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Old 07-06-2017, 05:40 PM   #1
Veeder
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Default Vacuum Advance stock 1941 V8 distributor

Could anyone tel me the basic systems of a Vacuum Advance not working properly? I have read a few notes that with today's gasoline it does not matter all that much which doesn't make a lot of sense to me that the Octane or misc additives would make a difference.
Thanks
Bob l
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Old 07-06-2017, 06:25 PM   #2
Kurt in NJ
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Default Re: Vacuum Advance stock 1941 V8 distributor

It's not a vacuum advance like more modern cars have, it is a vacuum relased retard----called vacuum brake, under conditions of low vacuum a piston rubs on a wheel that limits the advance-----if the piston is stuck up the advance could be faster, the piston stuck down and rubbing hard you won't get full advance
if the polished surface has rust damage on part of it and a different friction the advance can be erratic during low vacuum, and the leather puck on the piston gets chewed up ----all the cars I had with the adjusting screw backed out most all the way it never pinged on fresh gasoline (I don't know why it changed type in mid typing)
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Old 07-06-2017, 06:26 PM   #3
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Default Re: Vacuum Advance stock 1941 V8 distributor

The 1941 is the last of the old double cap or divers helmet type distributors. They actually have an vacuum retard system (vacuum brake). It does have a set of flyweights in there to give a bit of advance under rpm then the vacuum brake retards the system by applying a braking action to the advance rotor when the vacuum drops under load. The adjustment is a screw device on the top drivers side that adjusts the spring tension acting on the brake piston. Applying more spring tension increases the amount of retard so its an adjust and drive it sort of trial and error thing. Basically adjusting it to get rid of ping under load. The adjustment procedure is in the service manuals.

The flyweights were improved in 1942 when they upgraded the system to the crab type distributor configuration. The flyweight assembly from a 1942 through 1948 distributor can be installed in the earlier types for a bit of improvement in reliability and a bit better spark advance function.

The flyweights, piston, and the cam need to move freely so the thing might need some cleaning and oiling to get it up to par. Old Fords like their service schedules.
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Old 07-06-2017, 07:14 PM   #4
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Default Re: Vacuum Advance stock 1941 V8 distributor

Thks guys
I have had this totally apart multiple times and the weights are clean and greased up. All the surfaces have been on a brass wire brush so things are clean and appear to be moving properly. I have another distributor I just sent out to Skip Haney I thought I would take a stab at this one so I could drive it a bit till the one comes back rebuilt. The engine runs perfect at idle but very erratic on acceleration.
Can't work on it tomorrow legs to sore a little at a time is a good thing
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Old 07-07-2017, 06:20 AM   #5
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Default Re: Vacuum Advance stock 1941 V8 distributor

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Last edited by Hoop; 07-07-2017 at 12:15 PM.
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Old 07-07-2017, 07:33 AM   #6
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Default Re: Vacuum Advance stock 1941 V8 distributor

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Here is a link to a document dealing with the earlier Ford distributors which I have always found very informative - I suspect you guys have seen it but if not it is worth reading I think.

http://flatheadv8.org/rumblest/ignition.pdf
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Old 07-07-2017, 09:21 AM   #7
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Default Re: Vacuum Advance stock 1941 V8 distributor

HOOP
I don't see any confusion in my previous post. I think we can agree to disagree on this. The earlier (late type) helmet design was changed out for a reason more than just cost of production. There was more in play at the time that affected what design was going to work in there. New style cooling fans were brought into the picture that required a change. The crab in its first form (1942) could be problematic with moisture condensation under certain conditions but it gave more room for an improved fan and then the coil was relocated to a better position in my opinion. The war years improved moisture sealing which carried over to post war and on but the 1942 crab cap does work OK if properly set up. These units are, as you mentioned, easier to work on and therefore easier to maintain. There are still quite a few folks that use the 21A advance rotor on the earlier units out of preference so there is an improvement there. If they improved the advance rotor in 1941 (11A) which might be the case, then I could be wrong about that (my memory falters at times just like every one elses) but that would be a one year deal like many things on the 1941 vehicles and the advance rotors are interchangeable since that was the rotor used through 1948. I won't say that there was anything wrong with the early styles of helmet distributor since they performed all necessary functions for the engine designs they were mated to but they were more difficult to maintain and they could also have problems with moisture at times.

Hot rodders generally used crabs of one form or another with plenty of exceptions. If they were not as good as the early types, you wouldn't have seen so many in use.

Veeder
This could be something as simple as a bad condenser or you may have a fuel delivery problem. Several things can cause and engine to falter above idle.

Last edited by rotorwrench; 07-07-2017 at 11:37 AM.
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