914 Wear
We have a 914 S/N 4418263 placed in service in 2005. It now has 1275 hours on it.
This weekend we performed a differential leak down test with the engine cold and the results were between 60/80 and 65/80. When repeated on a warm engine they were essentially the same. We could hear air in the oil tank and a little in the intake manifold on cylinders 1 & 3.
We also did a direct compression test on the cold engine and the results were pretty uniform around 90 psi.
Borescope inspection of the valves and cylinder walls look normal.
All of these results are within Rotax limits, but barely. We have looked at our records and notice that the differential compression started to decline from roughly 79/80 about 200 hours ago (5/2020).
The tests were performed along with the crankshaft twist test and crankshaft runout test because of a short duration overspeed. Both of those tests showed no problems. We wouldn't have known about low compression except for the overspeed and would have been flying as usual until our annual inspection next Spring.
We think although we are flying with a worn engine, there are no safety of flight questions and it is safe to continue. Certainly in the near future we will need to address the wear, but for now, it is not a problem, just that we have to live with reduced performance.
We are looking to see if others agree with our analysis or have other ideas.
Thanks
Jim & Heather
