re: Measuring cam lift from the rockers : Unfortunately, this technique is not very reliable since the hydraulic cam followers can ’deflate" giving you a false positive.
I’ve said it before and I’ll say it again: the best way to monitor cam/follower wear is from collecting regular (every 25 – 50 hours) oil filter samples.
Peter wrote:
ou are 100% sure the maintenance company is actually examining them (many don’t).
If I were an owner I would DEMAND to see the open oil filter, better yet, have it opened and examined while watched !
It’s true that almost nobody would open up an engine just because some metal goes up on the oil analysis from say 10ppm to say 30ppm IF the oil filter and the oil strainer are clean AND you are 100% sure the maintenance company is actually examining them (many don’t).
The cost of opening up an engine, even if you don’t do anything with it, would be of the order of €5000 so is not to be undertaken lightly. And if anything is found which makes it unairworthy (any of a hundred different things) no engine shop (that isn’t a complete cowboy) will put it back together until the said issue has been rectified, so the likely bill is going to be way more than €5000.
Camguard does help a lot with wear reduction. It is perhaps the only additive which actually does anything.
This is also worth a read. You need to stick with the same lab.
Oil analysis, cutting the filter and inspecting the strainer are standard techniques. Oil analysis is so cheap that it’s not a big thing. What Michael rightfully complains about is that oil analysis does not tell you what to do, it’s just one tool and there are many ways to interpret a result.
Lycoming has a SB that details the valve travel measurement. That’s definitely in order in your situation but’s entirely trivial. Remove the rocker covers, attached the “measuring clock”, turn the prop and write down the value. Do that every 100h and you can see your lobe size.
This Lycoming has ~1400hours on it, in a ca. 2005 C172 (non-turbo).
Three pots are off for corrosion inspection (national AD).
So the idea is to continue to check the oil filter for metal, perhaps measure valve travel periodically? (How is that done? With a “measuring clock”?)
Would there be any point in running with Cam Guard in the future, is it too late anyways?
Also, Michael would disregard oil analysis (as always), while others would recommend trending the oil to look for metal. Not sure what to do on this one….
G
Must have been before “my time”…
There were bad camshafts, too. My previous aircraft was affected, O-320.
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.
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.
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.
