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Question about Chrysler marine 318 distributor rotor

M

MoparJoe

New member
Recently at a swap meet I picked up a box labelled as 318 marine parts, it included a rotor that had a wider contact at the spark-end than I'm used to seeing. Here's a pic:

P7262106.JPG


I understand that marine engines sometimes or mostly have the crank turning the opposite way vs how they turn in a car. But I'm wondering about that wide contact - can someone tell me the theory behind it? Does the marine 318 operate over a wider spark advance curve - and hence would need the wider contact to insure the spark can jump from rotor to post? I thought it would be cool to put that rotor in my car (I have small block 318) but the shaft end design is totally different, it won't fit. But my primary question is - what is the theory behind the wider contact ?
 
daves69 said:
You might pose your rotor question to a very knowledgeable group of Mopar enthusiasts here......
https://www.forabodiesonly.com/mopar/forums/electrical-and-ignition.54/

.....or in the Chrysler I/O section on this site.
Click to expand...

I'm a member of FABO but if nobody on this board can answer a question about the Sierra marine rotor and it's design then the odds of getting an answer on FABO are less than zero. I sure wish I could drop that rotor in my distributor. I'm not sure what the Chrysler I/O section is, I'll see if I can find it after I post this.
 
They are designed not to fit on a car on purpose. Marine design has to deal with factors cars don't.
  • Material Quality: Marine components use solid brass, copper, or bronze contacts to resist heavy moisture and salt corrosion, whereas standard car parts often use cheaper aluminum or thin steel that pits and fails quickly in marine environments.
  • Advance Curves and Design: Marine engines operate under a heavy, sustained load unlike cars. Marine distributors rely purely on mechanical centrifugal advance (no vacuum advance) with heavier springs to match the high-RPM performance curve safely. This is why it's wider, more room for error on the timing. Also marine motors are in enclosed high moisture areas with poor ventilation. Distributor units need to be sealed from moisture and to eliminate sparks jumping to surrounding air which could potentially cause an explosion.
  • Physical Fit: Depending on the specific marine distributor brand used (such as Prestolite, Mallory, or Chrysler-specific marine units), the shaft width, rotor mounting tab, or cam attachment style will not physically interchange with a standard automotive Mopar distributor. This is done on purpose.
 
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