Author Topic: Help on installing distributor into 68 390 GT  (Read 499 times)

Offline 68 S Code

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Help on installing distributor into 68 390 GT
« on: February 15, 2017, 11:10:40 AM »
To many this will seem like a fairly basic question but I could use some help. Back in October I needed to remove the distributor in my 68 GT 390 to have it looked at and worked on. I was told to make a mark on the body of the distributor case and the block to have that as a reference point and also after removing the cap the location of the rotor in relation to the case. Made both those marks. Also told to look at the rotor as I was lifting out the distributor as it would turn slightly in a direction due to the gears un-meshing between distributor shaft and cam. That was a slight twist counterclockwise. Do not rotate the motor after distributor is out.

So the refreshed distributor comes back from Indiana with the newly restored and installed dual vacuum advance unit. Since my car is a Thermactor equipped and C6 auto i had the correct advance rebuilt to replace the aftermarket single vacuum advance unit. I try reinstalling the distributor lining up all my marks I made but its a little stubborn. Will only mesh in one location at it appears slightly off. But it wont go in any other way so I figure its a match. Try starting the car but it appears i was off maybe a tooth. Currently I am unable to start the car because I cant swing the distributor in the direction i need to go because my nicely restored vacuum advance is hitting the upper water pump hose from the block to the pump. So now that ive cranked the motor I need to reinstall the distributor based on TDC and #1. So here is the question.

I will crank the engine over close to TDC and then turn by hand. But do I want to actually turn it to TDC mark on the balancer or to ^ degrees before TDC? The shop manual calls for 6 degrees BTDC as base timing. Whether I use 0 or 6 degrees on the balancer the more critical question is the distributor shaft has a hexigon cam at the top of it below the rotor. That mean we have 8 points and 8 flats. The points of the cam rub on the the plastic block of the actual points causing them to open and close. It would be my guess that as the points open, meaning the cam point pushes on the points block, that's the moment that a spark is sent to the terminal on the underside of the distributor cap. So do i want to get this accurate installing the distributor? Meaning balancer at 6 degree BTDC and points open for cylinder 1? i really need to have some more swing in the distributor between the water pump and the fuel line. The vacuum big dual diaphram advance will contact both. Sorry for the long dissertation. i may also need to move the oil pump shaft slightly. Ive been told thats a 1/4" deep socket. Can it be turned either way or only one direction? With ratchet or with finger pressure?

Offline carlite65

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Re: Help on installing distributor into 68 390 GT
« Reply #1 on: February 15, 2017, 11:14:45 AM »
you can turn the oil pump shaft either way. tape the socket to the extension so it will stay on. you should not need a ratchet to turn it. turn it in small increments so all marks line back up.
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Offline 68 S Code

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Re: Help on installing distributor into 68 390 GT
« Reply #2 on: February 15, 2017, 11:47:38 AM »
Yes I've already taped the socket to the extension. I believe this is why I had such a hard time trying to get the distributor to mesh in the right spot because I didn't adjust the oil pump drive shaft. Now I have to start from scratch lining up balancer marks because I tried starting the car.

Offline Bob Gaines

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Re: Help on installing distributor into 68 390 GT
« Reply #3 on: February 15, 2017, 06:29:23 PM »
I always take out number 1 plug and crank the engine with thumb or hand over spark plug hole until I get compression THEN line up with top dead center. But that is just me.
Bob Gaines,Shelby enthusiast, Shelby collector , Shelby concours judge SAAC,MCA,Mid America Shelby

Offline carlite65

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Re: Help on installing distributor into 68 390 GT
« Reply #4 on: February 15, 2017, 06:30:05 PM »
i do it the same way.
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Offline 68 S Code

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Re: Help on installing distributor into 68 390 GT
« Reply #5 on: February 15, 2017, 08:19:57 PM »
I'm close currently but just a tooth off as i cant swing the distributor enough clockwise. The vacuum advance is hitting the water pump hose. Friend is saying to stop worrying about over complicating this step.

Set balancer to TDC or 0
Mark on distributor case where #1 pin is off distributor cap.
If its off pull out distributor and re-install with rotor pointing to #1. Dont worry about distr shaft cam flats or points.
He said if oil pump drive is being stubborn push down on distributor case and bump the engine over. it should drop down. I don't know about this last step.

