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Wear

Wear and damage typically occurs at the nose of the lobe or slightly before the nose (right were the large pit is in this picture). 

Focusing on the wear only; notice how the entire length of the lobe is worn. Since the lobe is ground at a slight taper you don't get full contact across the lobe until it has a lot of wear. Top of lobe has rounded. This lobe has worn out. More wear than you would normally see at engine TBO but not unusual.  Now we'll focus on the pitting.

Pitting

Pitting is not normal for any lobe and is considered to be damage. Usually caused by corrosion pitting and metal fatigue. Very common with low usage engines.

Symptoms

None

Detectable in Oil Analysis

No

Detectable in Pre-purchase Inspection

 No

Stuck or Sticking Valve

Nothing destroys a camshaft lobe quicker than a stuck or sticking valve. One more reason why you want to fix it immediately and not depend on time or slow additive treatments to take affect.

If you even suspect you have a stuck valve, ground the airplane immediately and have it checked out.

If either valve sticks open you are making a forced landing. If either valve sticks closed you are making a forced landing.

If you are purchasing an airplane and the logs look like their may have been a stuck valve in the past - be suspicious of the condition of the camshaft lobes.

A stuck valve may be caused by valve overheating due to inadequate rocker box lubrication (rare) or a leaking exhaust valve (among other reasons).

On Airplane Camshaft Lobe Inspection

On most Continental engines, and the '76 series Lycoming engine, you can remove the camshaft follower for inspection. Usually the camshaft follower face wears before the camshaft lobe so you can sometimes save the camshaft by inspecting and replacing suspicious camshaft followers. Other engines use "mushroom tappets" that you cannot remove and inspect.

If you remove a cylinder from the engine you have a big access hole in which to inspect the inside of the engine. Use a small light to inspect the lobes. For areas that are hard to see you can use the fingernail test

 Some camshaft and camshaft followers are hard to get a good look at so reach into the engine and use your finger nail and rub it across the lobes and the followers. Your finger nail will "catch" on any small pits.

I use my left hand since it is slightly smaller than my right. I can drag my fingernail across each camshaft follower and camshaft lobe. 

If you find a lobe with slight pitting, such as the one on the left, it may not be bad enough to effects airworthiness, but  It is a sign to start budgeting for a repair.

tips on inspecting the O-320H2AD camshaft

Camshaft Lobe Inspection by Examining the Oil Filter

In the past when we were disassembling engines and found ground down camshaft lobes we would collect a sample of the oil and send it out for analysis. It always came back clean. In the late 1970's when Lycoming had a huge camshaft lobe problem with their '76 series engines, such as the O-320-H2AD, it became very apparent that oil analysis would not detect camshaft lobe failure until a very late stage. 

The particles that pits produce are caught in the oil filter and don't end up on the oil analysis sample. Those that might get past the oil filter settle to the bottom of the sump or sample jar and don't get examined. Those that get examined are too large for the Spectrometer to analyze

Lycoming outlined an oil filter inspection process as a result and it has worked for 20 years. Here is an adaptation that seems to work well:

The particles generated by the camshaft or camshaft follower pitting look just like iron filings you find when you take a magnet to a sand lot. They are not shiny, but dark and long, which makes them hard to see by looking into the pleats of the oil filter. Even if you do happen to see some, it is hard to access how many there are. You must remove and collect the filings to make any kind of judgment.

At the 50 hour oil change, rinse the filter media - I put the filter element into a coffee can with some Stoddard Solvent and shake. Use a toothbrush and wipe down the filter pleats. Take a stick magnet and drag it across the bottom of the can to collect all of your filings. Those long dark iron filings are from the camshaft lobe or camshaft follower face. If you have enough to cover the end of the stick magnet - bad news, your camshaft is bad. If there are just a few around the edge of the stick magnet - everything is normal.

I can't say that this method won't miss something as it will, but for the past 25 years it has proven effective, even if it isn't 100%.

Engine Symptoms

A engine with a camshaft lobe that has worn flat runs smooth but lacks power. For helicopter pilots the power loss is very noticeable - for fix-wing pilots it often isn't noticed.

Fixed pitched engines will not make rated rpm

 Each time our shop took apart an engine and we found smashed, damaged, and destroyed lobes on the camshaft,  I would ask the pilot how the engine operated. "Ran great" was the usual reply, even from very high-time experienced pilots.

For the airplane pilot, engine power is hard to measure. Each time we fly, the engine produces differing amounts of power due to changes in:

• Density altitude

• Temperature

• Humidity

Aircraft performance changes due to the same plus aircraft weight. Judging engine power based on aircraft performance is difficult. A helpful rule I use: Aerodynamics give you speed and horsepower gives you lift.

Symptoms I have heard from pilots with airplanes with smashed camshaft lobes are:

• its a dog (the airplane performance that is)

• takes longer to takeoff

• doesn't climb as fast

• I use more gas than normal

All of these symptom descriptions relate to lift. 

note: I haven't done, nor am I aware of, any tests of EGT temperatures on engines with smashed camshaft lobes - I would be interested if you have such data

Flying is the best prevention

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