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1931 Dual Point Timing- Advice?


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One other issue of note while timing:  Depending on your vantage point, where the timing marks fall on the bell housing change quite a bit.  If you are standing up over the mark and get it lined up and then kneel or lower your vantage point. the line on the flywheel "moves up" visually as you lower your eyes.   Depending on how high or low your head is, this can make quite a difference. Does anyone know the recommended eye position for performing this task?  I ended up doing it by setting my eye level as close to the level of the index mark on the bell housing as possible.  I basically set my chin on the splash apron.

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I suspect if you got your drafting board out and laid out the opening of the housing casting  over the flywheel, then developed the maximum possible parallax by drawing lines from the index mark on the housing tangent to the top and bottom edges of the housing opening closest to the flywheel and intersecting the flywheel then mathematically calculated the possible error in degrees by dividing the distance between the points where the lines of parallax intersect the flywheel into the circumference of the flywheel you would find a possible error of +/- a degree or 2.  You would have to sight the cylinder 1 timing mark at one of the worst possible angles then sight the cylinder #6 timing mark at the opposite worst angle to make that large an error in point synchronization and assuming you viewed both marks from the same position you could only be off on absolute timing by half the possible error you developed mathematically.  If you are really worried about parallax effect on absolute timing why not make a pointer that can be attached to the housing aligned with the index mark on the housing then bent into the opening on the crank centerline so it is within a 1/16" of touching the flywheel?  That would eliminate the parallax issue altogether.  If you take reasonable care to stand so you are looking from the same place each time you line up the marks you will be close enough on point synchronization even if you are a little off on the absolute timing.  There is probably enough lash in the gears, shafts and bearings involved to cause a larger error in absolute timing than the parallax  will cause. 

Edited by Str8-8-Dave
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  • 1 month later...

Just finished reviewing all of the great information and input on the dual point distributor timing.   I'm in the process of re-ringing my 32 - 50 series and replacing the cracked head courtesy of a long time member who assisted me with a replacement.   Prior to starting the engine work I had gone thought the timing procedure as outlined in this thread.  I always wondered if I had gotten things just right in the process.   I came across a distributor from a 1933 50 series.   This distributor physically is the same with the exception it is a single point unit with an 8 lobe cam.    So in theory I think I was able to do away with the syncing of the second set of points.   I just set  the single set to the initial #1 advance mark on the flywheel and was done.    I had had a 1935 40 Series and it had a single point unit and it always worked well, didn't see why the same wouldn't be true for a 32.  Car seems to run as good or maybe better than when I was running the dual point unit.   Not sure this would be proper etiquette for one wanting a number matching car but for a driver like mine it seems to work.   Until I came across this 33 unit I often wondered if the four lobe cam could be changed to an 8 lobe and just use a single set of points in an original correct housing for a 32.   This might be a little off the topic but thought I would throw it out for comment anyways.

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  • 11 months later...
On 7/10/2019 at 5:16 PM, maok said:

So what is the purpose of a dual points ignition system?

Dual point ignition is supplied for one of two reasons. In the case of your '31 Buick each set of points takes care of 4 of the eight cylinders so there is a longer saturation of the coil takes place increasing the available voltage. Otherwise you would also need an eight lobe cam in the distributor rather than four. Fast forward to the late 1950's Chrysler began using dual point distributors with the effect that each sets of points fire immediately after the first which made the spark DWELL increasing a good spark to plug.

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I have rebuilt approximately 6 1932 Buick (0 series distributors and it is nice to see how some have gone to a 1933 8 lobe cam. I disassembled one distributor which had no centrifugal

weights under the main plate. So the car would have had no possible way of advancing the spark. Some weights were found and installed, end of story. Does the 1933 8 lobe distributor have the same advance characteristics as the 4 lobe?

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Dont even mess with the dual points, just install the petronix module and be done with it.. mine runs great. No need to change distributers, they make one for the four lobe cam. But be sure to check your fly weights and springs before you press the rotor on the shaft. 

The 32 has mechanical advance dual points, the 8 lobber has vac advance I believe as in 33,34 and newer.  

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I've pondered the thought behind the 4 lobe 2 points concept.  It doesn't change dwell.  Points do ramp up and open and close guicker possibly reducing arcing  across the points.

 

My main conclusion was that points would last twice a long before needing changing as they work half as much.  

 

Bob Engle

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The reason for dual points was to give the coil more time to saturate before it fired. A necessity running 8,000 rpm's back in the day. It really didn't make any sense. I can see it on a V-12 & V-16, otherwise, a waste of time. 

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