Magneti Marelli S159B Distributor Help Needed

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
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login

 

Hey Rob,

The labels on the bodies look different from the ones on mine (still the same model - S 159 B. See pic below).

Theoretically, the splines should be in the same spot relative to the rest of the advance components of each distributor, but in the real world, this may not be the case and why we all have to rotate the dizzy a bit on the engine to get them on the timing mark. It takes a long time to dial in the IR triggers of my CraneCams so that when the dizzies are on the engine, they both fire on the marks and the bases are even and flush with the mounting flanges. Did the same thing in the beginning when I ran points. Lots of fiddling around though.

Are you sure you have everything marked properly and lined up when you put the dizzies back on the engine? One tooth of the spline makes a huge difference in timing. I've made that mistake before.

I bought two new dizzys because the ones on mine were so worn out, there was no more I could do to them to bring them back into spec. Thankfully, I got them just when our Canadian dollar was at it's peak value late last year, so the four-figure price tag wasn't such a blow to my wallet!
Image Unavailable, Please Login

 

If this is the case, move the rotor by 1 spline as Peter suggested (although you'll have to figure out which way). I can't recall how many splines there are (would someone please post the number of splines), but my recollection is that they made the adjustment slots large enough such that (if the distributor is properly set-up -- i.e., the point set opens when the rotor arm is pointing at the red notch) you can always get it to work properly (even if the distributor housing outline does not wind up well-aligned with the cam cover shape) -- i.e. the phase of the splines relative to the cam lobes can be anything, and you should be able to get it to work.

IMO, you should be able to set/confirm things manually to just a few degrees of error before even running the engine (and I'm assuming that you are still running an R1 points only set-up in your "new" distributors?):

1. (On the unmounted 1-4 distributor) Confirm that the R1 point set opens when the rotor arm is roughly pointing at the red notch (just using an ohmmeter measuring between the R1 electrical post and the dist housing should be good enough).

2. With the engine at ~7 deg BTDC from PM1-4 and the #1 cyl ready to fire (i.e., at the end of the compression stroke) -- Mount the distributor with the rotor arm still pointing at the red notch.

3. Rotate the dist housing to the position where again the R1 point set is just opening up -- tighten down the housing and fire it up.

Same for the 5-8 side except for step 2 rotate the crankshaft 90 deg (in the direction of normal rotation) to the ~7 deg BTDC from PM 5-8 and the #5 cyl ready to fire.

Right now either something is wrong with step 1 (i.e., the distributor really isn't set-up correctly) or step 2 (you're off a spline) -- Good Hunting!

 

Robert I seen your PM, sorry I didnt comment sooner.

As Steve was eluding, you more than likely have the points plate advanced or retarded in relationship to the rotor and its relationship to the distributor housing. Remember that the points assembly is slotted on its mounting screws, and can be "phased" to be in proper placement as the rotor swings past the tower inside the cap. Its takes a bit of fiddling to get it to the right setting, and once you do, make note of where the points plate sits in relation to the position of the rotor. IIRC, the rotor is just starting to go past the red alignment mark as the points break. Moving the points plate either direction will force you to rotate the body the same direction to place it in proper idle speed timing location. If you study pictures in the Bluemel book, you will notice many of the cars distributors are centered in thier adjustment slots so that the countour matches the cam cover, and thats what I believe we should strive for as the standard for setting.

 

I'm sorry guys, its been a few years since I did this.... It looks like I should have the engine pointer pointing at the 7 degree yellow and whit mark above when I mount the distributors, right? I ahve a few more questions.

The small sleeve on my org distributors broke, that is the one that rides the shaft and the advance weights rest against. On the newer ones tit is rubber and 2mm on my hot rodded org ones they were 14mm ID and 1mm thick. and some kind of black plastic that broke when I tried to remove one from age i think. What does this thinner bushing do? Allow the engine to idle at a lower advance?

I am running the one R1 points but I had the two condensers do you need tow condensers for once set and does the other 2 wire condenser that hooks up to the R1 point contact help the primary condenser? Also one condenser measured .25 micro fareds and one measured .34 which is better a higher or lower readings the condensers have 25mf on them???

Thanks again for all your help

Rob

 

Yes, you want the flywheel set on the idle speed ignition setting point to set initial static base timing.

The sleeve your refering to is used to keep total distributor advance to about 13 degrees IIRC. I assume its on the shaft instead of around the outside of the shell to keep the cam centered with where the points base needs to be?

