Piper J3
Well Known Member
My friend has a 5-year-old RV-12 with 912ULS @ 490TT, that he has flown since new, running 93E10 Mogas. On a recent flight we noticed a slight engine roughness just below cruise RPM of 5500. A speed reduction of just 150 RPM shows the vibration. Prop is dynamically balanced and 5500 RPM is very smooth. We called Lockwood and they said it’s a classic gearbox problem and most likely wear on the drive dogs, a symptom they call “pocketing”. Their advice is to stop flying and send gearbox in for repair.
Carbs have always been in good synch and slow engine speeds avoided to eliminate gear chatter. The gearbox feels and sounds completely normal when burping the engine. No excessive play in gear backlash or clunking sounds from the drive dogs. Slip clutch torque is within published specs. Oil has been changed every 50 hours with AeroShell Sport Plus 4 and magnetic plug is very clean.
For comparison, I have an early SN RV-12 with 900TT running 93E10 Mogas and no noticeable vibration problem. My engine is the original design and doesn’t have the new oil spray lubrication in the gearbox. I have been using Mobil 1 Racing 4T 10W-40 synthetic oil since new.
So, the question is…. Has anyone experienced a vibration at near cruise RPM that is attributable to a problem with the gearbox?
Carbs have always been in good synch and slow engine speeds avoided to eliminate gear chatter. The gearbox feels and sounds completely normal when burping the engine. No excessive play in gear backlash or clunking sounds from the drive dogs. Slip clutch torque is within published specs. Oil has been changed every 50 hours with AeroShell Sport Plus 4 and magnetic plug is very clean.
For comparison, I have an early SN RV-12 with 900TT running 93E10 Mogas and no noticeable vibration problem. My engine is the original design and doesn’t have the new oil spray lubrication in the gearbox. I have been using Mobil 1 Racing 4T 10W-40 synthetic oil since new.
So, the question is…. Has anyone experienced a vibration at near cruise RPM that is attributable to a problem with the gearbox?