Merc 470 no crank

[Mikeopsycho]

Everything worked fine then shut off and when we tried to restart it we got nothing. When it did work it seemed intermittent, would stop cranking before the key was released, but would crank again when the key returned to start. All connections clean, starter and slave solenoid bench tested OK, coil works fine in other engine. It seems the slave solenoid is grounded to the positive terminal on the coil (the same as the other engine). Oddly, the engine will start and runs fine when we disconnect the solenoid wire from the coil and ground it to the block. We are at a total loss as to what is going on. Any ideas? Thanks.

 

[kenny nunez]

Your engine requires a grounded base solenoid which has the “by pass” circuit which supplies 12 volts + to the coil while in cranking mode. You probably have a non grounded solenoid which is causing what you are describing.
Merc Marine# 65057 A1or T1
Sierra #18-5802
NAPA also has a marine solenoids and can cross over the Merc #

 

[Mikeopsycho]

Your engine requires a grounded base solenoid which has the “by pass” circuit which supplies 12 volts + to the coil while in cranking mode. You probably have a non grounded solenoid which is causing what you are describing.
Merc Marine# 65057 A1or T1
Sierra #18-5802
NAPA also has a marine solenoids and can cross over the Merc #

Thanks Ken. The solenoid was replaced because the old one failed. I will try your suggestion. It may take a few days to get the new one, I live on a little Island and will have to order it. I appreciate the reply.

 

[440roadrunner]

It's a sad sad commentary. In a previous life (mid seventies for 15 years) I sold auto parts, heavy hardware/ rigging, hydraulic hoses and more. NOW a days, NAPA, Oh'Reallys and others, have no decent catalogs and the computers are just like Google......zero help. Trying to find parts by description is difficult and no helpful specs are given. Take a multimeter with you to the store and check the thing for continuity.

 

[achris]

Everything worked fine then shut off and when we tried to restart it we got nothing. When it did work it seemed intermittent, would stop cranking before the key was released, but would crank again when the key returned to start. All connections clean, starter and slave solenoid bench tested OK, coil works fine in other engine. It seems the slave solenoid is grounded to the positive terminal on the coil (the same as the other engine). Oddly, the engine will start and runs fine when we disconnect the solenoid wire from the coil and ground it to the block. We are at a total loss as to what is going on. Any ideas? Thanks.

If, as already suggested, you're using a 'ungrounded' solenoid this would happen.

There are 2 variations of solenoid. One uses the 2 small terminals for the (internal) coil. You ground one, and then power the other to get the solenoid to activate.

The other solenoid uses the solenoid casing as the grounding terminal of the internal coil. You power the 'S' terminal and ground the casing. This type of solenoid also has a second small terminal, and from the outside it's dificult to pick the difference. This second terminal is a power connection to the ignition coil. It applies full 12v to the ignition coil during cranking.

Now, if you were to use an ungrounded solenoid and connect the ignition coil to the terminal the solenoid is expecting to be its ground, then it would only flow current (and thus 'pick' and power the starter motor) if the engine had previously stopped with the points closed. That would allow a path to ground for the solenoid to pick. If the engine stopped with the points open, the solenoid wouldn't be able to pick. And as you were cranking the points are opening and closing, and so the solenoid is 'bouncing' it's only the inertia of the engine spinning that it getting the points to be closed again that allows the solenoid to 'repick' as it were.

Yes, change to a grounded solenoid and that should solve your problem. Merc part number is -65057A1.

Chris......

 

[Mikeopsycho]

Thanks kenny nunez, your advice worked! Got the correct solenoid, and voila! She cranks. And thanks to all for your input! Good explanation of how the solenoids work achris! The mechanic I spoke with said all 12V solenoids are the same, the parts store said all 12V solenoids are the same, I thought all 12V solenoids are the same. Live and learn. Again, thanks folks! I wish I asked here before I wasted 4 days chasing my tail and banging my head against the hull.

 

[achris]

...The mechanic I spoke with said all 12V solenoids are the same, the parts store said all 12V solenoids are the same....

Ummm, yeah, NO...

 

[Scott06]

Ummm, yeah, NO...

yeah these guys are probably too young to know how a points system bypasses the resistor during cranking

 

[nola mike]

The other solenoid uses the solenoid casing as the grounding terminal of the internal coil. You power the 'S' terminal and ground the casing. This type of solenoid also has a second small terminal, and from the outside it's dificult to pick the difference. This second terminal is a power connection to the ignition coil. It applies full 12v to the ignition coil during cranking.

I wonder what the advantage is of doing it this way rather than just tapping off the 12v terminal supplying the starter.

 

[achris]

I wonder what the advantage is of doing it this way rather than just tapping off the 12v terminal supplying the starter.

The early 470 starter motors didn't have a 12v terminal...

 

[nola mike]

The early 470 starter motors didn't have a 12v terminal...

I meant the terminal coming off the solenoid to the starter.

 

[achris]

I meant the terminal coming off the solenoid to the starter.

Ah, ok, I think you mean why not use the same feed that goes to the starter. You can't. It has to be 'separately' switched. If you just use the stater motor feed cable, then as soon as you turn the key on, the fuse will blow. It would try to feed the starter motor through that wire, which is connected to the coil positive (which is powered the instant you turn the key on. )

Chris...

 

[nola mike]

Ah, ok, I think you mean why not use the same feed that goes to the starter. You can't. It has to be 'separately' switched. If you just use the stater motor feed cable, then as soon as you turn the key on, the fuse will blow. It would try to feed the starter motor through that wire, which is connected to the coil positive (which is powered the instant you turn the key on. )

Chris...

Oh yeah
Although it actually looks like it would just keep cranking the starter when the ignition was on? ("STR" terminal)

 

[achris]

Oh yeah
Although it actually looks like it would just keep cranking the starter when the ignition was on? ("STR" terminal)

Yes, but Merc have a 20A fuse in the line between the battery and keyswitch, and starters draw a little more than 20A, so the fuse would blow. Without the fuse, the wires would melt.

Even that drawing for the internals of that 'relay' aren't quite right... (I'll see if I can correct it)

Chris..

 

[achris]

Here's how the solenoid SHOULD have been drawn.

 

[nola mike]

Guess I'm not seeing where the increased current draw would come from, and why it would go through the key switch. Looks like in either drawing you have the bypass wire in parallel with the starter wire(s), so should be less current through it than the others. And your mention of the "starter wire" 20a draw is presumably the current draw of the Bendix/starter solenoid rather than the actual starter. And now we're the only 2 people still following this thread