely on the proper manuals to perform all maintenance.

    To sum it up, 'do the job'. If you replace a cylinder, do it per the appropriate instructions. EACH and EVERY instruction. If you do that, the cylinder will be just fine.

    Web
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    Yep, same author, but in AOPA mag. Very similar article, but no reference to engine size.
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    mvivion's Avatar
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    Yeah, Mike Busch, the self proclaimed "expert on aircraft maintenance" who has very little actual maintenance experience.....?

    He reads a lot, then writes and presents.....

    I've posted this before, but on the large Continentals we ran in Cessnas, specifically on floats, which is not kind to engines, when our maintenance folks started using only new cylinders, most of our cylinder "failures" went away. Buy junk cylinders that've gone through ten or fifteen runs and you may be buying someone else's mistakes.

    But, failures due to mechanics not installing "right".....seriously?

    MTV

  11. #11

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    Rich, Nobody touches rod nuts during a top. I don't get that one. But I don't get most of what that article says.
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    Richgj3's Avatar
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    Stewart,
    I wasn’t referring to rod nuts. Sorry I see that I wasn’t being clear. Some failures I’m familiar with, two actually, were determined to be rod failures due to bearings spinning and then those bearings not being lubricated properly. The primary cause was determined to be improper cylinder replacement allowing the case halves to shift subsequent to the work. Generally goes back to improper torque and/or procedure.
    I am not an A&P but spent a lot of time with my ex partner who is and also an IA and DAR discussing these issues before he topped our IO-520.
    I totally agree with Web. A competent mechanic using proper tools, parts and manuals would not scare me. The guy who changes one cylinder on his IO-520 and fails to torque the through stud nuts from both sides with two torque wrenches is asking for a catastrophic engine failure down the line. For example.

    Rich
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    jnorris's Avatar
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    Well, I've read enough of Mike's stuff, and talked to him enough, to only take his articles with the appropriate grain of salt. He makes some good points sometimes, but my own experience has led me to not always agree with his conclusions. His main mission is selling his services, so like any salesman's claims, one must trust but verify.
    Joe

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  14. #14
    mike mcs repair's Avatar
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    just because you buy a factory engine don't mean crap....

    seen one continental with a through bolt laying in cowling after flight from anchorage area to naknek.. with maybe 3 or 4 hours on it....
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  15. #15
    mike mcs repair's Avatar
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    Cylinder replacement—and especially
    replacement of multiple cylinders at once— is a procedure that needs to be executed perfectly.
    pretty much anything we do needs to be done perfectly......

    crazy article....
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    Quote Originally Posted by wireweinie View Post
    The torque is done wet or dry as spelled out in the maintenance manual.

    I think the author needs to come up here for a season or two and try to explain these claims. Apparently we are extremely lucky. Replacing a cylinder is just a maintenance item.

    Web
    Good answer, and what I always thought, but I’m not an A&P, and this article left me wondering if I would ever want a cylinder pulled for a pre-buy for instance.
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    It's a miracle airplanes were able to stay in the air before Mike Busch and Tempest spark plugs came along.
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  18. #18
    mike mcs repair's Avatar
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    Quote Originally Posted by Wingwrench View Post
    It's a miracle airplanes were able to stay in the air before Mike Busch and Tempest spark plugs came along.
    Wingwrench for the win!!!


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  19. #19

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    I wondered what kind of response this one would get. I only do small Continentals, and most of those on Cubs do not have through bolts. We have a 90 going together next week - I will suggest the double torque wrench idea.

    I often fix exhaust valves without honing - only thing I do is check valve lash, if it is a different cylinder. Never a problem.

  20. #20

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    Has anyone actually seen a maintenance entry signed by Mike Busch?
    You can't get there from here. You have to go over yonder and start from there.

