Q: I have a mid-time O-235-N2C. I recently pulled the engine from service due to low power reports from our renters. Initial troubleshooting revealed two cylinders with low compressions. One was 55 and the other was 62. Decided to do a top overhaul.
Put it all together, including an overhauled carb, and I still cannot get more than 2200 static on the ground.
All compressions are 77 or better on the overhauled cylinders.
I also performed the Lycoming valve lifter clearance procedure recommended after cylinder replacement.
The engine is installed in a 2004 AMD Alarus and the TCDS indicates 2550 min and 2750 max static. I also noticed the oil temperature was higher than usual.I would appreciate any ideas or troubleshooting steps you can recommend!
A: John, let me begin by telling you I really don’t think you have any issues here. If the TCDS for the AMD Alarus indicates a minimum of 2250 static RPM on the ground, my bet is you’re right in the ballpark with what you’re seeing on your tachometer.
This startling fact may not come as a surprise to you, but one of the most common situations is for an aircraft tachometer to provide an erroneous reading and, typically, they read low.
My suggestion is that you check the calibration of your tachometer or locate a local maintenance facility that has a Vue-Thru or other instrument to calibrate your tachometer.
I do have one question for you though and that is what RPM does the engine turn in straight and level flight? How does this compare to what you read prior to doing the top overhaul? Oh, and did you ever happen to check the static RPM prior to doing the top overhaul? Just had to ask this!
I haven’t provided very much information for you here, but I feel it may give you something to compare and find out exactly whether your engine is, in fact, producing less power than you think.