corn_flake Posted April 25, 2020 Report Share Posted April 25, 2020 One of the big unknown when purchasing an airplane with Lycoming engine seem to be the cam lobe condition. We all heard of stories of engines that is in otherwise serviceable condition but sat idle for a while that resulted in lobe spalling. This eventually led to premature wear of the cam lobes and a $10k repair bill. I'm sure someone else may have already tried this, but an idea came to me of using a dial indicator to measure the cam lift. This can be easily done with minimal effort during pre-buy. We only need to remove the valve covers. Granted it is not an accurate test, and it would not tell us if the the cam lobes are already spalled but are in early stage of the down hill decline. But, it would allow buyers to at least avoid engines with severally wore cam lobe. Few questions came to mind, and I'm hoping the collect knowledge here could help. 1. Since there are hydraulic lifters in IO 360, do we know if the oil in the lifters will drain out of the lifter body after engine shutdown. Or do we know if we hold the lifters in "compressed" state for extended period of time, is there enough clearance around the lifters allow the oil to drain out of lifter body? 2. Assuming if can't "trick" the lifters to drain, do we know the lifter's compressed length (without oil) vs extended length (with oil) in a IO 360? 3. Does Lycoming publishes the cam lobe height for their engines? If we know #2 and #3, depending on the numbers, we may be able to calculate the absolute minimal lift the buyer should reject during the pre-buy. Of course, if the lift is above the minimal, it may not guarantee health cam. Thought? Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 25, 2020 Report Share Posted April 25, 2020 Flake... There are two surfaces involved with the lobe challenge... The cam surface... The follower surface... As the cam drys out from not having oil refreshed on it... the surfaces become available to O2 molecules in the air with H20 molecules in the air as well... The hardness layer on the cam is important... once it is gone, the lobe starts shedding parts... before it is gone... measuring the lobe heights externally is possible but not precise enough to see the tiny craters that interrupt the oil film’s protection... Homework assignment.. find pics of cam followers that have surface corrosion craters.... imagine how they cut down the lobes like tool working on a lathe... When minimizing wear between two surfaces... the part designer needs to choose materials wisely... Matching hardness between two parts is the best way to minimize wear.... If one part was easier to replace than the other... you could select it to be slightly softer... the softer part preferentially wears a lot more than the harder part... Imagine how well DLC coatings are going to work... diamond hard vs hardened steal.... if the oil goes away often...diamond and steal are going to have a fight... Once you have seen craters on a cam follower’s surface... you realize the normal path of wear isn’t what is getting in the way of cam life... intergranular corrosion seems to be most important... see if DLC can avoid that... PP thoughts only, not a tribologist, or a machinist... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
philiplane Posted April 25, 2020 Report Share Posted April 25, 2020 Yes, this will only identify lobes & lifters that are already unserviceable. It won't detect corrosion pitting that leads to spalling of the lifter faces. It's already easily done with a dial indicator mounted to the rocker cover bolt holes. You compare the lift of all intakes to each other and all exhausts to each other. 4 1 Quote Link to comment Share on other sites More sharing options...
corn_flake Posted April 25, 2020 Author Report Share Posted April 25, 2020 7 minutes ago, philiplane said: Yes, this will only identify lobes & lifters that are already unserviceable. It won't detect corrosion pitting that leads to spalling of the lifter faces. It's already easily done with a dial indicator mounted to the rocker cover bolt holes. You compare the lift of all intakes to each other and all exhausts to each other. This is exactly what I'm suggesting. As I suspected, the idea is not new. I'm surprised this is not routinely performed during the pre-buy. Quote Link to comment Share on other sites More sharing options...
Cyril Gibb Posted April 25, 2020 Report Share Posted April 25, 2020 I think checking the oil filter for metals will identify issues LONG before any reduction in lift will show, and would (should) should be part of any prebuy. Redundant. 1 Quote Link to comment Share on other sites More sharing options...
corn_flake Posted April 25, 2020 Author Report Share Posted April 25, 2020 10 minutes ago, Cyril Gibb said: I think checking the oil filter for metals will identify issues LONG before any reduction in lift will show, and would (should) should be part of any prebuy. Redundant. We certainly should check the oil filter as well. However, dishonest seller could easily change the filter before the pre-buy to mask the issue. 1 Quote Link to comment Share on other sites More sharing options...
