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the cam/distributor gear issue

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Charles Smiley View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Charles Smiley Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2013 at 1:05pm
I went through that pin/hole issue several times. AMC may have changed the pin size when they went from Delco to Prestolite and finally Motorcraft distributers - somewhere along that trail. If there are still independent distributer rebuilding shops around they might know what's up.  
 
If you drill it don't overdo it or it might add chatter and spark scatter.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69 ambassador 390 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2013 at 3:41pm
Be careful of phasing the gear correctly also.  Cances are your mallor had phasing issues and they were corrected by moving the gear.  Find a good used original and copy the drive tang position relative to the new hole you drill.  Many aftermarket distributoers had the gear indexed incorrectly.  Set a known good used original distributor with #1 in the corect position and the rotor pointing to the spot the TSM shows as #1.  Note the drive position on the end and make the new hole in the new shaft in the same place.  If you don't, you will end up with tuning issues where you chase spark timing and can't get it adjusted except in a narrow range that won't allow factory setting.  The problem is the rotor is too far away from the cap contact at the proper firing poin.  Yoy will only be able to get the engine to run correctly in a very narrow range of distributor rotation before the spark gets erratic from jumping the too wide gap in the cap.  There should be a dimple on the gear to help.
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dane View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dane Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2013 at 4:21pm
Originally posted by 69 ambassador 390 69 ambassador 390 wrote:

Be careful of phasing the gear correctly also.  Cances are your mallor had phasing issues and they were corrected by moving the gear.  Find a good used original and copy the drive tang position relative to the new hole you drill.  Many aftermarket distributoers had the gear indexed incorrectly.  Set a known good used original distributor with #1 in the corect position and the rotor pointing to the spot the TSM shows as #1.  Note the drive position on the end and make the new hole in the new shaft in the same place.  If you don't, you will end up with tuning issues where you chase spark timing and can't get it adjusted except in a narrow range that won't allow factory setting.  The problem is the rotor is too far away from the cap contact at the proper firing poin.  Yoy will only be able to get the engine to run correctly in a very narrow range of distributor rotation before the spark gets erratic from jumping the too wide gap in the cap.  There should be a dimple on the gear to help.
 
The gear is from bulltear, they are suppose to be the best? I do not see a dimple? Now I'm getting concerned.Confused
 
We were just going to press it on and drill a new hole thru the shaft, thru the pin hole on the new gear? The old gear had been drilled to fit the original shaft hole...


Edited by dane - Feb/11/2013 at 4:25pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote whizkidder Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2013 at 4:39pm
Originally posted by dane dane wrote:



We were just going to press it on and drill a new hole thru the shaft, thru the pin hole on the new gear? The old gear had been drilled to fit the original shaft hole...


I'm worried too. No driven gear I've ever seen was a press fit to the distributor shaft. Measure the shaft and the inside of the gear. The shaft should be .491" if I remember correctly.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote whizkidder Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2013 at 4:58pm
Originally posted by 69 ambassador 390 69 ambassador 390 wrote:

Be careful of phasing the gear correctly also.  Cances are your mallor had phasing issues and they were corrected by moving the gear.  Find a good used original and copy the drive tang position relative to the new hole you drill.  Many aftermarket distributoers had the gear indexed incorrectly.  Set a known good used original distributor with #1 in the corect position and the rotor pointing to the spot the TSM shows as #1.  Note the drive position on the end and make the new hole in the new shaft in the same place.  If you don't, you will end up with tuning issues where you chase spark timing and can't get it adjusted except in a narrow range that won't allow factory setting.  The problem is the rotor is too far away from the cap contact at the proper firing poin.  Yoy will only be able to get the engine to run correctly in a very narrow range of distributor rotation before the spark gets erratic from jumping the too wide gap in the cap.  There should be a dimple on the gear to help.


Steve, I'm not sure changing the position of the gear on the shaft affects rotor phasing to the cap. The point at which the ignition fires is relative to the position of the breaker plate and points cam. The cam moves relative to the shaft based on RPM and the weights and springs, and the breaker plate moves with the vacuum advance (if used).

Changing the gear position on the bottom of the shaft will only require you to move the whole distributor -- breaker plate, housing, and cap by 1/2 tooth (~14 distributor degrees) to achieve what you had before, but won't change the position of the rotor relative to the points cam/breaker plate -- they're still in the same place.

I think you actually have to change the mechanical relation of the points cam to the shaft (different parts/weights) or change the "at rest" position of the breaker plate to affect/correct phasing.

Or... maybe I'm just an idiot.



Edited by whizkidder - Feb/11/2013 at 4:59pm
Ron Frost
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tsanchez Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2013 at 5:03pm
Do not drill a new hole in shaft, turn gear 90 and measure distance from washer to hole on shaft, subtract .010 and drill a hole i gear, then put gear on and drill through gear thru shaft and make new hole on other side of gear.

