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Thread: Camshaft condition assessment needed and life estimate

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    Camshaft condition assessment needed and life estimate

    Hi,

    I posted another thread on the pre-purchase inspection of a PA-18-150 I have been looking at buying. The engine has 750+ hours on it since it was overhauled. Through the process I ended up having the cylinder #2 removed to inspect for corrosion internally because the plane sat for a year in a hangar without use. When looking at one lobe there are a couple pits. I am wondering if this is "end of life" or just what I should expect for 750+ hours since the last overhaul. I am guessing this is closer to "end of life" but how close? Any opinions would be greatly appreciated. I know I should negotiate a price reduction if I do buy the plane, but that reduction would probably best be based on remaining useful life.





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    aktango58's Avatar
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    It should be fine to ferry home or to where the engine gets removed for overhaul I would think.

    But I am only a pilot. I would not want to be behind that through herring spotting season though, power loss will come, and engine wear will happen.
    I don't know where you've been me lad, but I see you won first Prize!

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    Cub Builder's Avatar
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    I'll offer my opinion, but I'm sure others opinions will vary significantly.

    I've never seen a pit on a lobe do any significant damage to the lobes or cam followers. IMHO, this is not a life limiting issue in a Lycoming engine that is going to be flown regularly. You'll run out the engine before it's a problem, but would be cause for replacement of the cam at overhaul time rather than regrinding.

    My observation has been that the "spauling" is caused by corrosion and pitting on the cam followers, which are hardened, so the pitting on them tends to peel the lobes off the cam like a machine tool. What I see in this engine is nice shiny cam followers.

    If the cam followers looked like the one in the attached photo, then I'd run away from it. But what I see in your photos is nice shiny cam followers. I wouldn't have any fear of buying this engine.

    -Cub builder


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    Pitted cam follower from improperly stored Lycoming engine. 6 of the followers looked like this.


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    Cam lobes rounded off due to pitted cam followers 135 hrs after the engine was put back into service with the pitted cam follower above.

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    Quote Originally Posted by Cub Builder View Post
    I'll offer my opinion, but I'm sure others opinions will vary significantly.

    I've never seen a pit on a lobe do any significant damage to the lobes or cam followers. IMHO, this is not a life limiting issue in a Lycoming engine that is going to be flown regularly. You'll run out the engine before it's a problem, but would be cause for replacement of the cam at overhaul time rather than regrinding.

    My observation has been that the "spauling" is caused by corrosion and pitting on the cam followers, which are hardened, so the pitting on them tends to peel the lobes off the cam like a machine tool. What I see in this engine is nice shiny cam followers.

    If the cam followers looked like the one in the attached photo, then I'd run away from it. But what I see in your photos is nice shiny cam followers. I wouldn't have any fear of buying this engine.

    -Cub builder


    Click image for larger version. 

Name:	IO-360_follower1.jpg 
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    Pitted cam follower from improperly stored Lycoming engine. 6 of the followers looked like this.


    Click image for larger version. 

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    Cam lobes rounded off due to pitted cam followers 135 hrs after the engine was put back into service with the pitted cam follower above.

    I have often wondered if it mattered which part had pits. If the harder part had pits I could see why that would machine off the softer part. I have seen automotive cams with pits and nice shiny lifters. I wonder if this is also maybe related to the fact that the lifters rotate in their bores.

    I am curious if other people have opinions on whether it matters if the lifter is smooth but the cam is not being OK and the other way around with the cam being smooth but the lifter being pitted being BAD.

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    I would wager that 50-80 % of you are flying around with cams that have similar minor pitts. You would never until you pull a jug. Seems pretty minor from your blurry photos. It is certainly not going to fail from a tiny pit or two in a cam.
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    mike mcs repair's Avatar
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    Looks good to me too. Fly it Wreck it, fix it then

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    Quote Originally Posted by mike mcs repair View Post
    Looks good to me too. Fly it Wreck it, fix it then
    Yeah, I hope I get to fly it a lot before I wreck it, but I get your point.

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    That looks like a very clean engine. just an opinion

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    Quote Originally Posted by aerialimage View Post
    That looks like a very clean engine. just an opinion
    I too noted how clean it was.

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    irishfield's Avatar
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    Exactly what I said in your first post.. clean engine.. mirror tappet faces.