ArtVandelay Posted April 25, 2020 Report Share Posted April 25, 2020 Engine monitor data could be useful to access engine condition including cam. Plus you can see how the engine was run. 1 Quote Link to comment Share on other sites More sharing options...
Cyril Gibb Posted April 26, 2020 Report Share Posted April 26, 2020 1 hour ago, corn_flake said: We certainly should check the oil filter as well. However, dishonest seller could easily change the filter before the pre-buy to mask the issue. A thorough engine run, probably a short flight would be needed to do a valid compression check. That should show some filter particles if the cam/lifters were really spalling enough to give a dial gage anomaly. The important point is that an engine sitting long enough to get a little rust on the cam has probably set the spalling process in motion before external checking will detect anything. Unfortunately, popping off cylinders is the only way to make reasonably sure. That, in itself can create maintenance induced failures. Purchase a plane that’s flown often to minimise, but not eliminate, cam issues. Otherwise, throw the dice. Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 26, 2020 Report Share Posted April 26, 2020 Dishonest sellers are going to be hard to come by... compared to sellers that are unaware of the actual condition of their cam... Either way whatever tests you can add to your PPI would be a great idea... Performance tests are pretty straight forwards... T/O distance and climb rates are pretty telling... Use a phone with a WAAS app to collect data... CloudAhoy and skyradar... (old school) Being down 10% power might show up as 50% longer T/O distance... (typical O1 to O3 performance numbers... actually measured) Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Nukemzzz Posted April 26, 2020 Report Share Posted April 26, 2020 Point of clarification on cam lobe and lifter failure mechanisms... Wear and spalling are two different things. Spalling occurs because of subsurface fatigue cracks. A sliding ball on a plate is more likely to spall the plate than a rolling ball because it has increased subsurface tension behind it as it slides. Thus...rolling tappers are less likely to spall. Spalling is aggravated by high friction coefficients and could perhaps be accelerated by surface corrosion for friction and stress riser reasons. If the lifter doesn’t turn for some reason this would increase the subsurface stresses so face corrosion might not be the only assignable case of lifters spalling in these engines. Friction is the actual driving mechanism for wear, hardness just determines the life of each part. Surface finish is a big player as is mating part form. Oil film thickness for a sliding lifter needs to exceed both of these in combination or wear is accelerated. This is why cold start up is the most damaging, and why things like cam guard (or Lucas oil and STP in cars) is used...To leave molasses consistency oil hanging on to the cam longer between starts. Adhesive wear is a big destroyer of high contact load parts (galling). This happens when you have similar materials and hardness with high contact pressures (steel on steel). DLC coatings are the cure for this. Dry steel on steel will wear faster than dry steel on DLC coated steel. It breaks the similarity of in-contact materials, it provides no additional wear risk when dry that I’m aware of if it is properly coated and nano nodules are removed. If lycoming changed to DLC Coated lifters it is likely to prevent galling on cold startup when the lifters and cam are dry and maybe the lifter gets stuck in the bore a little with corrosion so it doesn’t rotate. I don’t know that I believe that lifter face corrosion is the main cause of our lifters spalling 2 Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 26, 2020 Report Share Posted April 26, 2020 Nuke, Have you seen the pics of cam followers with corrosion challenges? Just to be clear... the cam follower (that I am referring to) is the foot of the lifter... the part that is in contact with the cam lobe... Galling, or transfer of metal, from one surface to the other... is usually pretty easy to detect... metal of the cam type would appear on the surface of the follower... the follower is a different type of metal... and bumps, not craters would appear. The pics, I urge you to see... show craters where metal is missing... not bumps where metal has been added... These craters can appear long before any cam wear can become excessive.... as if they got weakened by corrosion and had parts of the surface sluff off... Cratered cam followers will destroy the cam lobes... making it all look like some kind of corrosion initiated event... Let us know if you can’t find the pics... they are around here somewhere... IIRC correctly, the pattern of the follower damage is not related to any direction of travel, or rotation... followers rotate to distribute wear(?)... they look like they have lost hole granules of metal... Roller cam followers have some interesting attributes... it would be great if a whole new engine wasn’t required to get them... the roller bearing (?) at the foot of the lifter... could also use DLC coating, and camgaurd. To put a scale on what you are trying to measure... the thickness of the hardened surface of the cam lobe... it is measured in thousandth of an inch... And... no matter how crappy the surfaces of the cam and followers are... the engine produces good power and doesn’t show a lot of metal in the filter... once the hardened layer is worn through... the teaspoon of metal parts isn’t far behind... Cratered follower surfaces are strong enough to carve through the hardened lobe surfaces. It takes a few tens of hours... enough to get to the first annual... PP thoughts only, not a materials engineer... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
ArtVandelay Posted April 26, 2020 Report Share Posted April 26, 2020 FWIW, my cam had a bad lobe, I never saw any substantive metal in the filter or excessive iron in the oil reports. 1 Quote Link to comment Share on other sites More sharing options...
