I have just checked: a camshaft can be reground provided it is within a dimensional spec. It is then re-nitrided so the case hardening is restored.
New cams can be found for example here – around $2500.
It is better to regrind the old cam because it has already proven itself under stress, there is no issue with number of cycles (it’s steel, no aluminium) and it will be NDTd anyway.
Better make a new thread?
Peter wrote:
It is then re-nitrided so the case hardening is restored.
Are you sure about that? According to a post by Ed Kollin, camshaft are hardened using carburization. Crankshaft, OTOH, are nitrided.
BTW: seems like roller tappets don’t solve the camshaft problems
roller tappets don’t solve the camshaft problems
They won’t if it is corrosion, as in your URL.
It always is corrosion, isn’t it?
As is mentioned in follow up discussions in the Ed Killings thread, there appears be more to the story, like manufacturing mistake.
I was wondering about the failure mode, as a thought experiment, say you keep flying with a pitted/spalled camshaft. What phenomenon will become so excessive, prior to catastrophic engine failure? Even if the lobe breaks completely off, I should still have partial power, on five remaining cylinders,no?
Flyer59 wrote:
The main reason it’s so expensive is that I’m not lying about the real cost
You nailed it. My recommendation: Wipe the cost under the carpet and don’t think about it, because thinking about it won’t lower the cost. So what’s the purpose of thinking about it?
I don’t! I just wrote it down for this thread from an old .xls i had made when i firest bough the plane. The money i spend on it doesn’t interest me at all, as long as i can give my kids what they need and show them enough of the world … the money itself is meaningless to me.
Just look at hourly rental costs. Since a rental plane barely breaks even, if at all, its a good surrogate for true hourly operating costs. At my airport a C172 rents for $135, including fuel.
Check out this accident report
Because not all cylinder(group)s are equally affected by spalling, you will get different power out of different cylinders, thus a rough running engine. Also, they claim that some misfirings were caused by unignitable mixture – but don’t offer much of an explanation.
Furthermore, I don’t buy into their claim that the amount of gas entering the cylinder is proportional to the valve lift – there ought to be an inrush of gas before the gas flow tails off, and the shape of that flow is surely affected by the clearance between valve and seat.
But anyway, if you cut open your oil filter at all oil changes, you’ll very unlikely notice something bad with the engine before you see significant metal in the filter.