Offline Bob Gaines

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Re: Help on installing distributor into 68 390 GT
« Reply #6 on: February 15, 2017, 08:31:40 PM »
I'm close currently but just a tooth off as i cant swing the distributor enough clockwise. The vacuum advance is hitting the water pump hose. Friend is saying to stop worrying about over complicating this step.

Set balancer to TDC or 0
Mark on distributor case where #1 pin is off distributor cap.
If its off pull out distributor and re-install with rotor pointing to #1. Dont worry about distr shaft cam flats or points.
He said if oil pump drive is being stubborn push down on distributor case and bump the engine over. it should drop down. I don't know about this last step.
I have done this step too. Some people are uncomfortable doing it  however. Keep in mind that the vacuum advance when properly installed like factory and timed will be basically pointing straight ahead.
Bob Gaines,Shelby enthusiast, Shelby collector , Shelby concours judge SAAC,MCA,Mid America Shelby

Offline ruppstang

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Re: Help on installing distributor into 68 390 GT
« Reply #7 on: February 15, 2017, 08:47:12 PM »
I agree with the statements above and would add if the distributor will not drop where you want it just use the 1/4 socket and slightly turn the oil pump shaft. Reinstall distributer and it should drop, if not move the oil pump shaft again.

Offline 68 S Code

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Re: Help on installing distributor into 68 390 GT
« Reply #8 on: February 16, 2017, 09:37:50 PM »
Bob so the vacuum advance should be at the 6 o'clock position? Currently it needs to move further towards 7:00 to start but water pump getting in the way. That's why I think I'm a tooth off. Saturday its supposed to be 62 degrees so planning on spending the day working her. Stay tuned.

I was thinking about this bumping the starter and a bit hesitant to take that step. i was actually thinking that since i will be turning the crankshaft with a breaker bar to 0 TDC what if i just tried slightly moving the crank/cam to seat the distributor? Or as Marty suggests just keep adjusting the oil pump drive shaft.
« Last Edit: February 16, 2017, 09:41:34 PM by 68 S Code »

Offline Bob Gaines

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Re: Help on installing distributor into 68 390 GT
« Reply #9 on: February 16, 2017, 11:10:06 PM »
Bob so the vacuum advance should be at the 6 o'clock position? Currently it needs to move further towards 7:00 to start but water pump getting in the way. That's why I think I'm a tooth off. Saturday its supposed to be 62 degrees so planning on spending the day working her. Stay tuned.

I was thinking about this bumping the starter and a bit hesitant to take that step. i was actually thinking that since i will be turning the crankshaft with a breaker bar to 0 TDC what if i just tried slightly moving the crank/cam to seat the distributor? Or as Marty suggests just keep adjusting the oil pump drive shaft.
Yes on the 6 o'clock + or - a little.  Keep adjusting the oil pump drive should eventually get you there also.
Bob Gaines,Shelby enthusiast, Shelby collector , Shelby concours judge SAAC,MCA,Mid America Shelby

Offline Brian Conway

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Re: Help on installing distributor into 68 390 GT
« Reply #10 on: February 18, 2017, 11:39:06 AM »
ditto that;  TDC, verify by looking at your balancer timing mark and with a finger over the #1 spark plug hole, vac. adv at 5:30, rotor at 11:45 and 1/8 turns on the oil pump shaft.  Brian
« Last Edit: February 18, 2017, 11:58:57 AM by Brian Conway »
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Offline geo302b

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Re: Help on installing distributor into 68 390 GT
« Reply #11 on: April 28, 2017, 04:10:26 PM »
Ok here hows its done pull no1 plug bring up to top dead center + what degree you want [+6?] put in dist. with rotor pointing to no.1 plug wire. when it stops on the oil pump shaft stop there. put on cap lay plug with wire on it grounded on intake man. turn on key to run not start. turn dis. back and forth u will see spark at plug. when plug fires hold dis. there have friend bump engine over.[ bump] dis will fall right in. start up engine put on timing light. you will be suprised how close u are. Done this a million times.