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Re: Mag and plugs....rough mag question
Hello everyone,
I started up the plane and initially it had a 300-350 RPM drop on the left mag with the right mag about 25 RPM. Running it and getting it warmed up a bit on the ground seemed to help get the drop a bit better. After a short flight to get the engine up to normal operating temperature, the drop was even better (~250 RPM) but it was also having a slight miss and running rough when on the left mag. We removed all bottom plugs and cleaned them. They were pretty cruddy. We also visually inspected the wires and they looked good. We then started her up again and the drop was better but still about 200 RPM on the left mag with no miss or bad roughness. The mechanic checked to make sure both mags were timed the same and they are. He did indicate that this does not mean they are timed properly…something else we will check but were not in the position to do so yesterday. This was checked at the last annual about 10 hrs ago and the mags are only 60 hrs since new. We also cleaned the top plugs and the ercoupe cups out which had some grease/oil in them. We checked the top wires visually. In flight the mags sound good when switching to either mag.
Anyway the RPM drop is not consistent…sometimes it is 50 othertime 350 RPM and sometimes it is variable and goes up and down inside of that range if you leave it on the left mag for several seconds (particularly now between 50-250 RPM). We agreed it needs further analysis but in the mechanic’s opinion the plane was safe for flight to get it back to its hanger. The strange thing is after returning to the home airport (~ 1 hr flight) I taxied back to the hanger and did a run-up check prior to shutdown and the RPM drop was normal with 25 RPM on each mag and not a hint of roughness. It was the best run-up I saw all day.
Any further thoughts on where to go with this issue? We want to check the internal timing but have pretty much ruled out the plugs and wires at this point (unless someone thinks otherwise).
Thanks,
Brian
Hello everyone,
I started up the plane and initially it had a 300-350 RPM drop on the left mag with the right mag about 25 RPM. Running it and getting it warmed up a bit on the ground seemed to help get the drop a bit better. After a short flight to get the engine up to normal operating temperature, the drop was even better (~250 RPM) but it was also having a slight miss and running rough when on the left mag. We removed all bottom plugs and cleaned them. They were pretty cruddy. We also visually inspected the wires and they looked good. We then started her up again and the drop was better but still about 200 RPM on the left mag with no miss or bad roughness. The mechanic checked to make sure both mags were timed the same and they are. He did indicate that this does not mean they are timed properly…something else we will check but were not in the position to do so yesterday. This was checked at the last annual about 10 hrs ago and the mags are only 60 hrs since new. We also cleaned the top plugs and the ercoupe cups out which had some grease/oil in them. We checked the top wires visually. In flight the mags sound good when switching to either mag.
Anyway the RPM drop is not consistent…sometimes it is 50 othertime 350 RPM and sometimes it is variable and goes up and down inside of that range if you leave it on the left mag for several seconds (particularly now between 50-250 RPM). We agreed it needs further analysis but in the mechanic’s opinion the plane was safe for flight to get it back to its hanger. The strange thing is after returning to the home airport (~ 1 hr flight) I taxied back to the hanger and did a run-up check prior to shutdown and the RPM drop was normal with 25 RPM on each mag and not a hint of roughness. It was the best run-up I saw all day.
Any further thoughts on where to go with this issue? We want to check the internal timing but have pretty much ruled out the plugs and wires at this point (unless someone thinks otherwise).
Thanks,
Brian
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