PTK Posted April 26, 2020 Report Share Posted April 26, 2020 5 hours ago, ArtVandelay said: FWIW, my cam had a bad lobe, I never saw any substantive metal in the filter or excessive iron in the oil reports. At what frequency was oil changed and sampled? Could it be due to lower frequency? Quote Link to comment Share on other sites More sharing options...
Nukemzzz Posted April 26, 2020 Report Share Posted April 26, 2020 (edited) 11 hours ago, carusoam said: Nuke, Have you seen the pics of cam followers with corrosion challenges? Just to be clear... the cam follower (that I am referring to) is the foot of the lifter... the part that is in contact with the cam lobe... Galling, or transfer of metal, from one surface to the other... is usually pretty easy to detect... metal of the cam type would appear on the surface of the follower... the follower is a different type of metal... and bumps, not craters would appear. The pics, I urge you to see... show craters where metal is missing... not bumps where metal has been added... These craters can appear long before any cam wear can become excessive.... as if they got weakened by corrosion and had parts of the surface sluff off... Cratered cam followers will destroy the cam lobes... making it all look like some kind of corrosion initiated event... Let us know if you can’t find the pics... they are around here somewhere... IIRC correctly, the pattern of the follower damage is not related to any direction of travel, or rotation... followers rotate to distribute wear(?)... they look like they have lost hole granules of metal... Roller cam followers have some interesting attributes... it would be great if a whole new engine wasn’t required to get them... the roller bearing (?) at the foot of the lifter... could also use DLC coating, and camgaurd. To put a scale on what you are trying to measure... the thickness of the hardened surface of the cam lobe... it is measured in thousandth of an inch... And... no matter how crappy the surfaces of the cam and followers are... the engine produces good power and doesn’t show a lot of metal in the filter... once the hardened layer is worn through... the teaspoon of metal parts isn’t far behind... Cratered follower surfaces are strong enough to carve through the hardened lobe surfaces. It takes a few tens of hours... enough to get to the first annual... PP thoughts only, not a materials engineer... Best regards, -a- I’ve seen the pics before, and yes the failure mode is spalling. But that doesn’t mean that adhesive friction isn’t a factor. Anything that resists the sliding will increase the chance of spalling and friction includes adhesive components even if they don’t result in a transfer or smearing of material (galling). Roller tappets are a whole other ball game. They will fail if friction gets too low if you can believe it. If the roller skids it doesn’t have much longer to live. They are designed so the parts survive the rolling contact fatigue with enough spring load to keep it in touch with the camshaft at max speed, and to have sufficient traction to the cam to keep the roller from skidding. A roller tappet doesn’t have a wear component between the tappet and cam because there is no relative motion between the two, but there are new fail modes and risks that come with it. Edited April 26, 2020 by Nukemzzz 1 Quote Link to comment Share on other sites More sharing options...
ArtVandelay Posted April 26, 2020 Report Share Posted April 26, 2020 22 minutes ago, PTK said: At what frequency was oil changed and sampled? Could it be due to lower frequency? Every 30+ hours, and 5-6 times a year. Could it be due to higher frequency? Quote Link to comment Share on other sites More sharing options...
