Not enough inertia to raise starter?

[joshua.nunley]

I am working on a Mercury 115 Tower of Power and my starter is spinning but doesn't seem to have the inertia to jump up and spin the fly wheel. I thought it might be a bad starter so I took it apart and everything seems fine..hooked it directly to a car battery and it jumps up just fine but will not on the boat battery or while jumper cables are hooked to the boat battery..could this simply be not enough cranking amps?

 

[gm280]

:welcome: aboard joshua.nunley. Nice to have you join us...

Before doing anything else, remove and clean the two battery cables from the battery to the engine at both ends. You could have some corrosion going on there and that will zap the current pretty well. So clean the positive and negative battery AND the engine connections to bright shiny metal first and see if that fixes your problem. Also, make certain your cranking battery is fully charged. If after that it still doesn't spin up and connect the flywheel, then you may need a new battery. JMHO!

 

[schematic]

Be sure your battery is not connected in reverse polarity

 

[Barnacle_Bill]

The last time I ran into that it was corrosion inside the battery cable lugs where you couldn't see it. New lugs on both ends fix the problem. A voltage drop test would veirfy if that is the problem.

 

[Texasmark]

"Not enough cranking amps?" Yessir first guess on that problem.

A sulphated battery has a large internal resistance to go along with the possible problems the other guys mentioned, and a possible low charge to boot.

Take your battery to Wallmart or some place that can load check it for you. Have the tech crank up the amps to 200. You should have 11v at the battery terminals (the tester monitors the terminal voltage) with a good condition, fully charged battery. It takes 10v (for a number) at the starter terminal to case while cranking with plugs installed to spin the shaft fast enough to engage the Bendix.

If you have that and still sloppy service out of the Bendix the shaft could be dirty needing some cleaning (spray automotive breake cleaner works great) and lube.....graphite powder is a great product...stays put and doesn't attract dust and dirt, your starter brushes are in need of replacement, or a winding is shorted....seldom occurrence. On a Tower that they quit making the latter days of the 1980's, worn out brushes could very well be your smoking gun. That's a long time on one set of brushes.