Slow cranking speed

[mogfisher]

Could a very slow cranking speed cause a no spark situation? I noticed the motor I'm trying to get running cranks rather slow and draws a ton of current so I brought the starter to a rebuild shop to have it tested and they said the armature is shorting out. It "works" but its slow. I have no spark. Wondering if this could be the culprit.

 

[Texasmark]

Re: Slow cranking speed

The battery has so many amps it can deliver to whatever load under the required current draw. My 90 hp Merc manual says that my engine could draw as much as 150 amperes to roll over. That number is obviously a limit number.....die hard situation.

Since you only have 12+ volts at hand, 100 amperes for a nice round number being supplied by a 12v for a nice round number, to a starter expecting to get 11 or at least 9.5v, let's use 10 for a nice round number, means that all the resistances from the battery innerds to the terminals of the starter can only tolerate a resistance of 12-10= 2v/100 amperes = 20 thousandts of an ohm. For the lay person, that is nothing and you have multiple connections and cables with crimped connections and all that stuff that normally occurs in boating.

Soooo, with that said, and since that same voltage at the engine, usually at the starter solenoid hot terminal which is connected to the battery is also where the ignition gets it's voltage, with low battery voltage and sloppy cable and terminal connections, you are sucking hind teat....that saying is a farm expression where the mother cow is walking off and the calf is trying to get one more suck and the hind spiggot is the nearest one.....but the problem could be that as the mom walks off, it may be time to defecate, which happens frequently so the calf "sucking the hind teat" gets defecated upon.......happens all the time.

If you want more, I have more.

HTH,

Mark

 

[j_martin]

Re: Slow cranking speed

Skipping all the farm folklore, the simple answer is yes. Stator voltage to the ignition, and also trigger voltage is directly dependent on engine speed. It must crank briskly to spark and start.

I've serviced many no starts and hard starts that were merely tired starter motors. It even fooled me (the expert according to some) enough so I paid top buck for a sub standard (new) battery at a marina while on vacation and gave them a better one for trade in.

High current draw is usually brush debris build up the bottom of the starter, shorting out the commutator. It's starter time.