Why some of our cams are failing
What I have been finding at least on Franklin cams and lifters and I suspect that its happening on other cams as well is a mismatching of surfaces between the cam lobe and lifter, they are being resurfaced incorrectly and will fail prematurely if they do not have the correct contact pattern, the lifters will not rotate as they pass the nose of the cam lobe causing a scuffing action instead of a rolling action, generally it’s a slow death (several hundred hours or more) that sheds metal causing damage to other engine components as it fails. There are two styles of cam/lifter interface possible with a conventional flat tappet engine.
1. No taper on the lobe, and the lifter is ground flat (no radius) on the face. The cam lobe is offset to the lifter and does not fully cover the lifter face on one side, the lifter turns due to the differential of drag on the face of the lifter. Franklin and British cams
2. The cam is ground with a taper, most cams post 1940 are ground with a taper and the lifter is ground with a radius on its face, with this interface there is contact on only one side of the lifter face as it contacts the taper on the lobe, creating a force on one side of the center line of the lifter, now the lifter is rolling as it runs over the nose of the tapered cam creating very little friction.
3. Mixing these two designs is guaranteed premature failure or not having the correct radius/ taper interface or misalignment will have the same results.
4. How do you or your mechanic know if you have the correct relationship between them? Do you know any one that checks to see if they have the correct pattern? I have been a mechanic/ machinist and a hobbyist for over forty years and I have never known any mechanic to check this interface when installing a cam and a set of lifters, we have always trusted the cam manufacture or remanufacture to get it right, it wasn’t Intel I started investigating why Franklin engines ate cams and lifters that I discovered that they were being remanufactured incorrectly thus causing failures, I contacted several regrinding shops only to find that they believed that ALL lifters were supposed to have a radius and reground them accordingly. I asked what is the radius that your regrinding your lifters to? None of them could answer, they just had a machine that reground lifters and they kept it on the middle setting. This could very well be the reason so many of our cams are failing lets face it after several hundred hours it’s any ones guess or excuse. I also found that the British car racers and enthusiasts were having the same problems. Read this http://www.mgexperience.net/phorum/read.php?41,1666592
5. Another thing that can have the same effect is poor machine work at the factory, or warped cases, lifter bores that are not square to the cam, this will also have the same effect. Leave nothing to chance check the pattern on each lifter before final assembly of your engine. If they are not correct, the taper or radius can be adjusted to make the correct pattern. Save your engine!

How to print a lifter, clean the face and color with magic marker, insert lifter in lifter bore with the nose of cam lobe facing up (top of lift) "best method" for checking if a used cam is worn out,or facing away from lifter (heal of lobe) on a new cam, twist lifter face several turns against cam, remove and inspect pattern on lifter face, there are four possible patterns.
1. Full face lifter print, normal for stock Franklin cam and lifter, (cam without taper and flat lifter face NO radius ) GOOD
2. Donut shaped print, ( tapered cam lobe and radius on lifter face) GOOD
I believe that the sweet spot for the taper lobe is 30 to 50 of the radius from center. An educated guess.
3. Center print, contacting only on the center of lifter face ( cam lobe without taper, lifter face with radius) BAD, this combination will fail prematurely!!!
4. Edge print, contacting only the edge of the lifter face ( cam lobe with taper, flat lifter face or not enough radius ) BAD, this combination will fail prematurely!!!
I hope this helps someone and saves an engine or two, it took me months to figure this out. Even as simple as it seems I found that most engine builders and cam remanufactures no nothing about this pattern or how to check it.
Lets keep them all flying safe.

Example of exactly what you described above.....The following pictures are of a reground camshaft and lifter bodies that lasted a whole 10 hours in a 0-360 Lycoming...

Cam lifter bodies.... Top and left one are badly pitted... The other two were not rotating due to a bad grind...


This is one of the lobes... if you look close enough you can see the lobe starting to "flare" out on the edges....


I always use new cams and lifters.... I try to never put a reground cam / lifters in an engine because I have seen this happen so many times after a re-build.... But unfortunately, there are several engines that you can no longer get new cams / lifters for anymore and you just do not have a choice...

Brian..

Great write up 172H, thanks for taking the time to point this out.

Hopefully, I'll be blessed with many more hours on my Frank220.

Jr.CubBuilder wrote:That is some good information, and obviously not just limited to airplane motors.

Even a lawn mower!

Brian - Steve's Aircraft wrote:Example of exactly what you described above.....The following pictures are of a reground camshaft and lifter bodies that lasted a whole 10 hours in a 0-360 Lycoming...

Cam lifter bodies.... Top and left one are badly pitted... The other two were not rotating due to a bad grind...


This is one of the lobes... if you look close enough you can see the lobe starting to "flare" out on the edges....


