carusoam Posted March 23, 2017 Report Posted March 23, 2017 Some Lycoming specific issues that come up that make you go hmmmmmmm..... 1) One of the things that makes the Lycoming different from the other engine designs is the location of the cam. 'Oil starvation' probably describes what it is seeing...upon start-up. The surface 'drying up' describes the cam that sits for long periods of time where the oil runs down and off the cam. A dry (from oil) cam surface, is vulnerable to 'moisture aided' oxidation... 2) that are some Lycoming engines that got a special oiling device called Ney nozzles to try to better supply oil to the cam. 3) Some replacement cams got additional oiling holes drilled in them to better supply oil to these special locations 4) keeping oil on the lobes is a great idea, that is what Camguard is about... 5) Lycoming had some really well known metallurgy issues with a large number of cams. 6) Nobody has come back and said I have documented the use of these things and then had a cam wear out... 7) Some Ney nozzles have fallen out of their locations. 8) The six cylinder Lycoming IO540 is very similar in design to the four cylinder IO360, but we don't have a statistically similar cam issue come up around here...? 9) We only have one Lycoming IO720, but its owner is more maintenance-centric than most PPs. 10) The one thing that is known to work to keep Cams and cam followers in good health, good Use! Summary... 11) keeping the cam lubed by running it is good. 12) keeping the cam lubed by chemical additive is pretty good. 13) keeping the cam coated with something that will keep it from corroding is good. Some new cams get a temporary coating like this before they get installed. 14) Cams in dry environments don't corrode as much as those in high relative humidity environments. 15) Some people build and use dehumidifiers if they are not going to fly for weeks at a time. 16) some people are known to open the oil filler cap to allow steam to escape the engine's block. More stuff that comes to the mind of a PP. not a mechanic. Best regards, -a- 1 Quote
mooniac15u Posted March 23, 2017 Report Posted March 23, 2017 I'm not convinced that corrosion from sitting is the primary factor in cam and lifter failure. In all the pictures I've seen of cams with bad lobes the rest of the metal on the camshaft is bright and shiny. What factors would cause localized corrosion on the lobes and leave no trace of corrosion anywhere else? Lycoming cams that are left sitting on hangar shelves do not show signs of spontaneous corrosion. Lycoming's solution to this issue was to add roller tappets. How would roller tappets solve a corrosion problem? Since the damage is typically localized to the cam lobes and lifters where they make physical contact it seems that mechanical wear is the more significant factor. Perhaps mechanical forces are causing localized heavy wear at the surfaces which then make them prone to corrosion? If that's the case then simply sitting wouldn't be a problem for a cam that doesn't already have surface wear. 1 Quote
mooniac15u Posted March 23, 2017 Report Posted March 23, 2017 8 hours ago, Stetson20 said: I know. Getting it borescoped and having oil sample sent off for analysis. The current owner, as I understand it, lost his medical. The 2+ years of sitting has caused me some concern, but several sources have told me that, even sitting for extended periods, engines this far along toward TBO don't *usually have a catastrophic failure. They sorta slowly get worse until it's apparent that it's time for overhaul. What are your thoughts? Thanks for the input! Overall it looks like a nice plane. I wasn't trying to scare you away with my engine comment. Buying planes is about assessing value and managing financial risk. There are no certainties with engines but it is easier to assess the risk of needing an overhaul with some engines than others. This engine hasn't been overhauled since 1972 but most of the key components have been repaired or replaced in a piecemeal fashion over the years. What that means for longevity potential is anyone's guess. If I were buying this aircraft I would make sure I could afford an overhaul in the near future. I'm not saying that it won't run a good long time, there are just too many unknowns to not be prepared in this case. Are you getting it for a price that leaves you with the resources for an overhaul? 1 Quote
MyNameIsNobody Posted March 23, 2017 Report Posted March 23, 2017 Congrats. I really like the paint update and the interior of the plane. Somebody loved that bird and made some nice upgrades. You know the engine status so you are buying right and prepared for an overhaul expense sooner rather than later. No surprises are good. Have fun with your "new" bird. I have flown my E model, that was a hanger queen nightmare that was Mis-represented for 17ish glorious years. The E has fit my mission well. If you fly the numbers on landing you will find it docile as a Cherokee. ENJOY! Fly safe. Store tanks full and you will be less likely to "push" fuel levels and be flying a glider. 1 Quote
