Failure 172-SP cam shaft lobe

Failure 172-SP cam shaft lobe

     Several months ago, our flying club began performing an oil analysis at Aeroshell for the purpose of developing trend lines for our fairly new aircraft. The readings did not appear abnormal.  We then decided to also have the oil filter sent out for inspection and analysis, as well. The first filter report came back ABNORMAL. So did the subsequent two reports, despite visual inspections at the FBOs not turning up anything abnormal.

    Last week, (982 tach and 1248 Hobbs) we had the engine removed from the aircraft and shipped to a local engine repair/rebuilding shop, and watched the tear down. Lo and behold, we found large iron shavings in the bottom of the oil pan -- too large to be caught in the oil suction line, and too large to drain during an oil change. The #2 cam was "machined" down about 1/8" causing problems with the engine performance (incomplete valve opening for intake or exhaust on the opposing cylinders). In retrospect, we had some roughness reported during the past six months, but such could not be duplicated in a controlled environment (with a mechanic on board).

    We are led to believe there is a "congenital defect" in the cam design, despite the engine being FAA certified, in that no positive lubrication of the cam surfaces take place until the engine develops sufficient RPM to throw the oil upon the cam faces. If a pilot spends an "abnormal" period of time cranking, say one minute over a period of time, we suspect there is no hydroplaning of the cam and lifter surfaces taking place, and we, instead, experience metal against metal -- hence the initiation of the cam wear and removal of the hardened cam surface. And once this wear starts, it will continue to get worse.

    The aircraft is hangared in central Florida, and is flown several times each week, for a minimum of one hour and as long as eight hours. We have used Aeroshell 15W50, but originally used Aeroshell 100. We are not sure whether the change over to 15W50 could have initiated the problem. One unsubstantiated theory is the synthetic blend may not adhere to the metal surfaces while the aircraft is not being flown for a "prolonged" period of time, which requires further definition. Our log books indicate flight about once every week.

    There were times when pilots had difficulty starting the aircraft, due to (a) improper pilot procedure for the fuel injected engine as well as (b) a defective voltage regulator (which was erratic and took out three alternators before we could isolate the cause rather than the effect).

    If our assessment of the defect is correct, we desire to take some prophylactic measure, such as installing the nozzles which Chuck Nye has developed. With as little as 3 psi (developed during cranking), the oil will be sprayed upon the cam surfaces. Another suggestion we heard was to install an oil line pressurizer, but this does not get the oil where it's needed: on the cam surfaces.

   Anyone have similar problems, and if so, how were they resolved? What protective measures?

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Re: Failure 172-SP cam shaft lobe

I can see the problem in the little information that you gave. Stick with the straight weights. They have been working for years why change. The stick to the parts (cam) and dont run off. RC,ia

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Re: Failure 172-SP cam shaft lobe

I was cautioned by Maintenance personnel to use straight 100W during the spring & summer and fall and 80W during the winter. (I have O-300-E20 -150 Hp Lycoming most of the time located on the east coast between Delaware and South Carolina). They suggested, based on annectodal experience, that the engines in the fleet of planes they maintained for a flight school did better on straight weight oils.  The rationale was that these engines undergo more frequent power changes associated with training, then what would be experienced on a private airplane.  Nothing was said about the ability to maintain a "wetted" condition on parts.  However, it stands to reason that the straigth 100W would be more viscous than the multi-grade and apt to cling better to the metal surfaces.

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Re: Failure 172-SP cam shaft lobe

Alan M Hoffberg Wrote:
-------------------------------------------------------
> Several months ago, our flying club began
> performing an oil analysis at Aeroshell for the
> purpose of developing trend lines for our fairly
> new aircraft. The readings did not appear
> abnormal.  We then decided to also have the oil
> filter sent out for inspection and analysis, as
> well. The first filter report came back ABNORMAL.
> So did the subsequent two reports, despite visual
> inspections at the FBOs not turning up anything
> abnormal.

>     Last week, (982 tach and 1248 Hobbs) we had
> the engine removed from the aircraft and shipped
> to a local engine repair/rebuilding shop, and
> watched the tear down. Lo and behold, we found
> large iron shavings in the bottom of the oil pan
> -- too large to be caught in the oil suction line,
> and too large to drain during an oil change. The
> #2 cam was "machined" down about 1/8" causing
> problems with the engine performance (incomplete
> valve opening for intake or exhaust on the
> opposing cylinders). In retrospect, we had some
> roughness reported during the past six months, but
> such could not be duplicated in a controlled
> environment (with a mechanic on board).

>     We are led to believe there is a "congenital
> defect" in the cam design, despite the engine
> being FAA certified, in that no positive
> lubrication of the cam surfaces take place until
> the engine develops sufficient RPM to throw the
> oil upon the cam faces. If a pilot spends an
> "abnormal" period of time cranking, say one minute
> over a period of time, we suspect there is no
> hydroplaning of the cam and lifter surfaces taking
> place, and we, instead, experience metal against
> metal -- hence the initiation of the cam wear and
> removal of the hardened cam surface. And once this
> wear starts, it will continue to get worse.

>     The aircraft is hangared in central Florida,
> and is flown several times each week, for a
> minimum of one hour and as long as eight hours. We
> have used Aeroshell 15W50, but originally used
> Aeroshell 100. We are not sure whether the change
> over to 15W50 could have initiated the problem.
> One unsubstantiated theory is the synthetic blend
> may not adhere to the metal surfaces while the
> aircraft is not being flown for a "prolonged"
> period of time, which requires further definition.
> Our log books indicate flight about once every
> week.

>     There were times when pilots had difficulty
> starting the aircraft, due to (a) improper pilot
> procedure for the fuel injected engine as well as
> (b) a defective voltage regulator (which was
> erratic and took out three alternators before we
> could isolate the cause rather than the effect).

>     If our assessment of the defect is correct, we
> desire to take some prophylactic measure, such as
> installing the nozzles which Chuck Nye has
> developed. With as little as 3 psi (developed
> during cranking), the oil will be sprayed upon the
> cam surfaces. Another suggestion we heard was to
> install an oil line pressurizer, but this does not
> get the oil where it's needed: on the cam
> surfaces.
>
>    Anyone have similar problems, and if so, how
> were they resolved? What protective measures?
>
>

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Re: Failure 172-SP cam shaft lobe

To maintain the "whetted' surface of camshafts, Lycoming recommends the use of LW16702 additive. This additive is also contained in Aeroshell W100 plus.

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Re: Failure 172-SP cam shaft lobe

Thanks for the response, Tom. Your suggestion was right on the money.

We changed over to the Aeroshell 100 Plus following the break-in of the rebuilt engine. Due to poor initial advice and lack of knowledge on our part, we did not know about the additive requirement by Lycoming.

The proper oil solved the problem. Although the engine is currently near is TBO, it works just as well as when we had the enegine rebuilt. With proper fuel management, I achieve 7.5 gallons per flight hour or better,  between 115 and 120 knots, at altitude. No complaints.

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Re: Failure 172-SP cam shaft lobe

This is the second one that I have heard of in the 172S. The other was during the fist 1800 hours & was flow all the time.

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