You only need one condensor per points set, and the .25 mfd sounds correct for stock points and coils. If the condensor mfd rating is not correct you will have metal transfer on the points contact surfaces one way or the other.

Remember that maximum ignition advance is far above 5000 engine rpm. On the early carb cars its 3400 dist rpm/6800 engine rpm. After you set your advance curve on your machine correctly by shimming the springs etc., make sure that you adjust your ignition timing at 5000 rpm at the 5000 rpm flywheel timing mark. Idle speed timing should never take precedence over high speed timing. Correct your idle speed timing on your distributor machine if its out to far.

Those are very pretty distributors by the way.

 

Thanks for all your replies. I have some new info. I compared the original rear unit I took off and the rebuilt one I replaced it with when placed in the exact same mounting location on my distributor machine with both only running R1 points in the same location and both points plates centered and the rebuilt unit has a strobe arrow 39 degrees clockwise. What would cause this???? I think this is part of my problem??? I am pretty sure my other original unit had the strobe arrow in the same place. I assume this has to do with the cam to point relation but 39 degrees???

I just bought what I think are the last two NOS distributors in the country we will see what they are like when they show up. I will now have 8 units:

2 with worn cups, missing half the advance pins, and I broke the 1 mm thick plastic shaft bushing upon disassembly..........
2 rebuilt that I need to look at further
2 brand new units but they wont fit my car because they have the original GT4 dog drive, so the shafts and cups new but are useless to me (I heard they fit all the V12 units???) but I have all their new advance parts, they have some weird fiber advance weight bushings that ride in the cam assembly?
2 new single point japan versions coming........

So i will have 8 distributors and if I cant get the car running Ill get this years Darwin award!!

 

Does this mean that you controlled both 1) how the housings are mounted to the stationary base (the easy part), and 2) how the rotor shaft is mounted to the rotating drive shaft (maybe not so easy?).

Otherwise, have you compared things like:

Is the angular relationship between the rotor arm and the square cam shape the same on all distributors?

or

Is the angular relationship between the mounting holes for the R1 points and the housing the same on all?

As Paul mentioned, the slots in the R1 base allow some adjustability, but a 39 deg difference is a lot, and it should be quite noticeable if one distributor has its R1 point shifted one direction (relative to the mounting holes) and the other distributor has its R1 point shifted the other way.

Just some thoughts -- keep chewing -- you've got no other choice

(Although I don't see the need for buying yet another set of distributors. You've got the machine -- did you try just resetting the rebuilt unit to where it should be? -- i.e., rotor pointing at red notch when R1 points open -- or did you run out of the slot adjustment?)

 

both were mounted the exact same way and both points were exactly centered. On the sun machine i have a Ferrari spline adapter and no matter how you mount the rotor the strobe is always in the same place on the same unit. I am not sure what is going on, but I am chewing! I think I am going to see what the new ones are like then decide what to do. They japan only units have a new set of R1 points, new rotors and caps and supposedly NOS, supposedly the last set. I cant afford gold so I am buying up the S 159 market. My goal is to get 2 working sets and either part out or make a kinetic sculpture of the rest!

The dog drive one has a threaded shaft so maybe I can rig up an adapter and try that also to see what the curve is etc....

Rob

 

Robert, is it possible you have the R1 and R2 points positions confused? The R2 points are not 180 degrees opposed from R1, but are something like 176.5 or 183.5 ( I cant recall) from the R1, to retard 7 degrees crankshaft when the throttle switch is activated. If you run off the R2 points your rotor would point 3.5 degrees off with the points bases centered in there attachments. You should be able to swing the distributor on your machine by hand, and note the opening and closing points and the relative position of the rotor. The only real reason to have it spin up to speed is to check the advance rate.

 

So that's what they told you? Wow...

 

You do know that on your Sun machine you can rotate the degree dial to any position you choose?

 

Yes the sun machine dial rotates but when I put on the original dist. the dial at 0/360 and arrows stay the same no matter how you put it on. On the rebuilt unit the arrows (there are four for each lobe) are 39 degrees rotated clockwise and you have to rotate the degree bezel around for the new set of arrows. I just found this odd. I am pretty sure that my other dist. apart and broke (plastic bushing between shaft and weights) arrow was in the same exact place. I cannot work on the car today so I am just waiting for the other units to arrive and will get back to you all. Paul, the R1 points are clearly marked and the points plate has a short wire and i mounted the dist the exact same way, I am sure of this. Peter, yes that is what they said although he said he would try to get more but not sure if there were any more left. Steve I think it has to do with the relationship of the cam lobes to the points, but not sure how it can be that far off but thanks again for everyones comments!

