My plane ran well when I flew 1.5 hours Saturday. After I stopped to talk to a friend at another airport and took off, my engine on takeoff sounded like the exhaust was open at one cylinder. I almost aborted, but being a long runway I climbed, circled and (probably poorly) decided to fly the 10 minutes home while scoping out farm fields enroute (with my bush plane). The engine produced full rpm during takeoff and normal cruise and all the temperatures were normal. I tried to talk myself out of the sound. If you could not hear, there would be no indication of a problem. I have not flown it since.
The engine starts normal, but when I ‘blip’ the throttle (not something I normally do), it immediately makes a sound like an old tractor (exhaust sounding), more pronounced the faster I 'blip'. I checked the carb balance, and they were spot on both at idle and higher rpms. All the pipes are torqued at 133 in-lb nuts to the studs. The exhaust looks intact after careful inspection even under the heat muff; and when I hold a rag over the exhaust, although it does not stall, I do not hear any obvious break hissing. When I do a 4000 rpm mag check (which passes as normal), I continue to hear the same 'tractor exhaust-like' sound on either mag (and on either mag throughout the rpm range). At idle, everything sounds normal. I plan to do (but have not yet done) a differential pressure check (but I expect it will be normal) - it did 5 hours ago. I did check the prop bolt torques, and they were correct. I removed one plug from each cylinder and they all looked correct. I checked the torque on all plugs and they were correct. Could this be the gearbox (doesn’t sound it to me, but I have no experience here)?
I have not confirmed where the noise originates. I may try a stethoscope.
What can this be? Help.
The engine starts normal, but when I ‘blip’ the throttle (not something I normally do), it immediately makes a sound like an old tractor (exhaust sounding), more pronounced the faster I 'blip'. I checked the carb balance, and they were spot on both at idle and higher rpms. All the pipes are torqued at 133 in-lb nuts to the studs. The exhaust looks intact after careful inspection even under the heat muff; and when I hold a rag over the exhaust, although it does not stall, I do not hear any obvious break hissing. When I do a 4000 rpm mag check (which passes as normal), I continue to hear the same 'tractor exhaust-like' sound on either mag (and on either mag throughout the rpm range). At idle, everything sounds normal. I plan to do (but have not yet done) a differential pressure check (but I expect it will be normal) - it did 5 hours ago. I did check the prop bolt torques, and they were correct. I removed one plug from each cylinder and they all looked correct. I checked the torque on all plugs and they were correct. Could this be the gearbox (doesn’t sound it to me, but I have no experience here)?
I have not confirmed where the noise originates. I may try a stethoscope.
What can this be? Help.
