Overheated igntion points

[DavidMc]

We have a 1920's Packard that has had premature ignition points failure due to overheating.  

After only about 1000 miles  the plastic insulating bush at the pivot has melted and the last 1/4" of the movable points arm at the contact end has turned blue indicating it has been at red heat.  The points contact surfaces are not burned and are in excellent condition..

The ignition has not been left on.

There is excessive wear in the distributor shaft allowing side play ( which we intend to rectify) .  This would be allowing  the points gap to float.  Is it possible that the excess gap causes extra resistance and therefore overheating of the points?  

The coil and condenser and points were all new 1000 miles ago.

The original distributor used twin points operating off an 8 lobe cam.  This distributor has been converted to single points using a well known kit .  An identical car has done about 10,000 miles with no problem fitted with the same kit  so we have eliminated this a s a cause.

Any suggestions would be welcome

 

 

[DavidAU]

Does it have a Ballast Resistor on the coil feed or doesn't it have to have one?  

[DavidMc]

No it does not have a ballast resistor, standard 6v coil, modern Holden points and matching condensor.  Coil and condensor have been checked and are OK.

[tom_in_nh]

I suspect that your Packard is overcharging. Check the voltage regulator and all associated wiring connections very closely.

Good luck.

Tom

[DavidMc]

Thanks Tom, I will check that however the generator third brush is set to give about 5 amps on the ammeter so its doubtful but I will check the volts at the battery.  Could overcharging cause the points to get to red heat at the contact end?  Also to add to the mystery the actual contact faces of the points are in excellent condition barely any sign of burning?  

We will be re bushing the distributor and fitting a new shaft if necessary however I am not sure that the excess sideways play explains the overheating.  It certainly allows large variations in points gap.   We have fitted new points but are concerned that we have not found the cause.

BTW its not my car, I am helping a friend.

David

[tom_in_nh]

David,

Like most issues relayed via online, it is difficult to diagnose without actually being there. 

I would like to see what the contact point set looks like under magnification. Any way to take a photo and share it with us?

Which kit was used for the single point conversion?

Tom

 

 

[Spinneyhill]

It sounds like lightning damage in your distributor!

 

I have no idea what the problem could be, so lets try a little logic. Yeah, I know, another daft idea...

 

The low tension side is unlikely to provide enough current to heat it that much unless your have very large cables. Thus it must be high tension?

 

How can high tension get in there? It is coming in through the centre of the cap and moving across the rotor to the contacts inside the cap and so to the plugs. How is it possible it could arc across to the pivot post?

 

I suppose careful, magnified inspection of the rotor, cap inside and the pivot post area might reveal tiny burn marks if this theory is to have legs.

 

Could the sloppy shaft and concomitant rotor movement allow high tension to short across to the pivot post?

 

Could there be some problem with the rotor allowing HT to arc somewhere inside the distributor? I vaguely recall seeing rotors with a sort of counter weight of contact metal on the opposite side of the rotor to the contact. Is it like that?

 

Now I am stuck for further logic. Any use?

 

 

[F&J]

I was a mechanic since 1970.  The only time I ever saw blued point arm tip, was only one time ever. 

 

That was a 67 Camaro that was being run with a jumper wire which bypassed the resistor.   All these years later, I still do not understand how it can get "red" hot.   Maybe an electrical engineer could tell us how it is possible.

 

That Camaro still ran, as the point contacts looked pretty decent, but it misfired badly under a load, on the first 1/2 mile road test.  That is when we saw the blued color, and remembered that the owner recently had just started using the original resisted system, and not that temporary jumper wire.

[DavidMc]

Thanks for the responses, this is clearly not a common problem and  all comments help .

Tom, I have attached a photo hopefully you can see the evidence of overheating at the contact end.  I believe the blue color  indicates that the tip has been at red heat..  I have also attached a copy of the sheet that came with the points conversion.  I do not know if this kit is still available but It has been widely used.  The original set up was twin points operating from an 8 lobe cam so the points essentially operated in parallel.  The single point conversion using modern easily obtainable points works well. 

Spinneyhill, your comments are not unlike what we have been discussing here but with a new reproduction cap and rotor and no evidence of any tracking we are convinced that the current that has overheated the points is from the primary 6v circuit.  Thanks anyway and any other theories wild or otherwise will be considered.