  21. #21
    Steve Pierce's Avatar
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    Mike Busch has signed one log book in his life, his own. He started touting his stuff on Facebook a few years ago. He doesn't do as well in an open forum with a lot of mechanics with years of real world experience. Now all he posts are funny mems and links to his old articles. Like Joe posted, he is a salesman selling his service of over seeing the maintenance of your aircraft.
    Steve Pierce

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    we got that in the ag world also, all the grain experts have never sat in a combine or know which end the grain goes in. or a nickels worth of anything depends on there expertise. this spark plug deal makes me think about beef, we have to take all these beef quality assurance and packer assurance tests here in the u. s. and all these experts write articles on how this works, yet they import hundreds of thousands of lbs from 3rd world countrys were most dont even know how to use a pencil. moral of the story, its just the way news is today, use to get opinons on both sides of a story, now its just one side and you have to decide if you want to believe it or not. no big shake.
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  23. #23

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    one thing ive done right or wrong is retorque the cylinder nuts after 50-100 hrs when it works out, if this is right or wrong i dont know but i do it on the very few times ive messed with cylinders. just to check. is this a good thing?
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  24. #24

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    So What is his recommendation on big bore Continentals, factory reman when the first cylinder is due... got to wonder just how marketable a 800-900 hour TBO engine will be?
    Last edited by OLDCROWE; 02-24-2020 at 02:41 PM.
    Remember, These are the Good old Days!
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    Quote Originally Posted by tempdoug View Post
    one thing ive done right or wrong is retorque the cylinder nuts after 50-100 hrs when it works out, if this is right or wrong i dont know but i do it on the very few times ive messed with cylinders. just to check. is this a good thing?
    I’m not an A&P, but I have wondered if there would be anything wrong with that?

    I noticed that all my cylinder studs have a red mark to ensure no loosening has occurred.

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    Quote Originally Posted by tempdoug View Post
    one thing ive done right or wrong is retorque the cylinder nuts after 50-100 hrs when it works out, if this is right or wrong i dont know but i do it on the very few times ive messed with cylinders. just to check. is this a good thing?
    I personally see nothing wrong with doing that.
    It is not uncommon for a stud or long bolt to have some twist develop in them during the torquing process. Kind of why Lycoming calls for torquing both ends of a through stud.
    Before the advent of modern stretch to yield fasteners in more modern industries which might get discovered in the airplane industry in a few decades it was a common practice to come back and give one more pull to check that the torque has not backed off on bolts or studs.

    One thing to consider is after, say 100hrs is there is no longer and lubricant on the threads. I would go back to the fasteners much earlier, like the next few days being before the engine goes back in service.
    I will add that if 50hrs later you go for a check and find a fastener that needed a turn, I would try to find out why as well as to be grateful you found it.
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  27. #27

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    Quote Originally Posted by MoJo View Post
    I noticed that all my cylinder studs have a red mark to ensure no loosening has occurred.
    Common misconception. That is NOT what that torque seal lacquer is for. That putty is to be referenced only during installation so the assembler can keep track of what items have been torqued, and which have not. Once the engine is returned to service the paint marks are irrelevant and should not be relied upon for operational inspections.

    I have seen many newbies and homebuilders use inspection putty like drunken sailors for what could only be cosmetic reasons. They interpret these lacquer dots as a professional look rather than the place mark tools they are designed to be.
    Last edited by jliltd; 02-24-2020 at 01:41 PM.
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    Quote Originally Posted by tempdoug View Post
    one thing ive done right or wrong is retorque the cylinder nuts after 50-100 hrs when it works out, if this is right or wrong i dont know but i do it on the very few times ive messed with cylinders. just to check. is this a good thing?
    The proper way is to retorque about 24 hours after the initial torque. This is clock time, not engine operation! Torque it today, and then retorque tomorrow! It is surprising how much the case and studs relieve overnight and the nuts loosen.


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    Is that general practice? There's nothing in my Lycoming overhaul/maintenance manual that says to re-torque after initial assembly.

  31. #31
    Gordon Misch's Avatar
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    It doesn't seem like any of the metal parts would creep, but seems reasonable that gaskets and sealants could.
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  32. #32

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    Yeah, sealants. I re-torque after several heat cycles.

  33. #33

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    Consider the through studs as a torsion bar. The nut on each end has a fair bit of friction such that when it is turned it can impose a twist on the stud itself. There are plenty of considerations as to how much twist such as lubricity, speed of rotation and such.
    Now there are forces acting that try to unwind the bolt/ stud. Again the lubrication on the fastener can allow a slow creep for the torsion to relieve itself. How much, it might not be more then a few degrees, might be a fair bit more than that.

