1970 chevelle 454 burning thru points


#1

I have a 1970 454 ls5 that has been rotesserie restored with a complete engine rebuild on the original engine. I have had three sets of points burn up on it. The coil has 6.5 volts the alt 14.5 and the battery has 12.5 volts. The third set lasted only about 40 miles before burning up. The ground was checked and replaced the last time. Also when replacing points the condenser was changed also. Long time mechanics are perplexed on this one. Any suggestions


#2

Hello,possible a Ballast resitor,is going south.

good luck


#3

Thanks the car has a resistor wire and the voltage from the ignition switch is reduced from 12 to 6.5 to the coil.


#4

You didn’t happen to raise the compression ratio of the engine?

Tester


#5

Tester

Yes I do believe the compression ratio was raised during the rebuild. i seem to remember seeing that mentioned. What would the solution be if the compression was raised?

               Thanks  Tom

#6

Much could depend on exactly how they’re burning up.
Is a hole being burnt into the stationary side of the points or the pivoting side?
Is one side having buildup while the other side is becoming a crater?
What type of driving; pretty much stop and go, low RPMs stuff or highway?
Do you know the rating in microfarads of the condenser?
Is that 6.5 volts at the positive side of the coil when the engine is running?

There’s a reason for those questions.


#7

Both sides have a white round burn mark on it and they have a dark ring on the outside of the round white circle. Both side have the same appearance. This car did it with highway driving and stop and go. The stop and go was more like drive 4-5 miles stop at a light or stop sign and go.( not city driving ) The condenser and points were a set for a standard chevy big block. I dont know the microfarads rating
the 6.5 volts were measure by putting the volt meter on the positive and negative terminal of the coil. The car has a total of 100 miles on it since restoration and has gone thru three different sets. This is really stumping guys who have been working with these cars since the 70s. Any help would be appreciated.


#8

Partially failed coil? Can you measure your coil primary resistance cold and then hot?


#9

How do you do this? The coil was checked while the engine and ignition switch was off to see if the coil was being charged without the switch on . When we did this it read o volts. The car was hot and running when we measured the the coil from + terminal to - terminal and got the reading of 6.5 volts while idling.


#10

Roughly 33 miles is really too low to get much material transfer on the points and any examination would have to be done with a magnifying glass.
Normally any contact point burning problem is due to excessive voltage at the coil, faulty condenser, improper condenser based on type of use, or possibly the dwell being way off.

What I was wondering about when asking about the voltage is this. Could it be a wiring problem that is allowing 6+ volts to the coil when the key is on/engine not running but 12 volts is being provided when the engine actually is running? Maybe something being powered up from the alternator?

Another more obscure thing could be this. Some new contact points may come with a film on the point faces. It is recommended that a new set of points be brushed with a point file and cleaner before installation. This was true of some point sets many years ago but it’s been a few years since I’ve bought a set of points.

Since checking a condenser is near impossible has the condenser also been changed a few times on the offchance you could have gotten a bad one?
Based on the driving habits, I don’t see the mf rating of the condenser being a factor.


#11

I LOOKED AT THE POINTS UNDER A MAGNIFYING GLASS AND THE STATIONARY SIDE HAD BUILD UP AND THE OTHER DID NOT. BOTH WERE PITTED ALSO. THE ENGINE WAS RUNNING WHEN THE VOLTAGE WAS CHECKED FROM THE + TERMINAL TO THE - TERMINAL THIS GAVE A READING OF 6.5 VOLTS. WHEN RUNNING THE BATTERY WAS CHARGING AT 14.5 VOLTS. THE CONDENSER WAS REPLACED THREE TIMES ALONG WITH THE POINTS. THIS IS DEFINITELY A PERPLEXING PROBLEM. POTENTIALLY THE COIL AFTER HEATING UP FURTHER IS GOING HAYWIRE. THIS IS DRIVING ME INSANE WHEN IT IS SUCH AN EASY CIRCUIT.


#12

the voltage reads 6.5 volts while running


#13

Material being transferred to the stationary side of the points is generally caused by a condenser that is too weak.
Since the condenser has been replaced 3 times one can safely assume the condenser is not faulty each time. As to being possibly packaged with a condenser that is too weak - well, that could be debateable.

