the fifteen million cycle problem (cam failure)

[N601RX]

Quote: jlunseth

There is a company in CO, Firewall Forward, that has a camshaft STC for Lycomings, and I am pretty confident it covers J's.  They presented at the Mooney PPP in CO last year.  They provide a hollow cam with lube holes in each lobe and at the bearings, so that the camshaft is fully lubed, particularly at start up as soon as the oil pump begins to work.  Supposed to be pretty good, don't know myself I have a Cont.

[N601RX]

There are other things that can damage a cam.  Sticking valves, Lifters not rotating, hydraulic internals not functioning correctly, Incorrect pushrod length.

[M20Kid]

I'm not a mechanic and I don't have first hand information about this but I have been investigating many engine issues lately due to my own engine problems on my 231.  My current understanding is the Lycoming does have a higher cam failure rate because the cam is located at the top of the engine, which allows the oil to run off and leave it unprotected.  Continental puts the cam at the bottom of the engine allowing all the other parts to rain their excess oil onto the cam keeping it protected longer after shutdown.

[KSMooniac]

Quote: jetdriven

Unfortunately your care, operation, and use cannot undo what was done prior to your purchase.  You already posted how little it flew in the years before you bought it, and I suspect it was already going down the road of premature failure when you got it, and there was no way to back up and take a different turn...

[danb35]

Quote: allsmiles

Yes it did Byron. The consensus from everyone I've spoken with is to allow the engine to cool down at 1000 RPM for about 5 min prior to shut down. There are good reasons for this recommendation.

[johnggreen]

I have two posts and I'll seperate them for clarity.  The second may come after dinner and a couple of glasses of merlot so I may slur my words in #2 a bitl

I was acqainted with a gentleman who operated FBO's  over most of his life.  He was never a pilot, but just loved taking care of and fueling other people's airplanes.  He was in the service, Air Force, in the late 40's and early 50's and was a crew member on a C-97 Globemaster.  He related that when those aircraft first entered service they had a terrible maintenance history with the engines which almost never made it to 400 hours before requiring an overhaul.  Finally, they determined that the problem was lack of lubrication to various parts on start up.  They began the ritual of hand turning the props (which took several men to turn) before start up.  I can't remember the number of revolutions, but it was pretty impressive like 6 or 8.  He said that immediately, the engine issues disappeared and the engines regularly ran 12 to 1500 hours between overhauls.

I have, for year been a stickler on idle at start up and idle at shutdown.  I've owned a lot of equipment and almost never have internal engine issues.  

Post 2 will be on cool down and I'm with Allsmiles: always!

Jgreen

[KSMooniac]

Quote: johnggreen

 

Post 2 will be on cool down and I'm with Allsmiles: always!

Jgreen

[MooneyMitch]

"They began the ritual of hand turning the props (which took several men to turn) before start up.  I can't remember the number of revolutions, but it was pretty impressive like 6 or 8."

Interesting as our Savvy Aviator, Mike Busch recommends not doing this.  I believe his thoughts are that not enough oil is produced with this method and it only serves to aggrivate the lack of lubrication and can actually increase wear.  He says it's by far much better to start the engine right off. 

 

[fantom]

Quote: danb35

So what are the factual, observed, documented good reasons for this recommendation?  And are you talking NA engines, or just turbos?

My observations agree with Byron's--CHTs and oil temps are cooler at touchdown than they are when I get to my hangar.  And actually, both are cooler yet at pattern entry than either other time.  I don't have a turbo, so I can't speak to that from personal experience, but the folks at APS have instrumented one, and their observations agree that any ground time after landing is just going to heat things up.

I don't have any problem with "agreeing to disagree", but it seems pointless to do so regarding observable, measurable facts.

[PTK]

Quote: jetdriven

OK, it seems there is commonality with engines overhauled around 2001 or newer, and the failures occur around 1000-1300 hours.  I will post detailed specs of ours if enough interest is given.

[Shadrach]

Quote: fantom

The Lycomming techs here at Oshkosh suggest never idling at NA engine under 1000 RPM, at that 1,200 is the sweet spot for an IO-360. They didn't get into the engineering logic for it.

[N601RX]

What is the oil pressure at 500rpm?  I've never idled that low so i dont know.  If it drops below 40psi the piston oilers will shut off also. It would seem to me that you maybe getting hit with 3 things if this happens. 

At 40 psi the crank is going to only have 1/2 the oil from the bearings to sling off it.

The oilers have shut off and the oil that hits the piston and splatters back onto the crank is no longer available to be slung around.

The crank itself may not be spinning fast enough to sling cold oil up to the cam.

[PTK]

My understanding is that damage WILL be done when racing and forcing a pre-conceived RPM on a cold engine. Personally I never ever allow my engine to idle high at cold startup. If it will stay running at 500 RPM I'll leave it there, or if at 700 RPM I'll leave it there. Whereever it's happy until it warms up. No force. Forcing a cold engine to run higher without letting it warm up will cause damage and premature wear to internal components that depend on splash lubrication. Cold oil, cam and tappets don't mix. Just my opinion.

[jetdriven]

Ross is right, and so is Lycoming. 1000-1200 RPM religiously when running on the ground. 100% of the time.  The only time I ever ran it below that was a 40 degree start, 800 RPM for the first 20 seconds. Looking back that probably was bad practice.

[PTK]

Quote: jetdriven

Ross is right, and so is Lycoming. 1000-1200 RPM religiously when running on the ground. 100% of the time.  The only time I ever ran it below that was a 40 degree start, 800 RPM for the first 20 seconds. Looking back that probably was bad practice.