Doing A Tune Up On Th 39 Desoto

[desoto1939]

Well after 25 years of owning the 39 Desoto this is the first time that she would not start for me in the garage.

This si what happened.

I ran the old girl last week buyt she seemed to not run as smooth as she always does.

 

So this week I tookthe dizzy cap off to check the condition of the points and the cap.  I dressed the points and put the cap back on.  The car would not start.

 

Stated my dogisnotics.  HAd gound at the breaker plate. the car woulod turn over real strong. Had electical current at the ign switch.

 

Found my supply of NOS Brealer plate IGS3004A.  Installed the new breaker plate set the gap. But the dizzy backinto the engine in the same position that I took it out from the block. I make reference points to insure that its going back inat the same point or rotation.

 

The car would not start.  WHY or Why.  I had a freind over so we pulled the cap to watch the points. Hit the starter and he noticed that the point were not opening and that the rotor was not moving or rotating.

 

Ok first thought did i snap something or did the oil pump break. what could it be. 

 

Well, knowing that the MoPar engineers were well schooled they did us all a really big favor when the designed the dizz shaft and mae it a slotted end.  This way we alwasy know that the dizzy is right on in the correct reference or possibly 180 out of rotation.  So remember this point.

 

I then rotated the rotor by hand and did not get any resistance.

Ok now you all might have figured this out.  The dizzy was not fully down in the shaft and did not set into the slot.  So I lossened the dizzy and pulled it up spun it to get back into the slot then tightened it back down.

 

It still would not fire up. So remember the 180 degree point pulled it out agian just enought to rotate the rotor 180 degrees. put in back intot he slot and made sure this time that it was all the way installed.  Then fired up the car and HOORAAAY. she tuned over and ran.

 

Issue:  My supidity of not putting the dizzy fully intot eh slot and not checking to make sure it was engaging the oil pump keyway.

 

So the point always check and double check your work. For some of us we do not have to work on the cars that much and we get allitle forgetful as we get older.

 

Lesson well learned.

 

Rich Hartung

desoto1939@aol.com

 

[Don Coatney]

Good report and good reminder on insuring that the distributor is returned to the home position but as I read this that was a secondary problem. I did not see any report on what was the original problem and the fix? Were your points fused or had no clearance?

[desoto1939]

Don,

 

When I took the old breaker plte out I notice that the points had a major indent on the one side.  So What i determined is that either the points or the condonsor was bad. So i opted to replace the entire unit which is much easier to do.  I then will rebuild my old BP with new points and condensors. And when I mean new I use NOS autolite prts and not cheap china parts.

[desoto1939]

Don or anyoen ele:

 

Learning question?  If the correct gap is 20 on the points and the  degree angle onthe dizzy cam is 38  then what would be the correct dwell number. I can not find this number in my 39 Desoto shop manaul or even in any Motors or repair manual.

 

Education for me.  Or how do you calculate the dwell number??

 

Thanks,

 

Rich HArtung

desoto1939@aol.com

[Don Coatney]

I posted this in the resources section above but when I just tried to access it the font was so small I could not read it. This is from my photobucket and I hope you can read it. 39 Desoto is 35-38 degrees dwell angle @ .020" point setting. Is that what you are looking for?

 

[desoto1939]

Hey Don thnaks for the information.  I thought the cam angle equalled the dwell number.  I used my hand held engine analyser and the dwell was around 30.  I alwasy gap my points arounf 18-20 just to take in any wear or slop issues.  She runs strong so I might ajust or not.

 

Rich

[Plymouthy Adams]

Increase the dwell time to get greater saturation of the coil for a hotter spark...

[TodFitch]

Increase the dwell time to get greater saturation of the coil for a hotter spark...

Up to the point where the decreased gap on the points is insufficient to cleanly break the current flow. Then you get arcing that will decrease the coil output and will burn the points.

 

I figure that the factory knew what it was doing so set the points gap per the book. And every time I've checked the dwell after having set the points gap it has been right on.

 

If you really want longer dwell go to a dual points setup or electronic ignition.

[Plymouthy Adams]

breaker gap is going to equal the dwell angle..if it is not then you have something wrong in your distributor...dwell is electrical measure of the points closed period to saturate the coil for max spark....the dwell angle is nothing more than expressing the points gap in form of electrical duty cycle..the dwell angle is the only way to set any point that is used also...while mechanical gap is a get by setting and great for installing in the absence of a dwell meter, dwell is much more effective means of setting the points...of course if you content not to run at optimum conitions..so be it by me