Distributor cap HELP!

buelligan

buelligan

Junior Member
I have a bone stock 1940 ford 85hp Flatty that I am trying to do a complete tuneup on. I ordered a pair of inner caps from a decent dealer on the web, I revealed they have a manufacturing problem, as the resistance between where the ignition wire plugs in and where the wiper makes contact on the other side is in the thousands of ohms. Does anyone out there have a stock inner cap you could measure the resistance and post it up for me. I have .2 on the original one I have at 4 of 4 locations. This is what I would have expected. I actually found one terminal on each of the new caps that is "open". Not good.
Thanks in advance
 
The quality control for at least some of the reproduction inner caps is nonexistent. The plastic excess in the terminal openings has to be removed in order to get a good connection for the spark plug wire ends.
 
I recently acquired a set of NOS inner caps. I was skeptical about using them just because of their age, they have never been used. Having read this, I'll use them first.
 
Just make sure your ignition wire end is compatible with the inner cap socket. The OEM (?) ones I have require the contact at the "end" of the wire and the inner face of the socket. Seth if you have an ohm meter could you check the resistance from the inner socket face to the wiper for the rotor, on the opposite side? Let me know what that is....
 
buelligan said:
Just make sure your ignition wire end is compatible with the inner cap socket. The OEM (?) ones I have require the contact at the "end" of the wire and the inner face of the socket. Seth if you have an ohm meter could you check the resistance from the inner socket face to the wiper for the rotor, on the opposite side? Let me know what that is....
Click to expand...

I will do that, however I'm not near the cap at the moment. It may take a day or two to get that done.
 
I've heard/read about this same problem several times now on the various old car forums. You would think the manufactures would have a simple go/no go automatic continuity checking station as this cap comes out of the molding machine, but it seems like today's manufacturing philosophy is zero QC. Let the end user find the problems after a bazillion parts have been made. I just don't get the mentality of this.
 
JM 35 Sedan said:
It seems like today's manufacturing philosophy is zero QC. Let the end user find the problems after a bazillion parts have been made. I just don't get the mentality of this.
Click to expand...

Hmmmm.......Maybe we could bring manufacturing and the requisite QC back to our shores.........and begin to make AMERICA great again. DD
 
I have opened a can of worms, I have been in contact with three major distributors and they all have bad parts.
 
In my experience occasionally the rotor side brass 'points' require a gently tap to renew contact with the spark plug wire sockets on the the opposite side of the cap.
A nylon headed tiny hammer works well.
OR
Just get them from Vanpelt........his are the no hassle at all variety.
Charlie ny
 
Didn't want to name names here but Vanpelt is where I started, fine people to deal with and they tried to make it right, The parts are junk, C&G & Carpenter, also junk. I started with Vanpelt because I like to support the guys that most support the hobby, and their web page is a wealth of information.
 
buelligan said:
Just make sure your ignition wire end is compatible with the inner cap socket. The OEM (?) ones I have require the contact at the "end" of the wire and the inner face of the socket. Seth if you have an ohm meter could you check the resistance from the inner socket face to the wiper for the rotor, on the opposite side? Let me know what that is....
Click to expand...

My NOS inner cap is a "Standard" brand that is in the original box and never been installed. I checked the Ohms as you suggested and I came up with .3 ohms at all four sockets.
 
This is an issue that is very upsetting to me.
Those reproduced caps cost me a lot of time and a lot of money.
My engine on the dyno would not run above 2900 rpm. It wanted to
shake itself loose from the stand. I changed everything except the caps
as they were "new". It wasn't until a month later that I finally figured
out that the caps were bad. I was able to buy 2 NOS caps from
James @ Joblot, and 2 from Bubba. Problem solved, but what a nightmare.
My advice: Only use original Ford caps; even used inner caps will be far better
than any of the reproduced ones.
Oh yeah. The engine made 163 HP @ 2900 rpm.
Jim
 
Here is a photo of one of the Standard brand distributor heads. I think it is 1932-1936. Can any one confirm what years this will fit?

Just did a little research. It looks like Standard Motor Products is still in business. Founded in 1919. They manufacture and sell parts under the NAPA and CarQuest brand name as well as Standard Motor Products.
 

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I have been on an adventure to find out how these units are made and what the failure mode was, I’m an engineer and a little part of me would not let this go. I was able to procure a “bad” cap from Ken Isidor of Ken’s Carburetors in Connecticut. (Nice guy, thank you Ken.)
A little clarification here, I want to lay out some terms so we all understand what I am talking about. The item in question is called an “Inner Cap” I will simply call it the “Cap”. The cap has two sides, one has a “contact” that makes contact with the rotor, and the other side is the “socket” that the ignition wires plug into. The combination of the socket, contact and cap, at four locations, I call the terminal. So I will be talking about the cap, the socket, contact and the terminal.
My plan was to map the connections for resistance, then once the “open” terminal was found I would machine the cap down until I could see the interface between the post and the socket.
The results of the Ohm test are by position identified on the cap, 1-6 .18 ohms, 4-7 44 ohms, 2-8 .17 ohms, 3-5 “open” (no continuity).
I set the cap up in a miller and milled down to just break thru the area of the connection between the contact and the socket. Here is what I found:

see pix

I again checked the continuity and found the circuit open across the terminal. I carefully filed down the material left by the milling operation and proved my suspicions, there was an air gap between the contact and the socket. I was able to slide a .001 feeler stock between the contact and the socket.

See pix

Now you may say, “The spark may jump that gap”, and I agree it MAY … But there are detrimental effects of the spark jumping the air gap, the contact points of the arc would build up carbon, thereby increasing the resistance, this would cause pre-mature failure of the cap.
Here is a close up @20X

see pix


I was able to secure an OEM FoMoCo and an OEM “type” Bremi Cap all of the terminals were checked for resistance and found to be less than .2 ohms.
Everyone I have dealt with in this case has been nothing but helpful and professional. I have nothing but good things to say about the suppliers I dealt with. This is in no way meant to be a witch hunt, rather a yearning on my part to understand what caused my frustration and waste of time that Saturday in September.
 

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Thanks for providing the insight and doing the work here to provide us with details that you laid out very clearly. I appreciate it and now understand much better how these caps are built.
 
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