Tom3holer
MEMBER
Cape Cod
Hi,
I tried to find an appropriate section on the forum here to ask this question. I hope this might be the place.
A good friend of mine has a O-360 powered C-170. He and his AI found a high time engine and bought it. The AI did a major overhaul including new pistons.
The owner wanted a new electronic ignition installed on one side during the rebuild. A Shurefly was installed. It was set to run as a normal mag with no timing change for some 30 hours and all was fine. He then decided to move the dipswitch to activate the advanced timing with the help of another mechanic that was not familiar with the Shurefly. Apparently, he set the timing to the normal 27 deg btdc. The owner asked me to fly with him after some 10-15 hours as it was running rather rough. I did and agreed it was running rough so we cut the flight short. At that point I didn't realize he had changed the E I settings. Fortunately he had done an oil check shortly before and indeed there was metal in the oil. The AI grounded it and discovered what looked like severe detonation had/was occurring. The rod bearings looked like a high time engine and he showed me the pistons and they looked like somebody has sandblasted the skirts on all 4. The cylinders inside had a mirror finish with no signs of crosshatch anywhere. He then discovered the timing on the EI mag was supposed to be set at 0 deg not 27 btdc when the unit is running variable timing. So basically it was running at 54 deg btdc. The rods are being sent out for inspection and new bushings and bearings and he ordered new pistons.
The issue we discussed is whether the case should be split to look at the crank bearings. The AI was of the mindset that as the rod bearings look like high time bearings but no abnormal signs the crank bearings should be in good condition.
What do you Gents with many engine overhauls under your belt think?
I tried to find an appropriate section on the forum here to ask this question. I hope this might be the place.
A good friend of mine has a O-360 powered C-170. He and his AI found a high time engine and bought it. The AI did a major overhaul including new pistons.
The owner wanted a new electronic ignition installed on one side during the rebuild. A Shurefly was installed. It was set to run as a normal mag with no timing change for some 30 hours and all was fine. He then decided to move the dipswitch to activate the advanced timing with the help of another mechanic that was not familiar with the Shurefly. Apparently, he set the timing to the normal 27 deg btdc. The owner asked me to fly with him after some 10-15 hours as it was running rather rough. I did and agreed it was running rough so we cut the flight short. At that point I didn't realize he had changed the E I settings. Fortunately he had done an oil check shortly before and indeed there was metal in the oil. The AI grounded it and discovered what looked like severe detonation had/was occurring. The rod bearings looked like a high time engine and he showed me the pistons and they looked like somebody has sandblasted the skirts on all 4. The cylinders inside had a mirror finish with no signs of crosshatch anywhere. He then discovered the timing on the EI mag was supposed to be set at 0 deg not 27 btdc when the unit is running variable timing. So basically it was running at 54 deg btdc. The rods are being sent out for inspection and new bushings and bearings and he ordered new pistons.
The issue we discussed is whether the case should be split to look at the crank bearings. The AI was of the mindset that as the rod bearings look like high time bearings but no abnormal signs the crank bearings should be in good condition.
What do you Gents with many engine overhauls under your belt think?
Last edited: