Because it is derated. Don’t ask me why.
How is it derated? Fuel flow?
gallois wrote:
Are you considering that all 4 cylinders demonstrated a weakness/fault or just cylinders #3 and possibly #4? Both of which might suffer most from cooling airflow.
I ask the question because in reading previous posts you seem to do really well with gettlng more than many would reasonably expect from their engines. I think many schools are happy to get more than 2400hrs before changing a cylinder.
My though is the failure of all four cylinders are abnormal. I could put down one cylinder to bad luck.
Under old Swedish rules we were only able to run the engines to 2400 hrs as flight training fell under the same maintenance rules as commercial flying. With part-ML (and updates to part-M before it) a non-commercial school can run the engines beyond that. So we do have a lot of experience running to 2400 hrs, but not a lot of experience running beyond that.
LeSving wrote:
How is it derated? Fuel flow?
Redlining the engine at 2400 and using a prop suitable for that maximum rpm.
Peter wrote:
However, you don’t state what was actually wrong with them.
Cylinders 1-3 were found to have cracks. I don’t know about cylinder 4 (the first one to fail), at least not yet.
Airborne_Again wrote:
Redlining the engine at 2400 and using a prop suitable for that maximum rpm.
So that actually puts more pressure on the pistons than if it was spinning faster.
Airborne_Again wrote:
Redlining the engine at 2400 and using a prop suitable for that maximum rpm.
Derating the engine that way might do the job for protecting the engine mount, structure, etc. that is only certified for specific hp, but actually increases the stress on the engine rather than decreasing it.
Redlining the engine at 2400 and using a prop suitable for that maximum rpm.
Why would anyone do that? Noise? Is this a factory mod?
LeSving wrote:
Why would anyone do that? Noise? Is this a factory mod?
Ask Cessna – I have no idea. That’s how the Cessna 172R was designed. In the Cessna 172S, which has the same engine, the rating was increased to 180 hp @ 2700 rpm.
Certainly the lower rpm keeps the noise at a lower level.
I think those hours on the cylinders are excellent.
On a small continental that I know at 1100 hours all 4 cylinders needed an overhauled due to exhaust value problems. These were brand new superior cylinders and were about 3 years old. They would have been replaced with new but due to lack of availability they they were overhauled. One would hope that the engine will now go to TBO of 1800 plus 20% so 2160 hours.
On another factory rebuilt small continental 3 of the 4 cylinders had been removed within 500 hours due to exhaust valve sticking. These were brand new continental cylinders.
To answer your question
“Would I be correct in that you run them on unleaded fuel?
Yes, and so do all of our other aircraft. Why would it matter?”
Yes I think it does. I think enigines last longer when run on unleaded fuel. Although my sample size is small.
When UL91 first came about it was a few pence cheaper than avgas and I knew a couple of mid life engines in C150’s that ran on that fuel. They did a lot of hours something like 1200 hours in 6 months. They never had a single fouled plug, zero exhaust valve or exhaust value guide problems either. Although one cylinder was replaced due to cracking. I’m certain if they have been run on Avgas they would of needed cylinder work.
I was also certain that after a few hundred hours on the unleaded fuel the oil stayed cleaner longer and when the oil was changed the drags that came out of the sump didn’t have that silvery sludge like appearance you get with Avgas.
The 160HP O-360 is by all accounts the most reliable of the cont/lycoming engines out there. If I am correct all you need to do is reprop it to get 180HP.
“Should we have gone for an overhaul already when the second cylinder broke at 2245 hours?”
No. In fact I would of replaced/overhauled the 4th clyinder and then flew it to 3000 hours assuming everything else was ok.
When I didn’t work out in North America there was a very large school that used to buy the C172R and then 172S brand new. They ran the engine for 2000 hours then changed all 4 cylinders and then run the engine for another 2000 hours. They then sold the aircraft. As far as I know they all made 4000 hours.
Interesting to see the difference in allowed flight hours for training in the UK the very same engine would be allowed 2000 hours plus 10% plus 10% so 2400 hours in total. None of this 3000 hour business.
Its a shame as it holds back the UK industry as I knew of a school that wanted to copy the same business model as the one in North America but due to UK regulations its commercially not viable to do so.