F&J.  Your comments confirm what we are finding, this is not a typical problem.  Whether its an electrical issue with too much current &/or or too little resistance is still to be resolved.  The coil is a relatively new standard 6v Bosch and I believe it does not have a ballast resistor.  I any event the wiring circuit is very simple see attached schematic. The worn drive shaft and resulting variation in dwell time while driving is an obvious source but what we are having problems explaining is how that could cook the points. Once the wear has been eliminated it would be good to know that we have found and fixed the problem - but have we?

 

img-161015082921.pdf

img-161015105215.pdf

[maok]

Has it happened with other coils?

 

If there is an spark (arc)  at the points somewhere, its most likely caused by the secondary part of the coil (high tension/voltage) not the primary 12volt side. Its possible that your coil has an internal short from the secondary to primary side.

 

Give another coil ago.

 

[Frank Cerutti]

David

 

Another puzzle: with the "hammer" of the points being so hot, the current has not passed through the "anvil", because there is no similar discolouration. Does the current flow to earth only while the points are open? That is, when the points are open does the hammer rest against some other earthed metalwork? If this is the case, when the points open they virtually close immediately and severely limit the discharge from the condenser. No spark at the plugs will result.

 

My 2-bobs worth

 

Frank

[tom_in_nh]

David,

I am curious to know how well (or not) the engine ran for the 1,000 miles.

How about a photo of the bottom side of the contact point set?

Tom

[DavidMc]

Frank,  

"Hammer" &"Anvil" , I haven't heard then described that way but there is no doubt what they mean.  The hammer is live, the anvil is earthed.  The reason for the anvil not overheating would be that it is attached to a heavy brass plate which would act as a heat sink.  The hammer on the other hand is very light pressed fitting requiring much less heat to overheat.  Current flows to earth when the points close.

Tom, good question, the car ran perfectly until it failed suddenly.  We got it running a few times until it died completely.  A close examination of the points, later, showed that the plastic insulating bush at the pivot end had melted allowing the spring to short to the post, unfortunately we did not discover this at the time.  I will have to ask the owner for another photo however Frank's observation is correct , the anvil does not show signs of overheating.

David

[DavidAU]

I think I would try a ballast resister on the coil feed or a new coil with built in resister as it is quite obvious that too much power has been getting to the points.  

Most ignition systems with contact points use a resister or resistance wire in the system including Holdens.

 

The only other thought that I have is that maybe when it was running OK the points gap was good but when it stopped running the gap had closed up ( loose screw etc.) and it wouldn't take very long to fry it if they were closed up tight.

[DavidMc]

David,

I understand that ballast resistors did not come into use until the 1950's?.   Someone will correct me if that is not so.   This car is 1929 6v with a simple ignition system identical to vast numbers of cars and yet this seems to be a very uncommon problem.  It certainly seems that too much current is getting to the points.  

When the car stopped the points gap was one of the first things we checked and it was fine at about 0.018".  We were also thrown off by the the fact that the points faces were/are in excellent condition , we did not notice the overheating until we got the car home and removed the points.

The coil resistance will be checked along with other identical coils tomorrow, our efforts to do this with a cheap multi meter were unreliable.

We have also considered the possibility that the car may have been left with the ignition on while the points were closed but the owner is sure this has not happened.  

 

[F&J]

32 minutes ago, DavidMc said:

the car may have been left with the ignition on while the points were closed but the owner is sure this has not happened.  

 

I believe this was part of the reason.  The other influent thing that might have happened if the key was left on:...if the point surface was barely touching due to the cam lobe was almost closed, or points were slightly corroded, that "resistance" would cause overheating just like any bad connection does with a load.  The higher the load, the more heat is generated by a poor contact.

 

Point arm contact gets cooled just like an exhaust valve does.  They need a given amount of "contact duration" to the "heavy part" to transfer heat from the light part.  Also, as you must have seen, some points had a drilled hole in the center contact on the arm end, that was marketed as a cooling feature...maybe 1960s or so

 

[bob staehle]

David, as F&j has said it looks like the key was left on. But it is possible that that the point arm  and point contact tip or the point spring to point arm connection is faulty. with a good analog meter check between contact arm & point tip

and between the ign. wire mount & contact arm. I would also use a pair of pliers to see if one of the contact points is loose. 

                                                     just my $.02 good luck Bob 

[ArticiferTom]

I second above . May be loose contact to arm connection . It looks to be were heat is . Try new set .

[edinmass]

Interesting discussion. Why not run the distributor in stock configuration? 