PTK Posted April 26, 2020 Report Share Posted April 26, 2020 27 minutes ago, ArtVandelay said: Every 30+ hours, and 5-6 times a year. Could it be due to higher frequency? Yes, by lower frequency I meant less hours between oil changes or more oil changes! Could it be that metal was not being detected? But I think oil analyses correct for hours on oil sample. So theoretically it shouldn’t matter and should still be detected. Quote Link to comment Share on other sites More sharing options...
PT20J Posted April 26, 2020 Report Share Posted April 26, 2020 FWIW, I purchased a M20J with an IO-360-A3B6D. The airplane had not flown more than a few hours/year for the past several years and it was burning a quart of Aeroshell 15W50 every two hours. A recent oil analysis prior to purchase did not show excessive metals. Compressions were all high 70s, borescope inspection was good, and no metal in the filter during pre purchase inspection by Don Maxwell. Thirty hours later, it broke an oil control ring which took out a piston skirt and ran metal through the engine. (The engine was running fine, BTW. We found this during annual inspection). When we pulled the cylinder, the cam was also spalled. The cam in this engine had been replaced by the previous owner once before. I don’t think there is any accurate way to predict when a cam will go bad. I’ve been associated with several clubs and flight schools over the years and they all generally have obtained TBO or better with Lycomings flown frequently. Maybe Camguard and dehumidifiers help if you don’t fly a lot. I don’t know of any real data from controlled tests to prove this one way or the other. The roller lifters have been standard on everything coming out of the Lycoming factory (new and rebuilt) for several years. I haven’t seen reports of issues with them. Skip 1 Quote Link to comment Share on other sites More sharing options...
Nukemzzz Posted April 26, 2020 Report Share Posted April 26, 2020 46 minutes ago, PT20J said: FWIW, I purchased a M20J with an IO-360-A3B6D. The airplane had not flown more than a few hours/year for the past several years and it was burning a quart of Aeroshell 15W50 every two hours. A recent oil analysis prior to purchase did not show excessive metals. Compressions were all high 70s, borescope inspection was good, and no metal in the filter during pre purchase inspection by Don Maxwell. Thirty hours later, it broke an oil control ring which took out a piston skirt and ran metal through the engine. (The engine was running fine, BTW. We found this during annual inspection). When we pulled the cylinder, the cam was also spalled. The cam in this engine had been replaced by the previous owner once before. I don’t think there is any accurate way to predict when a cam will go bad. I’ve been associated with several clubs and flight schools over the years and they all generally have obtained TBO or better with Lycomings flown frequently. Maybe Camguard and dehumidifiers help if you don’t fly a lot. I don’t know of any real data from controlled tests to prove this one way or the other. The roller lifters have been standard on everything coming out of the Lycoming factory (new and rebuilt) for several years. I haven’t seen reports of issues with them. Skip When I called and talked to Jewel about rebuilding my engine I asked about roller lifters and they reported that there is one thing to consider. Apparently with a prop strike you must replace all 8 of them at $750 each. I’m not one to plan on preparing for a prop strike but that is one thing maybe to consider. Im planning on giving DLC coated lifters a go as a compromise. Quote Link to comment Share on other sites More sharing options...
Ragsf15e Posted April 26, 2020 Report Share Posted April 26, 2020 53 minutes ago, Nukemzzz said: When I called and talked to Jewel about rebuilding my engine I asked about roller lifters and they reported that there is one thing to consider. Apparently with a prop strike you must replace all 8 of them at $750 each. I’m not one to plan on preparing for a prop strike but that is one thing maybe to consider. Im planning on giving DLC coated lifters a go as a compromise. Don’t plan on a prop strike, but if it happened, and they are required to be replaced, insurance should take care of that. 2 Quote Link to comment Share on other sites More sharing options...
