Replaced a Cylinder.
We have one cylinder that has always had a lower pressure reading when we checked it at annual. This year it was 35/80 so we pulled it. If you look at the cylinder, it has a ton of corrosion that caused the rings to no longer seal. I suspect the rest of the cylinders are the same. When we borescoped them last year, we were looking for valves that weren’t seating properly and I don’t remember looking for corrosion.
Mike Busch has an article at AVWeb that talks about proper operation of big bore Continentals (ours is a TSIO 520-H4). I think I’ve read all of his articles. I don’t know if you do these things, but I always do. (Except for avoiding shock cooling.)
Lean Until the Engine Stumbles if you give it more than Taxi Power
One the engines are running and it’s time to taxi out, perhaps the most common mistake I see pilots make is failing to lean the engine properly. The Continental fuel-injection system is set up with a very rich idle mixture in order to facilitate cold starts. Taxiing with the mixture full-rich is like driving a car with the choke on…the engine is literally awash in excess fuel. This often results in fouled plugs, contaminated exhaust valves, and fuel dilution of the oil film on the cylinder walls.
Taxi
Incidentally, big-bore Continentals are supposed to idle smoothly at 600 RPM
I don’t think ours will. I usually need taxi at 800 or more and use a little braking from time to time.
Runup – Leaned Out
My preference is to leave the mixture leaned for idle when I do my runup. Others prefer to go full-rich for runup, and then re-lean for idle if there’s a delay.
I also lean for runup and when I make my call to the tower, I keep my hand on the mixture until cleared for takeoff. The plugs don’t have much in the way of lead deposits—especially compared to the Cherokee.
Takeoff – Slow increase in power. I don’t take as long as he does, maybe 5 seconds.
For optimum engine longevity, we want to minimize the gradient of this thermal event by throttling up as slowly as possible. If the runway is relatively long, I’ll try to advance the throttles just fast enough to reach full takeoff power as the airplane achieves rotation speed.
Climb
Normal cruise-climb in a Continental-powered airplane is normally 75% power. In many aircraft (including most Cessna singles and twins), this occurs at top-of-the-green manifold pressure and top-of-the-green RPM.
I normally pull the prop to 2300 at the end of the runway to reduce noise and then MP to 1” below the top of the green at pattern altitude. Our MP gauge reads 1″ high. I generally climb at 130 MPH.
You should be leaned for climb, cruise, descent, landing, and taxi. The only time you should be full-rich is for start, takeoff, and go-around.
If I am just burning gas or doing manuevers, I pull the power (usually a lot) and lean while climbing. CHTs are usually in the 250 range and TIT below 1200.
Cruise
I recommend reducing to a more conservative cruise power setting between 55% and 65% power. 55% provides near-optimum fuel economy, while 65% provides a good compromise between fuel economy and airspeed.
If I am flying with with passengers who want to get somewhere fast, I set the cruise to top of the green and 20-21 gph. If I flying to pick someone up, (or on the rare occasions when I am going somewhere) I do the more conservative power settings.
If your engines don’t feel smooth at bottom-of-the-green RPM, experiment to find the lowest RPM at which they do feel smooth, and cruise at that.
There is a Continental Service Bulletin (CSB09-11A) that says to never run below 2300 RPM in cruise. When we checked the prop, 2300 RPM was actually 2453. 2200 RPM is 2352. So I suppose I could cruise at 2200 RPM.
Descent
The one I use is to allow one minute for each 1″ of MP that I need to reduce to get from cruise power to approach power. …I recommend not enrichening the mixtures for descent unless the engines start running rough.
I do this if I am in cruise, but since I am usually running at much lower power settings, I don’t have to lose many inches. The consensus on AVweb is that shock-cooling is a myth. I think even Mike Busch no longer holds with this recommendation. Mike Busch, … has found it unusual to have them [CHTs] drop at a rate of even 30 degrees per minute with aggressive power reductions when ATC gives a slam dunk approach.
Landing
Every POH I’ve ever read instructs you to advance the mixture to full-rich on final prior to landing. Don’t do it! Pouring cold fuel on a hot cylinder head simply can’t be a good thing for cylinder longevity. I recommend leaving the mixture leaned out for landing and taxi. I also recommend setting the props to top-of-the-green RPM, not shoving them full forward the way the POH instructs.
I don’t do this. I normally set the prop to full when I am in the pattern and it is already at the stops. I also go full rich on final.
Shutdown
A turbocharger should be given the opportunity to cool down (and spin down) at idle for 3 to 5 minutes before shutting down the engine and thereby cutting off the flow of oil to the turbocharger. In many cases, the landing roll and taxi-in take enough time that no additional cool-down is required.
If the TIT is below 1000, I just shut down, if not I wait a couple of minutes.