I always use new cams and lifters.... I try to never put a reground cam / lifters in an engine because I have seen this happen so many times after a re-build.... But unfortunately, there are several engines that you can no longer get new cams / lifters for anymore and you just do not have a choice...

Brian..

There may be more than just an incorrect pattern at play here, note the lifter on the right the one with the straight line in the center for a wear pattern that’s a classic radius lifter face on a non-tapered cam lobe but that’s only part of your problem, if they were all like that one they would totally fail in several hundred hours or more a slow death. At a glance from a distance, there appears to be a corrosion issue and or spalling involved, spalling is the fatigue of the iron or steel matrix on the lifter face it can also be caused from hydrogen embrittlement, caused by moisture in the oil under extreme pressure, even though corrosion may not occur the water in the oil gives up its hydrogen atom under extreme pressure and causes the metal to become so hard that it shatters under load. I have seen this phenomenon multiple times primarily on large roller bearing assembles; cam and lifters have similar high pressure loading. Cams and lifters that have normal wear can be resurfaced and reused if done properly.
1. Never attempt to resurface a lifter that shows signs of spalling, the metal is coming apart and will continue to so after their resurfaced. (Find another one) look at them with a magnifying glass before considering resurfacing them.
2. Check the body of each lifter for excessive wear and out of round, Lifters that do not turn wear egg shaped and must be discarded.
3. Have the lifter face and the cam lobe checked for hardness.(a good shop does this as common practice on every lifter) There must be at least a 6 Rockwell difference between the two. Normally the lifter will be the harder of the two.
4. Be sure that cam re grinder knows what he is doing, I hate to say it but most are making parts that look pretty but will never last.
5. Check your pattern on all lifters before final assembly of the engine.
6. Check each lifter in its bore for smooth movement and excessive wear, many times a small fragment of metal is imbedded in the lifter bore preventing the lifter from turning; it only takes a small scratch.
7. Proper use of break in lube (High pressure lube, Molly lube). Cote only the face of the lifter and the lobe of the cam, never use it on the body of the lifter (oil only), the thick lube will prevent it from turning and cause premature failure. Check out DFL sold by Tech Line, I’m impressed! Will never wash off, cool stuff.
8. Run in; never let the engine sit and idle, 1200RPM for 10 min is the number that I have heard from more than one source once again the lifters may not turn at low RPM, once they start a pattern they want to stay that way, it’s over.

Hope this helps someone, makes an engine run longer, these things are two dammed expensive to be rebuilding all the time!

mountainmatt wrote:Great write up 172H, thanks for taking the time to point this out.

Hopefully, I'll be blessed with many more hours on my Frank220.

I feal just the same way.

Wow, THANK YOU 172H for that education !

I would like to suggest that you find a way to put this information into the hands of rebuild shops, cam and lifter resurfacing shops, etc. The old guys that knew this stuff automatically are mostly gone.

I would humbly like to suggest you contact EAA and AOPA with this information, and submit a write-up in their magazines.

I second EZ's recommendation.... I also urge any shop to print out this information and keep it handy, I did....

Also, just a little more information on those Cam pics I posted. The engine is a Lycoming 0-360 that is installed in a PA-28-180. The airplane rolled into my shop with a missing oil drain plug..... sounded like a diesel engine when it landed.... Took out all 4 pistons, the cam and lifters, #4 rod and the crankshaft. The owner of the aircraft could not afford to overhaul it so he offered it to us as a price we could not refuse. The Cam and lifters were given too us by another friend of ours.... Yellow tagged and supposedly good to go.... Absolutely no corrosion visible on the cam or lifters.... 10 hours and about a month later we had the engine back off and installed a new cam and lifters because of what you see in the pics.... The engine now has over 30 hours on it since the rebuild at the beginning of this year...( went to Minnesota and back ) Lesson learned....

This is what the bottom of the oil pan looked like after the engine ate up the #4 rod bearing due to no oil in the system.....


Brian.

EZFlap wrote:Wow, THANK YOU 172H for that education !

I would like to suggest that you find a way to put this information into the hands of rebuild shops, cam and lifter resurfacing shops, etc. The old guys that knew this stuff automatically are mostly gone.

I would humbly like to suggest you contact EAA and AOPA with this information, and submit a write-up in their magazines.

Every time that I have tried to explain this to a rebuild shop or re-grinder I get the same response, we have been doing it this way for thirty some odd years, then they start sounding defensive or sarcastic, like a big shop in Tulsa. They don’t want to here it. Here is a fact every franklin rebuild that I have seen and the majority of the used lifters and cams all show mismatched patterns, this is why there cams fail. The research took months to gather and almost every one was throwing red herrings. I came up with the method for checking the interface pattern, I know of no one else that doses it, we have always relied on the pro to do it right, what I found in the industry after visiting shops and talking to the machinists left me with night mares . The cams and lifters in aircraft should easily last till TBO as long as corrosion doesn’t attack them; low RPM and light spring tension make for a long life. Pass this info along to any one that wants it, I will send a copy to Mike Bush, see what he has to say.
Thanks for taking the time to read it. Hope it saves an engine.

