Means are provided for adjusting the relative timing of {TAIL ~ the two pistons} so as to vary {HEAD ~ the compression ratio} of the engine 
Means are provided for adjusting the relative timing of { TAIL ~ the two pistons } so as to vary { HEAD ~ the compression ratio } of the engine
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH