Please consider the following picture. Workshop suggests to run another 500h/5y (whatever comes first) and re-inspect. What would you guys do?
And – what could be the cause for this lobe to be worn more than the others?
I would bin the cam and its follower as once the hardening has failed it’s not going to be long before that wear rate accelerates dramatically.
Has the case hardening really failed?
It isn’t microns thick. I think it is about 0.050" thick.
The pic was taken with a pot off?
Run it, do oil analysis and measure the valve travel every 100h. It requires a simp!e fixture with a gauge. Your shop will have it or buy from Spruce and do yourself. You don’t really risk much at all.
Hard to tell from the photo how much wear there actually is. What’s the follower look like ?
If you choose to run it :
- Check your oil filter regularly, oil analysis won’t tell you jack;
- If it is indeed worn through the hardening, it will self-destruct in the next 25 hours or so and will spew bits of metal through-out the engine which could provoke collateral damage.
I don’t know about Conti but Lycoming have a bulletin for acceptable cam lobe wear which is measured by a reduction in valve travel. That is a very simple test and required in Germany for engines operated post TBO at each annual. If you’ve lost too much lobe material, the valve travel will be below the threshold and it’s time to buy yet another improperly manufactured camshaft.
yet another improperly manufactured camshaft.
Let me offer a contrary data point here.
A pilot on EuroGA recently found his engine well trashed. Suspecting the usual story of “crap Lyco metal” they had it lab tested and found the metal absolutely perfect, with the case hardening very consistent and to spec.
I have tried to get him to publish this data but he won’t, maybe due to a lack of motivation or possibly because his syndicate doesn’t want to.
I can’t go public with it (I have the data and the photos) without his permission, obviously.
This is a typical scenario in GA where really useful info won’t come out, frustratingly. The most common reason is that the owner is trying to sell the plane, quickly and smoothly…
In his case, the verdict is that the engine sat around for months, rusting away, before they bought the plane. I haven’t seen their logbooks but sometimes – I have no reason to suspect this in his case – this scenario is accompanied by logbook forgery to make it look like flying has been regular. Or the buyer just falls in love with the plane and buys it regardless, and perhaps avoids checking the oil filter for fear of what might be in there, etc. And syndicates have their own politics…
It is a fact that these engines are highly vulnerable to corrosion of the camshaft which then rapidly trashes the camshaft and the cam followers. Sometimes it doesn’t happen though and nobody knows quite why not; the suspicion is the amount of moisture in the air affects it. IMHO any engine in any hangar queen in Europe is vulnerable, but you might get lucky. In Arizona you are probably good for a few decades 
The camshaft pic above looks clean.
I didn’t say all Lyco camshafts are forged by chimps but a lot of them were/are, see the various ADs. The previous owner of my C172M got shafted by Lycoming with a “special replacement offer, virtually cost price, only 10k€”. Just recently Lyco pulled back a batch of bad cylinders and proudly offers free replacement including a (unrealistic?) labor allowance but what about the inconvenience and substantial extra cost for a break-in, not to speak of the risk of the break-in not working as expected and being at the risk of the operator?
I agree with your assessment, that cam should stay in operation, provided the valve travel is within spec.
That was a crankshaft AD, not a camshaft AD.
The full story on that is complex. Lyco used a subcontractor who missed out some heat treatment stage(s) resulting in brittle cranks which broke very quickly. Later it turned out that vanadium had been added for easier forging (and there was a long legal battle as to whether this was authorised by Lyco, which IIRC Lyco lost) but there was never any engineering evidence suggesting this weakened the cranks and AFAIK none of those ever snapped. Lyco implemented their official 12 year life as a MSB, later made an AD by the CAAs, to get the cranks out of service, in what is believed to be a purely legal move.
As regards cylinders, the best view I have is that Lyco make the best cylinders today. The various 3rd party cylinders have mostly had major quality issues.
I am not aware of Lyco camshaft issues. Have there been any? AFAIK every case of a trashed camshaft and/or cam followers is a corrosion candidate, but it cannot usually be proven or supported either way because the owner under whose ownership the engine falls apart and who flew every 2 weeks or so, regularly did not have it since new so could not be sure of previous history.
There were bad camshafts, too. My previous aircraft was affected, O-320.
