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Old 08-15-2020, 03:27 AM   #1
woofa.express
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Default measure gap between rotor and plug posts in distributor cap

simple question. how do I measure the gap between rotor and plug post striker post. or do I simply purchase new rotor and distributor cap. ??
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Old 08-15-2020, 05:18 AM   #2
Patrick L.
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Default Re: measure gap between rotor and plug posts in distributor cap

feeler gauge
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Old 08-15-2020, 05:33 AM   #3
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Default Re: measure gap between rotor and plug posts in distributor cap

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feeler gauge
Hi Patrick. it's inclosed. how do I go about it?
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Old 08-15-2020, 07:01 AM   #4
Mike Peters
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Default Re: measure gap between rotor and plug posts in distributor cap

You must have a the modern one piece distributor cap available from vendors. You need the original style two piece cap. (body and cap) Then get your feeler gauge out and measure the gap between rotor and body contacts.
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Old 08-15-2020, 08:37 AM   #5
Bob Bidonde
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Default Re: measure gap between rotor and plug posts in distributor cap

This may help. Make the gap 0.015" to 0.025" by gently /carefully bending the brass tab on the rotor. The rotor's tab should pass by the middle of the contact in the distributor body. If the tab becomes loose or the rotor breaks, get a new one.
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Old 08-15-2020, 09:06 AM   #6
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Default Re: measure gap between rotor and plug posts in distributor cap

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What I have found is that too large a gap causes the engine to not run as well and backfire occasionally. A slight gap or the spring touching the carbon contact work fine.
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Old 08-15-2020, 03:03 PM   #7
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Default Re: measure gap between rotor and plug posts in distributor cap

run my 31 roadster with a gap of thirty five thousands at the rotor tip . I like to run the same gap at the spark plugs .
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Old 08-15-2020, 03:54 PM   #8
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Default Re: measure gap between rotor and plug posts in distributor cap

thankyou all of you. I will take the distributor off my tourer with a removable cap and put it on the ute so as I can measure. the rotor looks warn so a new replacement may well be in order. thankyou again, gary
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Old 08-15-2020, 04:44 PM   #9
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Default Re: measure gap between rotor and plug posts in distributor cap

As in post #5 bend the brass tab on the rotor to adjust the gap. However to get the gap to the right distance you may have one or two that after bending the tab the gap is too small. On those I use a small file and take some off the posts on the distributor body.
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Old 08-15-2020, 06:14 PM   #10
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Default Re: measure gap between rotor and plug posts in distributor cap

Ditto with crosscut.

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Old 08-15-2020, 06:32 PM   #11
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Default Re: measure gap between rotor and plug posts in distributor cap

In most cases for me , the posts or contacts in the distributor cap body are different lengths . I measure and file as necessary to make the posts-contacts all the same length . I then install the rotor and remeasure the gaps and make them all the same . Ford recommended a conservative gap of twenty five thousands .
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Old 08-15-2020, 08:38 PM   #12
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Default Re: measure gap between rotor and plug posts in distributor cap

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What I have found is that too large a gap causes the engine to not run as well and backfire occasionally. A slight gap or the spring touching the carbon contact work fine.
Are you referencing the rotor spring and the carbon button on the cap? There should be no gap there, just a slight spring pressure as you push the top/cap down to lock it in place.
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Old 08-15-2020, 10:00 PM   #13
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Default Re: measure gap between rotor and plug posts in distributor cap

You might measure the distance between the opposing contacts in both caps to see if they are the same, might give you another reference point , once you have measured with the original cap.
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Old 08-16-2020, 07:07 AM   #14
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Default Re: measure gap between rotor and plug posts in distributor cap

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run my 31 roadster with a gap of thirty five thousands at the rotor tip . I like to run the same gap at the spark plugs .
Purdy, what is the advantage of having a wider gap that Fords .025?
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Old 08-16-2020, 09:21 AM   #15
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Default Re: measure gap between rotor and plug posts in distributor cap

The spark gets hotter when it jumps a gap . Just a way to get hotter spark for free if you want it . Of course an original model A doesn't necessarily need hotter spark . Hotter spark can be of benefit with modified engines .
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Old 08-16-2020, 10:14 AM   #16
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Default Re: measure gap between rotor and plug posts in distributor cap

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Make the gap 0.015" to 0.025" by gently /carefully bending the brass tab on the rotor
The rotors that I have have a steel, not brass, "tab", and methinks that trying to bend one would end up breaking the rotor.
The gaps between the rotor and the distributor body on my A are quite different from one terminal to another but the engine runs just fine that way.
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Old 08-16-2020, 06:58 PM   #17
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Default Re: measure gap between rotor and plug posts in distributor cap

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The spark gets hotter when it jumps a gap . Just a way to get hotter spark for free if you want it . Of course an original model A doesn't necessarily need hotter spark . Hotter spark can be of benefit with modified engines .
Purdy is right, as usual. "Air gap type" Spark Intensifiers work on the same principle.
I'm not sure the increased hotter spark is free though, it is a little bit harder on the ignition components. If you have Quality healthy parts, there should be no problem.
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Old 08-17-2020, 08:50 AM   #18
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Default Re: measure gap between rotor and plug posts in distributor cap

Back in the day I wanted to save as many electrons as I could just for the sparklers. So I soldered the distributor contacts to keep that gap as small as possible. I'd solder and then spin the shaft by hand to scrape off all the lead I could. I didn't want any misfires at 8K.
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Old 08-17-2020, 09:33 AM   #19
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Default Re: measure gap between rotor and plug posts in distributor cap

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I didn't want any misfires at 8K
I wouldn't even attempt to run an A engine at 8K rpm.
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Old 08-17-2020, 10:36 AM   #20
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Default Re: measure gap between rotor and plug posts in distributor cap

It will take a lot of mods for the model A engine to turn eight thousand RPMs .
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