Interesting video.
The NM guy is saying 80-90% of the metal coming off the camshaft ends up embedded in the piston walls. I don’t know enough to question that (it does seem really surprising) but looking at the large amount of corrosion (even the crankshaft is scrap due to corrosion) I doubt the owner has been doing oil analysis. Apparently the oil filter was clean, so perhaps at least some of the corrosion is historical.
With the scrap crankshaft, and crankcases having to go to the USA for machining, they are in a situation similar to the IO540 owners whose “maintenance” company forgot to check for the crankshaft AD. With a useless crankshaft, and even with usable crankcases, the core value of the engine is so low that a Lyco remanufactured engine was the least bad option, and AFAIK all such owners went for that (well, after the 2009 deadline, before which you could buy a crankshaft kit for $2.5k, which is what I did).
Interesting the crankshaft here had already had the inside of the flange machined out to remove corrosion, at some time in the past.
I just came on here to make you aware of the latest video, which hopefully answers a lot of your questions. Apparently we have been sending the oil to the lab for testing.
I am now wondering if the damage to the engine (apart from the top end stuff which prompted the current dismantling) happened a long time ago and that is why it has not been making metal in its “current life”.
There was a famous UK crash (it may have been the 4x fatal on Sandown, Isle of Wight, where a PA28 came off the far end of the runway, maybe 10 years ago) where the AAIB found the camshaft similarly dramatically worn but when they put the engine on a dyno they found the power output was only 10% below spec. And very few pilots, especially renters flying different ones, would have noticed that. The AAIB report is worth a read.
I don’t believe that, once the case hardening is worn through, the camshaft life is only ~50hrs as stated. With lubrication it should last a lot longer. Case hardening is not total magic. It is pretty good in that a camshaft can make several TBOs, but a 50hr life once the 0.025" or so of case hardening has worn through doesn’t sound right to me.
How many hours/years has this engine been in the current syndicate?
I don’t know too much history Peter. Our aeroplane has been fairly under-utilised, but has been flying 100-150 hours a year in recent times, I understand. It hasn’t had long layovers in our present group history as far as I’m aware.
What I meant was its life before your group started flying it. How much of that history is known? But you’ve answered that. My feeling is that probably some funny stuff went on back then, and you picked up the bill for it.
In your group it’s had plenty of use.
I am amazed you have found it economic to rebuild that engine, given a new crank is needed. But maybe the numbers still do stack up.
The problem is Peter, that once you’ve got to that point, you’ve already spent £££££ and you’d be starting again with a new engine. In other words, you’re in too deep.
Peter wrote:
I don’t believe that, once the case hardening is worn through, the camshaft life is only ~50hrs as stated.
I think it depends a bit on the engine – the O-320-H2AD (where AD in the model designation might as well mean ‘airworthiness directive’) is famous for rapidly eating camshafts. My PPL training was interrupted by an O-320-H2AD doing just that, and it wasn’t as if the engine didn’t get enough use – that particular C172 flew over 1000 hours a year and that time needed the engine to come off due to the camshaft at around 1200 hrs since the previous overhaul. On the other hand, a glider club I used to be a member of was suspected of going for years with a camshaft slowly getting rounded out in one of its tugs (O-360)
The Flying Reporter posted this video a few days ago
which was shot before the engine problem was discovered. Around 22:00 onwards there is a possible clue about the engine issues… always tricky to make these decisions.
Peter wrote:
There was a famous UK crash (it may have been the 4x fatal on Sandown, Isle of Wight, where a PA28 came off the far end of the runway, maybe 10 years ago) where the AAIB found the camshaft similarly dramatically worn but when they put the engine on a dyno they found the power output was only 10% below spec. And very few pilots, especially renters flying different ones, would have noticed that. The AAIB report is worth a read.
Just read that report (the mind boggles at trying to put four full sized people in a 140, let alone trying to take off uphill with a tailwind from grass) and the one they tested was a similar condition engine and cam, not the actual one. The AAIB basically speculated that the a/c was well down on performance even before the camshaft wear, which was enough to remove all doubt.
We scrapped our engine and put a new one in back in the autumn. Think it had done about 1800 hours and annoyingly had only just had a new cylinder a few weeks before. We all agreed it was well down on power and at the annual Thurrock came back and told us the camshaft was completely mullered. We looked at rebuild options and costs, and in the end opted for a ‘new’ rebuilt engine.
I don’t see how anyone could make useful assumptions on takeoff performance from grass, anyway. The takeoff run can be plus or minus 20% from one day to the next, according to how damp the ground is, etc.
Yes indeed, the comments on the aircraft loading made at the time were incredulous.
Interesting that your camshaft was knackered too. Was there any actual or potential period of inactivity?