[hchris]

The one thing that leaps out for me is that there is obviously an insulation break down in the points assembly, most probably in the plastic bush on the pivot post. It would only take an instant if the 6v primary current went directly to ground to melt the plastic and turn the metal blue.

 

Short answer to the problem is, fit another set of points and see what happens; I had a similar experience long ago, melted the pivot bush never worked out why but fitted new points and it never occurred again.

[Spinneyhill]

I agree with edinmass. It is easy to make up a little template to fit over the distributor to synchronise the points.

[DavidMc]

Update and thanks or the continuing comments.

New points have now been  fitted to the car and it ran perfectly, the concern is that whatever caused the overheating may reoccur unless we can ind the cause.  

We could not find any mechanical defect with the points, contacts are not loose, no evidence of shorting anywhere,  reasonable spring tension.   We believe the melted plastic pivot bush resulted from whatever overheated the points rather than it being the cause.  Note that the maximum heat discoloration occurred at the contact end.  The bush end got hot enough to melt the bush but the source of the heat was the contacts.  The owner is adamant that the ignition has never been left on.  Note also that the failure occurred at the end of a long continuous drive.  It was running perfectly up until it stopped.  If the overheating had been as a result of the ignition being let on before the drive,  it would have failed much earlier.

As or the use of single points, when the car was being restored the old points were badly burnt and new ones were not readily available.  The conversion kit for the single points was a practical solution. The kit is still listed for sale on the Max Merritt web site.   Also I have the same car with the same conversion and it has been on the road since restoration was completed in 2003, it has traveled many miles on long distance tours here in Australia, our last tour for example covered over 2000 miles. We have done that and other tours a few times.

The current situation is the coil and condenser will be checked again including a hot test by a more experienced person,  the distributor is out being examined for repair.

We may never be certain what caused this problem .

 

[tom_in_nh]

David,

Is this a Delco or North East distributor?

Tom

[DavidMc]

North East

[Graham Man]

My 1928 Graham Paige ignition switch has two on positions... so if you turn it too far to the counterclockwise position the ignition is back on.  What I did was add a small green LED light under the dash so I know when the ignition is on, works great.  Just got an LED indicator light and added a resistor for 6V, cost was under $5, no more burnt points...priceless

 

[trini]

 Let start at the beginning. New condenser of adequate size and properly grounded . Distributor must be properly grounded to the frame .Always remove old ground wire ,clean  and re install. Check for shorts using an ohmmeter or test light inside the distributor. It seems there is a hot wire shorting inside or a lack of proper ground . Do no forget to check the condenser for non function.

Good luck.

Harry. 

[DavidMc]

Final update, with thanks to all who offered advice.

We have failed to find anything wrong that could explain the overheating.  The coil and condenser have been hot and cold tested and are fine. Distributor shaft wear proved to be negligible when measured .  No mechanical defects could be found with the cooked points or their mounting.  There are no stray wires or shorts.

The conclusion is that the points overheated at the contacts end which then melted the plastic bush at the pivot pin.  The points either shorted to earth at the pin or they stuck open due to the melted plastic bush having held the points apart.  The melted bush resulted from the overheating rather than being the cause

We have failed to find a defect that explains the overheating and the car continues to run well after new points were fitted.  We will be keeping a close eye on these points but I think it is unlikely we will find what caused the problem or that the problem will re-occur.

 

 

 

[Friartuck]

Is it possible the point spring wasn't strong enough to fully close them and they "fluttered" causing an arc between the contacts? If this conversion runs OK on one car, and fails on another, I conclude, was this simply a case of a bad set of points?

[DavidMc]

That is pretty much the main conclusion we have reached although the spring does seem to have enough tension.  Its not a very satisfying conclusion.  I find it hard to believe that despite excessive resistance across the points, the car continued to run well, with the points approaching red heat, without stopping the engine. The excess heat finally melting the insulating plastic bush at the pivot creating a short or holding the points open.  You would expect that with sufficient resistance across the points to cook them the car would have simply stopped long before they got that hot

It could also be argued that these events happened in reverse - the plastic bush failed first leading to binding on the pivot preventing the points from closing properly and therefore causing extra resistance across the points but what would cause the plastic bush to fail?  

As F&J said in an earlier post he has been a mechanic since 1970 and has only seen this once and never found out why.  I think we will have to say the same albeit with less experience

[Spinneyhill]

There used to be points spring tension specifications published in the early days.

[Strach]

Would key left on cause points malfunction, melted points?

I just bought a Massey furguson tractor

Point melted.