Lycoming O-360 F excessive RPM drop during magneto check

[Jetjockey75]

Hello Everybody out there,

I got a problem on my overhauled O-360-F1AD during magnet check.

Since first run after overhaul RPM drops by 140 RPM during magnet check on both magnets. The difference is max. 10 to 20 RPM.
New installed EDM830 shows on all 4 cylinders slighly higher CHT and EGT. The guy who did the overhaul checked everything without finding any abnormals. In his opinion RPM drop and higher temperatures will be eliminated after first 20 hours.

Magnets are new, harness is new, spark plugs are new and I already replaced both magnets by different new ones - same problem!
Fuel Flow is sufficient and intakes are checked for any leaks.
Even after engine overhaul my recent experience of RPM drop during magnet check is between 50 and 75 RPM.

Does anybody have an idea where to look at next?

Thank you, brgds

[bcgallacher]

Possible that you have one plug on each mag in different cylinders not firing?

[bcgallacher]

On reflection that would give a bigger drop.Possible that both mag timings are out?

[NutLoose]

Also check you have the correct plugs installed.

[jxk]

I hope your engineer gave you the correct 'run in' procedure - it does require that you do a flight of about 2 hours with different power settings including a time at full power.
It usually takes about 50 hours for the engine to settle down and 'loosen' up by which time temperatures will reduce.