burned distributor rotor

[timer2]

Took our '54 out for the usual 80 to 100 mile drive Sunday and about 40 miles into the cruise the car started to misfire. I pulled over, checked the visual stuff, nothing out of order then drove the 40 miles back home with the engine misfiring all the way. Put it in the garage and pulled the distributor cap and this is what I found.... Funny thing is, the car idled perfectly. I had a spare rotor in the glovebox and we're back on the road but this is a little puzzling. I'm hoping it was a defective rotor, as it's only been on the car for about a thousand miles along with a good used distributor. Any thoughts?    T. Irvin

[dn010]

Are you using stock points and coil? I've burned many rotors when I used pertronix ignition and a high voltage coil. If you're stock, check the wiring to the coil and make sure the wires are in good condition and connections are tight. I'd also check the spark plug wires and spark plugs themselves, and if it has been a while, I'd simply replace them.

[TJ Hopland]

With that much damage to the rotor the cap at the very least has to be full of conductive carbon so that should be replaced too.  Can you post a photo of the inside of the cap?  I'm curious what its looking like and if we will be able to tell how well aligned the spark is with the terminals.

[badpoints]

Check the gap on your spark plugs, maybe reduce the gap a little.

[Dave Shepherd]

Make sure you coil is either internally  resisted or you have an external resistor to a 12v coil.

[timer2]

All stock engine rebuilt at 114K now has a little over 130K on it. Dwell is rock steady at 30 degrees...new plug wires, NGK plugs set at .035, points, all at the time I replaced the distributor but I did not replace the condenser. The terminals on the cap still look new, no arching or the normal "white stuff" that accumulates after many miles. The points are still shiny. After I immediately spotted the bad rotor, I inspected the cap for defects, none that I could see. I blew out the debris with compressed air and sprayed the cap with Zep electrical cleaner, put in the spare rotor and have put maybe 30 miles on it and it runs great again. I'm wondering if the rotor was defective because the cap contact is stainless and the cap terminal contact is brass, I believe. So maybe where the two should come together there was a fault...it looks to have burned from the inside outward. These rotors aren't cheap, $39 at NAPA but I got one from Rock Auto for $26 with shipping.  T. Irvin

[timer2]

This car still has the ballast resistor on the firewall and the wires have never been messed with...12v to the coil when cranking and around 8v when running. If the voltage was higher when running, my understanding is it would burn the points prematurely? T. Irvin

[bcroe]

It looks to me, like the (arc) point of the rotor
fell off or got broken by some cap mis alignment. 
Then the spark continued to jump the now huge gap,
most of the time, if you did not push it hard. 
Bruce Roe

[J. Gomez]

Terry,

If that rotor is an OEM I believe some of the older OEM had an internal resistor built-in in the rotor. I recall that our late friend Johnny Washburn had a SS article detailing his finding on these old OEM rotors.

So it is possible yours was arching across and burnt right through the insulator.      

[timer2]

Mr. Gomez, I believe you are correct. I found a small 1/8 inch round by 3/4 inch long "thing" laying on top of the distributor plate. I fished it out when I was blowing compressed air on the distributor innards. I'll dig it out of the garbage and take a photo if possible.  T. Irvin

[timer2]

Here it is. I can see two small "points", one on each end that appear to have had wires attached. Now to figure out what caused this resistor to fail...age?   T. Irvin 

[Lexi]

That sounds like it might be the piece. Clay/Lexi

[J. Gomez]

Terry,

I'm with Clay's comment above..!

Unfortunately I do not recall the year/month on Johnny's SS article, from memory he mentioned/show the resistor to be about the same as the one in your picture and place in between the center tab and the end.

So as your prediction "yes" is age and contamination, I believe those resistors are "carbon made" and in Johnny's SS article he stated that NOS in their box and never installed he checked failed.   

So even getting a new NOS rotor may not worth the $$ and the time to search for them.     At least you were lucky in limping back home with no major issues.   

Good luck..!

[timer2]

The replacement I had doesn't say made in the USA so I'll take it that it's not OEM. The one coming from Rock Auto will go  back in the glovebox. What really amazes me is the fact that it idled perfectly after I got home. I shut it off cause I have to manually lift my garage door and it started right up like it always did...fired on the first piston. I drove home about 55 to 60 mph, all two lane highway and I could feel and hear ( I have the resonators AND the mufflers installed) it firing through an adjacent exhaust valve!! I'll consider the problem solved unless it happens again. Thanks for all the input fellas. T. Irvin

[dn010]

Standard Motor Products (DR306) which is made in the USA can be had for $26 on Amazon.

[Poncholover]

Very common failure. Betting you have modern resistor plugs & resistor wires.
A definite NO-NO with a resistor rotor.
Run a standard rotor with modern plugs & wires and you will be set for the next ten years!

Oh, and welcome the the "club"

[Lexi]

Terry,

I'm with Clay's comment above..!

Unfortunately I do not recall the year/month on Johnny's SS article, from memory he mentioned/show the resistor to be about the same as the one in your picture and place in between the center tab and the end.

So as your prediction "yes" is age and contamination, I believe those resistors are "carbon made" and in Johnny's SS article he stated that NOS in their box and never installed he checked failed. 

So even getting a new NOS rotor may not worth the $$ and the time to search for them.    At least you were lucky in limping back home with no major issues. 

Good luck..!

Yes, Jose nailed it. I went through my parts and found an NOS Rotor for a 1956 Cadillac. MPL lists part # 1932135. Here is the box plus the "offending" resistor highlighted. Clay/Lexi

[Scott Nellis]

   Nicely done gentlemen. You guys would put Columbo to shame!

[TJ Hopland]

Since there are so many parts involved I would think maybe the failure was the rivet at the outboard end got loose?  Seems strange that much damage happened that fast and that for the most part it ran good.

Was the resistor in the rotor the same idea as the resistor wires?

[CadillacFanBob]

Terry,

I'm with Clay's comment above..!

Unfortunately I do not recall the year/month on Johnny's SS article, from memory he mentioned/show the resistor to be about the same as the one in your picture and place in between the center tab and the end.



So as your prediction "yes" is age and contamination, I believe those resistors are "carbon made" and in Johnny's SS article he stated that NOS in their box and never installed he checked failed.   

So even getting a new NOS rotor may not worth the $$ and the time to search for them.     At least you were lucky in limping back home with no major issues.   

Good luck..!

I also remember seeing a SS article on the rotors by John Washburn,

Does anyone know how to search for that article? If so please let us know.

I miss my friend, technical and tool advice from JW.

Bob