ground terminals inside distributor

[scotts435]

What is the purpose of the ground terminals in between the spark plug terminals in an old mallory point type distributor?

 

[Frank Acampora]

Re: ground terminals inside distributor

The distributor cap is most likely for multiple engines. Instead of making a discrete cap, they mold a common body and then modify it for its purpose.

IF the timing is incorrect, the spark will jump to the unused terminal instead of the terminal with a plug wire. Since there is nowhere to go, it will feed back into the CD box damaging it. The ground gives the high voltage pulse a place to go--the distributor body ground.

This also aids in making the distributor explosion proof. There is also an explosion proof screened vent (flame arrestor) in the side of the body.

 

[scotts435]

Re: ground terminals inside distributor

Thank you Frank. But now I have another question; what would cause a distributor to explode and how do the screened vents prevent it?

 

[Frank Acampora]

Re: ground terminals inside distributor

Well, I don't know if a distributor would explode, but all marine components are designed explosion proof.

Remember: The distributor has a LOT of sparking going on inside it. There is a slight gap (less that the spark plug gap) between the rotor and each terminal and, of course, it takes a spark to jump that gap.

Now, if there is a fuel leak inside the engine, fumes can build-up under the cowling, penetrate the distributor and be ignited. SO, even if fumes DO get ignited inside the distributor, the flame arrestor screen will stop them from passing through to the main body of the engine.

 

[scotts435]

Re: ground terminals inside distributor

It all makes sense now. Thank you, Frank. I appreciate you taking the time to answer my questions.