Is the VOM being used across both the pos. and neg. side of the coil at the same time? The VOM neg. probe should go to the engine block and the pos. probe to the + side of the coil. Assuming I’m reading this right of course.

At this point (pun not intended) the only thing I can come up with is either a weak condenser, maybe a coil problem (using stock coil or high output one?), or possibly the breaker plate in the distributor has a bad ground to the distributor body (would be unusual but I’ve seen a couple of Fords with this problem).

You might try filing the point faces and replacing the condenser with a higher rated one. Most condensers usually have a mf rating stamped on them so if it is a 25 mf cond. then try a 30 and see what happens.
(Also, the points are not closing up on you are they? If the dist. cam lobes are dry the fiber rubbing block on the point set can wear down pretty quickly which will allow the points to burn faster.)
Hope some of this helps. What a predicament to be in! Having to wrestle with a (drool) 454 Chevelle.


#14

I hate to be the one to ask this, but I think we should cover the basics first: Are you sure that you’re setting the gap correctly, and are you sure that the dwell angle is correct?


#15

The vom is used across both terminals at the same time and the reading was constant at 6.5 volts. This is a stock coil. Nothing is stamped on the condenser and the car runs perfectly with plenty of power. This car is nice as can be but this is really starting to become old.


#16

The gap was set by two different mechanics along with the dwell. The car runs perfectly until the points burn. It idles nicely and will accelerate to 70 very easily.


#17

Another possible explanation… Check for distributor shaft wobble (i.e. bad distributor bushings). This is rare (and usually only shows up when you have about a bajillion miles on the motor), but it is also easy to overlook when you do a rebuild.

Do you have access to an oscilloscope? This kind of problem is often easy to spot on the scope; look for high secondary resistance (bad plug wire, bad spark plug, wrong spark plug, poorly gapped plug etc.), wrong voltage, and erratic point opening (symptom you would see with the wobble, above). If all else fails, you can try increasing the resistance in your input circut (drop the voltage down to 4 volts and see if it makes a difference); if it does then you know what part of the system likely needs further examination.


#18

I don’t think that’s the right way to read the coil voltage. If you look at what you’re reading with an oscilloscope you’d see that you actually have something like a square wave at the negative side of the coil, and probably another square wave from coil voltage to battery voltage at the positive side.

I’d read the voltage from the positive side of the coil to ground, with the engine NOT running and with the points CLOSED. Have someone turn on the ignition switch briefly while you measure this. It seems to me that you should read something like 9 or 9 1/2 volts, but I may be completely wrong there. Then read the voltage from coil positive to ground with the points open. I’m guessing you’ll see battery voltage at that point. Using a DVM to read the voltage across the coil primary with the engine running doesn’t seem useful to me.

With the points failing so quickly it seems almost a sure thing that you’re running them at too hot a voltage, as if the ignition switch has failed or the coil positive side is wired wrong.


#19

I have a '71 SS 454. All the easy bases have been covered. An interesting problem that will require more thought but in the meantime, I thought I would point you to the premier web site dedicated to your car- http://www.chevelles.com/forums/.

Post there, many knowledgeable people likely to have run across the same type of problem.

I have modified all of my numbers matching, muscle cars to suit my uses. Hang the fanatics. I save all the parts and am careful to try not to do anything that can’t be reversed fairly easily in the event I sell one of them. I have carved up some of them quite a bit in the interest of serving my needs however. One thing I did to my Chevelle immediately was to swap in an HEI distributor. I show off the car but do not subscribe to the show car mentality so for me, it provides better driveability with less maintenance and is easily reversed. I haven’t had to mess with that setup since I installed it perhaps 10 years ago now. Just a thought.


#20

I assume you are trying to keep the car correct, but have you considered a “bolt on” type electronic ignition conversion. I’ve used optical type systems where you install an optical sensor in place of the points and have to hide a little black box someplace. It doesn’t modify the distributor and is reversible. Something like this:

http://www.mesaperformance.com/web_store/web_store.cgi?page=accescat/crane.html&category=yes&cart_id=69137.3761