172heavy wrote:Every time that I have tried to explain this to a rebuild shop or re-grinder I get the same response, we have been doing it this way for thirty some odd years, then they start sounding defensive or sarcastic,

The research took months to gather

I came up with the method for checking the interface pattern, I know of no one else that doses it,

Thanks for taking the time to read it. Hope it saves an engine.

It could easily save more than an engine. Making metal (metal from highly loaded parts yet) while flying in remote areas, or worse having it happen over congested areas, is a recipe for a big problem.

Although I am certainly not a highly experienced mechanic (like I believe some on this forum are), I will be happy to support your research by providing you with some pretty compelling written materials that your "audience" cannot easily wave away, or disregard, or question. It's what I do for a living.

IMHO this needs to be made available to any "stakeholder" with an interest in air safety or reliability. That includes our nice friends in OK City, who I believe would WELCOME this with open arms. The reason for that is that they are now paying attention to things related to aging aircraft, continued airworthiness, etc. Believe it or not, I've worked with FAA maintenance and certification people who really do care, and have earned their gray hair in aviation.

For BCP Member 182 STOL Driver - Bill, perhaps you might consider forwarding a link to this thread, to a certain recently retired Air Safety Inspector.

I think we still have issues becuase Continental and Lycoming still produce low tech old school pieces of crap........
Every time I see a piston I still cannot believe how large the piston skirts are, just ridiculous.

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In reply to your forum topic regarding camshaft and lifter failures, I feel that there is a very important point that needs to be addressed. Camshaft and lifter break in. General Motors and most automotive camshaft manufacturers (if not all) recommend the first 30 mins of operation be performed at a minimum of 2000 rpm for any flat tappet cams. I own a Franklin 220 hp airplane that had to be disassembled at 175hrs smoh due to a flywheel (viscous damper) failure. This engine had a new camshaft and reground lifters with a 2 to 3 degree crown which should be a ideal combination. I did not perform this overhaul however I did find 3 or 4 lifters that had not been rotating. I fully believe that this camshaft was not broken in properly. I had the lifters touched up with the same crown and re installed. At the initial engine start, rpm was taken right up to 2000 for 1/2 hr. My plans are to re inspect the lifters after approx 400 hrs to check for proper wear. I wish I could afford to fly more often and give an update in the near future however it will take some time to accumulate that amount of time. Thank You, Miles Reece Bayfield Co A/P I/A

dirtbag wrote:In reply to your forum topic regarding camshaft and lifter failures, I feel that there is a very important point that needs to be addressed. Camshaft and lifter break in. General Motors and most automotive camshaft manufacturers (if not all) recommend the first 30 mins of operation be performed at a minimum of 2000 rpm for any flat tappet cams. I own a Franklin 220 hp airplane that had to be disassembled at 175hrs smoh due to a flywheel (viscous damper) failure. This engine had a new camshaft and reground lifters with a 2 to 3 degree crown which should be a ideal combination. I did not perform this overhaul however I did find 3 or 4 lifters that had not been rotating. I fully believe that this camshaft was not broken in properly. I had the lifters touched up with the same crown and re installed. At the initial engine start, rpm was taken right up to 2000 for 1/2 hr. My plans are to re inspect the lifters after approx 400 hrs to check for proper wear. I wish I could afford to fly more often and give an update in the near future however it will take some time to accumulate that amount of time. Thank You, Miles Reece Bayfield Co A/P I/A

I also Fly a 220 HP Franklin in a 172.
If you have an original Franklin cam or a cam reground to original specs, (it has no taper) you should be running a dead flat lifter, I will bet any amount of money on it. That’s why I wrote this, if you don’t believe me buy a new Franklin lifter or just a lifter body and check it, I have, their flat with a small radius on the very edge. If you have a radius on the lifter face and a lobe with out taper and you print the lifter to the cam as I described, you will see that it contacts in the middle of the lifter, read my article and read the article on British cams, specially the quote from Kent cams. This is why Franklin s are eating cams. You said that there is a 2-3 Deg. crown did you mean bevel? How are they grinding it? It should be a radius, not a bevel and a radius is only used if you have taper on the lobe, No lifter is ever properly ground with a taper. Beware of experts that grind them at an angle! I lost thousands of dollars and years of my time. Good luck with your engine, I love mine.

For 172 Heavy. Finally got to read your reply after all this time. What you say makes perfect sense and I did ask Bruce Kown (who is supposed to be one of the more knowledgeable guys about Franklins) about this while I was repairing my engine. He originally built my engine and was the one to suggest having the lifters re ground with the radius. Sounds like I need to pull out and inspect my lifters and re grind or replace if necessary. Thanks for your reply.