Camshaft Question

bjb3013 · #1 10-16-2007, 08:02 PM

My neighbor had to remove his 100 hr since OH Lyc IO360 engine from his Mustang II because of a case crack on the alternator attachment area. Real Bummer. He did the OH work himself with A&P supervision 2 years ago.
When we split the case we found the #4 Ex lobe was slightly pitted and the tappet was beat up. Not good!
To me all of the other lobes looked good. The case will take several weeks to fix so he decided to send the cam to Aircraft Specialty Services for inspection. They say the cam is worn on the "toe" of several lobes?? I do not understand this description. Now it must be reground and all the tappets need to be ground. $$$
What could have possibly caused this this rapid wear on the cam? 100 Hrs!!!
I think he will use my A&P to re assemble this time. Could this be a pre lube problem? What the best to use on the cam and tappets. All the bearings look perfect so I do not know what to think.
He says all temps and press have always been OK.

Thanks,
BB

mannanj · #2 10-16-2007, 08:17 PM

How long did the engine sit between O/H and first flight? If it was a long time, was it preserved properly and not turned over before running?

It's amazing how fast a cam can rust when it's been cleaned of oil or preservative. Doesn't take much rust to eat through the hardened surface then the wear and spalling start.

bjb3013 · #3 10-16-2007, 08:28 PM

Overhaul to first flight 2 weeks. Flown regularly, 20 hr oil changes, Aeroshell mineral oil, I know the last filter looked good.

BB

mannanj · #4 10-16-2007, 08:44 PM

Listed all my "usual suspects". Were the cam and followers yellow tagged before the O/H?

I used an automotive "assymbly oil" from Auto Zone or NAPA. Can't remember the name of it now. I also pre- oiled the engine before start up by spinning it by the starter with the plugs out until it showed oil pressure. Only takes a few seconds.

Stephen Lindberg · #5 10-16-2007, 10:29 PM

I have heard that some Lyc camshafts are "soft", don't meet the specs for hardness. I heard this about a year ago from a well-known engine expert whose name you would recognize but I don't wish to reveal publically because it was a private conversation at an airshow, and he was not speaking for attribution. He told me that he has checked the hardness of many camshafts with his own Brinell hardness tester, and some weren't up to snuff. If you want your bad camshaft tested for hardness, email me and I will tell you who to send it to. Corrosion would be the first thing that comes to mind, but only two weeks from assembly to engine start tends to rule that out. Did the engine sit without running for a prolonged period of time at any point? Lycs are famous for premature cam failure but I don't think anybody can really say why in all cases, from what I have read and heard.

mahlon_r · #6 10-17-2007, 04:48 AM

You don't mention what the condition of the cam and tappets were at reassembly during the overhaul.
Once a cam and tappet combination has been run against each other, using a tappet that was running on one lobe on a different lobe can cause both to wear out prematurely. So, if during his overhaul he didn't get things reground or replaced with new and he swapped tappet locations around, he might get this result.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."

rgbewley · #7 10-17-2007, 08:00 AM

Mahlon's note is right on point. If you aren't going to regrind the cam and replace the tappets, it is essential that you mark them at removal. (A Sharpie will do the trick.) Another question is what type of lube was used at assemby? Improper lubing could have caused scuffing at initial start up and expedited the wear on the lobe.