Replacement Normally Aspirated Cylinder Discussion

Discussion in 'Maintenance Bay' started by MBDiagMan, Feb 8, 2021.

  1. Jdm

    Jdm Pre-takeoff checklist

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    I honestly don’t know why we even have a post office anymore. They are beyond worthless here. We go days without getting anything and then end up with a bunch of junk with half of it not even mine. I seldom check the mailbox anymore. I totally gave up after determining that my mail lady didn’t understand what the up/down flag logic means on the box. Very considering! Now I just play games with the damn flag and the post office too. I started returning all of the ‘no postage required” self return envelopes from my junk mail. Empty of course! I figure the post office could use the extra training and what better way to pay for it than from the annoying advertising companies. Hahahaha..
     
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  2. MBDiagMan

    MBDiagMan En-Route

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    There are 31,322 post offices in the United States. In my home town the office and the people in it are beyond incredible. The problem is that there 31,321 OTHER post offices, apparently many of them are much less than incredible. If they would just fire the management of the post office and put the crew from my home town in charge, they would have a chance.
     
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  3. Jdm

    Jdm Pre-takeoff checklist

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    Ha, I think the problem is a bit higher up than management. I have an incredibly bright friend who was in charge of the army post office while stationed in Korea. When he got out he expected and prepared himself to work for our civilian postal service. He figured he’d get in and work his way up to a high position. Nope. Not qualified. Sorry, and thank you for your interest. Wish you well in your endeavors! What a joke.
     
  4. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    USPS upper management has changed rural service such that what used to be me dropping a local letter in the box->postie picking it up and placing it in PO Box 302, about 15 feet away thus giving me Same Day Service, to:
    All mail is bagged and trucked 150 miles to a sorting station (aka damaging and losing station) then in a few days or even a week, the mail is then trucked 150 miles back to us and only then can the local postie go through this bag, find my letter and place it in PO Box 302.
     
  5. Scott MacMoyle

    Scott MacMoyle Pre-Flight

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    another vote for new lycoming cylinder kits
     
  6. MBDiagMan

    MBDiagMan En-Route

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    Okay all you aircraft engine builders, if you had no oil analysis to even give you a hint and you wanted to do exploratory surgery where would you start? Pull the cylinders? Is it possible that a cylinder is making the metal? One cylinder was removed for internal inspection about fifteen hours ago and everything looked fine.

    Would you send the prop Governor off for IRAN since it would need to be done at rebuild time anyway?
     
  7. Jdm

    Jdm Pre-takeoff checklist

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    Nope. While cylinders are still attached: I’d yank all spark plugs for a quick look inside. Then I’d pull all the rocker covers off all the cylinders. Then I’d inspect the rocker arms themselves. Then I’d yank the exhaust and intakes from all cylinders. Then I’d look inside those openings. Then I’d yank all the rocker arms off the cylinder heads for better inspection. Then I’d yank all the valve springs to inspect valve stems and valve movement. Then I’d yank push rods and push tubes. Then I’d look at lifters. Then maybe the cylinders.

    Sure, send the governor off while you’re at it, if you like
     
  8. RyanB

    RyanB Administrator Management Council Member PoA Supporter

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    Sounds like an awful lot of yanking!
     
  9. MBDiagMan

    MBDiagMan En-Route

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    Okay great! Now let’s say that after inspecting everything on the cylinders to include the cylinders removed and nothing is found wrong, what then? Split the case? Get an exchange engine? What are the chances the problem will be found somewhere in the cylinders?
     
