A Discovery? Green Wire is just an earth? MSD involved

[Robbbyg]

RE
The Shield wire from the Dizzy,

i cut out the plug as im hardwiring (trying to) my ignition in,

Ive noticed the Shield wire diverts to the Earth lead,well it does on a 77 Euro with an 8 pin CDI

see photo,

Possibly this is why im having trouble getting Tach working after putting in MSD, ?

It says to put violet wire to the shield,

but configurations are different
in my case where ive cut the plug out if i run the violet as notes then the coaxial of the green will no longer be going to an earth, or is the MSD violet an earth as well i wonder?

I havent heard or seen this mentioned previously in posts,
You can see in the photo where the coaxial veers off to an EARTH fronm the CDI PLUG
Anyone seen this before?

[T77911S]

i have seen some info on the 8 pin CD but thought i would never need it, now i cant remember where i saw it so i am going to ask what may be a dumb question, do you have points?

here is what i am thinking. for magnetic dist output.
even though the "ground" or shield is called ground, it is not really a ground. but, i suppose you could ground the shield and make it work, you would just have to ground the signal at the CD unit.

if you have points, the white wire from the dist goes to the white on the MSD.

if you dont this will get a bit confusing.
for a CCW dist connect the white form the dist to the green on the MSD, not violet. you will have to modify your wiring so that the shield can go to tthe violet and not be grounded.

for CW dist, connect as MSD says. white to violet and the shield to green, but DONT ground the shield.

if you start your car and the timing is extremely advanced, you have the wires from the dist crossed that goto the MSD.

[fredmeister]

Originally Posted by T77911S

i have seen some info on the 8 pin CD but thought i would never need it, now i cant remember where i saw it so i am going to ask what may be a dumb question, do you have points?

here is what i am thinking. for magnetic dist output.
even though the "ground" or shield is called ground, it is not really a ground. but, i suppose you could ground the shield and make it work, you would just have to ground the signal at the CD unit.

if you have points, the white wire from the dist goes to the white on the MSD.

if you dont this will get a bit confusing.
for a CCW dist connect the white form the dist to the green on the MSD, not violet. you will have to modify your wiring so that the shield can go to tthe violet and not be grounded.

for CW dist, connect as MSD says. white to violet and the shield to green, but DONT ground the shield.

if you start your car and the timing is extremely advanced, you have the wires from the dist crossed that goto the MSD.

How much difference in crankshaft degrees does the advance change when reversing the polarity of the green and violet wires? Will the car run at all so you can check the effect if you start at say 10 degrees BTDC one way and then reverse the wires? Just looking for an amount the timing changes.

I read the MSD website says the correct installation for a digital box like the 6AL2 programmable unit is the most advanced timing so this does not agree with your statement above, the way I interpret this means the most advanced timing IS the correct polarity. Its opposite for an analog box though.

thanks,
Fred

[Robbbyg]

Hi i odnt think i have points (Dum answer i know)
Its one area of the car i havent looked into, looking into the top of where the rotor goes it is just a 5 star i think wheel nothing much else,

Ill get to those wires soon and post more info as i find it

[LJ851]

One important thing that happens when you reverse the polarity of the wires going from an electronic distributor to the MSD is that it dramatically affects rotor phasing in relation to the distributor cap. It shifts the trigger point between the leading and trailing edge of the reluctor.

It's enough that my car won't run well at all with the wires one way because the rotor is too far away from the terminal and runs perfect with the rotor dead center on the terminal the other way.

[T77911S]

Originally Posted by LJ851

One important thing that happens when you reverse the polarity of the wires going from an electronic distributor to the MSD is that it dramatically affects rotor phasing in relation to the distributor cap. It shifts the trigger point between the leading and trailing edge of the reluctor.

It's enough that my car won't run well at all with the wires one way because the rotor is too far away from the terminal and runs perfect with the rotor dead center on the terminal the other way.

mine changed a LOT. no numbers and it did run. man did it sound funny. RPM's pretty hi and it sounded very "thin" or tinty.

you cant really think of it as polarity, its more AC power in your house or for those that no electronics, its like a balanced signal.

[T77911S]

here is my output. if you swap the wires, the signal flips top to bottom (not like a book). or bottom to top.
the sharp straight line is what triggers the CD unit to fire.
if you flip it, instead of the the straght liine going from (left to right) bottom to top, the straight line will go (left to right) top to bottom. then the the CD will trigger on the long sloppy curved part. and what the real problem with that is as RPM's go up, the signal increases in amplitude so that slppy part advances the timging.
not good.
i have not checked but i would think CW rotation dist's would not have this problem????

[LJ851]

Originally Posted by T77911S

here is my output. if you swap the wires, the signal flips top to bottom (not like a book). or bottom to top.
the sharp straight line is what triggers the CD unit to fire.
if you flip it, instead of the the straght liine going from (left to right) bottom to top, the straight line will go (left to right) top to bottom. then the the CD will trigger on the long sloppy curved part. and what the real problem with that is as RPM's go up, the signal increases in amplitude so that slppy part advances the timging.
not good.
i have not checked but i would think CW rotation dist's would not have this problem????

Interesting, my distributor is a CW carrera unit. I should look at how mine ended up being wired. I did tune mine on an old Sun distributor machine and i didn't notice any timing creep at higher rpms.