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    Quote Originally Posted by slowjunk View Post


    I'm going to take advantage of this picture to show another way to do a cursory inspection on the front part of the cam on an engine with a fixed pitch prop. See that hole in the center of the crankshaft at the top right of this photo? If you pull the crank plug in the flange, you have ready access to shove a lighted boroscope through from the front of the crank so you can get a good look at the very same cam followers and lobes we are looking at right here. No need to tear the engine apart. Cost of the plug is about $2 and it only takes a few minutes to do. You can buy a high quality recording boroscope for around $200 now days. I'll bet pulling the jug to inspect the cam here cost a whole lot more than that. This won't work on an engine that has the crank configured for a constant speed prop.

    -Cub Builder
    Last edited by Cub Builder; 03-25-2015 at 10:31 AM. Reason: Price of scope was incorrect.

  12. #12
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    You need to understand the definition of hardened metal. The surface is hardened to a depth of say .003 or .007 or whatever. Once you wear through that hardened surface, be it from corrosion pitting, lack of lubrication or just wear. You are done. Period. The end. This part will now make metal at an ever increasing rate. Steel in your engine from cam/lifter spalling is a pretty quick and ultimately expensive death. The spalled steel gets into the soft bearing surfaces and start grinding away on everything.

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    I remember reading somewhere were they were drilling holes in the cam lobes to help hold oil to lube the lifters. I think it was being done in colorado.

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    mike mcs repair's Avatar
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    Quote Originally Posted by nanook View Post
    ..... steel gets into the soft bearing surfaces and ....
    and is kinda the design of it.. to trap it....

    nothing to see now.... move along.....

    if they want a perfect & brand spanking NEW engine, BUY one!!

    they are buying a used one, gamble & price accordingly...

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    Steve Pierce's Avatar
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    Inside of the engine looks very clean to me. I an't see the pits in the pictures. What does the machanic that pulled the cylinder and inspected the engine think?
    Steve Pierce

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    Hardtailjohn's Avatar
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    Again, what pictures???? I see NO pictures in slowjunk's posts...but see pictures in Cub Builder's....

  18. #18
    SEFYK's Avatar
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    I would also look at the inside of crankshaft concerning corrosion and minimum wall thickness. We just had a case where a crankshaft has been treated acc. SB 505 during last overhaul (1000h ago) and we found corrosion under the corrosion protection coating eating into minimum wall-thickness. Crankshaft was scrap.

  19. #19
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    As referenced by Nanook, the cam and cam followers in a Lycoming are both surface hardened, although more like .030 - .050" deep. That's why they have this problem. Lycoming runs a hard faced steel follower on a hardened steel cam. Any pitting on the cam follower surface is sure to eat away at the cam lobe it rides on, which is an eventual death sentence for the Lycoming cam. The Lycoming setup of running two hardened surfaces works great as long as it has plenty of lubrication and the cam follower isn't allowed to corrode.

    Continentals use an iron faced cam follower, which is more porous, so holds oil better and is a softer surface. Pitting on a Continental cam follower isn't a death sentence. It usually polishes clean on the camshaft without damaging the cam. The pit becomes a nonabrasive hole that holds oil. Excessive wear on the cam follower is taken up by the hydraulic lifter and you don't notice anything until the engine is torn down for MOH. That is not to say that Continental cams don't fail, but the failure rate is significantly lower and they will take a lot more corrosion and abuse as compared to a Lycoming. It's simply better metallurgy. (See Continental Service Information Directive SID 05-1 for more detail)

    As for internal damage to the engine following severe cam spauling, the IO-360 parts I showed previously in this thread had 6 corroded cam followers and had destroyed all but 2 lobes on the cam (#1 & #4 Exh lobes). The oil filter saved the crankshaft and bearings, although we replaced the bearings anyway since I was already there. We found one sliver of steel from the cam that made it past the oil filter and was imbedded into the aluminum cam bearing saddle. I had to dig it out by hand leaving a tiny pit in the bearing saddle surface. The real damage was from all the metal being slung around free in the engine. The pistons had lots of steel from the camshaft imbedded into the skirts, although the nitrided cylinders were unmarked and only needed honing before reassembly. Two of the gears in the accessory case were damaged by metal running through the teeth. The oil pump impellers and aluminum body were unusable with deep scoring. The accessory case had to make a trip to Divco for rebushing of the drive holes as the vacuum pump and prop governor mounting holes in the case were badly worn from all the metal floating free in anything that gets splash lubricated.