Rob

 

Just an FYI for everyone trying to figure these cars out. On many other points ignition cars with mechanical advance mechanisms contained within the distributor, the rotor shaft is a seperate part from the drive shaft. On most cars you can grab the rotor and physically rotate it against the advance springs.

The Marelli unit does not work that way, the rotor shaft "IS" the drive shaft, and the rotor is directly connected to the camshaft, its all one piece. But the points cam is NOT part of the shaft, but is bushed onto it and can freely rotate around it, except being held by and controlled by the advance weights opening and closing via centrifugal force. As speed increases, force opens the advance, etc..The pins the weights attach to, the weights themselves and the points cam, are daubed with paint so they can be reassembled to original factory position. I dont believe rotating the cam 180 degrees, or swapping weights around could reposition the cam angles enough to matter, I believe the markings are simply to be able to re-match the original weighting and advance curve, and I mention it only as a possibilty and to help to explain how it works. I'll go take a look at a cam and see if would matter, but im sure it wont. I also counted my splines at 22 splines, so no matter if you installed the unit 180 degrees off you would still be centered.

There is really only one way to assemble the unit, and the only real adjustments once its assembled are the physical placement of the points within its very limited range of mounting position, and the placement of the distributor body to the cylinder head within the adjustment slots and the spline position in the camshaft in direct relation to the flywheel marks. That is "if" its assembled correctly. There are on some cars a bushing that the advance weights rest against that position the advance weights slightly outward for idle base timing. Altering its thickness or removing it will change the cams position relative to the ignition points in the low speed idle position. No bushing would retard the timing, and vice versa.

If the distributor is assembled correctly, and if the points are in the correct position with the correct dwell, then the distributor should sit against the head centered in its slots and aligned almost perfectly with the cam cover, not swung to the extremes of its range. If the points are swung to the limit of thier slotting, and you cannot achieve correct dwell AND be able to place the distributor against the head without it being rotated extremely one way or the other to time the ignition properly, I would inspect the inner bushing the advance weights rest against. If that is the case then as Steve suggested, something is wrong.

 

I can kind-of get a picture of what you're saying with that above statement and in my mind, I see that maybe your R1 points are accidentally mounted in the area of the distributor where the R2 points would normally reside, thus, throwing off the timing by that much (?...).

My Allen machine works in the same manner, the arrow fires with each dizzy firing and that would make four arrow points on that timing disc (see pic below). So what you're saying is that when you chuck the rebuilt dizzy onto your machine, all four of those arrow points are 39 degrees off from when the first dizzy was on there?

(Note: the pic is a bit out of focus and shaky because I had to take it without the camera flash. Previous attempts with the flash drowned-out the lights in the arrow points...)
Image Unavailable, Please Login

 

Peter, I assume that your degree scale is moveable also? It looks like it rotates to any position much like mine does, and I assume the Sun units do the same?

Robert, the picture above shows advance weights that are missing two of the four springs and pins. If there is not enough spring tension on the weights, they will fly out to full advance at very low rpm, perhaps far below 500 (dist., rpm). Try physically locking the weights in thier inner, low rpm idle speed position, and try running it again. Also, it may be possible that with pins missing, the weights could fly out farther than they otherwise would causing greater advance, so try testing it with the weights locked fully out. I looked at a points cam and it appears to be symetrical, so I dont believe assembling it one way or other would make any difference in timing position.

The OWM shows the R2 points 185 +/- 30' degrees opposed from R1. So even mistakenly running the points at position R2 instead of R1, would only shift your timing position 5 degrees. If you are truly seeing 39 degrees difference, I would definetly lock the weights in both the fully in and fully out positions and check it on your machine. You only need turn the machine on and rotate it by hand to observe the firing points by the strobe. Maximum advance from low to high should only be 13 degrees. IOW, block the weights closed, rotate by hand with test machine on to observe firing points and place dial at zero degrees to the strobe. Then lock weights fully open and repeat. The firing points should advance 13 degrees on the dial. Or whatever advance curve for your particular engine your looking at (or creating). Always remember that the distributor turns half engine speed, so that 13 +/-1 degrees at 3400, is actually 26 +/-2 degrees crankshaft at 6800 engine rpm.

 

Yes, it does rotate to any position.

