I'm having a problem with the left mag on my O-320 RV-9. It will not start normally when cranking on the left mag. When I turn on the right mag it fires right up. (verified only the left has the impulse coupling). I am using independent switches and not a key switch to control the mags. The engine turns over as it should with the lightweight starter, compressions as they should be, fuel etc. all verified as well.
The engine runs well once started and mag checks well at idle, at runup and in flight. My Skyview indicates cranking rpm of 370 but I have no idea how accurate it might be at that low rpm.
I had this problem before when I installed a Catto propeller and solved the problem by changing out the left mag for a spare I had on hand. I subsequently changed back to a sensenich propeller and did not have a re-occurrence of the problem until yesterday after changing out the right mag which had become problematic with mag checks. After changing out the right mag the problem reappeared. What the heck!!!!
During the last year or so I sent the original left mag to the shop for evaluation and repair. The shop could not find anything wrong with it, freshened up the points etc. and returned it.
This morning I installed the original left mag and the darned thing will not start on the left mag and fires instantly when the right mag is switched on. Mag checks are all very good.
Called the mag shop and he told me that my impulse couplings were probably at the low end of the tolerance and were the problem as the starter was spinning up too fast and throwing them out. I find it a little hard to believe that both couplings are bad. One has about 300 hours and the other about 550. So what do the collective minds on here think might be the problem?
PS: Pmags are looking pretty good right now but I really don't want to do away with my mags if a solution is available. I did a search on this problem and couldn't find much. Am I the only one with a starter that spins too fast?????
The engine runs well once started and mag checks well at idle, at runup and in flight. My Skyview indicates cranking rpm of 370 but I have no idea how accurate it might be at that low rpm.
I had this problem before when I installed a Catto propeller and solved the problem by changing out the left mag for a spare I had on hand. I subsequently changed back to a sensenich propeller and did not have a re-occurrence of the problem until yesterday after changing out the right mag which had become problematic with mag checks. After changing out the right mag the problem reappeared. What the heck!!!!
During the last year or so I sent the original left mag to the shop for evaluation and repair. The shop could not find anything wrong with it, freshened up the points etc. and returned it.
This morning I installed the original left mag and the darned thing will not start on the left mag and fires instantly when the right mag is switched on. Mag checks are all very good.
Called the mag shop and he told me that my impulse couplings were probably at the low end of the tolerance and were the problem as the starter was spinning up too fast and throwing them out. I find it a little hard to believe that both couplings are bad. One has about 300 hours and the other about 550. So what do the collective minds on here think might be the problem?
PS: Pmags are looking pretty good right now but I really don't want to do away with my mags if a solution is available. I did a search on this problem and couldn't find much. Am I the only one with a starter that spins too fast?????
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