    FWIW, I see a reflection in one photo that could be construed as a pit on the cam, which would be very unusual. But the other photos of the same part don't confirm it, so I'm thinking the one photo simply has a dark reflection. As others have stated, it sure looks clean in there.

    -Cub Builder

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    Cub builder,

    The he mechanic confirmed that he could feel the pit in the cam with his fingernail. It sucks... I am now speaking with the owner about a warranty, escrow, or a rebuilt 0 time engine. If those options don't work out then the deal will end.

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    mike mcs repair's Avatar
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    Quote Originally Posted by slowjunk View Post
    Cub builder,

    The he mechanic confirmed that he could feel the pit in the cam with his fingernail. It sucks... I am now speaking with the owner about a warranty, escrow, or a rebuilt 0 time engine. If those options don't work out then the deal will end.
    you are way to picky.....

    you best spend $250k and build a brand new cub to your pickyness level.....
    Last edited by mike mcs repair; 03-25-2015 at 09:37 PM.

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    Once again I think I agree with Mike. If you want a new airplane, they are available.

    About a half century ago I pulled my 65 off the Cub, and was told I would have to replace all the lifter bodies. They were twelve bucks each, and eight of them, and that was more than my monthly Navy paycheck. I just honed it out, put new rings and bearings in there, and flew it another 1500 hours. It probably still runs. I have more money now, and run C-85s.

  24. #24
    Eddie Foy's Avatar
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    Quote Originally Posted by slowjunk View Post
    Cub builder,

    The he mechanic confirmed that he could feel the pit in the cam with his fingernail. It sucks... I am now speaking with the owner about a warranty, escrow, or a rebuilt 0 time engine. If those options don't work out then the deal will end.
    Good luck with that! What is the asking price of the plane.

    Eddie
    Last edited by Eddie Foy; 03-26-2015 at 07:26 AM.
    "Put out my hand and touched the face of God!"
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    Quote Originally Posted by mike mcs repair View Post
    you are way to picky.....

    you best spend $250k and build a brand new cub to your pickyness level.....
    I'd like to know why you think I am being picky. When I speak to the mechanic and when I watch the video from the EAA with Mike Busch they both say the same thing; when you can catch your nail or a metal pick in a pit on the cam lobe then the cam needs to be replaced and the engine is not airworthy. Do you have experience to the contrary?

    Do these engines not normally make it to TBO? It is supposed to have another 1200 hours to TBO but based on the input I received the engine could have between 20hours and 200 hours left. That is, at best, 1000 hours short of TBO.

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    Quote Originally Posted by slowjunk View Post
    I'd like to know why you think I am being picky. When I speak to the mechanic and when I watch the video from the EAA with Mike Busch they both say the same thing; when you can catch your nail or a metal pick in a pit on the cam lobe then the cam needs to be replaced and the engine is not airworthy. Do you have experience to the contrary?

    Do these engines not normally make it to TBO? It is supposed to have another 1200 hours to TBO but based on the input I received the engine could have between 20hours and 200 hours left. That is, at best, 1000 hours short of TBO.
    And all the input you have received is somebody's best guess based on their experience. Obviously Nanook has seen one or more exactly like it that shortly went to hell. And Mike and Slowjunk have seen one or more exactly like it that ran forever. What will this engine do? Nobody can say with 100% certainty that it will or it won't. Even brand new engines and fresh overhauls sometimes go to hell. That is why they usually have a warranty. Just how many hours will you fly this airplane if you buy it? Will you fly it 150 hours every year for the next ten years? Will you fly 75 hours the first year,40 hours the next, then maybe ten a year until it sits in a hangar for 2 or 3 years and you decide to sell it? Will it become the highest time Cub in history or will it be hangar queen again? None of us can see into the future with any certainty. Noone can give you a guarantee on a used engine. Oh, everyone likes Mike Busch and squeezing every hour out of an engine, TBO be damned. Read Lycoming Service Instruction 1009A. It's attached. Even Lycoming doesn't guarantee a new engine will reach TBO if it doesn't run regularly. Lycoming says O/H at 12 years for inactive engines. You wanna squeeze every hour out of an engine TBO be damned? Just suppose your engine has 700 hours on a 15 year old O/H and while you and a buddy are enjoying a flight something engine related goes to hell and the resulting forced landing takes your buddy's life, heaven forbid. Now you and the IA that signed your aircraft off as airworthy are sitting in court, being sued by his widow and her sharp lawyer. Hey, its not her fault the kids are hungry and she needs money from somebody. And the lawyer asks you why you operated your engine past it's manufacturer's recommended TBO effectively putting your buddy's life at risk and ultimately causing his death.. What's your answer? Whatever the answer, the next question is,"So how do you know more about engine reliability than the Lycoming engineers who designed and tested the engine?" What do you answer? The jury is gonna see that you and the IA feed her kids for a long time. John Schwaner is out of fashion now but I still like his books and thoughts on engines and maintenance. Here's one attached. Best of luck with your decision. And, yes, my old engine is way past TBO in calendar time and operating time. jrh
    Attached Files Attached Files
    You can't get there from here. You have to go over yonder and start from there.

