Welcome to the world of our great aero-engines where a certification stamp turns a turd into a gold nugget.
Love it 
A comment from a pilot who is not an engineer, if I may. I have trusted my several aircraft over many decades to a single shop here in the UK and never had a prroblem with their knowledge, their reliability or their detailed explanations of anything and everything. I have always been welcomed into the workplace to look with them at what they are doing and why. They have zero timed engines for me and they have run without problems for hundreds of hours with oil analysis showing no abnormalities. Of course, just as we all do, I trust my life to these guys and they have never let me down. Good UK shop in my view and they build a LOT of engines at sensible cost. Keep looking, there are good UK shops out there.
New camshaft and followers (tappets) were fitted at the 2010 zero time rebuild, including near every other thing that moves.
The parts bill was over £9,000 (GBP)
We did the same but sometimes I think if you happen to have a cam and tappets which did fine until TBO maybe it is best to keep them. If those parts are of proper quality and lubricated well they will probably run forever. But instead we often exchange such parts for new parts of unknown quality just because they are new…
We did the same but sometimes I think if you happen to have a cam and tappets which did fine until TBO maybe it is best to keep them.
I don’t think that is the right thing to do. There is a very strong metal to metal contact between the cam lobes and the tappets and even though an oil film is supposed to be between it, there is wear. This is why you regularly measure the valve travel to determine how much material you’ve lost. Only the surface of the lobes is hardened.
In all cases of overhaul or even repair I’ve come across lately, the camshaft was replaced with a factory new part.
I’ve asked an engine overhauler some time ago what the average age of TBO is. He said considerably less than 100 although they didn’t have statistics.
100 hours?
Better post his name so we can all avoid this cowboy.
Unfortunately it is actually possible if all his customers are clueless on CHT management, which is statistically very possible. I assume he means 1000.
If I wanted to, I could trash my engine in minutes, just by climbing out of one of these Greek airports at Vx, and I could guarantee six cracked cylinders by the time the thing won’t climb any higher. Now, we could debate whether it should be possible to trash a $60k engine like that. Obviously it should not be possible. But people do it, and then they slag off these engines all over the internet, without disclosing what they actually did (mostly, they don’t know, anyway – they have no working CHT gauge). Engine management is a fairly recent thing which came about only via the internet (last 10 years or so) and even then only to pilots who are online – and even then many absolutely refuse to learn.
So blank statements about engines making only X hours (or whatever) are just meaningless.
Most engine builders know nothing about flying. Almost none of them are pilots.
I think something happened to Warley Air’s engine. It was mismanaged in some way – probably a combination of sitting around and some other stuff.
It is a normally aspirated engine after all. With a turbo engine, all bets are off and most need major work around the 1000hr point. That’s why I have not bought a TB21. I could buy one tomorrow if I wanted to…
Welcome to the world of our great aero-engines where a certification stamp turns a turd into a gold nugget.
That’s true in any certification environment. Look at ISO9000. You produce your own “quality manual”. If you state in there that all your products will self destruct in 12 months, you could NOT be denied ISO9000 certification. This is not a joke. Obviously, if you of your customers got hold of your manual and actually read it (unlikely) they would not buy your product. But this is unlikely to happen because most ISO9000 enquiry forms (I get ~1 per day) are written as
State your certification number
If provided, skip the rest of the form
If not provided, answer the following 50 questions (these are a load of crap like e.g. “do you segregate defective material” – I am always tempted to answer “no, we send out all the non-working crap first, Sir”).
Aviation has merely produced a certification environment which is quite tight. ISO9000 isn’t at all tight. If you want to buy toilet paper, you can probably get it from an ISO9000 supplier but it will cost you more, so companies make many exemptions. In aviation certification, exemptions reduce profit very directly, so everybody colludes in operating the system, and generating a load of FUD.
There is no easy way around this problem. The only solution is to do heavy incoming inspection. NASA started x-raying switches in the Apollo programme, after the famous solder blob which was floating inside one of them. But then NASA had extremely competent people, back then. Lycoming is today a shell of a company, average age 64.9 years.
The forum swallows the percent sign, I wrote 100 percent of TBO.
I think something happened to Warley Air’s engine. It was mismanaged in some way – probably a combination of sitting around and some other stuff.
How can you mismanage an engine so that the camshaft spalls after only 150h? The engine was not old enough to really suffer from downtime and according to WarleyAir it didn’t have significant downtime. Maybe some of the oil channels were blocked and the engine didn’t splash enough oil onto the camshaft?
Most likely it’s defective camshaft material which is very common.
How can you mismanage an engine so that the camshaft spalls after only 150h?
Standing around for a month in salt-laden (UK winter) air will do it. And the UK winter is the very time when a plane is least likely to be flown.
Maybe some of the oil channels were blocked and the engine didn’t splash enough oil onto the camshaft?
That would also do it – i.e. an incompetent overhaul/rebuild. That is slightly curious because any “zero time” rebuild would involve NDT of the crackcases which means cleaning off all the paint and cleaning any crap out of the oil galleries before and after that.
This may be an example of why an engine warranty is likely to be worthless. You can never prove anything like this.
Most likely it’s defective camshaft material which is very common.
Lyco did have a problem c. 2000 with crankshafts on which a heat treatment stage was left out. These cracked typically within 100hrs, with some fatalities… The whole story is much more involved because they also got their crank mfg contractor to add vanadium which was done without due research, and this resulted in the infamous 12 year life limit but there is no evidence that any of these actually broke.
I am not aware that there were similar QA issues with camshafts, but it’s possible.
The forum swallows the percent sign, I wrote 100 percent of TBO.
This is 100% or 100 % or 100%. . So for me the % sign seems to work OK.
Circumstantial evidence does seem to point to inactivity and humidity as substantial factors in the Lycoming cam issue. I fly year round in a (relatively) dry climate and it doesn’t seem to be an issue here. I know one person personally who has has this problem, actually he’s had it twice, on the same O-320 that he’s been running since the mid-1970s. But he’s in Florida where humidity is high.
Otherwise I wish people would learn the difference between clearances and tolerances – a pet peeve of mine!
Otherwise I wish people would learn the difference between clearances and tolerances – a pet peeve of mine!
OK, lets see if I’ve got this right. I should have as background is mechanical engineering. My explanation maybe less than perfect, but I know what I’m talking about – oxymoron ?
A ‘clearance’ is the ‘gap’ between TWO components, be it circular or two flat surfaces. or whatever. A ‘tolerance’ refers to ONE component only and concerns it’s dimension.
So if the designer chap says something has to be manufacture 50 mm long or diameter, he has to put a plus or minus ‘tolerance’ on it, as in principle nothing can be made exact and it also depends on what the components function is in life.
So on the drawing he would put 50mm + or – 0.001. May be +0.001 and – 0.003, stating both figures.
If you’ve got a bar (say a gudgeon pin) that goes in a hole (the hole in a piston) the hole has to be that bit larger than the diameter of the pin.
If the hole is made say 25 mm dia minus 0.001 (bottom tolerance) and the pin say 25 mm dia plus 0.002 (top tolerance) then it wont fit and it’s know as ‘a clash of tolerances’ and the designer has ‘cocked-up’ and specified the wrong ‘tolerances’ for the job.
A ‘clash of tolerance’ would be required ‘by design’ if the pin was meant to be hammered into the hole and NOT come out.
If a ‘clash of tolerances’ is by design, so one component has to pressed or hammered in to the other, it’s know as an ‘interference fit’. There are varying degrees of ‘interference fits’.
