Bartman Posted June 15, 2018 Report Share Posted June 15, 2018 We sent my dual mag to the specialty shop for 500 hour service and I assisted in installation. We set exactly at 25 degrees BTDC and she runs great, but I noticed some differences in the engine monitor. Prior to the mag service the EGT used to peak about 1,510 but now peaks about 1,460. Last night on takeoff my balls-to-the-wall EGT's which used to be about 1,250 on takeoff are closer to 1,200 and at 8,500 while about 10-15 LOP the CHT's are about 10-15 degrees higher too even at my normal setting at that altitude. I did a 50 degree LOP mag check and you can detect some minor roughness when on one mag only, but on both its still smooth. I'm trying to wrap my head around why I'm seeing these changes. If the CHT's are slightly higher that means I'm producing more power, and if the peak EGT's are lower then more combustion is taking place in the cylinders and less residual combustion in the exhaust. The magneto had about 500 hours on it and it was set at 25 deg BTDC when it was installed about 5 years ago. I remember the EGT's at that time peaking about 1,475 but has crept up to about 1,510 so it sounds like the timing has become progressively less retarded as time went on. Now I'm gonna have to do an unscheduled beach trip next week and figure out my new sea level takeoff EGT for my new target.... Quote Link to comment Share on other sites More sharing options...
INA201 Posted June 15, 2018 Report Share Posted June 15, 2018 is LOP mag check showing similar roughness and EGT rise for L and R? Similar mag drop on both for ground check? If so might just be the less efficient combustion while 50LOP. Quote Link to comment Share on other sites More sharing options...
Bartman Posted June 15, 2018 Author Report Share Posted June 15, 2018 I'm not concerned about the 50 LOP mag check, it's doing what it's supposed to do. Not really concerned about the EGT and CHT numbers either, just posting an observation. If someone else is seeing slow rise in peak EGT they may benefit from this thread. Quote Link to comment Share on other sites More sharing options...
Bob - S50 Posted June 15, 2018 Report Share Posted June 15, 2018 Sounds to me like your magneto has a little more advanced timing than it used to. If the EGT's rise and CHT's drop over time, to me that would indicate less advanced timing or as you put it ...more... retarded timing. Seems like that could happen due to wear on the cam or cam follower. If there is wear, the cam would have to rotate further to open the breakers which would cause the timing to become less advanced. 4 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted June 15, 2018 Report Share Posted June 15, 2018 What bob said. It is correct now it was wrong before. That's why we do periodic mag service. 2 Quote Link to comment Share on other sites More sharing options...
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