For some time now I have had a banging noise while warming up the engine.
The noise appears after maybe five minutes running at 2500 rpm. At lower and higher rpm the noise goes away, and I have never heard it in the air, or while taxying post-flight.
At first I thought it was the exhaust banging against the lower cowl. I checked the exhaust springs. All were intact, but on a couple the safety wire I had threaded through the spring had broken. I repaired this and the noise persisted. I also enlarged the exhaust outlet hole in the lower cowl because there was possibly some evidence of contact. No joy, so far.
At the annual (which I am doing) I checked the four engine mount bolts, because I suspected that might be a possible cause. All the bolts are secure. So now I am running out of ideas.
As an aside, I also found a small (half-inch) crack in the lower starboard firewall, adjacent to the lower cowl mounting point.
Cheers...Keith
The noise appears after maybe five minutes running at 2500 rpm. At lower and higher rpm the noise goes away, and I have never heard it in the air, or while taxying post-flight.
At first I thought it was the exhaust banging against the lower cowl. I checked the exhaust springs. All were intact, but on a couple the safety wire I had threaded through the spring had broken. I repaired this and the noise persisted. I also enlarged the exhaust outlet hole in the lower cowl because there was possibly some evidence of contact. No joy, so far.
At the annual (which I am doing) I checked the four engine mount bolts, because I suspected that might be a possible cause. All the bolts are secure. So now I am running out of ideas.
As an aside, I also found a small (half-inch) crack in the lower starboard firewall, adjacent to the lower cowl mounting point.
Cheers...Keith
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