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- Apr 20, 2009
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Greetings. This engine is not on a biplane, but is in a hanger next to my bipes, so I hope that will qualify. 
Regarding an older AEIO-320-E2B. We have an “interesting noise” issue that I hoped someone else has encountered or could possibly steer us to someone that can counsel us.
Our noise is a low frequency rumble/growl (not a whine) that occurs on start up of a cold engine (like 60F ambient). It sounds much like a failing gyro. It is very prevalent and dominates engine noise until you get up to 1200 rpm or so. It also reduces some as the engine warms up but never totally leaves; especially at rpms below 1000.
The engine has a Christen inverted system that is piped correctly, about 600 hours total time and likely has never been disassembled or cleaned for several years (on the to do list). There is a Casper Labs remote oil filter installed with the stock Lycoming vernatherm in place. The original oil bypass valve has been removed from the top port above the oil filter housing per Casper instructions. History beyond this is somewhat sketchy but there reportedly was no single change or event that initiated the noise. “Has always been there” is the report.
We know what it is “not” after much testing. No electric gyros are operating. Vacuum pump removed so all vacuum gauges disabled. Alternator belt removed. Tach cable removed. None of these made any difference. Mag drive gears inspected. Timing properly set. Engine compression all 75/80 plus. Starts great and runs smooth.
The oil cooler circuit seems to play a roll in the issue. The cooler supply is taken from the lower center port of the accessory case per Lycoming and Casper instructions. The cooler return is to the proper top left rear port of the engine just below the case vent line. We have run the engine with the oil cooler in the circuit and also with just a bypass hose in place of the cooler and it makes no difference on the noise, always there.
However, we have also run the engine with the oil cooler supply and return lines capped and plugged where they exit and enter the accessory case. In this condition the noise totally goes away and the engine sounds just like all the other O-320's on the field with similar cooler installations. But, as soon as we open the line and allow flow through the cooler circuit the noise returns.
Has anyone ever experienced anything like this? Any ideas on how to correct or what to look for?
Thanks for any counsel you can provide.
Jim C
Regarding an older AEIO-320-E2B. We have an “interesting noise” issue that I hoped someone else has encountered or could possibly steer us to someone that can counsel us.
Our noise is a low frequency rumble/growl (not a whine) that occurs on start up of a cold engine (like 60F ambient). It sounds much like a failing gyro. It is very prevalent and dominates engine noise until you get up to 1200 rpm or so. It also reduces some as the engine warms up but never totally leaves; especially at rpms below 1000.
The engine has a Christen inverted system that is piped correctly, about 600 hours total time and likely has never been disassembled or cleaned for several years (on the to do list). There is a Casper Labs remote oil filter installed with the stock Lycoming vernatherm in place. The original oil bypass valve has been removed from the top port above the oil filter housing per Casper instructions. History beyond this is somewhat sketchy but there reportedly was no single change or event that initiated the noise. “Has always been there” is the report.
We know what it is “not” after much testing. No electric gyros are operating. Vacuum pump removed so all vacuum gauges disabled. Alternator belt removed. Tach cable removed. None of these made any difference. Mag drive gears inspected. Timing properly set. Engine compression all 75/80 plus. Starts great and runs smooth.
The oil cooler circuit seems to play a roll in the issue. The cooler supply is taken from the lower center port of the accessory case per Lycoming and Casper instructions. The cooler return is to the proper top left rear port of the engine just below the case vent line. We have run the engine with the oil cooler in the circuit and also with just a bypass hose in place of the cooler and it makes no difference on the noise, always there.
However, we have also run the engine with the oil cooler supply and return lines capped and plugged where they exit and enter the accessory case. In this condition the noise totally goes away and the engine sounds just like all the other O-320's on the field with similar cooler installations. But, as soon as we open the line and allow flow through the cooler circuit the noise returns.
Has anyone ever experienced anything like this? Any ideas on how to correct or what to look for?
Thanks for any counsel you can provide.
Jim C
