2005 60hp Merc 4 stroke will not start

[Gstan]

starter shaft extends, gear meshes with flywheel. starter shaft turns but gear does not, starter shaft does not retract. Battery fully charged. What shall I try next>

 

[Texasmark]

The starter has to spin at a fast enough speed to cause the "Bendix" to spin up and the gear on the starter shaft extend to the point where it engages the flywheel gear. Second, the starter must have 150 amperes, give or take, to spin the engine with the plugs installed. Both functions require a fully charged, non sulphated up (high internal resistance caused usually by age) battery with all connections clean, bright, and tight (on the inside where current flows, not necessarily on the outside where it looks pretty)....which includes the high current contacts INSIDE the starting solenoid and if you have a standard lead posted battery, the interface between those battery posts and the cable posts.....and includes the crimps where the terminal lugs are crimped to the high current cables....both plus and minus wiring. A voltmeter can show you your bad connection if that including a sulphated battery. Just look for a voltage drop while cranking. None of the contact points should have a measurable voltage across them.

The starter needs at least 10v across it while cranking to function properly. A 12v system -10 volts at the starter leaves 2 volts of total (plus, minus, and battery) circuit voltage drop. At 150 amperes, Ohm's Law states that the total circuit resistance can't be more than 2/150 = 0.013 ohms and brother, that taint much!

Gonna bet your boat is violating one of these requirements and that is your problem. A little WD 40 on the starter shaft wouldn't hurt either.

 

[Gstan]

Checked terminals they are clean and fully connected. Checked voltages: 12.1-12.2 at the battery. Voltage at starter terminals runs 10.99 - 11.1 when cranking. Starter shaft spins, no movement of the starter gear or flywheel. Tried light oil on the starter shaft (not too much) and even some small hammer tapping on the end of the starter shaft. Shaft is still extended and engaged on the flywheel, not retracted into starter body. Any other help is appreciated.

 

[Silvertip]

1) a fully charged battery is 12.6 volts (12.1 is not fully charged and certainly not at 10.9 under load)
2) The starter shaft does not extend or retract into the starter housing.
3) The bendix (the gear) has a clutch in it. The bendix rises up the shaft when cranking and drops back down when the starter is not running.
4) Stop banging on the end of the starter shaft (see #2)
5) If the shaft is spinning but the bendix gear is not -- replace the bendix.
6) Verify your voltage readings with a known accurate meter.

 

[Texasmark]

In addition to what ST said, clarify a point.

If the starter is not spinning the flywheel, the voltage readings you took are meaningless as the starter is not under a load and is not drawing/attempting to draw any 150 amperes; more like 10-20 amps if that much and circuit problems aren't necessarily visible at that point.

At rest, is the gear engaged in the flywheel teeth?

I am assuming it is from your comments. If so, the Bendix may be frozen on the starter shaft at the "flywheel engage.....start the engine" position. If this is the case and the last time the starter started the engine and you ran the engine for any length of time you could have not only a stuck Bendix gear, but burned up your starter motor. However, if it is engaged, how can you spin the starter shaft when in the "start position of the switch" and the Bendix not turn unless the bendix to starter shaft interface is stripped. If so, then how is it that the gear remains at the end of the shaft (flywheel engagement position) with the power off?

Something not making sense here.