How do you tell when an engine is worn out? I mean beside the - no compression, crankshaft moving more than 1/32"? I have an engine (lapped piston) that cold has a good snap when flipping. If you slowly turn it over it holds for a bit but will leak off after 10 - 15 sec. It has been running a little erratic. I have found some trash in the NVA and hope this cures the crazy running, seemed lean then rich, would smooth out if I climbed slowly to the top of the circle. I think the trash in the NVA moved and it went rich. Had some crackling at first then it slowed, no sag just slow (10% N 26% Oil). I have it cleaned and will try it this weekend. Any thoughts?
Generally, it will be hard to start. Also, iron-piston engines will tend to go lean in the air. But, mostly, as they wear, the fuel consumption goes up and the power goes down. As the power goes down, you usually have to start setting it slower on the ground to get it the right speed in the air. As it becomes weaker, it wants to unload more, so to get a particular in-flight speed, you have to start lower.
Wearing out piston rings was a a few weeks/nearly monthly occurrence when I was running ST46s, I could tell when it was time to change it when the required launch RPM fell below some threshold - new fresh ring was something like 8500-8600, tons of power in flight, worn out might be 7800-7900. This to get the same in-flight speed.
The one quality engine I have ever worn out just from excessive use was a 40VF, when after thousands of flights over 10ish years, I was sitting there on Circle 3 at the NATs, was leaning it out a bit to get the desired RPM, and went "over the top" to the point it was starting to sag off lean. At that point, it just didn't have enough power left for normal operation. Even with that, I backed it off, launched as absolutely as fast as it would go in those conditions, and got one of the higher NATs flight scores I have seen, 595 as I recall, and wound up first on my circle.
With just about any modern engine, they are practically impossible to wear out in any reasonable number of flights, just from use. Dust/dirt/self-generated FOD is another story. I have had several instances where various internal failures caused self-generated FOD to score or damage the piston or liner, to the point it needed to be replaced.
Given that essentially all currently-competitive engines and the vast majority of sport engines are ABC/ABN/AAC, just wearing out with no extenuating circumstances can probably be dismissed as a cause of problems, unless you sucked up too much dirt or had an explicit failure.
Brett
Topic: How to tell if an engine is worn out? (Read 999 times)