  10. Jdm

    Jdm Pre-takeoff checklist

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    Almost all of that has to be yanked anyway to remove cylinders, which is what he’s considering
     
  11. Jdm

    Jdm Pre-takeoff checklist

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    Lot's of options here. If you’re going to send the prop governor off for OH anyway maybe go ahead and knock that out while looking at the previous items mentioned. At some point (assuming you find nothing in the meantime) you’re going to have to throw in the towel and bust into it deeper.
    Seems like I remember you saying it’s a high time engine or close to TBO maybe. If that’s indeed the case, I’d probably opt for a good overhaul from a reputable and recognizable overhaul shop using new lycoming cylinders. Just ship out the old engine. When it comes to this decision, I’m thinking quality first, but also aircraft value, and resale. It costs a lot for a teardown-inspect-rebuild. I’d be more likely to add this expense into my airplane by way of an overhaul. Again, there’s a lot of options. Another thing I’d do, considering you choose to overhaul or replace, is knock out the eng mount and all accessories while I’m at it, but that just me. In regards to the mount, I suggest sending it off to have it blasted, inspected and overhauled. It’s well worth the money to get this right while you’re at it. I’d go with new ignition harnesses.The other components can be overhauled.
     
  12. MBDiagMan

    MBDiagMan En-Route

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    It is 1100 hours SMOH.
     
  13. Jdm

    Jdm Pre-takeoff checklist

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    How many years SMOH? Lycoming recommends 12yrs or 2k hours for the TBO. Who did the last overhaul? Surly they have a vested interest in seeing their engines make it to TBO.

    As far as 1100 hours goes, that is a tough one. You’re sorta at the point that either way makes sense. Tearing down-inspecting-repairing-reassemble, vs a full up overhaul.
     
  14. Magman

    Magman Pre-takeoff checklist

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    I would stop and regroup.

    Maybe I missed it but I don’t think the Alloy was ever determined.

    I don’t believe SOAP will tell you that.

    Chip Analysis may.

    As I said there are folks that can identify the Alloy can possible sources on your

    Engine.

    The manufacturer often will assist on this.

    Iron or Aluminum is not enough.

    A metallurgist could possibly be helpful.

    Applying various acids to the chips will cause different reactions.

    An example is sulphuric acid ( I think) will cause visual differences between

    4130 steel and 1020 steel.

    If you KNOW the Alloy and KNOW possible sources you then KNOW where to look.


    It is entirely possible that it is not a current problem.

    The present evidence may be from an event of long ago.



    I met an O-200 that had what appeared as a slight bronze mist on the

    Pressure Screen.

    All 4 Rocker Covers had the same sheen.

    Accessories were removed and nothing found.

    Pulling the Sump showed more very fine bronze particles.

    The Vacuum Pump drive has a large bronze bearing that is often overlooked at

    O/H but did not show abnormal wear when removed.

    Could it be Rod or Main Bearings?



    About this time we went back though the Engine Log.

    It revealed that the Key Start Starter Clutch had been replaced about 400 hrs ago.

    No other details.

    Contacting the folks that rebuild them resulted in knowing that the Clutch

    was a possible source of the bronze “ film”.

    All components were throughly cleaned and reassembled.

    After some ground runs the Screen and Rocker Covers were removed and looked

    much better.

    After more ground runs and checking and cleaning the aircraft flew in the pattern

    for some time.

    The metallic sheen finally completely disappeared.

    After a couple hundred hours my thought is it was the Clutch.


    There are places in an Engine that may hold particles for some time and eventually

    release them.

    The O -200 has a welded seam along the bottom that provides a home

    for particles.

    It’s not that easy to clean even with it removed,


    So cylinder or accessory changes from a while back may present much later

    even if they are not a factor.
     
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  15. MBDiagMan

    MBDiagMan En-Route

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    We’ve been snowed in all week and I will be out of town most of the week. If there is no analysis results by the end of this coming week, I will have to get started. I think the first thing I will do is send off the prop Governor and get that going. Then start pulling apart and removing the cylinders, starting with number three because it is the one that ran hot. If that doesn’t reveal anything, I guess we’ll split it.

    I will have to look in the logs to answer the calendar time question.
     
  16. Magman

    Magman Pre-takeoff checklist

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    Most cylinder problems can be identified via borescope or compression check.

    Wet piston tops or fouled lower plugs is another.

    I don’t think you stated a particular cylinder .

    Sorry if I missed it.

    Consider pulling the Sump first.

    You may find sufficient metal to identify the source.
     
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  17. Jdm

    Jdm Pre-takeoff checklist

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    A compression check is only a small piece of the cylinder inspection. It doesn’t always identify a problem, even when one is there. Usually it does, but not always. I’ve had bad cylinders assemblies pass a compression check perfectly.
    I do like the idea of stopping and regrouping. That’s never a bad move. It’s easy to overlook the obvious. Sometimes stepping back and getting a second opinion is beneficial.
     
  18. MBDiagMan

    MBDiagMan En-Route

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    There are no symptoms of cylinder problems. The only negative symptom of any kind is that it is making metal. This engine starts immediately, runs like a purring kitten, makes good power, holds very good and very consistent oil pressure and temperature. The only malady in its recent history, other than making metal, was a hot number three cylinder for a while and then cooled off and ran normally.

    I do believe that in the aviation world there is often the idea that if compressions are good the engine is healthy. There are other parts of an engine that can cause havoc or make you look for a clear, flat area to glide it down to.
     
  19. Magman

    Magman Pre-takeoff checklist

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    My belief is that you should pursue type of alloy and source.

    I’ve found metal from someone that must have thought a box wrench was better

    than a Socket for Spark Plugs.

    The Crushed Pushrod Shroud scraped quite a bit of metal from the Pushrod.

    Hope you could find a culprit like this before a complete tear down.


    Lycoming Customer Service has had some good people there over the years.

    They seem to favor dealing with the Owner ( they buy Engines) rather than a Tech.

    Pieces of metal on masking tape could lead you in the right direction.
     
  20. MBDiagMan

    MBDiagMan En-Route

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    Got the oil analysis today. It shows high iron which they say could be cylinders or rotating shafts. We’re going to pull the cylinders beginning with number three which was the hot one. Also gonna send the prop Governor for IRAN. With the oil pressure and temperature being so steady plus the fact it’s at 1,100 hours, we just can’t imagine the bottom end being the problem. My mechanic and I are on the same page.
     
  21. Jdm

    Jdm Pre-takeoff checklist

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    Ha, cylinders, or rotating shaft. That really narrows it down:) Sorry, I kinda had to say that.
    Glad you finally got it back!

    I do like the way your tackling this, but I wouldn’t be so quick to yank cylinders. There are a number of cylinder related issues that can be checked prior to removal of the cylinder.
     
    Last edited: Feb 23, 2021
  22. MBDiagMan

    MBDiagMan En-Route

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    Yes, we will start by pulling the valve covers and just keep peeling the onion from there.
     
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  23. thomasdr72

    thomasdr72 Pre-takeoff checklist

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    What's your operating history? I've seen plenty of engines that only get run occasionally and then will have high iron content from being in a fairly corrosive environment (Florida) and sitting idle for a week or two between flights. I'd be hesitant to split the case if all of your other parameters are acceptable. Good oil pressure/operating temps/compression/throttle response/passes static rpm checks/etc... Like many have said previously, "making metal" isn't the whole story... It's a scary term, and definitely a cause for caution--but not necessarily the end of the story.
     
  24. MBDiagMan

    MBDiagMan En-Route

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    This engine has indeed lived through a few periods of non use. I don’t concern myself as much with iron in the oil analysis as I do with metal in the filter. I really believe we will find something in the course of disassembling and removing the cylinders.
     
  25. thomasdr72

    thomasdr72 Pre-takeoff checklist

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    As owner/operator, definitely your call on what you want to have done... I remember the first oil change on our bird after purchase was a bit unsettling with a fair amount of ferrous "sludge" on the oil filter magnet. But no recognizable flakes and no other debris in the filter paper or elsewhere. Fifty hours and six months later, both the filter and the magnet were pristine, and I'd say we had added less than 3 quarts of oil in that 50 hrs. Compressions at last annual were better than ever, and life is good. Our bird had only 400hrs, but nearly 15 years TSMOH (Conti IO-470S). I attribute the ferrous sludge to minor surface corrosion on cylinder walls from disuse. Now it runs better than ever, and I've flown the bird nearly 20 hours in the last month...

    Working on previous birds, I wouldn't be nearly as confident with a Lyc. I've seen too many of them eat a cam lobe/tappet, even had one eat a piston on a maintenance test flight on me once...

