big twin starter wiring/ground issue

[pcrussell50]

1959 rds21b super seahorse, 35hp...

the metal box that contains the starter solenoid has a lug on it where three "negatives" are congregated... the fat negative ground from the engine block, the fat black cable that goes to the battery negative post and one more that goes forward to the dash to provide a negative source for a couple of switches i have up there. anyway, sometimes the starter engages the flywheel, but doesn't quite have the "umph" to spin it. other times, it does. both cases can occur in the same few minutes. i was just in the beginning stages of troubleshooting today. when i throw the start switch, the solenoid jumps up onto the flywheel, [as it should, and always does], but in the cases when the starter fails to turn the flywheel, if i hold the starter switch in "start" for a few seconds after the failed attempt, that lug where all the grounds are congregated starts to smoke.

this is telling me that there is a bunch more resistance showing up there than there should be. the smoking stops the instant i release the starter switch.

when it comes to electrical things, i am mostly self-taught, and there are gaps in both my experience and my knowledge of troubleshooting. can anyone suggest a course of action for troubleshooting?

other info:

i removed the stock key starter, split into three functions, and wired up three separate toggle switches:
a momentary on for the starter
a momentary on for the choke
a regular on-off for the ignition

also, on a related note, i forgot, but which side of a load should you put a switch, the positive, or the negative, IOW, should the switch be in the line from the positive battery terminal to the load, or the negative battery terminal to the load? IIRC, both will work, but one is better.

motor runs really well, otherwise...
-peter

 

[tashasdaddy]

Re: big twin starter wiring/ground issue

switch positive. clean and tighten your grounds. also check you cable for any nicks, as the cable will deteriorate from inside out. you could make a fused buss bar for your switches, and connect them directly to the battery. nothing should be attached to the motor circuits except the motor.

http://www.teleflexsierra.com/FS405...*****.073321051--store_id.373--view_id.492049

 

[jay_merrill]

Re: big twin starter wiring/ground issue

While I agree that the first place to start is in cleaning all of the electrical connections, you may also have bad brushes in the starter. There are a couple of different brands of starters that were used in your motor, both of which should still be rebuildable. I had a couple of them rebuilt for a matching set of '58 Bigtwins that I own - I paid about 100 bucks each for the work.

Also, some of the older starters were two brush, while most were four brush units. You can tell the difference by looking at the barrel of the starter - the two brush units will have only two large, straight slot screw heads in them, while the four brush units will have four of them. If my memory serves me correctly, the four brush units are also longer than the others.

That said, you can still buy the starters new and they cost about the same as rebuilding the old ones. One of the reasons why it is so easy to find them, is because they are still used on some industrial engines. EBay can be a good resource for finding the starters.

 

[tashasdaddy]

Re: big twin starter wiring/ground issue

dbelectrical has them

 

[pcrussell50]

Re: big twin starter wiring/ground issue

switch positive. clean and tighten your grounds. also check you cable for any nicks, as the cable will deteriorate from inside out. you could make a fused buss bar for your switches, and connect them directly to the battery. nothing should be attached to the motor circuits except the motor.

http://www.teleflexsierra.com/FS405...*****.073321051--store_id.373--view_id.492049

thanks as usual, td.

can you'all examine my wiring scheme here:

the grounding lug on the external solenoid box has:
1] the ground cable from the engine
2] the negative cable to the battery
3] a negative cable to the dash to for the starter and choke switches
4] and that's it, nothing else

there are no consumers of electricity on the boat that are not part of the engine, not even a tach. the only wiring in the dash is for the starter, choke and ignition cutoff switches.

-peter


-peter

 

[pcrussell50]

Re: big twin starter wiring/ground issue

While I agree that the first place to start is in cleaning all of the electrical connections, you may also have bad brushes in the starter.

and jay, thanks for pointing me to the starter as a consideration. is it possible that the starter has some kind of faulty internal resistance that is causing the overheat in the ground?

-peter

 

[pcrussell50]

Re: big twin starter wiring/ground issue

in the end, i think it was the starter. finally, i got around to testing it by connecting it directly to the battery with jumper cables it did not turn. so i dropped it off at the rebuilder's shop this morning. he called me back a couple of hours later with the verdict. there was a short in the windings of the armature. i gave them the go-ahead to rebuild it. i'll report back when i try it out in a couple of weeks.

-peter

 

[lindy46]

Re: big twin starter wiring/ground issue

thanks as usual, td.

can you'all examine my wiring scheme here:

the grounding lug on the external solenoid box has:
1] the ground cable from the engine
2] the negative cable to the battery
3] a negative cable to the dash to for the starter and choke switches
4] and that's it, nothing else

there are no consumers of electricity on the boat that are not part of the engine, not even a tach. the only wiring in the dash is for the starter, choke and ignition cutoff switches.

-peter


-peter

3] There should be no ground to the starter or choke switches at the dash. There is a 12 volt wire which comes from the large solenoid post where the battery connects. This wire goes to the start switch (and jumps over to the choke switch if there is a separate choke). Then there is another wire which runs from the other post of the start switch back to the small post on the solenoid (next to the large battery post). There is a return wire from the choke switch which goes directly to the choke solenoid. Then there are the two kill wires. If there is another wire, it was used if there was a generator. It would go from the ammeter on the dash to the voltage regulator though a 20 amp fuse in the junction box.