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