    V/r,

    -Dana
     
  26. MBDiagMan

    MBDiagMan En-Route

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    Okay, exploratory surgery has uncovered a source of metal and in all likelihood THE source of metal. One cam lobe is pretty much gone and the lifter on that lobe beat up severely. Cylinders look really good as does everything else we’ve looked at.

    The plan is to IRAN the cylinders, split the case with intention of replacing cam, lifters and main bearings. We’ll see what we find when we split the case.
     
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  27. Jdm

    Jdm Pre-takeoff checklist

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    That’ll do it! Good job of getting to the bottom of it. So with that your not going to send it off to an overhaul shop?
     
  28. Scott MacMoyle

    Scott MacMoyle Pre-Flight

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    I had the exact same problem on my O 360. Just one lobe and lifter on a 1500 hour TT engine. I sent it off to Pen Yan and grit my teeth, You can repair it but I would suggest a new cam not a reground one. You dont want to go back in there anytime soon.
     
  29. MBDiagMan

    MBDiagMan En-Route

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    Unless we find something unexpected when we split it, we are planning on new cam, lifters, bearings and back together with it.
     
  30. Jdm

    Jdm Pre-takeoff checklist

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    I guess pulling the push rods and lifters was not such a bad idea after all:) Glade someone thought of that, hehe.

    So what exactly do they think caused that cam lobe to wear down? Stuck lifter maybe? We just had that issue on a O360 recently but it was caught before any damage occurred.
     
  31. MBDiagMan

    MBDiagMan En-Route

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    Yes, your idea of exploratory surgery was the right prescription and I appreciate it. My mechanic wasn’t ready to do much of anything until we got oil analysis. After that we talked and he agreed that with the engine running so well it just couldn’t be the bottom end and agreed to pull the valve covers and keep peeling it apart. That is what led us here.

    I guess it is worthwhile to explain that I have lots of automotive engine experience although it wasn’t my lifetimes work. I grew up in my dads independent auto repair shop in the days when in frame overhauls and valve jobs were common. I point this out because I am not someone who is not able to understand engine issues. My mechanic ran a multiple aircraft crop dusting service as well as aircraft service work for many years. His hangar is straight across a very wide taxiway between his hangar and mine. He has done every different type of work on aircraft engines, both radial and opposed for probably fifty years. He has two mechanics, one almost as experienced as himself and the other a sharp young apprentice. I get to see progress and participate in decisions as we go. I have a lot of confidence in this shop.
     
    Last edited: Mar 6, 2021
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  32. MBDiagMan

    MBDiagMan En-Route

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    In my research, it appears that is much more important to use new lifters from Lycoming than it is to use a new cam. In my case I will buy both new from Lycoming, but new lifters now have a coating called DLC that prevents the corrosion that leads to this destruction. Corrosion results in small pock marks that start tearing out like chunks out of a pothole. This is why allowing a high cam Lycoming to sit long enough for the oil film to run off of it results in this destruction.
     
    Last edited: Mar 7, 2021
  33. Jdm

    Jdm Pre-takeoff checklist

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    Good info right there. Glad to see Lycoming addressing the corroded lifter situation. It’s caused a lot of problems recently! It can cause slight a hesitation when advancing RPM through about 1400RPM. That’s what lead us to finding a couple of frozen lifters. Luckily we caught it in time. Good decision going with Lycoming new.

    Did you happen to notice a very slight hesitation as the throttle advances through about 1400?
     
  34. Dan Thomas

    Dan Thomas Final Approach

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    That corrosion is less due to the oil running off the cam than to ground-running the engine and then putting the airplane away. Ground-running lets a lot of blowby gases get past the large clearances in cold cylinders, and the blowby includes water vapor that then condenses in the case. As the engine cools that condensation affect the cylinders, cam, and a lot of other stuff. The engine needs to be flown for an hour or left alone altogether. Nothing else will drive out the moisture faster than a hot crankcase kept hot for a while, and ground-running it will not achieve that.

