Re: Bad news - free advice sought
Posted: Wed Nov 02, 2016 5:28 pm
Jim-
There are as many opinions on how to break in a new engine as there are people who are willing to give an opinion.
After overhaul, the bottom line is the whole engine is in as good shape as it will ever be with the exception of the piston rings are not seated-in to the cylinder walls. If the rings don't seat properly during break-in, the engine will use excessive oil the rest of its life, there will be excessive blow-by fouling spark plugs, and the cylinder compressions will likely be sub-par.
The way aircraft cylinders are prepared for break-in is the cylinder walls are intentionally left roughed up microscopically so the rings can wear down the high spots and lap themselves in giving a good seal. The only way to seat the rings is for the engine to produce enough internal combustion pressure to force the rings against the cylinder walls long enough to wear down the jagged peaks to the point where they are smooth and not generating excess heat due to the friction of the lapping process.
The only way for the engine to produce maximum internal combustion chamber pressure required to seat the rings is to run the engine hard, at the highest allowable continuous power setting until the rings are seated making sure the cylinder head temps do not exceed max allowable. The CHTs will run hotter than normal due to the obvious higher friction between the rings and cylinder walls as they seat-in together and that is to be expected. This cannot be done on the ground so any ground run time should be absolutely minimized, only long enough to check for proper mag function, oil leaks, and oil pressure. NO PROLONGED GROUND RUNNING!
The first flights should be made at as low altitude as possible to make highest manifold pressure. Cooler ambient is better than warmer as well. Each flight should be about an hour to let everything stabilize. Circling the field in the pattern at pattern altitude is a good way to spend the first hours in case you need to make a quick landing. This also eliminates having to fly low over folks who might not want to see you there. Then land quickly as possible with the least possible low power operation and check for leaks, etc after shut down.
You can use a prescribed break-in procedure from the cylinder manufacturer or you can use max power for takeoff and max continuous for the rest of the break-in. I have broken in several new engines and top overhauls using max power for takeoff and max continuous until break-in is achieved with excellent results and never have had a problem.
Being able to see how the engine is behaving in real-time with a fuel flow computer and all-cylinder CHT/EGT instrumentation is another key ingredient in achieving a good break-in. Not required but very helpful. Cylinders will all be running at different CHTs and the hottest cylinder will be the controlling factor no matter which one it is and might change positions inflight. Power settings and mixture will have to be set so the hottest cylinder will not exceed max allowable.
What I have observed is each cylinder will break-in at different times, new cylinders usually take around 3 to 3-1/2 hours if everything is right. Chrome cylinders might take longer. CHTs will make a noticable drop of 20-50°F over a ten minute timeframe when the rings seat-in on each cylinder. Watching for that drop is important and why I use max continuous power instead of varying power as some procedures specify. Its difficult to see the drop when other factors are changing at the same time.
Once all cylinders have seated-in, I use at least 75% power until the cylinders have at least 10 hours on them before returning to normal operations, ensuring good break-in. If done properly you have a good chance of making TBO on the cylinders. If not done correctly, persistent problems can be expected.
A few key points:
-You only have one chance to seat-in the rings correctly, you don't get a do-over
-Don't "baby" the engine thinking you should be easy on it to break it in slowly, poor results will be your reward
-Don't exceed CHT limits, that is very important!
-Break-in the new engine at as low altitude and high power as possible
-Continuous power settings allow you to see when CHT drop occurs
-If all-cylinder CHTs are not available, run max continuous power at low altitude for at least 10 hours
And of course, since we have ambulance chasing lawyers and bleeding heart juries without any common sense, everything you just read is my own personal opinion and not a directive on how you should operate your airplane, but it is how I have done break-ins for over 45 years with good results.
There are as many opinions on how to break in a new engine as there are people who are willing to give an opinion.
After overhaul, the bottom line is the whole engine is in as good shape as it will ever be with the exception of the piston rings are not seated-in to the cylinder walls. If the rings don't seat properly during break-in, the engine will use excessive oil the rest of its life, there will be excessive blow-by fouling spark plugs, and the cylinder compressions will likely be sub-par.
The way aircraft cylinders are prepared for break-in is the cylinder walls are intentionally left roughed up microscopically so the rings can wear down the high spots and lap themselves in giving a good seal. The only way to seat the rings is for the engine to produce enough internal combustion pressure to force the rings against the cylinder walls long enough to wear down the jagged peaks to the point where they are smooth and not generating excess heat due to the friction of the lapping process.
The only way for the engine to produce maximum internal combustion chamber pressure required to seat the rings is to run the engine hard, at the highest allowable continuous power setting until the rings are seated making sure the cylinder head temps do not exceed max allowable. The CHTs will run hotter than normal due to the obvious higher friction between the rings and cylinder walls as they seat-in together and that is to be expected. This cannot be done on the ground so any ground run time should be absolutely minimized, only long enough to check for proper mag function, oil leaks, and oil pressure. NO PROLONGED GROUND RUNNING!
The first flights should be made at as low altitude as possible to make highest manifold pressure. Cooler ambient is better than warmer as well. Each flight should be about an hour to let everything stabilize. Circling the field in the pattern at pattern altitude is a good way to spend the first hours in case you need to make a quick landing. This also eliminates having to fly low over folks who might not want to see you there. Then land quickly as possible with the least possible low power operation and check for leaks, etc after shut down.
You can use a prescribed break-in procedure from the cylinder manufacturer or you can use max power for takeoff and max continuous for the rest of the break-in. I have broken in several new engines and top overhauls using max power for takeoff and max continuous until break-in is achieved with excellent results and never have had a problem.
Being able to see how the engine is behaving in real-time with a fuel flow computer and all-cylinder CHT/EGT instrumentation is another key ingredient in achieving a good break-in. Not required but very helpful. Cylinders will all be running at different CHTs and the hottest cylinder will be the controlling factor no matter which one it is and might change positions inflight. Power settings and mixture will have to be set so the hottest cylinder will not exceed max allowable.
What I have observed is each cylinder will break-in at different times, new cylinders usually take around 3 to 3-1/2 hours if everything is right. Chrome cylinders might take longer. CHTs will make a noticable drop of 20-50°F over a ten minute timeframe when the rings seat-in on each cylinder. Watching for that drop is important and why I use max continuous power instead of varying power as some procedures specify. Its difficult to see the drop when other factors are changing at the same time.
Once all cylinders have seated-in, I use at least 75% power until the cylinders have at least 10 hours on them before returning to normal operations, ensuring good break-in. If done properly you have a good chance of making TBO on the cylinders. If not done correctly, persistent problems can be expected.
A few key points:
-You only have one chance to seat-in the rings correctly, you don't get a do-over
-Don't "baby" the engine thinking you should be easy on it to break it in slowly, poor results will be your reward
-Don't exceed CHT limits, that is very important!
-Break-in the new engine at as low altitude and high power as possible
-Continuous power settings allow you to see when CHT drop occurs
-If all-cylinder CHTs are not available, run max continuous power at low altitude for at least 10 hours
And of course, since we have ambulance chasing lawyers and bleeding heart juries without any common sense, everything you just read is my own personal opinion and not a directive on how you should operate your airplane, but it is how I have done break-ins for over 45 years with good results.