ORIGINAL: plugin
.....
I want to stress that when the improper break in was done, the engine wasn't able to reach its 17,000rpm even on the leanest setting because engines at this altitude loose about 25% of their power. In those terms it was probably able to reach 13,000rpm at best.
Plugin,
My break-in method is elaborately detailed in [link=http://www.rcuniverse.com/forum/Tapered%2DBore_Engine_Break%2Din_%2D_Upgraded/m_1850473/tm.htm]this RCU thread[/link].
Had your brother followed it, there would have been no doubt about the good results.
1. The OS A3 is too hot for general running of this engine - you want the #8, or another medium-hot glow-plug.
But when breaking it in somewhat rich, it is OK.
2. Idling the engine during break-in achieves absolutely and utterly nothing!
3. An OS.46AX and most other ABC/ABN/AAC engines are unlikely to sustain any damage at all, if run leaned to maximum RPM (but not leaner), right out of the box. If it was not run leaner than max and
with enough castor oil in the fuel, it is probably OK.
4. Check if the engine still shows a small amount of pinch at TDC (the piston 'catches' slightly at the top of the stroke), with the engine at room temperature (20-22ºC/~70ºF). If it does it is OK for sure and even if not, it is an OS and it doesn't care...
5. 17,000 RPM is a fairytale OS tell you, so you would be tempted to buy the engine... You would need an 8.5x6.5N pylon racing 'toothpick'... Oops! prop, to see anything close to this number. And if 16K is exceeded, the PowerBox muffler will disintegrate repeatedly, even if you JB-Weld its parts together...
6. ...And an 8.5x6.5N prop at 17K is just short of 1 HP... Where did the 'other' 0.65 HP (as OS claim) go? Did anybody see them?
7. According to Harry Higley's book, an ABC engine is capable of surviving a lean-run and returning to its old self after cooling down.
I cannot be sure about that... so I will never try it.
8. As you go to a higher altitude, the engine's power goes down, but the prop's drag goes down
to the same extent. RPM remains about the same, despite the (even dramatic) power reduction. Thrust is reduced significantly, despite the engine making the same sound pitch...