    The other factor in cam wear is the oil. The Lycoming O-320-H2AD engines must, by airworthiness directive, use a specified oil additive that prevents scuffing of the cam and lifters that causes that wear. The other engines also benefit from it, and Shell's 15W50 has that additive in it. We used the 15W50 in all our flight-school Lycomings and had no cam issues whatever. In the early days of the school they used other oils, including Ram aviation oil, and they had cam problems. That cam/lifter interface is the most highly loaded spot in the entire engine and it needs good lubrication all the time. A cold engine at low idle doesn't fling enough oil up onto that cam, either, so preheat and then idle a little higher once it's started and the oil pressure is up.

    Lycoming went to roller lifters and a matching cam around 15 years ago to stop the cam wear issues. It works well.
     
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  35. mondtster

    mondtster En-Route

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    I believe the high loads on the cam/lifter interface plus the oil selection and lube system design cause more of the problems than anything else. I’ve torn down engines that have sat in unfavorable conditions for extended periods of time, fully expecting the cam and lifters to be terrible and they were fine. I suspect rust gets blamed for everything because people don’t go looking for the problem until it is too late and by that point in time it can be nearly impossible to determine the real cause of the problem.

    If people look at Lycoming’s history and how many different cam followers they’ve tried it suggests that there has been an ongoing problem for decades. The roller followers and cam are just the latest in a long string of attempts to fix things. I suspect the roller engines will fare better but it isn’t a silver bullet. When the roller stops rolling it will make quick work of destroying the cam and follower. One only needs to look at the volume of cam and lifter failures in late model cars to see where this is headed for airplanes.

    Is the DLC treatment Lycoming is using right now good? I guess we’ll see how it fares in the years to come too.
     
  36. MBDiagMan

    MBDiagMan En-Route

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    never noticed hesitation. It has run like a Swiss watch all the time. I would not have known there was a problem if we weren’t cutting the filters.
     
    Last edited: Mar 7, 2021
  37. nrpetersen

    nrpetersen Line Up and Wait

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    Maybe roller lifters might only be a partial solution to Lycoming cam problems? If nothing else, the Hertzian stresses on the camshaft running on a radiused follower would be higher than if the same cam profile was running against a simple tappet flat surface.

    My own WAG is that it may well be also an initial lubrication problem caused by cold/whatever starts. IOW you never get to start one without preheat if it's cold, been a while since it was run, or if it has the wrong/heavy oil in it. Cam/lifter surfaces once spalled from marginal lubrication, never recover.
     
  38. Jdm

    Jdm Pre-takeoff checklist

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    As an A&P I recently took a an airplane into a very reputable engine overhaul shop. I interacted with the lead shop mechanic on behalf of my customer. He told me the exact same thing about flying vs ground running. Totally agree.

    I will say, the same overhaul shop strongly recommended staying away from 15w50. He convinced me to use 100p or 80p instead. Says they are having considerably better results. Because of this they are now recommending it’s use with all their overhauls, once they break in.
     
  39. Dan Thomas

    Dan Thomas Final Approach

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    The real solution (besides preheating) would be the Firewall Forward cam that's drilled to send oil directly to the lobe faces.

    upload_2021-3-7_12-26-4.jpeg

    https://firewallforwardengines.com/stc/

    The oil enters the cam at its main bearings, is channeled down the center of the shaft and exits at tiny holes in the lobe.

    That, plus an STC'd preoiler pump, would be about perfect.
     
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  40. Dan Thomas

    Dan Thomas Final Approach

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    Well, I got full TBO out of every Lycoming with 15W50, and the oil pressures were still good, no metal in the filters, and the compressions were still in the high 70s when I took them off the airplane. I wasn't about to try to improve on that by fooling with straight-grades of any sort, especially in the cold Canadian prairies. 15W50 has the viscosity of Aviation 30 oil when cold, and Aviation 100 when hot, and it has the anti-scuffing additive as well. It costs more, but it costs less in the long run. We sold a couple of high-time 172s with the engines at or near TBO, and I bet they still had another 1000 hours left in them, if they were treated well.
     
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