Originally Posted by Brutus1967
Unfortunately, Cox states their engines only require a short break in (one or two tankfulls) but that is due to the residue forming: it doesn't break in any further as the residue arrests that process. On a synthetic oil, they just need the same break in period as any other engine, which can be up to two hours of running slobbering rich.
Er, no, I've broke in my Coxes with several tanks of fuel. In the first 2 tankfuls, one will notice silver flakes of eroded metal, then after that very little. Glenn Cox developed very fine machining and honing techniques down to the millionths of an inch, so they did not require an extensive break in to achieve seating the piston.
OTOH, older tech engines were not as finely machined, and required a more lengthy break in process. The fit was not as precise. This is similar to your automobiles. The break in process is less rigorous with the newer vehicles, because the machining is more precise and finer. The older automobiles of 30 years ago or more used courser hones. Those had a longer break in period and limited speeds during break in.
I remember breaking in a Testors McCoy .19 CL engine. Ran a half dozen tankfuls through. It was not capable of breaking into a solid 2 cycle peak run yet. I flew it 4 cycling using flying time for break in. The Coxes OTOH come up to peak power in a relative short amount of run time.
One poster referred to washing the congealed Castor oil film on the engine, which ruined the seal on an E-Bay purchase. I surmise that the engine was already well worn, and the build up of Castor helped keep the compression seal.
He's got a couple options: 1) run the engine on Castor oil based fuel to rebuild the seal; 2) have the cylinder chrome or nickel plated to reduce the clearances restoring compression; 3) clean up the engine, mount on the shelf for display and install something more solid running.