Mercruiser Replacement Engine Coupler | Sierra 18-2171 SIERRA Mercruiser Replacement Engine Coupler 18-2171 Engine coupler connects early model Mercruiser GM engines to stern drives. Engine coupler is used on Mercruiser GM engines except MR, Alpha and Bravo with triangular 3 bolt coupler Fits Mercruiser 153 CID model 110 from 1963 to 1966 with serial number range 1537370-2044033 Fits Mercruiser 153 CID model 120 from 1964 to 1982 with serial number range 1537370-6229717 Fits Mercruiser 181 CID model 140 from 1968 to 1982 with serial number range 2508261- 6229717 Fits Mercruiser 181 CID model 3.0L from 1987 to 1989 with serial number range B450801-C856558 crankshaft mounted coupler Fits Mercruiser 229 CID model 185 4bbl from 1983-1984 with serial number range 6330183 - 6919655 Fits Mercruiser 305 CID model 228 from 1977 to 1982 with serial number range 4765100 - 6218461 Fits Mercruiser 350 CID model 260 from 1978 to 1982 with serial number range 4908850 - 621846 Replaces Mercury 32492A2, 32492A3, 32492A5, 38965A1, and 76850A2 Replaces Mallory 9-72502