new problems arose 1966 merc 950

[Mortamie]

I took my boat down for the first time since I had it in the shop and I rebuilt my fuel pumps.. I had my battery completely charged up and fired up the motor. The motor started for a few seconds then died.. I hit the key once more using the choke and the motor roared to life it stayed running for about 2 mins idling by itself before it started dying.. I thought I would double check my battery hookups at that point in time and when I reached down to check the nut with my fingers it burned me bad..... I decided to keep playing with my motor to get it running but could only keep it running by choking it then letting it idle until it was starting to choke out and then I would hit choke again causing it to roar back to life... after about 20 times of hitting the key and starting the motor my battery died (not sure but I think my deep cell battery should not have lost juice that fast) and i also noticed that my battery cable had gotten so hot it actually started melting the plastic on my battery a bit and the nut had turned colored like I had it in a fire..... Any ideas on what to do with any of these problems I am having??? it is a 1966 merc 950 I just rebuilt fuel pumps, cleaned the carbs, had the rotor replaced, replaced two points, and replaced my spark plugs.... any ideas on how to solve this issue of battery dying and wires getting hot and the motor not staying running in neutral would be of great help.... I am thinking about replacing my whole wiring harness?? not sure if this is helpful or not...

Thanks,
Mort

 

[Bosunsmate]

Re: new problems arose 1966 merc 950

It could be a ground happening somewhere from a corroded wire.
Does the battery get hot if the key is turned off?

 

[Mortamie]

Re: new problems arose 1966 merc 950

no it seems to only get hot when I am trying to start the motor.. I think anyway

 

[Moody Blue]

Re: new problems arose 1966 merc 950

Sounds like a sure case of bad connection or bad starter motor. Remove and clean all terminals/connections that connect between the battery and the starter motor.

When there is a bad connection (high resistance) the voltage drops across the high resistance resulting in a higher current draw from the load, in this case the starter motor. Higher current draw = more heat. Basic ohms law Power=Voltage x Current. If the starter motor requires a certain power to spin the motor and you have a big voltage drop across a dirty connection, then the current must increase to meet the power requirement.

Example;
starter motor needs 800Watts of power to start the motor (ideally 12Volts x 66Amps)

With good connections and proper wire gauges, voltage drop might be 2 volts. Therefore voltage at the starter is 10V. Since the power requirement is 800W, the current draw would be 80Amps.

Add a dirty terminal which could drop 6V across a connection. Now the starter voltage is only 6V. Since the starter motor still requires 800W of power, the current increases to 133Amps.

As you can see, the worse a connection is, the higher the current draw and the more heat is generated.

The extreme example of this is a dead short. There is a full voltage drop and maximun current draw (melted wires, fire etc)

Get to the root of the problem because you have a fire hazard with the existing situation.

 

[Mortamie]

Re: new problems arose 1966 merc 950

thanks you for that.. I am planning on taking every connecting wire on the motor off one at a time cleaning and then reconnecting.. I also can tell that the wiring is rather crappy in the wiring harness itself because the insulation on the battery cables is cracking and falling apart so I am going to replace the wiring harness.... if there is anything else you guys could think of for me to do let me know...

 

[Mortamie]

Re: new problems arose 1966 merc 950

Sounds like a sure case of bad connection or bad starter motor. Remove and clean all terminals/connections that connect between the battery and the starter motor.

When there is a bad connection (high resistance) the voltage drops across the high resistance resulting in a higher current draw from the load, in this case the starter motor. Higher current draw = more heat. Basic ohms law Power=Voltage x Current. If the starter motor requires a certain power to spin the motor and you have a big voltage drop across a dirty connection, then the current must increase to meet the power requirement.

Example;
starter motor needs 800Watts of power to start the motor (ideally 12Volts x 66Amps)

With good connections and proper wire gauges, voltage drop might be 2 volts. Therefore voltage at the starter is 10V. Since the power requirement is 800W, the current draw would be 80Amps.

Add a dirty terminal which could drop 6V across a connection. Now the starter voltage is only 6V. Since the starter motor still requires 800W of power, the current increases to 133Amps.

As you can see, the worse a connection is, the higher the current draw and the more heat is generated.

The extreme example of this is a dead short. There is a full voltage drop and maximun current draw (melted wires, fire etc)

Get to the root of the problem because you have a fire hazard with the existing situation.

How do I check this on the starter?