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    As the prop turns. More to add to the pot. So lets say the guy says he will rebuild it. Is it just to replace the cam? Are the mags, carb, and starter. How about the exhaust valve guides I would lay money the are out of tolerance by this time.
    If you want this plane I would ask for a reduced price and have the engine rebuilt by my IA who is going to be the one taking care of it. If possible don't let someone else make the calls on a engine you will be flying.
    As far as making TBO, it depends on how and who did the rebuilt and how often and hard they where flown. I recently saw a total rebuild torn down at less than 500 hours due to crank bearing issues (most likely from improper rebuild). A rebuild at this time should be cheaper than one once a lot of metal got into the motor. You would have to know the complete history of the motor including prop strikes. Which you don't so I would say you should send the cases to Devco and get the crank checked new cam and followers, exhaust valve guides and whatever else is worn. If the cylinders have already been overhauled once than just get new ones. Just some things to look at. A major overhaul in the aviation can be a lot of different things from all new parts to all used parts. It is important to know which one you are getting.
    DENNY
    Last edited by DENNY; 03-26-2015 at 11:03 AM. Reason: HIT WRONG BUTTON

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    My guess is that the potential purchaser is hemming and hawing over a $75K Super Cub. This kind of scrutiny might be important if he was looking at a $125K Cub, but I am willing to bet that this one is a bargain from the get-go.

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    Quote Originally Posted by bob turner View Post
    My guess is that the potential purchaser is hemming and hawing over a $75K Super Cub. This kind of scrutiny might be important if he was looking at a $125K Cub, but I am willing to bet that this one is a bargain from the get-go.
    Thanks Bob.

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    N86250 and Denny,

    The replies were great and helpful. It is great being a member of this forum. The knowledge and support is awesome.

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    Eddie Foy's Avatar
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    So? What was the outcome?

    Eddie
    "Put out my hand and touched the face of God!"

  32. #32

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    Thought I'd resurrect this thread since it discusses lifter spalling. I recently had all the hydraulic lifters replaced on my C180. All were spalled except one. I've read SID05-1B and the Australian CASA Airworthiness Bulletin 85-014 Issue 1 trying to understand the failure mechanism - corrosion seems the most likely culprit.

    Anyway, as I read about the lifter body in SID05-1B, it mentions the "The lifter body is made of cast iron with the face being “chilled” during casting to provide an extremely hard wear-resistant material."


    So, trying to understand why the lifter body is made from cast iron and not a wrought material such as a medium carbon steel, 1045 to 1055 for example, or even 4140 or 4340 HSLA steel.

    I would really appreciate any insight or a contact who may know more about the cast iron material choice over a wrought steel.

    Thanks,

    MartyC
    Last edited by MartyC; 10-22-2021 at 12:08 PM. Reason: word choice

  33. #33
    wireweinie's Avatar
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    Cast iron is relatively porous and tends to hold oil because of that. Also cast iron has a certain amount of self lubrication due to the high carbon content. Grab a drill and free hand drill a hole into cast iron. You'll see that it machines way easier than most people expect.

    So, I expect the cast lifter faces are designed as such to hold the oil film between the face and cam lobe and have a secondary benefit of slower wear if it gets run dry for any reason.

    Web
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  34. #34

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    Web,

    I believe you are correct about the cast iron characteristics. Grey cast iron has about 3-4% graphite dispersed throughout the microstructure. Heat and cooling history affects the size, dispersion and shape of the graphite flakes The graphite really helps with machining; good example are refacing automotive brake rotors and drums.

    I cross-sectioned a failed lifter body many years ago and as I recall, I did not see any graphite, which I then thought was cast steel until I read the SB recently.

    I picked these images off the web.

