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Have cam failures in Lycoming engines always been a problem?


nels

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This has been a question in my mind since getting involved with Mooneys several years back and hearing about all the cam failure problems and everyone’s perception of why it happens.  Being an old car nut, along with a Mooney nut, I am aware of the auto industry totally moving away from flat tappet cam shafts and onto roller type cam shafts and the reason for the move. Lycoming has also moved to roller cam shafts. The additives of zink and phosphorous have been removed from motor oil mainly due to them not getting along with catalytic converters. The zink is a high wear and extended corrosion additive that is especially useful with dry starts with metal to metal contact. In particular with flat tappet cams. Our Mooney’s often sit for long periods of time allowing most if not all the oil to run off the cam and lifter surfaces so they are often subject to dry metal to metal starts. The zink evidently doesn’t totally leave the cam surfaces over time and allows for lubrication needed during the initial dry cam start.....at least that’s how I understand it.

So, for those that get oil samples sent off and analyzed , when an oil sample is returned from a lab check, does it give the amount of zink or zddp in the oil?

Also, did Lycoming’s cam problems coincide with the oil industry’s time line of reducing or eliminating these additives in auto motor oil? Or have Lycoming cams been a problem since day one?

Here is an interesting article in the Hemmings Motor News blog: https://www.hemmings.com/blog/2012/10/18/tech-101-zinc-in-oil-and-its-effects-on-older-engines/

 

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The only cam and lifter problem I had was on my first Mooney. This problem happened in 1985. The engine was the original 1967 factory engine.

Cams and lifters have been made from chilled cast iron from the 1930. The same material used today in auto and aircraft engines.

I have read some scholarly articles about lifter spalling and they all say they are caused by sub-surface stress cracking, not corrosion.

I have seen corroded and pitted cam lobes and lifters that weren't spalled and I've seen spalled lifters that had no signs of corrosion.

My data set isn't large enough to draw any concrete conclusions. My thoughts are that it is related to the relatively high lift our cams have compared to auto engines. This causes greater stress on the cam and lifters. The stress cracks can come from having lash in the lifters and the hammering that takes place. I suspect this can be caused by the lifters bleeding down after long periods of disuse. I think this may be more of an issue than the metal to metal contact.

Just my 2 cents. 

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3 hours ago, N201MKTurbo said:

The only cam and lifter problem I had was on my first Mooney. This problem happened in 1985. The engine was the original 1967 factory engine.

Cams and lifters have been made from chilled cast iron from the 1930. The same material used today in auto and aircraft engines.

I have read some scholarly articles about lifter spalling and they all say they are caused by sub-surface stress cracking, not corrosion.

I have seen corroded and pitted cam lobes and lifters that weren't spalled and I've seen spalled lifters that had no signs of corrosion.

My data set isn't large enough to draw any concrete conclusions. My thoughts are that it is related to the relatively high lift our cams have compared to auto engines. This causes greater stress on the cam and lifters. The stress cracks can come from having lash in the lifters and the hammering that takes place. I suspect this can be caused by the lifters bleeding down after long periods of disuse. I think this may be more of an issue than the metal to metal contact.

Just my 2 cents. 

A few differences on modern automotive engines are the metal surface hardening and treatments that are typically done these days, advanced or synthetic oil blends, and generally running at higher rpm than the typical aircraft engine.   Very few automotive engines use pushrods these days, and few have solid lifters.   Even though lift may be less on on auto engine, the valve springs may be stronger to handle the higher revs, so I don't know whether the surface stress at the cam/lifter is really any better or worse.

As always, some similarities, some differences, but the comparisons are interesting.  

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17 minutes ago, Yetti said:

1940s design These engines are so loose they have a breathing tube on them

So does every car I’ve ever seen. Sense the 70s the breather is vented to the intake through the PCV valve. So the crankcase fumes won’t get into the atmosphere.

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5 hours ago, nels said:

So, for those that get oil samples sent off and analyzed , when an oil sample is returned from a lab check, does it give the amount of zink or zddp in the oil?

Well, I send it off and it does not come back :rolleyes:but Blackstone reports zinc (sic). Mine engine has shown a consistent 3 ppm. (IO360A1A, ASW100, Camguard)  

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6 hours ago, N201MKTurbo said:

I have read some scholarly articles about lifter spalling and they all say they are caused by sub-surface stress cracking, not corrosion

DING DING DING!!!! Now, sell that to legal so they can spin the lack of lubrication and resultant stress cracking and valve stem coking on something like flying thru an ozone layer or running LOP.

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4 minutes ago, mike_elliott said:

DING DING DING!!!! Now, sell that to legal so they can spin the lack of lubrication and resultant stress cracking and valve stem coking on something like flying thru an ozone layer or running LOP.

OK, sure.

Has there ever been an accident caused by spalled lifters? It usually just hurts your wallet. The power of your engine slowly decreases until one cylinder stops firing. None of which will necessary bring a plane down.