carusoam Posted March 23, 2017 Report Posted March 23, 2017 (edited) 15U, See if I can describe the cam lobe issue better... Lubrication requires smooth surfaces and an oil film... The final detail is called the 'lubrication approximation', engineering term for... as two pieces of metal get closer together, the oil pressure between them starts to increase towards infinity... pock marks caused by localized oxidation eliminates the smooth surface required for the lubrication approximation... metal to metal contact increases. pock marks on the cam followers look like a piece of metal sandpaper. putting a roller on the end of the lifter instead of a piece of sand paper sounds like a way to eliminate the grinding that goes on. even if the roller surface gets pocked, it won't grind the cam surface as much... If the roller stops rotating... it won't be as good as the flat tappet...surface area and pressure keep the metal surface away from each other. The tappet has a large surface compared to the roller. Metalurgy... The hardened surface layer of the cam is not very thick. Oxidation caused pock marks in the cam destroy the hard layer. Once the hard layer is gone the rough surface of the follower grinds the lobe down quickly. Lycoming seems to have the infamous 'bad batch' of cams... 'quickly' seems to be between a couple of oil changes... hardness doesn't seem to slow oxidation very much. Rust/oxidation changes the volume of the molecule and it no longer fits in the metal matrix. Knowing something about the metal's matrix might help some... oxidation can occur between the metal's granular structure releasing whole granules... This is outside my area of expertise of polymer processing, but the lubrication approximation is something I could rely on to keep metal parts away from each other in plastic processing machinery. Polymers with abrasive additives would wear through hardened surfaces in a similar way as these cams. Metal bits showing up on the filter downstream occurred the same way as our oil filters.... slowly at first until the hardened surface gets compromised... The hardened surfaces are measured in thousandths of an inch. Once they are compromised... millimeters of metal gets removed quickly... same 'quickly' as described before... Stainless steel used in aviation and plastics processing overlap in some areas. Xalloy and Inconel are brand names for SS that are corrosion resistant at very high temperatures. Our mufflers are made out of sheetmetal versions of these or similar SS. Best regards, -a- Edited March 23, 2017 by carusoam 1 Quote
mooniac15u Posted March 23, 2017 Report Posted March 23, 2017 29 minutes ago, carusoam said: 15U, See if I can describe the cam lobe issue better... Lubrication requires smooth surfaces and an oil film... The final detail is called the 'lubrication approximation', engineering term for... as two pieces of metal get closer together, the oil pressure between them starts to increase towards infinity... pock marks caused by localized oxidation eliminates the smooth surface required for the lubrication approximation... metal to metal contact increases. pock marks on the cam followers look like a piece of metal sandpaper. putting a roller on the end of the lifter instead of a piece of sand paper sounds like a way to eliminate the grinding that goes on. even if the roller surface gets pocked, it won't grind the cam surface as much... If the roller stops rotating... it won't be as good as the flat tappet...surface area and pressure keep the metal surface away from each other. The tappet has a large surface compared to the roller. Metalurgy... The hardened surface layer of the cam is not very thick. Oxidation caused pock marks in the cam destroy the hard layer. Once the hard layer is gone the rough surface of the follower grinds the lobe down quickly. Lycoming seems to have the infamous 'bad batch' of cams... 'quickly' seems to be between a couple of oil changes... hardness doesn't seem to slow oxidation very much. Rust/oxidation changes the volume of the molecule and it no longer fits in the metal matrix. Knowing something about the metal's matrix might help some... oxidation can occur between the metal's granular structure releasing whole granules... This is outside my area of expertise of polymer processing, but the lubrication approximation is something I could rely on to keep metal parts away from each other in plastic processing machinery. Polymers with abrasive additives would wear through hardened surfaces in a similar way as these cams. Metal bits showing up on the filter downstream occurred the same way as our oil filters.... slowly at first until the hardened surface gets compromised... The hardened surfaces are measured in thousandths of an inch. Once they are compromised... millimeters of metal gets removed quickly... same 'quickly' as described before... Stainless steel used in aviation and plastics processing overlap in some areas. Xalloy and Inconel are brand names for SS that are corrosion resistant at very high temperatures. Our mufflers are made out of sheetmetal versions of these or similar SS. Best regards, -a- I understand the issues and how lubrication functions. It is the source of the pock marks that I have an issue with. There is no reason to expect oxidation to occur on the hardened cam lobes over any other surface. Hardened steel is typically more resistant to corrosion than non-hardened surfaces. Clearly once the hardened surface is compromised the loss of metal can happen quickly. I think we have been quick to assume that corrosion is the first step in the process but I'm not sure we have data to support that. I believe we see cases of cam failure in engines that are run fairly regularly. There is a temptation to look at the outcome (cam failure) and then go hunting for a cause. If the population of engines that have sat for some time is higher than the population that haven't then it is likely to drive a false conclusion that the two are related. The scientific approach would be to look at the total population of engines and see whether cam failure occurs more often in engines that sit than engines that don't. 1 Quote
