Engine Making Metal

[AESpecialists]

Corrosion initiated cam failure is by far the most common occurrence. While it's possible a cam could just wear out, we've seen cams make almost 9000 hours in service with two regrinds and still be servicable (although the third grind would be pushing it)

 

Cam failure and spalling lifters may not be immediately recognizable in the oil or filter. The flakes of metal are flung into the cylinder bores and become embedded in the piston skirt which keeps them out of circulation.

 

One of the issues with flat tappets (and true of old cars as well) is that the EPA mandated the removal of phosphorus based additives from base oil stocks. These were the additives that helped with 'wiping' friction such as cam on tappet. With roller lifters such as in most automobiles or overhead cams, this isn't an issue. Lycoming sells a phosphorus additive that addresses this lack, as do some of the proprietary oils and additives on the market.

[Yetti]

Seems that the small spaces of the mooney engine compartment could also be an issue

 

http://egaa.home.mindspring.com/engine2.htm

 

 

Tell us about the compression lost on the cylinders.  What is the cause

[mooniac15u]

Corrosion initiated cam failure is by far the most common occurrence. While it's possible a cam could just wear out, we've seen cams make almost 9000 hours in service with two regrinds and still be servicable (although the third grind would be pushing it)

Cam failure and spalling lifters may not be immediately recognizable in the oil or filter. The flakes of metal are flung into the cylinder bores and become embedded in the piston skirt which keeps them out of circulation.

One of the issues with flat tappets (and true of old cars as well) is that the EPA mandated the removal of phosphorus based additives from base oil stocks. These were the additives that helped with 'wiping' friction such as cam on tappet. With roller lifters such as in most automobiles or overhead cams, this isn't an issue. Lycoming sells a phosphorus additive that addresses this lack, as do some of the proprietary oils and additives on the market.

Is there some evidence that the spalling is initiated by corrosion or is that just presumed? Your next statement suggests friction is the issue.

[Yetti]

Seems that we need to be running more zinc dialkyldithiophosphate (ZDDP)

 

http://www.motorweek.org/features/goss_garage/too_much_zinc_in_your_oil

 

And then blackstone did some tests

 

http://www.blackstone-labs.com/Newsletters/Gas-Diesel/November-1-2010.php

 

So maybe it is lack of lubrication around the valve guide.   Can the Mooney TLS kit be fit to other engines?

[M20F]

Corrosion initiated cam failure is by far the most common occurrence. While it's possible a cam could just wear out, we've seen cams make almost 9000 hours in service with two regrinds and still be servicable (although the third grind would be pushing it.

Not disputing that but really find it hard to believe 3yrs of 200hrs a year is going to have a corrison problem assuming normal oil changes and the hours reasonably spread.

There are more than a few shops that will take your good cam to resell and put in one of those three time plus ground cam's right at tolerance in. I think you would agree that some overhaul shops are a bit better than others. Overhauls even when you comply with SB240 can vary greatly.

No way to really tell the problem for sure either way with the information the OP gave but just doesn't seem like a corrosion issue (though I have been wrong a lot before!).

[KSMooniac]

 

So maybe it is lack of lubrication around the valve guide.   Can the Mooney TLS kit be fit to other engines?

 

That is a strong theory... it is probably a combo of valve sticking (due to insufficient oil flow & cooling) leading to higher mechanical stresses at the cam/lifter interface.  Sub-par metallurgy and/or existing pitting can cause a breakdown of the metal with these higher stresses.  

 

It would be interesting to find out how many Bravo engines fail the cam prematurely.  I can't say I know of ANY.  

 

I know I would do the Bravo mod to my IO-360 in a heartbeat if I could.  It is a shame that we can't since our cylinders work just as hard as those on an M20M.

[jetdriven]

I don't think you can put ZDPP in an aircraft do five because it can leave deposits in the chamber that can lead to preignition. AD oil stands for Ashless Dispersant.

[Guest]

I've got a number of camshafts in a box under my work bench which have been there for years with no oil on them. None are rusting any more than when they were taken out. I'm a strong believer that the issue is metallurgy or materials more than oil type, change intervals or corrosion.

Clarence

[merrja]

Curious if your missions were long flights with constant power settings.   Also sounds like a switch to Continental since they figured out the valve tappet issue

 

http://precisionengine.home.mindspring.com/engine3.htm

 

Maybe we should be running diesel truck oil.  Does anyone know the source of the lifters for Lycoming

 

http://www.hotrod.com/how-to/engine/flat-tappet-cam-tech/

Most of my flights are > 1.5 hours and probably average ~3 hours @ ~ 9K feet  

[RobertGary1]

remember that the quoted price for an overhaul assumes a perfect working engine to start with. Any damaged parts (case, cam,crank, etc) adds to the cost. A totally unusable core adds an additional $20K to the cost. I know the hard way. plus add cost for hoses, cooler etc.

-Robert

[ryoder]

Not sure I buy the cam destroys itself from rusting due to non use argument either since my plane sat for fifteen years before the second owner and then it sad for almost a year before I bought it and knock on wood the thing is working fine. I do have an oily cylinder that is probably responsible for my higher than new oil consumption though. But I have no metal at this time with over 100 hours personally and 2550 total engine time.

[mike_elliott]

That is a strong theory... it is probably a combo of valve sticking (due to insufficient oil flow & cooling) leading to higher mechanical stresses at the cam/lifter interface.  Sub-par metallurgy and/or existing pitting can cause a breakdown of the metal with these higher stresses.  

 

It would be interesting to find out how many Bravo engines fail the cam prematurely.  I can't say I know of ANY.  

 

I know I would do the Bravo mod to my IO-360 in a heartbeat if I could.  It is a shame that we can't since our cylinders work just as hard as those on an M20M.

What a  beautiful Segway into LOP vs ROP! What causes valves sticking? Why does oil coke on the valve stems? what causes high cyl tepms? Do you think Lycoming (we don't need no steenkin' valve stem lubrication) put in roller cams in all their reman's now because they like us, or is it because they want to quietly back out of this design weakness and keep their beans their beans. 

Have at it boys!

[Yetti]

It would seem that if you want more than 400 hours out of your Lycomig (based on SB 388) http://www.caa.si/fileadmin/user_upload/pageuploads/AD-NOTE/AD-2006/093_sb_SB388C.pdf%C2'> people will need to ream their valve guides out.

[Yetti]

Several more good reads

 

http://www.secure4host.net/upload/files/LycomingValveBillScottDiscussion2013-08.pdf

 

 

Starting at page 55

 

http://www.joespiper.com/Lycoming.pdf

[merrja]

One more question, can I get your thoughts on the cylinders? New, nickel or remanufactured? Not sure which direction is prudent?

[jetdriven]

New, unless you have first run cylinders, then overhauling them at a good shop is an option.

[merrja]

Thank Byron