 

Dear Friends,

First to answer above questions the R1 points are all in the right place, and the two pin pic above is just for reference as they were my original units and they had advance curves
pretty radical but the car ran exceptional with them like that, so i could not figure out if the guy that did it was a genius or just missing parts. My goal was is to see if there is a performance
improvement by running units with the factory specs. My car seems to out accelerate and perform as well or better than other 308's I've compared it to. New info below:

As you all know I am working on my distributors trying to get my car to run the best it can. With a Tip from Peter I found apparently one of the last sets of NOS Magneti Marelli 159 C
distributors meant for the japanese 308. I have 8 distributors now and still at a loss to figure out what to do so i thought i would update you guys top get some advice. I took off my original
distributors and checked them on my Sun machine. Even thought the car ran exceptional I was amazed at how far they were off, 25 degrees dwell and two erratic advance curves. The previous
mechanic hot rodded the original S 159 B red label units with only 2 advance weights. I bought a set of rebuilt distributors but could not get them to run on my car so I bought these units. I was
very happy at their condition and price and since I am running R1 points only I thought WOW. I took them apart to day to clean and re-grease them and found that they only had 3 advance weights
in the first unit I disassembled! I measured and photographed the parts for my files, re-greased them with Bosch distributor grease and put them back together.

I called Peter as he also has a set of the "C" units and we talked about the advance weights and I thought that since the Japanese units had the R1 points only maybe they were designed to optimize
performance over emission standards. I could not check the advance curves as I have a friend making me a new adapter for my Sun machine from a stock distributor mount. While talking to Peter he
mentioned that the "C" units had a radically different cam profile. When I compared the "C" unit and my original "B" unit the difference is striking! I cannot figure out why the different cam profile as all
it would seem to determine is dwell and that is controlled also by the eccentric point plate screw. I am confused and thought I might post these pics and you all could comment or make suggestions.
While I think this over I am going to mount my original units in their original settings because the car ran so great and since I have been running it for 14 years like this with no apparent ill effects, I will
ponder what to do next or a Steve said chew on it, however I already have a mouthful!!

I also have a set of NOS S 159 "A" units which were originally "B" units but switched by the factory and marked "A" now, they have a complete set of advance weights and the rounder cam so I may drop
their advance weights and cam into either my original units or in the cups of these new "C" units. I have not measured the shafts but assume they are the same. The "A" units have a dog drive for the early
308 GT4 models. If you are confused now so am I........

Here are my distributors:

set 1: S 159 B red label (original units with only 2 advance pins, running only R1)

set 2: S 159 A silver label (NOS with dog instead of spline drive shafts, 4 advance pins/unit and fiber cam bushings (?) No points plates or fittings)

set 3: S 159 B silver label (rebuilt from TR could not get them to run on my car, not sure why however I think I can if I move the points plates to the extreme one side, R1 & R2, with R2 removed)

set 4: S 159 C red label (NOS for japan model, only 3 advance pins, radically different cam profile (squarer), only 1 set of R1 points, otherwise look exactly like "B" model with new caps and points) What is weird about these units I do not find them in my 74, 76 or 79 parts book?????



I am determined to figure this out and maybe shed some light onto this subject!

Sincerely,

Rob
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login

 

I notice in those pictures that between the two cams, the squarer one seems rotated more to the right. Maybe its an illusion?

 

I think it is an illusion it was hard to get a pic comparing them. Why would the cam profiles be so different and what would this mean or accomplish. It seems that it would wear the follower out quicker.....???
I spent all day putting my original set re-greased and back together. I measured all the shafts etc and all are the same except for the cam??????? The only thing I changed was the small bushing that was plastic an 1.00mm on the shaft that the weights rest against. It was cracked and broke when I tried to remove it. I replaced it with a 1.75mm rubber one that was the same as the on other 3 sets?? What difference will this make, advance more at idle? Reduce the overall advance curve?
Image Unavailable, Please Login

 

I was refering to was the "indexing" of the high points of the two cams relative to their arms. The one on the right (with the more squarish cam shape) seems more rotated to the right (clockwise). This would make it open the points in a more retarded or advanced condition, depending on distributor rotation.

As to the inner bushing, it would achieve the same effect. You would generally have your dwell set to factory specs with the points slid up or down to phase the opening point of the points to the rotor pointing at the red mark. As we know that moving the points up and down will move the mark, so will a larger or smaller inner bushing that the weights fall against.

