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Mallory YLM distributors on Chrysler 360s

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Act Three

Contributing Member
I have one year-old Mallory YLM series distributors on my engines. Both start and run fine and both are wired identically. Since these distributors were installed, I have had recurring coil failures on the starboard engine after running long enough to get the engines up to operating temperature or perhaps a little longer. The port engine never fails but the starboard engine ignition breaks up so badly that the only way I can keep it going is to change the coil while underway.

This winter, I went through the ignition systems on both engines. Both use Mallory ballast resistors, caps, rotors, etc. all installed at the same time a year ago. The only difference I could find between the two engines' ignition systems was that the gap between the reductor (or whatever that 8-pont gear is called) and the magnet pickup on the port engine was a gap of close to .047" and that's what Mallory specifies. This is the way the distributor came, out of the box, and this is the engine that runs without a problem.

The starboard engine (the engine that keeps eating coils) showed a gap that was much wider an again, this is just the way the distributor came out of the box when new. To measure the gap, I used a little piece of Mylar film provided by Mallory. Beyond that, they have been no help.

I've adjusted the pickup on the offending engine to match the good port side engine. Now all I have to do is take a relatively long cruse to see if that difference in gaps was the problem.

If you know anything about Mallory YLM distributors, I'd love to hear your comments or suggestions.

Bill
 
A change to the air gap, between the reluctor and sensor unit, causes a change to the effective dwell angle. Yes..... electronic triggering involves a dwell angle similar to contact points.

I'd have to give this some thought, but I'm wondering if the excessive air gap (and change to dwell angle) has affected your ignition coil.

Give Mallory a phone call. Explain your problem, and ask what an air gap difference can cause.

I've found it best to call back in a day, and hopefully speak with a different technician.
If you get the same response, you've probably received good advice.


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I hope that starboard distributor was designed to absorb the thrust load on it from the reverse rotating camshaft. If not, the distributor shaft will eventually move upwards as the bearings go away and the rotor will smash itself to death on the cap.

Jeff
 
From others who have had bad experiences with "marine" distributors (one made by a company whose first initial is "P").

Jeff
 
Thanks for the replies. Shortly after writing the original post, I got the boat back into the water and was then delayed a couple of weeks by the weather. After that I took the boat on a 65 mile trip to our summer slip and the starboard engine ran perfectly. No coil failure and the engines stayed in absolute sync for more than three hours at cruising speed.

Mallory was of no help during all of this. Multiple calls to several different techs netted me nothing. One tech told me to remove the ballast resistor that Mallory specifies for that particular coil and distributor. That's after I carefully explained that the port engine (with all the same components) ran perfectly.

To make sure that I had covered everything on the starboard engine, over the winter I replaced the coil (again), ballast resistor and finally, the electronic module in the distributor. The directions that came with the distributor module were far more detailed and included the reductor-to-pickup gap info that I had never seen before. They also included that little piece of Mylar to set the gap at .047". I used that to check the gap before I removed the ignition module from the distributor and it was perhaps four or five times wider than it should have been. I also checked the gap on the port (good) engine and it was exactly the thickness of the Mylar or .047".

I'm posting this to let everyone know that the problem has finally been fixed and for one other reason. Both of the Mallory YLM distributors that I'm using were purchased at the same time from the same source (Summit). But right out of the box, one distributor had exactly the right gap and the other was way off and to make matters worse, the instructions that came with the distributors never mentioned checking the gap or even mentioned what that gap should be.

Just a note to be careful, even with distributors from a well known manufacturer. In this case, Mallory's quality control wasn't good and if that happened to me, it will probably happen to others.

Bill
 
Bill, good for you.

The gap being incorrect caused a change to dwell, and was likely your problem.

You've got a good system. Like I've said in the past, the VR triggering is tough to beat.


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Trojanman said:
Jeff, how do u know all this crap?
fastjeff said:
From others who have had bad experiences with "marine" distributors (one made by a company whose first initial is "P").
Click to expand...
Click to expand...
Jeff, I believe that Mallory's parent company is now Prestolite.
Are you refering to the Prestolite ignition, or the Mallory ignition with regard to bad experiences?

I've had very few problems with the Mallory systems.

What I don't like about the Prestolite, is their use of Hall Effect triggering..... (I.E., the Pertronix technology)
I don't really care for Photo-eye as much as I do VR, but I'd take Photo-eye over Hall Effect any day.


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