Dear Forum members
We have just had our O-320-B2B engine overhauled. Due to several replacement parts not being available in the short term (covid...), we exchanged the engine for another one that was already refurbished and ready to go (same model, same specs). While we are still running the engine in at TSO = 8 hours, I found a few peculiarities that I would like to discuss and ask your advice about it.
We operate the plane for glacier landings, typically around 8'000 - 10'000 ft. However, the behavior also occurs at lower elevations. First thing to note is that for a cruise power setting at 8'000 ft (2400 to 2450 rpm), I need to pull back the mixture quite a bit more than with the old engine - roughly 1.5 fingers. We have an Alcor EGT with Cessna/Vernier mixture, so it can well be I just need to adjust the EGT indication a bit lower to see a good reading on the EGT (good use of the scale available). For best power, let's say peak -100°F, I need to apply a lot of mixture. If I pull a bit more, the engine quickly runs rough. It seems quite non-linear with mixture setting. That's not of concern yet.
However, when I apply from this power setting full throttle (without even enriching the mixture), the EGT drops by 150 - 200°F and I have the gut feeling that the engine is not producing significant surplus of thrust. Also, going to climb full throttle (and optimized mixture setting for cruise, as before) will only yield 2400 rpm with 70 mph indicated, with a less than thrilling climb performance. Since we do glacier landings, we typically have 1700 - 2000 rpm during the final approach, and then apply full throttle on the uphill part and of course for take-off. If I pull the mixture all the way out to optimize for full throttle operations, it runs very rough once I reduce to 1700 rpm. Thus, this is not very practical.
To me it looks like the part I should look at is the carburetor (Marvel Schebler) which was also refurbished. The carburetor float is made of composite I guess.
What are your recommendations? What should I do or look at? Static pull tests at various power settings? What should I test in flight to get a better idea of that is going on? Regarding idle mixture setting, it looks like it's not really far off the optimum. It's really the behavior when transiting from cruise throttle to full throttle.
Thanks a lot for your help,
Maurice
We have just had our O-320-B2B engine overhauled. Due to several replacement parts not being available in the short term (covid...), we exchanged the engine for another one that was already refurbished and ready to go (same model, same specs). While we are still running the engine in at TSO = 8 hours, I found a few peculiarities that I would like to discuss and ask your advice about it.
We operate the plane for glacier landings, typically around 8'000 - 10'000 ft. However, the behavior also occurs at lower elevations. First thing to note is that for a cruise power setting at 8'000 ft (2400 to 2450 rpm), I need to pull back the mixture quite a bit more than with the old engine - roughly 1.5 fingers. We have an Alcor EGT with Cessna/Vernier mixture, so it can well be I just need to adjust the EGT indication a bit lower to see a good reading on the EGT (good use of the scale available). For best power, let's say peak -100°F, I need to apply a lot of mixture. If I pull a bit more, the engine quickly runs rough. It seems quite non-linear with mixture setting. That's not of concern yet.
However, when I apply from this power setting full throttle (without even enriching the mixture), the EGT drops by 150 - 200°F and I have the gut feeling that the engine is not producing significant surplus of thrust. Also, going to climb full throttle (and optimized mixture setting for cruise, as before) will only yield 2400 rpm with 70 mph indicated, with a less than thrilling climb performance. Since we do glacier landings, we typically have 1700 - 2000 rpm during the final approach, and then apply full throttle on the uphill part and of course for take-off. If I pull the mixture all the way out to optimize for full throttle operations, it runs very rough once I reduce to 1700 rpm. Thus, this is not very practical.
To me it looks like the part I should look at is the carburetor (Marvel Schebler) which was also refurbished. The carburetor float is made of composite I guess.
What are your recommendations? What should I do or look at? Static pull tests at various power settings? What should I test in flight to get a better idea of that is going on? Regarding idle mixture setting, it looks like it's not really far off the optimum. It's really the behavior when transiting from cruise throttle to full throttle.
Thanks a lot for your help,
Maurice