Leaning C210L & Cylinders Hrad Temps
Re: Leaning C210L & Cylinders Hrad Temps
I hope you were able to find this thread. Seems this owners group has no collective memory for this stuff.
Eugene Watson Wrote:
I own a T210N and it went in for its MPI with 480 hours on the engine. They have found that it has vale stems have been worn and overheating has occurred. We have Millennium cylinders (had) and we have found that even the conrod bearings have moved. The inlet and exit valves are badly worn and have to be replaced as well as the pistons, sleeves (rebored) and all the other moving parts. We have always flown at 65-70% of power, below 400 and 50 rich of peak. I spoke to our AMO and they are finding it more and more that the valve guides do not last.
I am looking at putting in a JPI 800 to try and monitor the whole mess a bit better. What else can we do and do anyone have advice for us?
I hope you don't mind, but I am going to post the meat of our conversation for everyone else's collective benefit - with selected edits where necessary.
You got a couple problems, one of which you mentioned the solution for - a JPI. But it does not end there.
As you have discovered, the t210 runs hot, very hot infact. It is likely the most temperature sensative aircraft in the world at this point, perhaps with the exception of the cessna 400 series. You have a cowl, and baffling that likely is not hermatically sealed.
But let's drive the following home so there is no confusion - HEAT is your worst enemy. For all intents and purposes, 380 cht is the highest practical limit you want your engine to be for any continuous period. At 400, oil is no longer effective and you begin to suffer viscosity breakdown. Anotherwards, you get metal on metal contact, the pistons expand exponentally faster then the steel barrel of the cylinder, and you get an effect in the cylinder called an "out of round condition." this is akin to sticking a square peg in a round hole, since the piston now instead of gliding up and down the cylinder buffered by oil and the rings, now finds itself physically contacting the cylinder walls. This, in turn leads to a nasty process called Thermal Runaway. rub your hands together vigerously, they get hotter and hotter from friction. The same process is with your cylinders, it gets hotter until it stops rubbing. Continue operating like this for a few minutes leads to burnt pistons, trashed valves and pushes your cylinders closer to detonation margins.
But that is only part of the story - with 1 cht you have absolutely no clue how the other 5 cylinders have lived the previous 500 hours. Oil analysis would likely show elevated levels of nickel from the exhaust valves and valve guides, iron from the rings and rust, and chromium from the cylinder metallurgy itself, and maybe a bit of lead from piston blowby. If u have analysis, let me see it. If not, the best group in the world is Blackstone Labortories. Www.blackstonelabs.com buy a 12 pack from them, I'll send u some of my reports so u know how the reports are. Anyway, if there was trouble brewing, you would've had advanced warning had this been done.
I hate to put it in this light, but the damage is in most cases because the way you were taught to run the engine. Now before you jump out of the window - here me out. 90% of pilots on the planet were taught incorrectly, unless you run into folks who drove big radials like the r3350 and r4360 for the military or the airlines. And what you will hear from those folks and the millions of hours on radials, is they did NOT operate rich of peak. This was an operational consideration to allow them to get extended longevity from their engines.
Let's do a test: which way of operating your engine results in higher internal cylinder pressures and CHT; 50 ROP or 50 lean of peak? If you can answer this question correctly, I'll explain the rest of your engine problem and how you ended up where you are.
Thanks, I started reading about the problem for the last few days. It seems that lean of peak is cooler, but how can that be?
Sent by Eugene Watson
You are coming toward the ah-ha and holy shit moment in life simultaneously. First a little background information.
Lean of Peak Engine Operation with LOP Curves Explained
Lean of Peak Operation simply put, gives you a 20% reduction in fuel flow, with corresponding lower CHTs, EGTs for more simplistic engine operation. In a typical 4 hour cross country, the cost savings is between 12 and 20 gallons, allowing you an increased payload carrying capacity and lesser fuel loads.
This is a "concept" chart, intended to represent all internal combustion, spark-fired, fixed-timing, gasoline-powered engines. It is taken from the TCM chart in the back of the Installation and Operations Manual, generalized, and the ICP (Internal combustion pressure) curve has been added from actual test stand data. The Brake Specific Fuel Consumption (BSFC) curve has been inverted, so instead of the customary "pounds per horsepower," it shows "horsepower per pound." This way, the BSFC curve also peaks.
Imagine a ruler held vertically, and moved from left (rich) to right (lean), representing the leaning process (a "mixture sweep"). Each of the curves will touch the ruler and show what that parameter is doing at that point on the mixture curve.
