Ferrari Mailing List: Mageti Marelli S159B Distribtuor Advice Needed

[Robert W. Garven Jr. (rgarven]

Friends,

I am having a problem and I hope one of you can help?

I have a 75 GT4, running standard ignition with only the R1 points. I  
had a coil wire come loose and the car ran on 1 bank for about 30  
seconds so I decided to replace my spark plugs. While I was doing that  
I have a Sun Distributor Machine that I have not had much time trying  
to figure out so I decided to test my distributors. The PO had a  
distributor overhaul and whoever it was that did the work hot rodded  
my distributors leaving in only two advance weights for each unit. The  
car always ran very well so I kept it like that, however the two units  
were so out of spec that I decided to replace them with a set of  
rebuilt distributors I got from TR about 5 years ago, thinking that  
this would solve all my problem and I also wanted to see how the car  
would perform with factory specs. I spent two days checking them and  
learning how to use the Sun ( which was pretty easy) and everything  
seemed fine, they were a little off but within factory specs. They  
were rebuilt very well by a well know expert and the points were all  
centered etc. Even though I had marked everything when I took my  
original distributors off I decide to make double sure I put them on  
right and rolled the engine around to the PM 1-4 for the rear unit and  
PM 5-8 for the front one.

This is where I noticed something weird. The rotor lined up sort of to  
the line up mark but not as close as the units i took off? Below is a  
picture. When I bought them they did not come as a matched set as they  
were supposed to all be rebuilt to the same specs, and I assumed that  
the units were identical. I tried to time the engine but both of the  
distributors seemed to be so far off i could only get a glimpse of my  
timing marks when they were at their extreme rotation. The only  
difference between my units and these are mine had a red label and  
these were silver with red lettering, however both say S159B. What is  
weird is the front set needed to be rotated extremely to the left and  
the rear set to the right so next week I will try to switch them. I  
this does not work I will try to move their weights into my original  
distributors.

What my question is are these splined shafts identical for the front  
and rear distributors or are the different, or could the later one  
have a different spline due to a different camshaft variation due to  
emissions? I have spent 3 days on this so if any can lend a hand I  
would appreciate it. I think they are different, am I overlooking  
something???

One other weird thing, I ordered the spline o-rings from several  
Ferrari parts places and all sent me ones that were so wrong they were  
up to an 1/8" off. I ended up using my old ones but they are worn.  
Does anyone know the correct size of that o-ring? I would try to  
source it but I have only really worn or wrong ones. What is funny I  
bought a set of metric o-rings with 50 sizes a while back and none of  
them are the right size!! Go figure

The last pic is of my original advance weights with notations that  
Mike F. here on the list added. What is weird is the car ran so great,  
always started never stumbled revved to redline and just screamed all  
this with 25 degrees of dwell and these weights?????????

Sincerely,

Rob Garven

pics are here

http://www.ferrarichat.com/forum/showthread.php?p=137531139#post137531139