The boat has a 1984 Mercruiser I/O with a 140 hp (3.0L), 4 cylinder engine SN 6752683, sterndrive SN 6748519 (aka R/MR/Alpha One). The engine needed rebuild due to 3 out of 4 cylinders being out of spec on compression. This was performed over the winter of 2015/16 by a local Mercury shop. When engine was pulled the boat needed some major restoration so this was performed through 2016 and did not get the engine back in until fall so postponed start-up and launch until this spring. Here is the sequence of events:
- Engine rebuilt over the winter of 2015/16.
- Carburetor was removed and rebuilt while engine rebuild underway.
- Engine and drive reinstalled and aligned fall of 2016.
- New battery installed spring of 2017.
- With the first attempts to start and get running, including attempting to set the timing, it was discovered that
- Distributor had been installed 180 degrees out of phase.
- Engine compression was not in spec. The valves had not been adjusted properly.
- The boat was taken to re-builder for valve adjustment.
- Timing again checked and adjusted and the boat launched (now into July).
- Had ongoing difficulty with rough running as though there was miss-firing.
- Decided to get new ignition parts: ignition coil, tune-up kit (includes distributor cap, points, condenser, rotor), spark plug wire set
- Installed ignition parts, rechecked timing and all seemed to be running well. Seemed like there was still a slight miss at high RPMs.
- The boat was used the weekend of August 5[SUP]th[/SUP]. Ran all day Saturday for water skiing and tubing and it ran great. On Sunday morning (the blower had been left on over night), it ran poorly, extremely rough running, decided not to use.
- Did trouble-shooting: checking dwell, timing, connections, carburetor adjustments. It did not want to hold timing constant. Thought maybe distributor was bad but did nothing about it.
- A few days later, started it and ran good without any adjustment. Dwell was right on, tweaked timing, made minor adjustment to idle mixture. Ran steady in and out of gear on the lift. Took it out on the lake and ran RPMs up slowly. Ran good up to 2100. Beyond that it ran like crap. Came in and checked compression, good on all cylinders: 130, 138, 136, 130 on 1 through 4. Noticed that it was sensitive to voltage drop. When drive running at idle and trimming down voltage dropped and engine not so smooth. After compression check, started engine and now runs with a flutter and timing has gone from 6 BTDC to 4.
- At one point, the boat would not start, as if battery was low. Checked and it was. Charged the battery fully. Then began suspecting that the alternator was not putting out full charge. This turned out to be true. Got 12.5 volts off the alternator terminal while running using multi-meter. The dash volt meter read well below 12 when running. Using a Mercruiser service bulletin test, indicated the diodes were bad.
- Ordered a new alternator (which replaces the OEM part 1105065 but is rated at 110 Amps instead of 42) and installed.
- After putting it in everything looked good. Ran up to WOT with no misfire and all seemed good. Slowed down and turned around to head back. Engine started to idle bad, then had mechanical noise and it died. Did not want to start. Had to get towed home. When got back on the lift, started it again and got the same mechanical noise. Shut it down. The mechanical like noise seems to come from back end of engine.
- The engine will start but will not run more then about 30 to 40 seconds when idle drops off and it dies. Almost seems like the engine seizes up.