 

I received this reply from a well known Ferrari mechanic that I think rebuilt my TR distributors. It asks more questions that its answers:

The S159C with square cam lobes is for European single distributors. the idea is to be able to fit both 1-4 & 5-8 points into one 4-lobe cam. Some Japanese markets used this distributor. It also uses a different upper shaft and rotor, and an 10- wire cap for both coils. It is possible to install the "square cam" on other distriburor shafts, like comp. Alfa Romeo twin plug engines, or any other Marelli similar distributor. Please note that all of your distributors have twin weights, but may use only two or more pin/springs as required to have the optimum advance curve. Changing the spring/pin combinations is how you can set your curve, obviosly you must have a supply of different rate springs and shims to accomplish this.

First of all the US versions had two sets of points so I assumed that a standard S159B would work on the euro 10 wire cap with the proper points and round cam. Second the "C" unit I have from japan has only one set of points with the radical square profile. Why? and what difference would it make in performance? My "C" unit have the exact same shaft and rotor as the US model the only difference being the one set of points and different cam???

Rob

 

I modified one of my distributors to run both banks coils. Basically I took a dual distributor and converted it to a single (in operation), by relocating the other set of points. By the sounds of it you have a standard single distributor that someone removed one set of points from and your attempting to use it as a dual distributor.

And not to confuse anyone, most (but not all) US cars run dual distributors, most (but not all) euros run a single distributor, though primarily because the oil resirvoir for dry sump cars leaves no space. The duals operate like a 4 cylinder distributor, and thats basically what they are. The single has a dual plane rotor, two sets of points (one for each bank), and two planes of 4 plug wires. Its basically two four cylinder distributors combined into a single unit with an 8 plug wire cap and two coil wires.

The points cam shape, or profile, would effect dwell based on points gap. Given the same points gap, the squarer shaped cam would provide more dwell period (time the points are closed) against the rounder shaped cam. With the square cam you would have to set the points gap wider to achieve the same dwell period as the rounded cam. All things being equal I think the squarer cam would induce wear more aggressively if you tried to maintain proper dwell.

 

I ended up putting my old distributors on but with the new thicker shaft bushing the advance was messed with and I had a hard time getting the distributors to line up. I ended up having them at the extreme of their mounting position and moving 1 spline over was the same just in the opposite direction? I am going to experiment with my new distributors. No one has responded on what the funky square cam profile would accomplish. I will post more pics and info here is a funny pic of the different o-rings that i have bought several are like about 1/8" too big. I ended up using a standard one from my local (Great) hardware store. Although not the same it is a little thicker and a little smaller but way closer than the supposedly real part!!!

here is another question. There are two completely different advance curves in the GT4 WSM. Which is correct??????? And which would yield the best performance?
Thanks again for all your help.


Rob
still confused
Image Unavailable, Please Login
Image Unavailable, Please Login
Image Unavailable, Please Login

 

Those straight-line advance curves from the 308GT4 WSM Section L are for the S159A distributor operating with a static R1 advance of 16 deg BTDC (see the specs given in the first pages of section L). The bent advance curves from Section O are for the S159B distributor operating with a static R1 advance of 6 deg BTDC. If you calculate the total advance at 5000 RPM you'll see that it is about equal (i.e., on the S159B system they reduced the advance in low RPM range relative to the S159A system).

My guess on those cam lobe shape changes would be that it was just the natural evolution to an improved design as the manufacturing (grinding) equipment got better (although that doesn't explain why they changed the relative angles). The round-looking one is the easier one to make where you start with a round shaft and grind on some flats (note that the centers of the curved areas on the corners coincide with the center of the shaft); however, this has some downsides:

1. Where the flat meets the curve there is a slight discontinuity (which they try to post-polish out a bit), and

2. to keep this discontinuity to a minimum, the depth of the flat is kept to the minimum, but this results in a more "sluggish" opening/closing action for the points.

The square shaped cam lobe on the S159C has no discontinuity at the junctions between the flats and the curves (note that the center of the curves on the corners are not coincident with the center of the shaft). Consequently, the flats can be deeper, and this "sharpens" the opening/closing action of the points (which helps with things like the timing not changing so much with wear).

You've confirmed that the F engineers were smart enough to make sure that the adjustment range covered an angle slightly greater than 1-spline , but I still don't see why you are having so much trouble. You've got all the bits and the Sun machine -- just make it happen as it should on the bench (rotor points at red mark when R1 point opens) and mount it on the engine the same way with #1 cyl ready to fire, and (operationally) it doesn't matter if you are centered in the slots or not.