Point gap diminishes

[Business_As_Usual]

Hello Everybody, I need some help solving a problem. When I set the gap on the points to .015 and take the car for a ride, after a short drive, it starts to miss and act like it wants to die. I take it back home and find that the points gap has gotten smaller to a point where the car won’t run. Adjust the points again, making sure they are screwed down tight, recheck the points gap, take it for a ride again, and get the same results. Why won’t my points hold their proper gap.  The shaft on the distributor has no lateral movement. Any advice will be much appreciated. Thanks, Tom.  The car is a 40’ Buick Special Business Coupe. 

Edited July 19, 2023 by Business_As_Usual
Forgot to identify car year and model. (see edit history)

[JFranklin]

Do you lube the distributor cam? Is it mirror smooth? 

[Business_As_Usual]

I did lubricate it with lithium grease, but I did not check to see how smooth it is. I guess I can use some emery cloth to polish it up, being mindful not to let any grit fall into the distributes. Thanks for your idea. Tom

[1937 Buick 66C]

Whenever my various old cars begin to run strangely, the fault is usually the points.  Since you know that the points are slipping closed, I have a couple of things to assist with your diagnostics:

• Lubrication:  Once the fiber block that rides on the distributor eccentric cam begins to wear, the points close pretty quickly.  The distributor cam (eccentric) should be lightly lubricated with special points grease or vaseline.  Lithium grease is not recommended because it hardens when subjected to temperature extremes.  
• Wear:  Remove the moving point and carefully inspect the fiber block that rides on the distributor cam.  Ideally, if you have another unused point set available, you can compare the profiles of the fiber blocks to see see how severely worn it is.  Once the sharp edge of the fiber block has worn off, the points will not remain in adjustment.
• Mounting Issue:  When you revisit the points, after they have slipped, is the screw that holds the points in place still tight?  I've had these small screws begin to strip in a way that is not obvious when you are tightening them, but the threads are sufficiently damaged that they will not adequately bind the points during heat cycles and engine vibration.  If the screw is not really tight, the points will close up.  If the screw is tight, maybe using a wavy washer under the screw to secure the points more aggressively.  If the screw is suspect, you may want to replace it with a slightly larger, self-tapping screw and washer to secure the points.

The ultimate solution is to replace the points / condenser with a Pertronics or similar ignition trigger that replaces your points and condenser with an electronic module.  This change is not obtrusive, and solves all manner of issues related to ignition.  I have made this change in my Porsche 912, and will do it to my 1937 Buick when I rebuild the distributor this fall.  

 

Edited July 19, 2023 by 1937 Buick 66C (see edit history)

[EmTee]

What kind of car is this?  If it's like my '38 Century, you should check that the vacuum advance is operating properly.  If the vacuum diaphragm and or the breaker plate suspension is binding or sticking, you may be inadvertently setting the gap while the breaker plate is not in the proper (i.e. zero advance) position.  While driving the plate might 'unstick' and the point gap setting is now incorrect.  Make sure the breaker plate doesn't bind in the housing.  Also make sure that the mechanical advance weights are working smoothly.  It's much easier to make these inspections and perform any cleaning and adjustment with the distributor on the bench. 

[Business_As_Usual]

Thanks for all the replies.  Hope to get a chance to work on it in the next few days. Tom

[Hubert_25-25]

Tom, 

    If you stay with points, immediately after setting the gap, check the dwell using a dwell meter.  Write that dwell number down.  Then you can quickly see how fast the point gap is changing over time.  I also had a set of points in my Jaguar.  They switched the rubbing block from micarta to plastic.  As the points got hot the plastic got soft and the gap started to close.  Consider another brand of points.  Same car, and I also switched it to Pertronix.  I did have a problem for a while with coil failures.  I still replace the coils but I am also still on the Pertronix unit. 

Hugh  

[Brian_Heil]

Check for wear in your distributor shaft bearing. 

[DonMicheletti]

Make sure the 3 balls holding the breaker plate are OK and the breaker plate is free to move.

I once had the balls on my Roadmaster come out

[Gary W]

On 7/19/2023 at 7:01 PM, EmTee said:

Make sure the breaker plate doesn't bind in the housing.  Also make sure that the mechanical advance weights are working smoothly.  It's much easier to make these inspections and perform any cleaning and adjustment with the distributor on the bench. 

 

Much easier on the bench!  Here is my step-by-step distributor restoration.  Maybe it can help as you check each part is working correctly.

 

 

[Jolly_John]

Hi, Tom (and Bill). If you find you've "lost your balls" so to speak, I do have the much-improved ball bearing breaker plate available. New-in-box, and specifically for your distributor. A lot of guys used these back in the day as an upgrade from the original BUICK factory three balls and plastic channel pieces. Best of luck to you both as you work to solve this problem. John in Wisconsin

[EmTee]

7 hours ago, Jolly_John said:

I do have the much-improved ball bearing breaker plate available

Can we see a picture of it? 

[Daves1940Buick56S]

Maybe it is the DynaFlite. I love those things. Classic overengineering but they last forever. I too do any major work in the shop. I have a homemade test fixture where I can set up the distro exactly to spec and run it at 3000 rpm (crank) to check operation.

Edited July 25, 2023 by Daves1940Buick56S (see edit history)

[drhach]

On 7/24/2023 at 6:03 PM, EmTee said:

Can we see a picture of it? 

I think this is what he's talking about. I just put one of these in my distributor. This eliminates the ball bearings. The breaker plate kind of "skates" on the black shoes. It looks like it should last a while. 

 

[EmTee]

Thanks, it looks like it basically replaces the balls with a groove for the plate to slide in.

[Steve_bigD]

I have been running a 6V Pertronix in my '38 Special for the past 10 years and it does work well with no problems. However, the minimum voltage for its internal logic control is about 5V so your charging/starting system must be in top shape. When I first installed the unit, the car would not start after a long run, which I determined was due to voltage drops in the battery wiring, terminal resistance and battery internal resistance. The voltage during cranking at the coil was dropping to 4.5V. I replaced the weak battery, and installed new 000 gauge battery cables which solved the problem.  I also found that there was a drop of 0.2V in the wiring between the battery/generator and the coil + when running or cranking, so I replaced the wire runs from the coil to the ignition switch with new 16AWG wire which reduced the drop to <.05V. Each little bit of drop adds up and becomes significant when the voltage margin is only about 1V or so when cranking. No problems after these changes.  

Another caution, do not use those cheap battery disconnects that have a plastic knob that tightens down to make connection (see photo below). These do not have a low enough resistance when tightened for the 300A or so needed for a 6V starter.

[Jolly_John]

Yes, Dave, the NOS aftermarket ball bearing distributor breaker plate I was referring to in my post above is the Dyno-Flyte unit. It was quite popular in the 1940's through the 1960's. This replacement distributor breaker plate rides on 54 ball bearings, and more or less puts the Delco-Remy replacement breaker plate pictured above to shame.

 

I know this is not the "for-sale" part of forum, but I will get around to posting this NOS ball bearing Dyno-Flyte breaker plate as being available for $35, plus shipping in a week or two. John