FE autolite distributor dwell questions

s55mercury66

s55mercury66

Senior Member
I recently got into the centrifugal advance in my FE distributor. While reassembling it, I took a good look at how the breaker plate moves in a different arc than the distributor cam does. It actually plays hell with the dwell. With the points set at .017, I put my meter on it and got 45° at idle, and around 30° with some vacuum at 2000 rpm. I can't be the first person to notice this. While I love my old points and condenser, this is a good reason, IMO, to go to an electronic trigger, like a Pertronix. I will check all this again this weekend. Does anyone have a tuning compromise they use to compensate for this, or is the points setting the compromise itself? I would think the dwell change plays havoc with the coil, if only in voltage output.
 
I had problems with FE distributors wearing the shaft bushings out. When they are like that, they will run OK but will miss every now and then and they just don't idle quite right. Replace the bushing and all is good. Once I set the points, I don't worry too much about the dwell. Someone with a distributor machine like Bubba's Ignition could tell you a lot more about whether it's working correctly or not.
 
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I believe the changing dwell was intentional. Cant remember if it was for economy or something else. Be sure the nylon buttons between the 2 plates are there.
 
Dwell angle is the amount of time, measured as degrees of rotation, that contact breakers close in a distributor. Unless dwell angle is accurate, ignition timing won't be accurate. The period, measured in degree of cam rotation, during which the contact points remain closed is called the dwell angle.
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DWELL is important, especially for mechanical points style distributors. Electronic distributors can compensate, mechanical can't.
 
Dwell can vary some and not be a problem. As far as timing is concerned, the point at which the points open is very critical. The point that they close is less so. Dwell is important on the older coils that needed all the time they could get to build up the flux for the next collapse of the magnetic field. On the more modern coils with epoxy insulation, the dwell time can be shorter but not by a lot. Battery ignitions with points & condenser were generally always just good enough to do a decent job. Now days, there is a coil on each cylinder with electronic breaker control. They can be a lot hotter than any of the old stuff could ever be.
 
Drawing on my GM experience, I will guess that as long as the dwell is 30° or more, it should be good as far as coil saturation time goes. This particular distributor is in really good shape, no slop or wear that I could find anywhere. I cleaned and lubed all the contact areas and pivot points. That was when I noticed how the point plate moved on its pivot, and that it changed the point gap when it did. I am probably way overthinking this, but it gives me something to do and think about.
 
s55mercury66 said:
Drawing on my GM experience, I will guess that as long as the dwell is 30° or more, it should be good as far as coil saturation time goes. This particular distributor is in really good shape, no slop or wear that I could find anywhere. I cleaned and lubed all the contact areas and pivot points. That was when I noticed how the point plate moved on its pivot, and that it changed the point gap when it did. I am probably way overthinking this, but it gives me something to do and think about.
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JFYI, correct (target) dwell angle for most/all Ford single point V8 distributors is 27 degrees.
 
Thanks, Bob. Im going to check some more with a vacuum gauge and the dwell meter. I also have another distributor that is almost new, and will be looking closely at its pivot points. The car runs ok as it is, but if an improvement can be made....
 
While you can just put the points in and gap them with a matchbook cover and she will run, a dwell meter is necessary if you want it to run correctly consistently.

That is why both mounting holes are elongated, to arrive at the proper dwell angle.
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While I am sucking up dust, the second adj hole in the points set is also for adjusting points breaker arm spring tension.

I expect oldmics to call me on the carpet and tear off a few patches...
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The dwell should be 26* at 600 rpms. Set the timing after you set the dwell.
I hope this helps.
 
Marv said:
The dwell should be 26* at 600 rpms. Set the timing after you set the dwell.
I hope this helps.
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600 rpms is for a standard and 500 for a automatic.
sorry about that. I was a mechanic at a Ford garage when these were new but my memory has slowed down.:)
 
After looking, all my points, and both of my breakers will only allow the points to move around the pin. One thing that occurred to me is the vacuum advance lever, at rest, has the breaker plate pulled over where it is centered around the cam. If I can figure a way to lenghten the lever, it would tighten up the points spread (insert chuckle here). With the points set at .017, applying the vacuum advance opens it up to .024. That is quite a variation, but this distributor I am looking at is not the one on the car either. Limiting the vacuum advance would help, but might hurt mileage also. I will take a good look at the one Im running tomorrow, and see if I can dig up some more advance canisters.
 
Thanks Marv, I just noticed your replies. That is the procedure I followed, well, let me say I set the points first, then the timing. Thanks all for the replies.
 
s55mercury66 said:
I recently got into the centrifugal advance in my FE distributor. While reassembling it, I took a good look at how the breaker plate moves in a different arc than the distributor cam does. It actually plays hell with the dwell. With the points set at .017, I put my meter on it and got 45° at idle, and around 30° with some vacuum at 2000 rpm.
Click to expand...

s55mercury66 said:
After looking, all my points, and both of my breakers will only allow the points to move around the pin. One thing that occurred to me is the vacuum advance lever, at rest, has the breaker plate pulled over where it is centered around the cam. If I can figure a way to lenghten the lever, it would tighten up the points spread (insert chuckle here). With the points set at .017, applying the vacuum advance opens it up to .024. That is quite a variation, but this distributor I am looking at is not the one on the car either. Limiting the vacuum advance would help, but might hurt mileage also. I will take a good look at the one Im running tomorrow, and see if I can dig up some more advance canisters.
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You are absolutely certain the distributor shaft bushing(s) and the breaker plate bushing (1960/ ) is good? All of this noticed movement does not sound correct.

The dwell angle should not change over increased RPM more than 3 degrees. The OEM distributor is not a precision piece as are some aftermarket/speed models and/or electronic models.
 
Any time the points plate moves when the cam is motionless, it will change the opening gap since the cam spacing it so close with an 8 lobe cam. Any play in the pivot movement of the points plate could be problematic too. The vacuum advance will move the plate but centrifugal generally only moves the cam. If there is any play in any of these movements then that would be problematic as well. Many of these old units never get any lubrication service and stuff does wear out. Even the cam can get worn out since a lot of backyard mechanics never even apply lubricant to the follower wick. If the points plate is not concentric, it is likely defective.
 
s55mercury66 said:
Thanks Marv, I just noticed your replies. That is the procedure I followed, well, let me say I set the points first, then the timing. Thanks all for the replies.
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It is important to check the dwell at the recommended rpm. You set the dwell at 26 cranking the engine with the starter to set the dwell first. Then check the dwell at the recommended rpm. If it is not correct then correct it by cranking it over and set with the degree difference. You were going for 26* and it showed 24* running at 500 rpm the you set it at 28* running and test again. A
ford is not really that sensitive ,but if you want it perfect tat is the way. GM and Chrysler is.
 
I got busy with another project today, and didnt get to tinker with it today. The distributor is in good shape, it has 34,ooo miles on it and no wear I could find anywhere. Everything cleaned and lubed on reassembly. I will be playing with the vacuum advance to see if I can get it to center the points plate a little better, if it will retain the advance characteristics I need. The spare distributor I have looks like a replacement, that was installed on my donor motor when it was poorly rebuilt. Sounds like some of you are as surprised as I was to find out there was that much dwell variation, I appreciate all the replies.
 
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