P15 1948 starter motor question

[Cudan]

The starter motor only gets the engine turned when I take the sparksplugs out. The battery 6 v 160 ah is new and for testing  i connected the battery - directly to the starter.

 

What could be wrong, the starter ? Not enough power to turn the engine with compression ?   Needs new brushes ?
 

Dan

 

 

 

[busycoupe]

Make sure all of the connections in the starter circuit are clean and tight.  Also, you can check the battery by turning on the headlights then try to crank the engine. If the lights go out immediately the battery is not up to snuff.  

[Oldguy48]

Don't overlook the starter solenoid.  It's simply a relay in the starter circuit, but if the internal contacts in it aren't in good condition, the starter will not get enough current to do it's job.  If you measure the voltage across the large terminals of the solenoid when cranking the engine, you should see nearly zero voltage, if it is operating normally.

 

[vintage6t]

What gauge are your battery cables? Typical 12 volt 4 ga cables are not large enough to carry enough current for the starter. For 6 volts you should be using 00 ga. Also make sure your battery ground has a good chassis/engine connection.

[Cudan]

19 hours ago, busycoupe said:

Make sure all of the connections in the starter circuit are clean and tight.  Also, you can check the battery by turning on the headlights then try to crank the engine. If the lights go out immediately the battery is not up to snuff.  

The battery is new and fully charged and only the engine is on the chassis

 

[Cudan]

15 hours ago, Oldguy48 said:

Don't overlook the starter solenoid.  It's simply a relay in the starter circuit, but if the internal contacts in it aren't in good condition, the starter will not get enough current to do it's job.  If you measure the voltage across the large terminals of the solenoid when cranking the engine, you should see nearly zero voltage, if it is operating normally.

 

The p15 starter directly connected to the battery

[Cudan]

7 hours ago, vintage6t said:

What gauge are your battery cables? Typical 12 volt 4 ga cables are not large enough to carry enough current for the starter. For 6 volts you should be using 00 ga. Also make sure your battery ground has a good chassis/engine connection.

I used for this trial  12 volt starter cables tot the ground an starter I wil check them.

[Cudan]

On 5/2/2021 at 12:03 PM, vintage6t said:

What gauge are your battery cables? Typical 12 volt 4 ga cables are not large enough to carry enough current for the starter. For 6 volts you should be using 00 ga. Also make sure your battery ground has a good chassis/engine connection.

I used the original battery cables and the engine with sparkplug turned, thanks for the solution.