David Lloyd Posted April 26, 2020 Report Share Posted April 26, 2020 If they are required to be replaced due to a prop strike, insurance will pony up. On the other hand, I had a prop strike several years ago, the cam and lifters were pitted. I was on the hook for the new parts unrelated to the prop strike. 1 Quote Link to comment Share on other sites More sharing options...
mike20papa Posted April 27, 2020 Report Share Posted April 27, 2020 The lifters stay full of oil. If you ever change out a cyl. you have to fish out the lifters and release the oil pressure in each of the 2 lifters of you'll never be able to slip the rocker arm shaft back in place. The lifters have a ball type check valve that is released by inserting/pressing a small dia. brass wire into the oil tube. - When done, the lifter releases it's oil. Pretty cool. Also, when you have a cyl. off, you can use a small mirror and examine all lifters and cam. Here's s photo of one lobe at about 350 hr.s 1 Quote Link to comment Share on other sites More sharing options...
corn_flake Posted April 27, 2020 Author Report Share Posted April 27, 2020 @mike20papa Thanks for sharing the picture and the info on the ball check valve. Quote Link to comment Share on other sites More sharing options...
carusoam Posted April 27, 2020 Report Share Posted April 27, 2020 This just in today... Bob posted some nicely detailed pics of his engine’s cam and followers.... check out the lunar surface on the followers, and the threads of the towel snagged on the lobes... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
MBDiagMan Posted March 21, 2021 Report Share Posted March 21, 2021 After having bought a plane that after setting up an extended period, I think I have an experience on the subject worth sharing here: To the sellers credit, before putting it up for sale, he removed the cylinders and inspected the cam and lifters finding everything apparently fine. He honed the cylinders, replaced the rings and put it in service running very well. I flew the plane regularly saving for a few multi week periods of setting up while working through gear problems. After about 65 hours, metal showed up in the filter. We pulled a cylinder at that point and inspected with mirrors finding only a faint line of very light corrosion on one lobe, but lifters looked good as best we could tell. I ran another 15 hours before doing an oil analysis. It was not good and there was metal in the filter. We pulled all the cylinders at that point and found two adjacent lifters significantly spalled. I won’t go into the rest of the actions taken at that point because they’re not Germaine to the thread subject. What I now believe is that Inspecting Lycoming cam and lifters is a non conclusive process. If there is the tiniest spec of material missing from a lifter face that is undetectable with an inspection. Once there is a tiny crater, it will start to come apart much like a pothole. One tiny piece will come out, then another tiny piece and so forth. After this experience, I believe that the flight history of the plane might be much more important than a cam and lifter inspection. The cam is high and if the engine sets for an extended period, what length of time I’m not sure, without roller followers or DLC lifters can very easily lead to the problem I’m dealing with. It only takes a small area of corrosion on a lifter face for this destructive process to begin. I believe there is no set time limit for it setting up. It’s not simple. The problem is related to time but not indicated purely by the length of idle time. The root of the problem IMHO is CORROSION. Many factors effect the amount of time before an amount of corrosion occurs that is damaging. If it is flown often enough, for periods of time long enough at an oil temp that is hot enough to drive out all the moisture then corrosion probably won’t be a problem. It also has to do with the storage climate, its temperature and humidity. I have not done any research on Camguard. I don’t know it’s claim to fame. I THINK that the idea is that it makes the oil cling to the cam for a longer amount of time. I have heard people rave about it being totally convinced that it will completely eliminate the problem forever. I have heard others claim that it is nothing but snake oil. I have not looked into it so I have yet to form an opinion. I believe that the best preventive option lies with roller lifter or maybe DLC coated lifters. The only real conclusion I have drawn is that setting up can be terribly destructive for a Lycoming. 3 Quote Link to comment Share on other sites More sharing options...
MBDiagMan Posted March 21, 2021 Report Share Posted March 21, 2021 On 4/27/2020 at 9:21 AM, mike20papa said: The lifters stay full of oil. If you ever change out a cyl. you have to fish out the lifters and release the oil pressure in each of the 2 lifters of you'll never be able to slip the rocker arm shaft back in place. The lifters have a ball type check valve that is released by inserting/pressing a small dia. brass wire into the oil tube. - When done, the lifter releases it's oil. Pretty cool. Also, when you have a cyl. off, you can use a small mirror and examine all lifters and cam. Here's s photo of one lobe at about 350 hr.s The lifters staying full of oil within the hydraulic plunger area is not related to the lifter face erosion problem. If the oil stays on the lifter face and cam lobes then this will prevent the destructive corrosion. Quote Link to comment Share on other sites More sharing options...
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