A week ago I posted a request for advice about a recent engine roughness issue. The IO-360 (C/S prop, dual P-Mag, AFP injection, 32 hours since new) had developed a distinct roughness when operating on both P-Mags, which went away when operating on either P-Mag alone. The roughness was felt through the floor, and other parts of the airframe structure. Advice from several posters, especially N941WR, helped focus efforts to a solution.
Yesterday I was able to get back to the hanger, and found that both P-Mags were timed 3 degrees before top center. I was also surprised to see that the A-curve jumpers had never been installed as intended. Re-timing to TDC and adding the A-curve jumper essentially retarded timing by eight degrees.
Two hours of test flight proved that the dual mag roughness was gone. So apparently the over advanced timing was creating roughness when operating on two mags, but when operating on a either mag alone the timing was retarded just enough to prevent the roughness. The roughness was subtle, but I suspect that it would have caused premature engine problems. Now I know what over-advanced ignition timing feels like.
Still not sure why / how the timing jumped by three degrees, both mags. My perception was that the roughness started abruptly on climb-out, but cannot be sure.
I intend to add an EICommander to the panel. This is a device that monitors the health of P-Mags during operation and allows additional manipulation of their performance.
Thanks to all who helped put the RV grin back on my face! And thanks to DR for keeping this great asset growing
- Roger
Yesterday I was able to get back to the hanger, and found that both P-Mags were timed 3 degrees before top center. I was also surprised to see that the A-curve jumpers had never been installed as intended. Re-timing to TDC and adding the A-curve jumper essentially retarded timing by eight degrees.
Two hours of test flight proved that the dual mag roughness was gone. So apparently the over advanced timing was creating roughness when operating on two mags, but when operating on a either mag alone the timing was retarded just enough to prevent the roughness. The roughness was subtle, but I suspect that it would have caused premature engine problems. Now I know what over-advanced ignition timing feels like.
Still not sure why / how the timing jumped by three degrees, both mags. My perception was that the roughness started abruptly on climb-out, but cannot be sure.
I intend to add an EICommander to the panel. This is a device that monitors the health of P-Mags during operation and allows additional manipulation of their performance.
Thanks to all who helped put the RV grin back on my face! And thanks to DR for keeping this great asset growing
- Roger