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the cam/distributor gear issue |
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Charles Smiley
AMC Apprentice Joined: Oct/26/2011 Location: CA Status: Offline Points: 205 |
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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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69 ambassador 390
Supporter of TheAMCForum Joined: Nov/22/2009 Location: Peoria, AZ Status: Offline Points: 3539 |
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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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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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dane
AMC Addicted Joined: Jul/13/2008 Location: Ponca City, OK Status: Offline Points: 530 |
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The gear is from bulltear, they are suppose to be the best? I do not see a dimple? Now I'm getting concerned. 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 3:25pm |
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1974 Matador Coupe Brougham aka "The Mat"
1975 Matador Coupe Oleg Cassini Edition 1969 Javelin SST (Project Car) - SOLD but not forgotten |
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whizkidder
Supporter of TheAMCForum Joined: Mar/03/2008 Location: North Georgia Status: Offline Points: 2972 |
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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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Ron Frost
marne1ancient @ gmail.com 910 nine two two 0563 "There is no limit to what a man can do, so long as he does not care a straw who gets credit for it. Charles Montague |
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whizkidder
Supporter of TheAMCForum Joined: Mar/03/2008 Location: North Georgia Status: Offline Points: 2972 |
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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 3:59pm |
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Ron Frost
marne1ancient @ gmail.com 910 nine two two 0563 "There is no limit to what a man can do, so long as he does not care a straw who gets credit for it. Charles Montague |
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tsanchez
AMC Addicted Joined: Jul/09/2007 Location: Arizona Status: Offline Points: 4303 |
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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 4:05pm |
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69 ambassador 390
Supporter of TheAMCForum Joined: Nov/22/2009 Location: Peoria, AZ Status: Offline Points: 3539 |
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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.
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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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69 ambassador 390
Supporter of TheAMCForum Joined: Nov/22/2009 Location: Peoria, AZ Status: Offline Points: 3539 |
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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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dane
AMC Addicted Joined: Jul/13/2008 Location: Ponca City, OK Status: Offline Points: 530 |
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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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1974 Matador Coupe Brougham aka "The Mat"
1975 Matador Coupe Oleg Cassini Edition 1969 Javelin SST (Project Car) - SOLD but not forgotten |
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tsanchez
AMC Addicted Joined: Jul/09/2007 Location: Arizona Status: Offline Points: 4303 |
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The shaft with two holes will be weakened, need to drill the gear.
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