Merc 900 Starter Questions

[nate_evans79]

I have a 1978 Merc 900. I got a new starting battery, its a 550 cranking amp battery, I also replaced the starter solenoid. When I charged up the battery, it started fine. took it out for an hour or so, and it ran great. Got home and went to start it to flush the water, and it wouldn't fire up. The starter just turned real slow. I checked the battery on the charger, at it was at about 30% charge. So obviously its not charging off the motor. So I put the battery back on charge, and also took off the stator, and ran new wires to that, as the old ones were pretty corroded. After the battery had reached full charge, I put it back in, and the starter was still turning slowly. I checked the voltage on the battery just sitting there it was 12.68, I checked the voltage at the solenoid it was also 12.6. With the ignition turned to "start" the voltage dropped to 7.8v on the solenoid, and at the starter. The battery read 10.0 volts at "start" possition. I'm a little lost now. I put the jumper cables onto my car, from the boat battery, and tried starting with the car running also, and the starter still turned slowly. I'm just trying to figure out what is at fault here, with out replacing unnessesary things. <br /><br />Is it the battery?, Starter?, or is the new solenoid that I have bad? Or even cables. All wires are new execpt for the power and ground at the starter. <br /><br />Thanks for any help, sorry for the long post.<br />Gotta get this thing running, cause fishing is great right now.<br /><br />Nate.

 

[Laddies]

Re: Merc 900 Starter Questions

If a fully charged battery drops to 10 volts you either have a bad connection or a bad sterter. You can tell if you have a bad connection by hooking the voltmeter direct to the battery

 

[nate_evans79]

Re: Merc 900 Starter Questions

The reading on the battery terminals was 10v in the "start" possition. So it sounds like a bad starter?

 

[Laddies]

Re: Merc 900 Starter Questions

Yes

 

[nate_evans79]

Re: Merc 900 Starter Questions

Thanks for the quick reply.<br /><br />Nate.<br /><br />Should I try cleaning the starter and brushes? or just get a new one?

 

[studlymandingo]

Re: Merc 900 Starter Questions

Make sure all of your ground wires are good and that they are all secured well. I had a similar problem with an old 'rude and it turned out to be in the wiring. Try jumping from the battery directly to the starter terminal and see if it cranks there.

 

[Kevin W]

Re: Merc 900 Starter Questions

I would double check the battery with a car battery and if it still fails get the starter rebuilt.<br />its rare but sometimes new batteries fail or are low on acid.

 

[Texasmark]

Re: Merc 900 Starter Questions

Before you spend any money let's back the truck up.<br /><br />Where did you measure the "7.8 volts at the solenoid and the starter"?<br /><br />If you measured 10 across the battery terminals during starting and 7.8 elsewhere in the circuit, you lost 4.88 volts across something and you don't do that(and survive)......course I'm used to farm tractors with big diesels and 00 sized wire. <br /><br />Loosing 2.88 v due to internal battery resistance during starting is high. Then you loose another couple of volts due to something else and now you have lost almost half of your whoopie from your battery. No wonder your engine is slow turning.<br /><br />For a new battery, that internal resistance is very high (causing the loss of 2.88 v at the battery terminals).......unless we find out that your starter is shorted (last thing to determine) and instead of 150 amperes flowing in the circuit there is something like 300 trying to run around.<br /><br />First thing to do is to disassemble all the connections between the battery and the engine, both positive and negative, on both ends of any interconnect cables and clean them up nice and bright and shiny. If you have the standard lead terminals at the battery take them off and clean them too.....ANY interconnection that high current passes through.<br /><br />Remove the starter and where it contacts the block, clean up that interface too as that is where current gets back to the battery (via the block).....usually. <br /><br />Hook all that back up. <br /><br />Then measure the solenoid drop by pressing the tips of your meter leads INTO THE ENDS OF THE STUDS on it. During start you shouldn't drop more than a half volt across it. If you measure more the contacts are pitted and it needs to be replaced.<br /><br />Then go to the starter and press the points of your leads into the case (ground)OF THE STARTER and the END OF THE STUD where power is applied to it. In start you shouldn't read more than 1.5v less than what you had across the battery. If you do, THEN worry about fixing/replacing the starter.<br /><br />Mark