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2 hours ago, Bob_Belville said:

Well, I send it off and it does not come back :rolleyes:but Blackstone reports zinc (sic). Mine engine has shown a consistent 3 ppm. (IO360A1A, ASW100, Camguard)  

Bob. Are you saying your oil analysis says you have 3 ppm zink? The Hemmings article says many rebuilders will not warranty an engine if the failed engine’s oil has less than 1200 ppm.

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12 minutes ago, nels said:

Bob. Are you saying your oil analysis says you have 3 ppm zink? The Hemmings article says many rebuilders will not warranty an engine if the failed engine’s oil has less than 1200 ppm.

Aircraft oil doesn't have ZDDP (zinc)

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47 minutes ago, nels said:

Bob. Are you saying your oil analysis says you have 3 ppm zink? The Hemmings article says many rebuilders will not warranty an engine if the failed engine’s oil has less than 1200 ppm.

What shows in the oil analysis is Zn (Zinc). It comes into the used oil from brass and copper components in trace amounts. Blackstone calls 4 ppm a universal average. 

(The Hemmings article is discussing automobiles oils, not aircraft. And the reference to zinc is a shorthand for a compound not used in aircraft oils.)

 

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4 hours ago, N201MKTurbo said:

So does every car I’ve ever seen. Sense the 70s the breather is vented to the intake through the PCV valve. So the crankcase fumes won’t get into the atmosphere.

I've often thought about how to do this on our engines.

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4 minutes ago, N201MKTurbo said:

Aircraft oils are ashless. That is because any ash will deposit on out valves and make them stick. ZDDP is ash forming along with a lot of other additives put in auto oil.

I think I saw someone mention synthetic zink or zddp in camgaurd. Maybe that is why? 

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5 minutes ago, 1964-M20E said:

I've often thought about how to do this on our engines.

It wouldn't be hard to do, but until the EPA mandates it I wouldn't do it. PCV valves have failure modes. They can fail closed and pressurize the crankcase. They can fail open and cause a big intake leak. 

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3 minutes ago, nels said:

I think I saw someone mention synthetic zink or zddp in camgaurd. Maybe that is why? 

I just checked their website and they never mention ZDDP except that their automotive formulation helps with low ZDDP oils. It doesn't say it contains it.

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15 minutes ago, N201MKTurbo said:

It wouldn't be hard to do, but until the EPA mandates it I wouldn't do it. PCV valves have failure modes. They can fail closed and pressurize the crankcase. They can fail open and cause a big intake leak. 

Yes but cleaned and checked regularly at annual I don't think it would be a problem.  I think our engines would leak a little less oil as well and by moving the combustion bypass from the crankcase maybe the oil will stay cleaner.

Yes it would not be difficult to install.  However, we still have the FAA to deal with on the issue.  Wonder if an IA would be willing to sign off on it as a minor modification.

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2 hours ago, nels said:

I think I saw someone mention synthetic zink or zddp in camgaurd. Maybe that is why? 

I use CamGuard along with Aeroshell W100 (not plus). The Camguard results in elevated calcium in the oil analysis. 

Ms. Google thinks a man my age might need more ZINChttps://www.healthline.com/health/testosterone-and-zinc#zinc-and-hypogonadism

Table of Elements

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I use CamGuard along with Aeroshell W100 (not plus). The Camguard results in elevated calcium in the oil analysis. 
Ms. Google thinks a man my age might need more ZINChttps://www.healthline.com/health/testosterone-and-zinc#zinc-and-hypogonadism
tableofelements.png


You thinc you need more zink?


Sent from my iPad using Tapatalk Pro
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5 hours ago, 1964-M20E said:

I've often thought about how to do this on our engines.

All it takes is to take the engine’s drain hose and pipe it directly to the intake...

Not as technically challenging as the EGR valve... exhaust gas recycle valve, where the exhaust gets recycled to burn some of the remaining fuel that hasn’t been converted yet... a 10% recycle rate is great for efficiency, but crap for power production...according to my  chem-eng friends...

Lots  of messy challenges come with that...cleaning the intake behind the butterfly valve becomes a usual piece of maintenance for those in the know...

But the risk is there as well... oil and moisture in the line is going to be deposited into the intake at any time... so procedurally, you are going to remember to switch that valve off before every take off....

As for not pressuring the engine case... that is easy... the pressure relief valve (PCV) is mounted in a rubber grommet in the valve cover... If the valve gets blocked, The rubber grommet gets ejected with the blocked valve... now the smell of oil starts to escape making the problem sort of known...

PP thoughts on engine design, not a mechanical engineer or mechanic...

Fun MS topic!

Best regards,

-a-

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On 7/3/2018 at 6:26 PM, 1964-M20E said:

I've often thought about how to do this on our engines.

I would think the oil separators (air wolf) essentially do this.  Although not putting the oil through the combustion cycle.  I would think through combustion path this is a bad idea and would be a change to the engine design. (FAA involvement)   If you are going to do that then just take a BMW boxer Engine with better tolerances and stick it in a plane.  Oh that was already tried.   It was not long ago that you could see city buses pumping oil out onto the street through their breathers.  The FAA preventor of progress.

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