Stetson20 Posted March 24, 2017 Author Report Posted March 24, 2017 14 hours ago, MBDiagMan said: My thinking is that if the engine were started and run to full oil temp, THEN cut the filter and do an oil sample, you would know if there is a cam problem. My experience is automotive, but in an auto engine, once the flat tappet cam and lifters are thoroughly broken in, unless they are totally oil starved they will hang tough. Until full break in, they are more delicate. If the engine has had CAMGUARD or Aeroshell PLUS (which includes a CAMGUARD additive) in it during the set up time it has a better chance. If I were purchasing, I would want to run it and cut the filter and send off a sample. IF it is recently run without making metal, holds strong oil pressure and makes solid compression, it could have hundreds or even a thousand hours or more left in it. The time to run it and check for metal is BEFORE you purchase it, not after. My Cessna 140 with O200A is well past TBO and is very strong. They are known for running reliably to a point almost double TBO if cared for properly. With the reputation of the Lycomings engine used in our birds, it wouldn't surprise me if they too commonly fun far beyond TBO for those who choose to do so. That said, my C Model has an engine with less than 300 hours total time, so I have not researched the statistical engine life of these Lycomings. my$0.02, Doing an oil sample and filter check as part of the pre-buy. Quote
MBDiagMan Posted March 24, 2017 Report Posted March 24, 2017 I understand Stetson, but my point is the importance of running this engine before looking for metal because it has set so long. If you were to take an oil sample before running it, you could miss any problems that might arise from a no oil on the cam problem. Quote
jetdriven Posted March 24, 2017 Report Posted March 24, 2017 Isn't it's been sitting 2 years I would set aside 25-35k for an overhaul. 25k gets a field job which may last a year or ten, the higher number gets you a factory roller motor which has a near zero statistical failure rate of the cam. Some owners here are on their third engine because of this. Quote
Yetti Posted March 25, 2017 Report Posted March 25, 2017 I kind of think cam failure in the Lycoming is: 1. Cams made between 1990 and early 2000s are a different metallurgy .2. Poor lubrication design on the valves causing the valves to coke up and get tight. Which causes spalling to occur with the added pressure on lifter face and cam lobe. 1 Quote
jetdriven Posted March 25, 2017 Report Posted March 25, 2017 (edited) I've taken engines apart and the first sign of this is pitting on the lifter faces. Then it progresses to outright spalling. But you can often see several stages of this progression in one engine. We just pulled the lifters out of one cylinder on a 2002 ovation with 1400 hours. Both were starting to pit. I would have inspected all the The lifters and replaced the pitted ones and saved the cam but the owner cheaper out. And that's a Continental engine with a better failure rate than the lycomings. It's so bad no way that most beechtalk guys have taken to pulling every lifter out on the prebuy and half of engines have bad lifters. I think the crappy metallurgy is in the lifters. Edited March 25, 2017 by jetdriven 2 Quote
Stetson20 Posted March 25, 2017 Author Report Posted March 25, 2017 On 3/23/2017 at 9:27 AM, mooniac15u said: Overall it looks like a nice plane. I wasn't trying to scare you away with my engine comment. Buying planes is about assessing value and managing financial risk. There are no certainties with engines but it is easier to assess the risk of needing an overhaul with some engines than others. This engine hasn't been overhauled since 1972 but most of the key components have been repaired or replaced in a piecemeal fashion over the years. What that means for longevity potential is anyone's guess. If I were buying this aircraft I would make sure I could afford an overhaul in the near future. I'm not saying that it won't run a good long time, there are just too many unknowns to not be prepared in this case. Are you getting it for a price that leaves you with the resources for an overhaul? Yes I will have the funds for an overhaul if needed. It would hurt, but I could manage it. 2 Quote
gsxrpilot Posted March 25, 2017 Report Posted March 25, 2017 I think you're gonna want an autopilot... and a GPS. But otherwise it looks good and hope it comes up clean for you. 1 Quote
Stetson20 Posted March 31, 2017 Author Report Posted March 31, 2017 Update: pre-buy went mostly well. Only squawk was seeping left fuel tank. Owner agreed to reduce the price by 2AMUs, approximately half the repair cost. It's a very well kept plane and I'm excited to be the new owner. One last hurdle before the sale is final. I sent off the oil analysis to Blackstone today. Hope to have the sale finalized next week. Weather permitting, I will bring her home then. 2 Quote
highlowfastslow Posted March 31, 2017 Report Posted March 31, 2017 Good to hear! Do you plan to patch the tank for now or do a full strip and re-seal? Love the panel layout, lots of space for upgrades. Let us know when it's finalized. Sent from my iPhone using Tapatalk 1 Quote
Stetson20 Posted March 31, 2017 Author Report Posted March 31, 2017 Just now, highlowfastslow said: Good to hear! Do you plan to patch the tank for now or do a full strip and re-seal? Love the panel layout, lots of space for upgrades. Let us know when it's finalized. Sent from my iPhone using Tapatalk Probably patch for now. I hope to fly it over to Guitarmaster's home field and ply him with adult beverages and a steak dinner to go over it with me! Very knowledgeable person and he's helped me a lot with this first purchase. 1 Quote
Beedel Posted August 8, 2017 Report Posted August 8, 2017 What happened Stetson? Saw N22VA for sale and googled it. Found this thread. Why are you selling? Quote
Marauder Posted August 8, 2017 Report Posted August 8, 2017 What happened Stetson? Saw N22VA for sale and googled it. Found this thread. Why are you selling? https://mooneyspace.com/topic/22888-1965-m20e-n22va-forced-to-sell/Sent from my iPad using Tapatalk Pro Quote
Beedel Posted August 8, 2017 Report Posted August 8, 2017 thanks, i should have searched first 1 Quote
Mcstealth Posted August 8, 2017 Report Posted August 8, 2017 3 hours ago, Beedel said: What happened Stetson? Saw N22VA for sale and googled it. Found this thread. Why are you selling? Welcome to the forum. Hope you stick around. Please post in the main board and introduce yourself.. df Quote
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.