Mercruiser 5.7L Black Scorpion grinding noise when in neutral

[Oxide]

Hello all - new forum user here looking for some expert opinions. I recently bought a 2007 Centurion Avalanche C4, with a Mercruiser 5.7L 330 Black Scorpion engine. When we took it out on the lake for the first time, I noticed that it was making a loud grinding noise whenever it was in neutral (maybe not 100% of the time, but close enough). The noise would go away whenever I put it in forward or reverse gear.

I drove it back to the dock and put it in neutral. Noise returned immediately, and so I turned the ignition switch off, tied it up, and went to get the truck+trailer. While I was walking back to the truck, the engine restarted itself even though the ignition switch was still in the off position.

I got back to the boat as quick as I could and killed the engine by putting it in gear while the ignition switch was still in the off position. Once the engine was off, I disconnected the battery so it wouldn't restart itself.

My suspicion is this is either faulty ignition switch, or faulty/stuck solenoid or slave solenoid resulting in power being applied to the starter even though the ignition switch is in the run position.

Earlier this evening I started the boat (starter sounded rough - making the grinding noise while it was cranking), but after it started it ran fine in neutral for several minutes with no noise. So just to test my hunch, I turned the key to start position with the engine still running, and the loud noise immediately returned.

Am I in the right neighborhood on root cause, or is it more likely I've got something else going on?

I'm also worried that this issue has damaged the starter motor or other engine components. When it happened at the dock it took me a bit to get back to the boat and kill the engine. By the time I got there I noticed little bit of smoke in the engine compartment, kind of near the port side exhaust elbow. Would welcome opinions here as to what the heck is going on.

 

[Oxide]

On a related note, where the heck is the slave solenoid on this engine? Maybe I'm just overlooking the obvious, but I did not see it when glancing around engine compartment.

Haven't gone digging yet to look under wires/hoses for it. There seem to be quite a few wires and connectors tucked under the outer lip of the plenum/cover, so maybe I have to remove that to get to it?

 

[Scott Danforth]

your starter is probably already damaged. so pull it and inspect / test it
your ring gear is probably chewed up if the starter was engaged while the motor was running. so the motor must come out to fix that.
follow the yellow wire with the red stripe from the starter. it leads to the pilot solenoid.
replace your ignition switch.

 

[kenny nunez]

The slave solenoid is under the cover. Look for yellow wires with a red stripe. The other place to look is where the ignition switch is. At one time Mercruiser ignition switches had a problem starting the engine without the key turned. Since the starter only activates in neutral I think the source is in the instrument panel area.
Pay close attention to where the wires are connected to the starter. Take pictures of how the wires are situated.
As AD said the starter needs to be replaced and hopefully the flywheel is not chewed up.

 

[Oxide]

Thanks, guys, for the quick response and helpful info. I'm going to get it in to Mercruiser mechanic to have them check starter and ring gear and replace if needed, along with replacing that ignition switch (which I'm thinking is probably the original source of the problem).

Re: Solenoid - tracing the yellow/red wire leads a white connector/coupler. Other side of the couple feeds up into the instrument panel. Can't tell more without pulling the panel, which I don't have time to do this AM. Guessing solenoid is probably tucked up there someplace.

Either of you able to ballpark cost to have mechanic replace starter + ring gear? I don't have the equipment or the time to pull the engine myself, but also don't want to get taken for a ride by the service department.

Thanks again for your responses!

 

[Lou C]

That can be a big job in terms of labor, is this an I/O or a straight inboard?
If it were my boat I’d check to see if I had good enough access to the starter, on some boats you have to remove the exhaust on that side to gain enough access. If you can do that and the ring gear looks OK I’d probably just replace the starter. It’s probably the lighter PMGR starter so they don’t weigh near as much as the old Delco direct drive starters.
The other thing you could do and that prob should be done first is to disconnect the yellow/red wire at the starter and with a helper put a test light or volt meter on the terminal to that wire (other end of light or meter to ground) and watch it while someone turns the key to ignition on and then off several times. The light or meter should not show current on that wire unless you turn it to start. If so your problem is a switch or relay problem & needs to be fixed first.

 

[Lou C]

Curious so I looked these appear to use a V drive with the rear of the engine in the forward end of the engine compartment it looks like the frame for the tow rope needs to be removed prob along with the exhaust to get at it. Might not be that bad of a job.

 

[Bondo]

Re: Solenoid - tracing the yellow/red wire leads a white connector/coupler. Other side of the couple feeds up into the instrument panel. Can't tell more without pulling the panel, which I don't have time to do this AM. Guessing solenoid is probably tucked up there someplace.

Ayuh,.... It's on the motor, not under the dash,....

 

[Oxide]

Curious so I looked these appear to use a V drive with the rear of the engine in the forward end of the engine compartment it looks like the frame for the tow rope needs to be removed prob along with the exhaust to get at it. Might not be that bad of a job.

Finally had a minute to poke around a bit more just to find where exactly the starter's at on this motor, and you are correct. It's tucked under the port side exhaust. Not exactly a spacious spot to work, but it doesn't look too bad to DIY replacement. From what I can see it's like two bolts to get it out of there.

 

[Lou C]

Finally had a minute to poke around a bit more just to find where exactly the starter's at on this motor, and you are correct. It's tucked under the port side exhaust. Not exactly a spacious spot to work, but it doesn't look too bad to DIY replacement. From what I can see it's like two bolts to get it out of there.

Yep it's two bolts but they are under the engine, kinda close to where the bell housing would be. A lot depends on how big of a person you are. I have done mine a few times over 20 years with this boat, but I re configured the rear seats so they can be removed individually and I can lie down next to the engine to get at it.

 

[Oxide]

Replaced the starter and ignition switch. Fired right up and sounds great - problem solved. Fortunately, the ring gear was still in good shape!

 

[Lou C]

Congrats on fixing it you just saved yourself a pile 'o cash!