## 1 Introduction
### Prior Engines with Moving Liners and Prior RLE Results  
A detailed description of prior engines with partially rotating cylinders, Sleeve Valve Engines, has been provided by [PERSON] et al. (2012). A lengthy review will not be presented here. However, the reader needs to know that the aircraft SVEs operated under BMEPs comparable to heavy-duty diesels, but the cylinder rotation during the high-pressure part of the cycle eliminated the typical wear pattern in the TDC area and also reduced overall FMEP, despite the fact that the sleeve valve added considerably more rotating components than the conventional valve train that it replaced. The reason for this decrease in friction while adding more sources of friction was initially mystifying. [PERSON] (1968) eventually determined that the decrease in FMEP was due to the motion of the \"sleeve\" (liner) near the TDC, which minimized the presence of metal-to-metal contact from the piston assembly components around the TDC of compression-expansion. The first RLE prototype was a single cylinder conversion of a GM Quad 4 light-duty SI engine [4]. Unlike this current Diesel prototype, that light-duty conversion was designed such that the space of the neighboring cylinders was invaded by the RLE components, condemning the engine into a single cylinder. The face seal, while similar in overall function, had certain design limitations which were corrected for the current heavy-duty design. However, the initial design allowed hot motoring tear down tests, which facilitated the measurement of friction characteristics. The rather large motoring FMEP reduction, along with a tear down test to confirm that the difference was from the piston assembly, is shown in Figure 3.  
The authors have received questions about the relatively large amount of FMEP reduction presented in Figure 3, especially in light of tear down tests performed by other researchers that show the overall FMEP contribution of the piston assembly to be lower than the reduction shown in Figure 3. The precision of these tests by [PERSON] et al. (2005) [6] is not likely to be the issue, since these measurements were extremely straight forward  
Figure 3: Hot motoring friction of the light-duty RLE compared to baseline, borrowed from [PERSON] et al. (2005). The x axis shows the engine speed, and the y axis shows the measured motoring FMEP for the two engines. This was performed after the tear down process allowed the isolation of the piston assembly FMEP from the other terms (i.e., crankshaft, camshaft, etc.). and conducted with two independent measuring techniques, while the margin of error is considerably smaller than the FMEP improvement shown. The authors are convinced that the primary source of the misconception is that most of the published tear down tests (particularly on light-duty engines such as the one tested by [PERSON] et al. [6]) are almost always performed in the wrong order. The valve train is disabled before the piston components are removed, and this difference in torque is assigned entirely to the valve train. This is an erroneous conclusion, because when the valve train is disabled, the piston ring gas pressure loading is also eliminated, and therefore, piston assembly boundary friction is mostly eliminated. The result of this is that the observed reduction in friction by removal or disabling of the valve train, while caused by the fact that the piston assembly is no longer loaded by gas pressure, is erroneously assigned to the valve train. Therefore, piston assembly friction appears lower than its true contribution. A good example of this is presented by [PERSON] (2013). In the [PERSON] case, removal of the cylinder head generated a reduction in FMEP of the order of 8 psi (55 kPa), while the final removal of the pistons generated a reduction of 2-5 psi (14-34 kPa) in FMEP. (Note, in the [PERSON] (2013) test, the valve train was entirely removed by removing the cylinder head, but disabling the valve train while the head remains in place has an identical effect.)