 

[Texasmark]

Re: Merc 900 Starter Questions

Before you spend any money let's back the truck up.<br /><br />Where did you measure the "7.8 volts at the solenoid and the starter"?<br /><br />If you measured 10 across the battery terminals during starting and 7.8 elsewhere in the circuit, you lost 4.88 volts across something and you don't do that(and survive)......course I'm used to farm tractors with big diesels and 00 sized wire. <br /><br />Loosing 2.88 v due to internal battery resistance during starting is high. Then you loose another couple of volts due to something else and now you have lost almost half of your whoopie from your battery. No wonder your engine is slow turning.<br /><br />For a new battery, that internal resistance is very high (causing the loss of 2.88 v at the battery terminals).......unless we find out that your starter is shorted (last thing to determine) and instead of 150 amperes flowing in the circuit there is something like 300 trying to run around.<br /><br />First thing to do is to disassemble all the connections between the battery and the engine, both positive and negative, on both ends of any interconnect cables and clean them up nice and bright and shiny. If you have the standard lead terminals at the battery take them off and clean them too.....ANY interconnection that high current passes through.<br /><br />Remove the starter and where it contacts the block, clean up that interface too as that is where current gets back to the battery (via the block).....usually. <br /><br />Hook all that back up. <br /><br />Then measure the solenoid drop by pressing the tips of your meter leads INTO THE ENDS OF THE STUDS on it. During start you shouldn't drop more than a half volt across it. If you measure more the contacts are pitted and it needs to be replaced.<br /><br />Then go to the starter and press the points of your leads into the case (ground)OF THE STARTER and the END OF THE STUD where power is applied to it. In start you shouldn't read more than 1.5v less than what you had across the battery. If you do, THEN worry about fixing/replacing the starter.<br /><br />Mark

 

[nate_evans79]

Re: Merc 900 Starter Questions

Originally posted by Texasmark:<br /> Where did you measure the "7.8 volts at the solenoid and the starter"? I had my meter on the main power post from the battery to the solenoid, and on the main post from the solenoid to the starter. <br /><br />First thing to do is to disassemble all the connections between the battery and the engine, both positive and negative, on both ends of any interconnect cables and clean them up nice and bright and shiny. If you have the standard lead terminals at the battery take them off and clean them too.....ANY interconnection that high current passes through. I have the threaded posts on the battery, and they are brand new shinney. I also have a new wire harness to the engine, and in the engine. <br /><br /> I will check the grounds and power on the starter itself, and clean all of them up really good. <br /><br />Then measure the solenoid drop by pressing the tips of your meter leads INTO THE ENDS OF THE STUDS on it. did that, that is where the 7-8 volts reading was at start. <br />During start you shouldn't drop more than a half volt across it. If you measure more the contacts are pitted and it needs to be replaced. The solenoid is brand new, no pitting or anything there. <br /><br />Then go to the starter and press the points of your leads into the case (ground)OF THE STARTER and the END OF THE STUD where power is applied to it. In start you shouldn't read more than 1.5v less than what you had across the battery. If you do, THEN worry about fixing/replacing the starter.<br /><br />Mark

 

[nate_evans79]

Re: Merc 900 Starter Questions

Well, I jumped the starter straight from the battery, and got the same result, very slow turning. Jumped the power, and the ground directly to the battery.<br /><br />So I took out the starter, and opened it up, here is what it looks like.<br /> Starter Pics on my webshots page. <br /><br />It looks as though its really corroded up in the center motor part. Can I just clean that out with a soft wire brush and some electrical cleaner solvant? Or does it look totally shot?<br /><br />Thanks.<br /><br />Nate.

