PCT No. PCT/AU92/00323 Sec. 371 Date Dec. 2, 1993 Sec. 102(e) Date Dec. 2, 1993 PCT Filed Jul. 1, 1992 PCT Pub. No. WO93/01402 PCT Pub. Date Jan. 21, 1993.A two stroke cycle engine cylinder block (9) has exhaust ports (14) controlled by power valves which rotate on an axis extending longitudinally of the block (9). Along this axis the block (9) has a plurality of aligned recesses in which are located bearing members (24) for the power valves. Bores (25) in each bearing member (24) are axially aligned and the bearing members (24) immobilely retained in the aligned recesses by assembly of the exhaust manifold (16). Spigots on the power valves are received in the bores (25) and coupled together so that the power valves rotate in unison.
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