Seized distributor

Arachnd

Daily Driver
Hi all,

Back in the late '70s I put a Marelli S118 in either my '70 or '72 850 Spider. I understand that they were used in the 843cc engine, but I liked the accessibility and simplicity of the design. It seemed to work fine.

I now have a different '72, and I found an S118, and had it very nicely rebuilt. I dropped it in and it started up fine. Within a mile and a half the shaft had seized in the body. (Amazingly, the drive gear pin sheared and the cam screwed it right down the shaft and out of mesh - nothing broke!)

Has anybody experienced something like this? Is there something about lubricating the distributor shaft that I needed to do? I'm actually a little mystified about how it does get oil when running.

Any thoughts appreciated - thanks!

Kelly
 
Hi - I had two seize in one engine, there was galling between the shaft and the case. I never figured out why (ended up replacing the engine block during a rebuild). I contacted Jeff Schlemmer Advanced Distributors in Michigan (easy to find with Google), and he rebuilt one for me using long oil-impregnated bushings. Runs like a top now. Not sure if that helps at all, best, Loren
 
Pin failure isn't common but is one of the weak points of this engine. Abarth at one time made a machined ONE piece unit-gear and shaft from billet. Scuderia Topolino in Germany (and others) sell front camshaft bearings with a small oil line outlet which shoots oil on the gear. A regular front bushing can be altered to accomplish this. Another method is to braze/weld the gear to the shaft taking care not to cook the gear teeth.
 
Thanks Frank! In this case I was glad that the pin did shear, and protected the cam teeth or something else awful from breaking when the distributor seized. The gear seemed oily when I took it out - but I don't really get how oil is supposed to reach the distributor shaft inside its body.

For amusement, here's my shaft compared to another used one.
 

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I had a brand new electronic dist from Germany seize and the drive gear pin did not shear. Loud bang, the engine quit and the cam gear pin sheared. Scuderia sent me a new one but what a pain. never had a stock setup seize
 
The strong downward force on the pump-distributor shaft during the seize & gear-displacement event made that pump rotor cut a nice shiny gouge in the lower plate of the oil pump. I faced most of it off with 180-grit sandpaper on a good plate.
 

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I discovered, while perusing the Midwest Bayless site, that the shaft that drives the oil pump and distributor came in 2 different lengths. The one for the early cars is 4mm shorter. As far as I can tell, that Marelli S118 was supplied on the early cars. If I dropped the S118 into the car on top of the later shaft, is there any chance that the inside of its drive spline was bottoming out against the top of the later drive shaft?
 
If I recall correctly, the oil pump/distribotor drive shaft is longer on the 903 engine to compensate for a thicker head. I have used S118, S140 and S156 distributors interchangeably on my 903 engine with no obvious problems (the advance curves for each were adjusted to match the engine rebuild). I posed a somewhat related question on this forum when I was dealing with an oil leak at the hold-down clamp and learned that the weight of the distributor shaft is supported by the oil pump/distributor drive shaft. Based on that I just make sure that the distributor shaft is resting on the drive shaft and that there is some up/down play left when it is tightened down (there is some play between the advance mechanism and shaft as well, so I need to look closely to make sure that there is play at the oil pump/distribitoed drive shaft and the distributor). Hope that makes sense, as I am 1.5 beers past dinner :). Best, Loren
 
Indeed, this particular S118 was not compatible with the later shaft. The spacer got pushed up against the bottom bushing so hard it started melting the brass and bonded it to the shaft. Next time I put it on I'll observe vertical end play closely and install some shimming between the distributor body and the head if needed.

Jeff Schlemmer at Advanced Distributors, who had rebuilt it for me, very kindly got it diagnosed and unstuck at no charge. He's been great to work with, both for the original rebuild and this problem.
 
Here's the smoking gun. If only I had looked at this when I put the distributor in the first time. It's sitting in place, with the distributor shaft resting on the oil pump drive shaft, and there's a .011 gap between the head and the base of the distributor. I need to get a spacer made that's .011 thick plus a little more to allow for the right amount of end float.

Now my main hypothesis is that the head was shaved somewhere along the line, and the S118 just doesn't have enough vertical elbow room to get away with a direct swap. The total vertical movement of its shaft in the distributor body is .023 . The same measurement in the Ducellier that came off is .068.
 

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I bet that would work, if I took off the same amount as the planned spacer. It seems like there would be plenty of spline left for good enough operation. But I'm kinda hoping not to have to drop the oil pan a third time. :-/
 
I meant the oil slinger on the distributor - the plastic unit that is held onto the distributor shaft with a roll pin....
 
This Marelli just has a collar on the shaft below the body. But it does seem like shaving that down would work. It would certainly be an easier machining task (which I have to mooch). I'll have to see what Jeff thinks.
 

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Unless I am mistaken, the oil slinger is the lowest structure on the shaft in your picture. I am suggesting to trim at the arrow. You would just need to drive out the roll pin with a drift and sand the slinger...
 

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Unless I am mistaken, the oil slinger is the lowest structure on the shaft in your picture. I am suggesting to trim at the arrow. You would just need to drive out the roll pin with a drift and sand the slinger...
Looks different than mine. Mine looks like this:
 
Thanks, Loren, that seems like a very direct fix.

The Ducellier distributor that came out of the car has that tapered plastic skirt. Above that are two thin steel rings with a thin ring of something else between then. The drawing in the Haynes manual shows this skirt too, even on what appears to be an S118. (The parts breakdown calls it a "collar.")

The large OD of the tapered skirt is .864 , the OD of the collar on the Marelli is .746 . Does anyone have any idea of any difference in effectiveness between these two? I don't completely understand what's supposed to happen there - does the skirt keep oil from splashing up into the distributor?

I can get a skirt from Australia on eBay for $40 - https://www.ebay.com/itm/333596897400 . Wonder if I should do that and then analyze all the clearances again.
 

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