 

[Laddies]

Re: Merc 900 Starter Questions

You could probably clean it up and make it work, if you need brusles thats a standand boech starter and even lawn tracters use the same brushes and carrier so you can get them most anywhere

 

[Texasmark]

Re: Merc 900 Starter Questions

Need another answerfrom you .....assuming your battery is still charged.<br /><br />If you measured 7.8 volts across the starter....case of starter to power terminal stud end while cranking with a fully charged battery it indicates a shorted starter.<br /><br />3 good reasons for a shorted starter:<br /><br />1. Brush residue (from normal wear) leaking across from pole to pole which essentially amounts to a shunt path for current.<br /><br />2. Varnish insulating the windings worn off/melted off, and adjacent windings touching causing a shunt path for current.<br /><br />3. Laminations shorted (adjacent) which increases eddy currents which increases dissipation (loss) that would otherwise be used to spin the armature.<br />-------------------<br /><br />In the first pic I think I'm seeing melted varnish deposited on top of the laminations. This indicates overheating and the windings are probably shorted and starter has to be rewound or replaced. It should feel just like paint in that you can flake it off and will be darker than the varnish that you see on the wires in your picture running the full length of the armature. Also the armature should have a burned smell to it.<br /><br />2nd pic. More of the same goo (melted varnish). What I don't like is the surface where the brushes ride. Looks to be very rough. To run the starter the brushes need a smooth surface (for long life and electrical connection). This surface is actually the "pole contact area" where the poles, or little circuits of the starter that make it turn when you apply power, get energized. If the poles are shorted together by worn brush residue, you have a shunt path from the pole you are trying to energize and a "shorted" starter. Sometimes (most of the time) they clean up and sometimes they don't.<br /><br />Lams look ok (Lams are what you see, besides varnished wire, when you look at most of the area of the armature. Look like a bunch of little rectangles adjacent to oneanother). The epoxy in the center (and end) is just to hold the wires in place and does nothing for the performance of the unit.<br /><br />3rd a repeat of first.<br /><br />4th hard to see. Brushes appear to be well worn, but again hard to see. If bad brushes were the problem, you could not supply adequate current through the poles of the starter to spin it under load and the OB motor would spin slowly as you said happens. <br /><br />But what bothers me is the voltage you posted. Bad brushes mean low current and low current would be cause for higher voltages (than normal starting voltages) across the starter.<br /><br />Whereas a shorted starter, would also spin the OB slowly, but a low voltage and very high current would be associated with it.<br /><br />Looking at the armature, where the brushes ride, tells me that the brushes failed due to a rough armature mating surface.....but I would have to persoanally eyeball it to say that for sure.....maybe I'm just seeing things and a new set of brushes, a little cleanup of brush residue and polishing of contacts where the brushes ride, and you are on your way.<br /><br />But if this is the original starter and on a '78 engine, maybe new brushes and a little cleanup.<br /><br />-----------<br /><br />On installing brushes, normally there is a small hole in the housing adjacent to the brush where you can insert a very small drill bit to hold the brush off the armature till you put it back together....then pull the drill out and the spring pressure will seat the brush against the armature. Otherwise you have to have access to the rear of the brush to hold tension against the spring while you reassemble the unit. This usually takes a dual set of hands. Grin.<br /><br />HTH<br /><br />Mark

 

[nate_evans79]

Re: Merc 900 Starter Questions

Thanks mark, after taking the pics, i realized that the bottom of the casing also comes off, to give access to the brushes. I cleaned up the brushes, and everything, and re-assembled the starter, and tried to start the motor. This time, the starter did nothing at all. just got really hot. I'm realling thinking that this starter is shorted out or something. This is the original 1978 starter on here.

 

[nate_evans79]

Re: Merc 900 Starter Questions

Well, figured out what I did wrong. The small insulator washer was left off the power post. I put that back in, and it fired right up. I still have a new starter on order, and it should be here on monday. Now I have to figure out why I'm not getting charge to the battery. But thats a different post. <br /><br />Thanks for all the help with the starter. You guys are great.<br /><br />Nate.