Timing question

[Dan Hiebert]

When I timed our D24 recently I noticed that the timing vacillates a bit.  I time it at 2 degrees after TDC.  (Don't let that be the squirrel of distraction, that's not the question.)  The mark is right on enough to easily time it "correctly", but it does retard and advance 1 degree without input often enough to readily notice.  It doesn't jump 2 degrees, just the 1.  This still happens after the distributor clamp is tightened.  What could that be a symptom of?  Something appears worn, but what?  The shaft?  Should I even worry about it?

 

I can find all kinds of information and opinions on timing, but have yet to find anything that touches on the above symptom.  The car runs great, no noticeable miss or anything.  I'm not overly concerned about it, except that none of our other cars do that.

[Sam Buchanan]

Remove the distributor cap and try moving the rotor laterally. Most likely you will feel some play as you move the shaft side-to-side. Worn bushings on the shaft will allow the timing to wander. Timing jumping one degree probably isn't enough to worry about, when it starts wandering several degrees it's time for a distributor rebuild.

[soth122003]

Agee with what Sam is saying. Sounds like the shaft has a little play. Not enough to hurt the timing, just enough to notice. Something to put on the to-do list of future things to fix. 

 

Joe Lee

[desoto1939]

Also check the entire breaker plate assembly. If it is original to the car it might be worn and have some slop in the two pieces.  A friend has a 39 desoto and when coming up to my house the car would back fire and also run rought. We tookto my od time mechanic and the firt thing he did was remove the dist cap and rotor and tested the breaker palte and he showed us the slop in the unit. Came back to my house pulled the dizzy and replaced the breaker plate with a NOS unit and that solved his pbm.

 

This is just a thought.  He kept the old plate for the small wires and parts and then got a second NOS breaker plate.

 

Looked in my Autolite catalog the breaker plate is an IGS-3004J  but if a Canadian car and engine then an IGS-3004A..

 

Rich Hartung

[Dan Hiebert]

Thanks!  It is the original, unmolested, distributor.  I made a halfhearted attempt to source a replacement distributor and so far found only one that looks like a bear ate it then pooped it over a cliff.  Bushings and breaker plates I can find.  Something else to add to the to-do list with a note to check the timing more often for additional indications of wear.  I'm thinking 2 degrees wobble or noticeable running issues, whichever comes first, would be about time to definitely fix it.  I have no recollection of it doing this beyond the most recent timing session, which of course doesn't mean it hasn't been doing it all along.  If push comes to shove, there's a high-speed-low-drag auto electric shop in lil' ol' Houlton that I'm sure can rebuild it for lots of money. 

[desoto1939]

They are two bushings in the dizzy upper and lower.  On the shaft there isa pin that has been peened over. This has to be removed and then the shaft can come apart. I have the miller factory to to push the bushing in and out and also burnish the bushings.

 

Rich Hartung