Twin Mercurys 40hp EFI - double starter failure?

[DutchCs]

We fish and cruise in the Apostle Islands, Lake Superior. We're running twin Merc 40hp EFI motors on Aeolus, a 22' cruiser. Aeolus is on the trailer when not in use.

A couple days ago, after a day of cruising with all systems normal, we made a stop for photos near an island. After the stop the port engine starter would not engage, it just made a spinning sound. I initially thought it was low voltage on the port battery. We were 18 miles out in the islands and evening was approaching, so we scrubbed plans to anchor for the night and cruised back to town on the starboard engine.

Three hours later, well after dark, we made it back to town and decided to anchor near town for the night and load up in the morning. The starboard motor ran normally back to town. The battery voltage indicated 12.8 volts with chart plotter, autopilot, VHF, and LED nav lights running.

After dropping the hook, I went to set the hook with the engine and no go with the starboard engine, only a whirring sound from the starter, just like the port side earlier! I shut down power to the electrical panel for the night (Perko switch to OFF). The next morning I was able to start the starboard engine manually with a pull cord and we cruised to the ramp an loaded up.

At home, I checked both batteries individually on a charger, both indicated 12.8 volts, and 90% charge. After charging both batteries, the problem remains the same, neither engine starter will engage, both starters spin but don't engage the flywheel. (Perko swith set to OFF)

Bad batteries? Corroded battery cables / connections?? Double starter failure?? It seems unlikely to have both systems fail on the same day!!!

Has anyone had a similar occurrence or have any insight to possible cause of this situation? I'll post my findings as I dig in and trouble shoot the problem.

Thanks!

[T.R. Bauer]

Wow. It's completely possible, although certainly not probably, that you went through 2 starters on that trip if everything checks out like you said. But it is suspect and weird. They are on separate batteries and all so there really is no common theme, except these starters apparently last exactly as long as one another.

[thataway]

I would start by pulling all of the cables off their terminals one by one--then clean, wire bush, re swage cables if necessary. My bet is you have corrosion some place in those large cables. Put a little dielectric grease on each terminal as you re-assemble. I carry wire brush (SS and Brass) in my tool kit just for times like this.

[colbysmith]

If both starters are spinning, ie, you said you heard the spinning sound, but they are not engaging, I would think that is a starter failure. I agree, possible but odd that both at the same time. Do they both have the same number of starts or hours? I should rephrase. It could be the starter solenoid is not moving the starter gear into the flywheel. Or you have some bad teeth on the flywheel. I guess it would be worth pulling the cowling and look at where the starter engages the flywheel and see what is happening there. If OTOH, the starter only spins for a second and then stops without turning the engine over, I would consider the battery. If you have a separate battery for each engine, then I would check the ground cables. Would be odd that both positive cables failed somewhere. But I suppose that could be possible too. But if both starters sound like they are spinning but not engaging, that would have to do with the solenoid that throws the starter teeth into the flywheel teeth. If it were a battery or cable problem, I would expect that all you would hear is a click. Colby

[T.R. Bauer]

In reflection, I think I would check and see if you have a good solid zero ohm ground going to both of your starting batteries to the outboards. Spinning starters without engagement is usually the solenoid...usually. But maybe there is a bit of corrosion on the wire that engages the solenoid? I'd check you have battery voltage there when you try to start the thing. Again...this whole thing is suspect and weird. Please let us know what you find.

[thataway]

What happens especially with corrosion and/or poor grounding, is that the starter spins, but enough power is not available for the solenoid to move upward and engage to start turning the flywheel. In other words--enough "power" to spin the starting motor with no load, but not enough to energize the solenoid or spin the outboard motor. The starting battery apparent voltage is lower, as the demand for more current is increased. Normally a battery has the voltage drop simnifically during the starting process. If Voltage drops below 9.5 at the starting motor/solenoid it may not function. You can simultaneously measure the voltage at the battery and at the starter terminals. There should be little difference. Also if you have a friend or have one, there are higher end volt/amp meters which clamp around the wire to neasure current--and you want the Maximum current or "inrush current". Not all meters will do this.

This is the most likely scenario for both engines to fail to start.

[DutchCs]

Thank you for your thoughts and comments on this issue. Following is more information on the boat electrical system and an update on my course of action and findings.

Each engine has its own battery. Each battery is wired to a Perko switch that feeds a fuse block for the electronics and house electrical load. (Much to our wives’ chagrin, my boat partner and I have installed lots of electrical devices.) The batteries are 5 years old. The engines are 2012 model year and have about 450 hours on them. The boat has NOT been in salt water.

I started with the batteries. Both were removed, inspected, and charged. The charged batteries tested 12.8 to 12.9 V. Battery terminals and cable ring terminals were cleaned with a steel brush. Reconnected the batteries.
Then removed the motor and flywheel covers to get access to the starter motors. Measured voltage at the engine terminals and found about 0.05-0.07V drop in voltage from battery. Seems reasonable.

Next inspected the starter pinion gear and flywheel gear. No missing teeth, chips, or excessive wear observed. Tested each starter by engaging ignition. Both starters spun but did not engage the flywheel. The Strb starter sounded loud and rougher that the Port side, which was quiet and smooth. I measured the voltage across the starter terminals with the starter engaged, both were at 12.0V.

The starters are inertia drive type, meaning the rotation of the motor shaft causes the pinion gear to slide out along the starter motor shaft to engage the flywheel. The pinion gear appeared stuck in the retracted position, and would not move out as it was twisted or pulled by hand. With the help of a friend, a large flat screwdriver was used to apply pressure to the pinion gear pushing it towards the flywheel as the ignition was energized. With moderate pressure the pinion gear popped free and engaged the flywheel. After that, the starter worked as normal, engaging the flywheel, and turning the engine. The same procedure was done on the other engine with the same results. Both starters worked normally.

Both starters were removed and taken to a rebuild shop for inspection and rebuild. I briefed the rebuild technician on the situation and asked him why the starters were “stuck”. He stated that older starters accumulate grease and dirt that might have caused it to stick, but he speculated that low battery voltage was likely a factor as well. He strongly suggested to have the batteries load tested. The starters will hopefully be rebuilt in about a week pending parts shipping time.

I had the batteries tested at a reputable battery shop. Under load the battery voltage dropped to about 10 volts on each battery. This is low, and indicates the batteries are at or near the end of service life. So, two new marine starting batteries were purchased.

In summary, it appears the root cause of this issue was older, marginally performing batteries. The “sticky” Bendix/pinion gears required full voltage to function properly, which the batteries didn’t provide.

In the future we will monitor battery health more closely! We are considering adding a third battery to help attenuate the house load on the starter batteries. Please advise if anyone has thoughts on this!

I hope to be back on Gitchagomi in a week or so. I’ll let you know if any problems continue.

Thanks again for everyone’s thoughtful comments and suggestions.

[thataway]

Ever since my first boat over 20' I have had separate house batteries. This includes my all of my C-Dorys. I recently have added a "house" battery to my 18' Caracal Cat.

I have seen the bendix gears stick with built up grease--never two at the same time---but life happens. Not at all surprised at the "end of useful life" of the 5 year old battery,

Thanks for following up for all of us!

[T.R. Bauer]

Thank you for posting what you found. And, I'm glad you got it fixed and going again. I've had starters do just what you described if they sat a long while. But never like you experienced. You added to our collective knowledge