Swiss14A
Active Member
I was lately introduced to the concept of "****up-sessions", where in a company you do a competition for the biggest ****up. The goal is obviously to learn and avoid the same mistakes in the future. My latest attempt in P-Mag ignition timing would be a good candidate for such a session.
After doing our second annual/100H maintenance this week, my wife and I wanted to finish up with a ground run and check everything. It was already 11p.m. and I was tired after getting up at 4 a.m., working an early shift, then 10 hours in the workshop to finish the annual. It was already dark outside and we pulled the plane out of the hangar and onto the apron. I went into the cockpit to do the runup, because my wife had to go to the loo. She agreed to observe from the outside. The cowl was not installed, so we could check for leaks after the runup...
When attempting to start the engine, I didn't use the checklist. And the engine just didn't want to start... After realising my mistake, I turned ignition on (dual p-mag with separate switches) while the engine was turning. of course it "shot" twice, but didn't start. I stopped, waited half a minute and tried again. Also no success. And my wife even saw some fire/flames but couldn't locate them exactly. It was dark, so you could see them, during the day probably not...
Because we were both tired and suspected the engine to be flooded, we decided to pull the plane in the hangar again and try on the next day. So we finished everything up and went home.
Only then we were thinking about what happened and what we could have done wrong. Spark plugs were in, fuel was ok, p-mag timing was set, ... Just to be sure I checked the manual again for the timing... Only then I realised, that there are two ways of timing! The marks on the flywheels propeller side for the starter, AND the mark on the flywheels engine side for the crankcase top line!!! I mixed up and used the propeller side for the crankcase top line, where the crankase halfs come together! That explained everything.
So the next morning we went back to check. And sure it was exactly what happened! It seems like the position I set the P-mags was such, that the intake valves were still open. So it fired probably back into the air intake. We removed the plugs, borescoped the cylinder, removed the snorkel and inspected the fuel injector (Air Flow Performance 150). The injector had a lot of black soot inside the fuel injector and also a bit in the snorkel… so those were the flames my wife saw, probably shining trough the snorkel in the dark…
After cleaning and checking everything, we made sure to set the timing correct and did another runup… Now as always, fired up after one or two blades and run smoothly. We did a runup, high power check (as high as the brakes allow) and everything seems fine.
We checked the engine after the runup and couldn’t find anything worrying. The post maintenance check flight had to be postponed because of some shower cells and thunderstorms moving through the area, but we will do that tomorrow. It seems that we were lucky and did no damage!
What did we learn:
- it was the third time we set the timing (initial, 100H, now 200H), not enough to be experienced, but enough to feel so…
- our life is packed with things just now, that’s why we split the 100H-Maintenance into several small parts, ans also did maintenance after tiring morning shifts and until late; we have to slow down
- I marked the flywheel clearly and hope my markings survive 100hours of flying
- It’s not really a failsafe design from Lycoming to have two different markings stamped on two sides of the flywheel
Black soot inside the fuel injector by Fabian Hummel, auf Flickr
After doing our second annual/100H maintenance this week, my wife and I wanted to finish up with a ground run and check everything. It was already 11p.m. and I was tired after getting up at 4 a.m., working an early shift, then 10 hours in the workshop to finish the annual. It was already dark outside and we pulled the plane out of the hangar and onto the apron. I went into the cockpit to do the runup, because my wife had to go to the loo. She agreed to observe from the outside. The cowl was not installed, so we could check for leaks after the runup...
When attempting to start the engine, I didn't use the checklist. And the engine just didn't want to start... After realising my mistake, I turned ignition on (dual p-mag with separate switches) while the engine was turning. of course it "shot" twice, but didn't start. I stopped, waited half a minute and tried again. Also no success. And my wife even saw some fire/flames but couldn't locate them exactly. It was dark, so you could see them, during the day probably not...
Because we were both tired and suspected the engine to be flooded, we decided to pull the plane in the hangar again and try on the next day. So we finished everything up and went home.
Only then we were thinking about what happened and what we could have done wrong. Spark plugs were in, fuel was ok, p-mag timing was set, ... Just to be sure I checked the manual again for the timing... Only then I realised, that there are two ways of timing! The marks on the flywheels propeller side for the starter, AND the mark on the flywheels engine side for the crankcase top line!!! I mixed up and used the propeller side for the crankcase top line, where the crankase halfs come together! That explained everything.
So the next morning we went back to check. And sure it was exactly what happened! It seems like the position I set the P-mags was such, that the intake valves were still open. So it fired probably back into the air intake. We removed the plugs, borescoped the cylinder, removed the snorkel and inspected the fuel injector (Air Flow Performance 150). The injector had a lot of black soot inside the fuel injector and also a bit in the snorkel… so those were the flames my wife saw, probably shining trough the snorkel in the dark…
After cleaning and checking everything, we made sure to set the timing correct and did another runup… Now as always, fired up after one or two blades and run smoothly. We did a runup, high power check (as high as the brakes allow) and everything seems fine.
We checked the engine after the runup and couldn’t find anything worrying. The post maintenance check flight had to be postponed because of some shower cells and thunderstorms moving through the area, but we will do that tomorrow. It seems that we were lucky and did no damage!
What did we learn:
- it was the third time we set the timing (initial, 100H, now 200H), not enough to be experienced, but enough to feel so…
- our life is packed with things just now, that’s why we split the 100H-Maintenance into several small parts, ans also did maintenance after tiring morning shifts and until late; we have to slow down
- I marked the flywheel clearly and hope my markings survive 100hours of flying
- It’s not really a failsafe design from Lycoming to have two different markings stamped on two sides of the flywheel
Black soot inside the fuel injector by Fabian Hummel, auf Flickr
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