    Some say to just give some force back on a fastener.
    And there are plenty of reasons to back it off a touch and bring it back to final torque.

    There is a school of thought to over torque everything a little bit and it will settle back to what it should be. They do not have any understanding of elastic structures and that little bit of "over torque" might well bring something to it's yield point.
    Be this to stretch the stud or bolt, shear the threads some small amount.
    Yield the lubricant be it the plating on the fastener, a liquid lubricant or other resulting in microwelding the mating surfaces. Call that galling should you choose.
    Just a lubricant failure can result in a rise in friction resulting in false torque readings.

    I tended to wander about there but each time I read about through studs being under torqued resulting in a bearing shell moving followed by a connecting rod failure.
    The through studs need to be torqued from each end which has to do with a balance of friction and twist in the fastener.
    Going back to these the next day is a good thing.

    Decades back a cylinder came off a Cherokee down Georgia way. It was discovered the engine case had been painted before assembly, they painted the mounting faces. The paint warmed up and "Cold flowed" from under the cylinders resulting in the fasteners being under torqued.
    Nothing good came from that.
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  34. #34

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    I'm not buying it. If I stage torque the bolts in sequence as directed in the overhaul manual there's no threat of sealants settling. We're talking about a thin coating of Hylomar and two silk threads. Nothing in the manual specifies or even suggests re-torquing once the sequential torquing is complete. With that I believe the manufacturer has provided adequate torque procedures to accomplish the task. The manual has procedures for changing cylinders, too, FWIW.
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  35. #35
    BC12D-4-85's Avatar
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    Here's a question. I've had a few engines overhauled and some have required more machining to correct crankcase fretting and crank/cam bore wear. I've assumed that it was normal. Is it related to change in fastener torque over time or do they all just do that?

    Gary

  36. #36
    nanook's Avatar
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    Torquing a through bolt from both ends at the same time is not some new revelation. The Lycoming Engine School that I attended in the mid 80s, was very adamant about following the proper torquing technique and sequence, when replacing a cylinder. We replaced 100s of cylinders on Part 135 operation aircraft. There was no mandatory re-torquing of cylinders. P&W had an AD on some of their radial engines, to check for loose cylinder base nuts, that is a different animal though. Sounds like they are turning loose A&Ps, that don’t have the needed training or knowledge about changing cylinders...

  37. #37

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    Gary
    That is an issue up in Alaska, I am not aware of anyone in the state that decks and line bores case. So now you need to pay several hundred in shipping to get the work done. It is not cheap but neither is have to redo a bottom end that someone just slapped back together.

    Some advice to tighten until you feel the threads strip then go 1/4 turn. I would say do what the book says and agree if you go back 24hrs latter and retorque you will find some that move a bit. Also like to go over pan bolts after 50-100 hours, that does require a calibrated wrist because no way are you getting a torque wrench on most of them once everything else is in place.
    DENNY
    Last edited by DENNY; 02-24-2020 at 04:21 PM.
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  38. #38
    SuperCub MD's Avatar
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    Quote Originally Posted by DENNY View Post
    Gary


    Some advice to tighten until you feel the threads strip then go 1/4 turn.
    DENNY
    Please tell me I'm reading that wrong.

  39. #39
    wireweinie's Avatar
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    Quote Originally Posted by SuperCub MD View Post
    Please tell me I'm reading that wrong.
    My dad told me that when working on tractors, lol.

    Web
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  40. #40

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    Quote Originally Posted by Gordon Misch View Post
    It doesn't seem like any of the metal parts would creep, but seems reasonable that gaskets and sealants could.
    If you have never had the “privilege” of machining a “green” casting, you can’t appreciate how much metal moves when stresses are either applied or removed. We used to burry castings in the yard for a year before machining to allow the stresses to work out. I’ve had castings move as much as .050 within minutes of machining to tolerance.

    In addition to the internal stresses of the case and thru studs, you also have the sealant on the parting surface extruding, and the cylinder base o rings compressing. Lots going on in those first hours after torquing those nuts.


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