When you lean from FULL RICH on a properly set up engine, EGT, CHT, power output, horsepower per pound of fuel, and internal combustion temperatures and pressures ALL rise at first. At some point during that leaning process, FIRST the Horsepower peaks, THEN the CHT and internal pressures peak, THEN the EGT peaks, THEN the HP per gallon peaks, all at slightly different fuel flows.
THE RED FIN
The "Red FIN" defines a region where higher internal cylinder pressures, and the resulting higher cylinder head temperatures, will result in decreased engine life and engine damage. The limits of the red box are defined in terms of degrees rich or lean of peak EGT, and the "width" of the red box changes depending on how much power you are producing (NOT altitude). So to set your mixture so as to respect the red box limits, you first need to know, at any point, how much power you are producing. You can then look at the table, find the row for that percentage of power, and make sure you are at or outside of the limits shown for that amount of power. For example, if I'm developing 70% power, I can look at the table and see that for that power setting I need to be 125 degrees rich of peak or richer, or I can be 25 degrees lean of peak or leaner. It shows me that at 70% power the area between 125 ROP and 25 LOP is to be avoided – that's the red box at 70% power.
So the red box is "wider" at high power settings, and smaller or nonexistent at lower power settings. As a matter of fact, a look at the red box table will show you that at 60% power or less, there is no red box, so you can put the mixture control anywhere!
So now that you know how to get the EGT limits from the table, you need one piece of information to set your mixture control: "How much power am I developing?" Lean of peak, the answer is surprisingly easy, because when lean of peak, power is directly proportional to fuel flow. It turns out that you can simply multiply your fuel flow in GPH by 15 to obtain horsepower. So for 8 GPH * 15 = 120 HP. Dividing your horsepower by 200 (for the SR20) yields percent power. 120 / 200 = 60%.
BIG MIXTURE PULL
The so-called “Big Mixture Pull” is a means of setting the mixture control to “park” your engine in a safe place. This will place your engine well lean of peak by moving rapidly “through the mountain” of peak temperatures and pressures to a safe place on the lean side. To perform the Big Mixture Pull, pull back on the mixture control smoothly and fairly rapidly until you feel the airplane decelerate. Stop! You’re there. The pull should take about 5 seconds or so. Do NOT enrichen a little when you feel the deceleration. Any time you want to park your engine in a known safe place, such as before finding peak EGT or for level-offs during climb or decent, just perform a Big Mixture Pull.
So to your question - HOW CAN IT BE COOLER. Lets look at that diagram with respect to PEAK EGT. Look at where the hottest CHT and highest INTERNAL CYLINDER PRESSURE (ICP) are located. You pretty much notice how they are ALL at their maximum precisely where you have been running your engine ROP? Time to get a beer, because this is the part that hurts. You can now infer that 50* ROP is pretty much the worst place you can ever run an engine from all power settings down to 65%. You can also infer that ROP has a much wider region of real-estate from which you will be doing damage to the engine unless you are running extremely rich mixtures (Well beyond the TCM spec SID-97-2; you would need to exceed those values by 10% at least to ensure you were out of the red-fin on the ROP side.
Now, something to really piss you off. TCM's operators manual instructs us to run 50* ROP or greater. So here you are, motoring along, and the entire time you are breaking something when you are working under the assumption that you are doing it according to the manufactures recommended best practices.
As to why your engine is damaged the way it was - there is a relatively simple explanation. Since you were operating in the middle of the red fin - at a setting where you by sound engineering principles had the engine working at its highest internal cylinder pressures, highest CHT, and generally all around worst possible conditions: everything got burned up. But heat (CHT) wise isn't the only worst enemy, but in your example ICP. When you have high ICP, you are putting a tremendous strain on the con-rods, bearings, pistons, rings, and the cylinders. I'd like you to ask your mechanic if ANY of the piston rings had any rigidity left in them (They should snap in place and hold their station.) I'd bet they were very very elastic.
Now cross over from peak to the Lean side of peak and look at the relationships between ICP, CHT, EGT and Brake Specific fuel consumption. Notice how the first 3 are lower, and your BSFC (efficiency) is through the roof (good). Suffice to say, this is the lesson here - lower ICP and CHT will prevent you or anyone from experiencing what you did. The only way you will do that is either by running rediculously rich, or running Lean of Peak. And the only safe way to run LOP is by having the proper equipment in place, being on a spectrographic oil analysis program - and lastly - being re-educated.
You need to go back to school - and the only school for LOP in the world aside from me is [www.advancedpilot.com]
You have George Braley (the guy who invented GAMI), John deaken, and Walter Atkinson. Its around $400 USD and can be taken online or flown out to in person, but considering the amount of money you are about to spend on a top-overhaul + internals, it pocket change.
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