    The first image is what I recall the cross-section appeared to be.




    Above image is white cast iron





    The second image is the grey cast iron. Not sure of the magnification of these images, but you can see how the dispersed graphite flakes in grey cast iron can help with machining. Also, I believe lubricants could be absorbed into the graphite for improving wear characteristics.

    Plus cast irons typically corrode more readily than steels. Which makes me wonder again why use cast vs. wrought.

    Then thinking from a manufacturing standpoint, would it be easier to make them from a forging? I imagine it would be easier to maintain quality control of material, machining, heat treat, etc., with forging than casting.

    Then again, maybe I'm making a mountain out of a mole hill....

  35. #35
    Cub Builder's Avatar
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    Quote Originally Posted by wireweinie View Post
    Cast iron is relatively porous and tends to hold oil because of that. Also cast iron has a certain amount of self lubrication due to the high carbon content. Grab a drill and free hand drill a hole into cast iron. You'll see that it machines way easier than most people expect.

    So, I expect the cast lifter faces are designed as such to hold the oil film between the face and cam lobe and have a secondary benefit of slower wear if it gets run dry for any reason.

    Web
    What Web said. Additionally, by having a cast surface on the cam follower, by design, it will be the part that will wear away if there is a corrosion issue, rather than the cam. The hydraulic lifter will adjust to make up the difference in lifter face wear, and typically you won't know there was a cam follower wear issue until you overhaul the engine for other issues. It's not unusual to tear down a Continental at TBO and find the cam followers dished out and the cam lobes all still there. In a Lycoming, if the cam follower is corroded and wearing, the matching lobe on the cam is almost always badly worn.

  36. #36

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    Web and Cub Builder, thanks for your replies Sorry, I thought the white cast iron microstructure was included in my other post. So, here it is:




    This microstructure is similar to what I recall when I sectioned a lifter body a few years ago. As you see, very different than grey cast iron.

    Anyway, I believe you both are saying the cast iron lifter body corrodes sacrificially to the cam and may well be the intent of the original design.

    However, I'm curious if the lifter bodies were ever made from wrought, heat treated steel, rather than white cast iron. If so, then I think any corrosion would most likely be pitting rather than spalling and therefore less abrasive to the cam lobes.

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  37. #37

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    Well, I researched the white cast iron as the material of choice for the lifter body. I spoke with a product engineer at Superior Aircraft and a PhD Metallurgist from one of our National Laboratories.

    My PhD friend pointed out white cast iron is very suitable for high wear applications because of the microstructure; carbides within pearlite. Basically, the carbides are very hard and provide the wear resistance with proper lubrication.

    The Superior Airparts Product Engineer mentioned an internal report from years past how low RPMs produced the highest force at the cam lobe/lifter interface. Of course, it would be worse at the initial start-up with minimal lubrication at the cam lobe/lifter contact points, increasing chances for spalling. The SA Product Engineer mentioned the forces may be lesser by increasing the idle up to 1000 or 1,100 RPMs; not always practical on floats.

    So for float plane operations, we get the worst of both worlds, low RPM on start-ups/taxiing coupled with operating in a moist environment. Of course with long times between flights, it only gets worse.

    So, it appears the best remedy is inspection per Continental Service Directive SID05-1B and replace as necessary.

  38. #38
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    This is where an engine pre-oiler pump can help. I had one on my PA-12-180. Flip on the pump and see oil pressure before startup. Probably helped get it flung around sooner. Not my invention.

    Gary
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  39. #39
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    Quote Originally Posted by MartyC View Post
    Web and Cub Builder, thanks for your replies Sorry, I thought the white cast iron microstructure was included in my other post. So, here it is:

    Anyway, I believe you both are saying the cast iron lifter body corrodes sacrificially to the cam and may well be the intent of the original design.

    However, I'm curious if the lifter bodies were ever made from wrought, heat treated steel, rather than white cast iron. If so, then I think any corrosion would most likely be pitting rather than spalling and therefore less abrasive to the cam lobes.

    Exactly.Cast iron holds oil better than hardened steel, so lubricates the cam better. Additionally, it does become the sacrificial material when there are imperfections in one of the surfaces.

    As for hardened steel cam followers; That's what Lycoming does. I think we are all familiar with the issues that has presented over the years.

    FWIW, I retired from the metallurgy group at a national lab. Deformation processing and heat treating is what I used to do... and am quickly forgetting.

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