Edited by tsanchez - Feb/11/2013 at 5:05pm


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69 ambassador 390 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2013 at 5:30pm
That is correct Tony.  You don't want the two holes in the same plane or too close together.  And,  In some applications with late model brackets and Saginaw pumps, there is simply no room to turn the distributor that extra 14 degrees to get correct phasing.  That is why 90 degrees of turn on the new gear is a good tactic.  It will put the new pin hole in the correct place and out of plane with the old one.  But, be careful if there are already multiple holes in the shaft.  Max of two spread apart by ninety and off plane with each other.  If that is not possible because of multiple rebuilds or gear changes then you have to replace the shaft at least.  You don't want to shear one off.
Steve Brown

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84 Grand Wagoneer

69 Cougar XR7

65 Fairlaine 500XL

79 F-350 Super Camper Special



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Post Options Post Options   Thanks (0) Thanks(0)   Quote 69 ambassador 390 Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2013 at 5:40pm
Originally posted by whizkidder whizkidder wrote:

Originally posted by 69 ambassador 390 69 ambassador 390 wrote:

Be careful of phasing the gear correctly also.  Cances are your mallor had phasing issues and they were corrected by moving the gear.  Find a good used original and copy the drive tang position relative to the new hole you drill.  Many aftermarket distributoers had the gear indexed incorrectly.  Set a known good used original distributor with #1 in the corect position and the rotor pointing to the spot the TSM shows as #1.  Note the drive position on the end and make the new hole in the new shaft in the same place.  If you don't, you will end up with tuning issues where you chase spark timing and can't get it adjusted except in a narrow range that won't allow factory setting.  The problem is the rotor is too far away from the cap contact at the proper firing poin.  Yoy will only be able to get the engine to run correctly in a very narrow range of distributor rotation before the spark gets erratic from jumping the too wide gap in the cap.  There should be a dimple on the gear to help.


Steve, I'm not sure changing the position of the gear on the shaft affects rotor phasing to the cap. The point at which the ignition fires is relative to the position of the breaker plate and points cam. The cam moves relative to the shaft based on RPM and the weights and springs, and the breaker plate moves with the vacuum advance (if used).

Changing the gear position on the bottom of the shaft will only require you to move the whole distributor -- breaker plate, housing, and cap by 1/2 tooth (~14 distributor degrees) to achieve what you had before, but won't change the position of the rotor relative to the points cam/breaker plate -- they're still in the same place.

I think you actually have to change the mechanical relation of the points cam to the shaft (different parts/weights) or change the "at rest" position of the breaker plate to affect/correct phasing.

Or... maybe I'm just an idiot.

You.re not an idiot.  It works just like when I teach kids to sail.  The wind is relative to the boat.  In this case the wind is the distributor body and the boat is the breaker plate.  Move the boat(breaker plate) and the relative wind changes.  You have to re-trim the sails(rotor position).  If you cannot move the body 14 degrees in one direction or the other and have the rotor and #1 in the correct place, then phasing becomes an issue.  Some applications simply don't have that much room to turn the vacum cannister before it hits a belt or the pump bracketry.  My wagoneer has this issue.  The belt slaps the can at one end or I hit the pump at the other.  Very little room.  I just moved the wires one aroud but according to the TSM they are in the wrong place.  Number 1 is nowhere near where the books say it should be. 
Steve Brown

Algonac, Mi.

69 Ambassador sst 390

84 Grand Wagoneer

69 Cougar XR7

65 Fairlaine 500XL

79 F-350 Super Camper Special



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Post Options Post Options   Thanks (0) Thanks(0)   Quote dane Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2013 at 5:46pm
Originally posted by 69 ambassador 390 69 ambassador 390 wrote:

That is correct Tony.  You don't want the two holes in the same plane or too close together.  And,  In some applications with late model brackets and Saginaw pumps, there is simply no room to turn the distributor that extra 14 degrees to get correct phasing.  That is why 90 degrees of turn on the new gear is a good tactic.  It will put the new pin hole in the correct place and out of plane with the old one.  But, be careful if there are already multiple holes in the shaft.  Max of two spread apart by ninety and off plane with each other.  If that is not possible because of multiple rebuilds or gear changes then you have to replace the shaft at least.  You don't want to shear one off.
 
We were going to put the new hole in the shaft 90 deg from the other original hole. The old/bad gear that was on there had 2 sets of holes at different heights or lengths from the teeth? I think it was modified to fit back when I had this issue before in 99 or so? Dont remember, I had a mechanic do it for me??
 
So bottom line if I drill the shaft it wont work? I just wasnt real enthused about drilling into my brand new dist gear! Why the he*l dont these just lineup anyway? Just to make it a PITA?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tsanchez Quote  Post ReplyReply Direct Link To This Post Posted: Feb/11/2013 at 5:48pm
The shaft with two holes will be weakened, need to drill the gear.


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