Ferrari Mailing List: Re: Mageti Marelli S159B Distribtuor Advice Needed

[robert_h_bowser [at] juno.com (robert_h_bowser]

Robert -

I'm doing this from memory...but....

Does sound like the camshaft/rotor connection is off one spline.  If I remember 
correctly, the rotors in both dizzys normally rotate clockwise (CW).  For the 
dizzy casing that is rotated all the way to the left (i.e., counter clockwise - 
CCW), pull the dizzy out until the rotor shaft is just beyond the splines, 
rotate it slightly CCW, then re-insert into the camshaft.  For the dizzy that 
is rotated all the way clockwise (CW), pull it out and rotate the rotor 
slightly CW, then re-insert.  Retime both dizzys.  

Perhaps you already are aware, but the Ferrari dizzys are a bit different in a 
couple of ways.  One, the timing adjustment available by rotating the dizzy is 
only about ten degrees.  If you need more, you have to pull out the dizzy, 
rotate the rotor one way or the other, and re-insert.  Two, the advance 
mechanism does not act on the rotor at all.  All it does is advance the dizzy 
cam.  So the rotor has a large area facing the distributor cap contacts.  When 
static timing using the firing marks on the flywheel, the rotor will not be 
pointing directly at the cap contact.  It will appear to be pointed a bit 
beyond the contact.  The spark will jump from the trailing edge of the rotor 
face.  On full advance, the spark will jump from the leading edge of the rotor. 
 The rotor has to be positioned to cover the full range of timing, from no 
advance to full advance.

I assume you have already done a check to make sure the cam/points plate is set 
up properly with respect to the rotor position.  When the points open (e.g., 
check with an ohm meter), the trailing edge of the rotor should cover the 
distributor cap contact.

The dizzys do use standard metric o-rings.  I just measured the id of the 
groove using calipers and bought some of various thicknesses until I got the 
right size.  I checked my record book, but evidently I didn't record that info.

Hope that helps.

Bob
'78 308GTS
'01 Corvette Z06

-- "Robert W. Garven Jr." <rgarven [at] gmail.com> wrote:
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
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