Distributor Malfunctions - loose pickup plate?

[maxm50]

Hi all,
I have never opened a distributor before today, so forgive me if this sounds amateur:

I've had a bit of a rough idle on my 1981 FI Spider that I've been trying to trace down. Today I was checking timing and noticed the following:
- With timing light pickup on wire from coil to distributor, the light flashes very quickly - as would be expected.
- With timing light pickup on wire to #4 cylinder, light flashes at a slower rate most of the time (as expected, probably 1/4 the rate of the wire from coil to distributor), but every so often it flashes VERY quickly again, just like it's on the coil-to-distributor wire! Almost as if every single coil discharge is being transmitted. Sometimes when not flashing quickly, it will skip a flash - almost as if the spark plug didn't fire once. Similar symptoms seen on other cylinders.

Then I took the distributor cap off and noticed that the plate holding the pickup appears to be loose on the shaft. There is a LOT of play. There's no way I could adjust the thing to have 0.5mm clearance as spec'd, because it wiggles around probably 1mm or so. See video here:
https://www.youtube.com/watch?v=T8r9VGaoHu8

I'm not sure if these two problems are related, but I'm guessing so. Can anyone tell me if the pickup plate is supposed to have that much play? Is my distributor missing a bearing/bushing or something? This distributor was supposedly rebuild by the PO's shop before I got the car. Did they forget a part?

And, what do the weird firing symptoms point to? Just a bad distributor? Or should I be investigating the coil and/or control module? I've done the resistance checks for the coil listed in the shop manual, and it checks out OK. Is there any way to check the control module?

Thanks!
Max

[SteinOnkel]

I think your diagnosis is spot-on. I'm not sure about the FI cars, but do they still have vacuum advance? If yes, then some play in the rotor and the plat below the pickup is normal, but only in one direction. And it should still feel snug.

[maxm50]

Hey Steiny,
Yes, it has a vacuum advance in addition to the mechanical centrifugal weight advance. And yeah, the vacuum advance mechanism does cause movement in this plate when the rod actuated, but all the movement shown in the video is “slop” without even actuating the vacuum advance rod.

I see a distributor rebuild kit is about $100 and a whole new distributor is $140... is there any reason to prefer a rebuild vs a new one? Ie is a new one inferior quality? I’d spend the extra $40 to save the rebuild time...

[spider2081]

I see a distributor rebuild kit is about $100 and a whole new distributor is $140... is there any reason to prefer a rebuild vs a new one? Ie is a new one inferior quality? I’d spend the extra $40 to save the rebuild time...

It looks to me like the pick-up coils mounting plate compression swage has broken free of the shaft. A regular distributor rebuild would reuse the shaft/plate assembly. I don't think your distributor can be repaired with this part broken.
A usual repair is to remove the drive gear,replace the oil sear and the 2 bearings for the shaft/plate assembly and replace the drive gear.
The original distributor was manufactured by Magneti Marelli. They are over 35 years old and were of pretty good quality. The new distributors may not be manufactured to the same standard but might be worth consideration. I believe a used part would be needed to repair your distributor along with the usual seal and bearings. So the total cost could exceed the price of the new distributor.

[maxm50]

Excellent - that’s exactly what I needed to know! Thank you. I will order a new distributor and put this one in the ever-growing Retired Parts Bin...

[SteinOnkel]

Hey Steiny,

I see a distributor rebuild kit is about $100 and a whole new distributor is $140... is there any reason to prefer a rebuild vs a new one? Ie is a new one inferior quality? I’d spend the extra $40 to save the rebuild time...

To quote a common vendor "At that price you know exactly where it's built. And let's just say they make 1 million smartphones there, but only a minuscule amount of fiat distributors."

I haven't had any problems with it, but someone on this forum has. I'll let him tell the story but basically it exploded and the vendor replaced it free of charge outside of warranty.

[maxm50]

Gotcha - yeah, I'd expect as much. Unfortunately since it looks like mine won't be fixed with the normal rebuild components, I think a new one is my only option. If it ever blows up on me, I guess I'll source a used Fiat original one and rebuild it then

As an aside, I've worked my entire professional life in overseas (and some domestic) manufacturing, and I've learned that "Made in Texas" can be a LOT worse than "Made in China". There's obviously a huge range of manufacturing quality in ANY country, but the prevalent blanket perception of China as a completely "inferior" manufacturing location is simply about 15-20 years out of date. There is some INCREDIBLE stuff being done there that other countries can't (or won't) even attempt. Of course, there are also plenty of tiny back-alley garages pumping out utter TRASH products. It's quite an interesting and surprising country from a manufacturing perspective.

(Steiny, for the record I realize that you weren't bashing China - I just like talking about this topic, to the utter boredom of some of my friends...)

Interestingly, decades ago "Made in Japan" used to carry the same connotation as "Made in China" does today.

Anyway, I'll go back to waiting for my new distributor...

[SteinOnkel]

Ooooh, let's go back in history a bit. Way back.

The original Made in xxx was actually "Made in Germany" - a very derogatory label placed on German made goods before WWI sold in Britain. It was us flooding the world with cheap, inferior goods much like a lot (but not all) of Asia does today.

As far as electronics goes, well looking around my desk I'm sure that 90% of those items are made in China. And I worry about the failure rate on exactly none of them. All of them see much higher usage rates than any car.

Years ago my family used to own a bunch of Saabs. The 80's trapezoid cars. And they were absolutely bulletproof except for the one component that was made in America; the transmission. All 7 of them died due to transmission woes.

[spider2081]

maxm50 did you happen to see a manufacturer name stamped in the distributor anywhere, It could be me, but the one in the video may not be an original. To me the magnet looks too thick and pick-up coil wire color are routing seem different.
I have seen a couple of the "new" distributor assemblies have a n issue of clearance for the pick up coil bracket and the distributor cap.
Last point is to make sure the the pins are locked in the 2 pin connector correctly. They should not move when the wire is pulled while connector is held.

[tima01864]

I agree on that 2081

[Nut124]

The play on that pickup plate is excessive. There is a sleeve brg or bushing that is worn out at least.

The erratic timing light frequency is not that unusual. The pick-up clamp and the clamp cable can pick up the trigger signal from nearby coil, plug wires pretty easily. Keep the pick up clamp away from other wires and keep the clamp cable away as well.

[maxm50]

Steiny, that's fascinating about Germany! Thanks for sharing. I had no idea. I've done some work in Germany and if I had to pick a country to manufacture in (with cost being no object), man, Germany is it. It's a wonderful country.

Spider2081, it is indeed stamped Magnetti Marelli on the centrifugal advance mechanism. It obviously has a newer cap, rotor, and electronic pickup installed.

Nut124, good to know. After I disassembled the distributor I could find no physically possible way for it to pass "extra" pulses to each spark plug, so I concluded the same - I must have been to close to a neighboring plug. But the "misses" I do believe were true, and were likely caused by this terrible pickup mechanism.

It's actually kind of amazing that this thing even ran at all!

[SteinOnkel]

Could it be that this is some aftermarket pickup? Like pertronix? Which I will go on the record once again as saying is junk, due to things like this.

[geospider]

OK Steiny, I'll jump in.
THEY CAN EXPLODE>

My original was flopping like yours, not quite so bad, but first noticed the seals leaking, so replaced it, with the whole cost idea in mind.
I got a new one from AR. the base plate must have loosened, the rotor then hit the pick ups on the cap and POW.



they replaced it right away, and as Steiny said, they make very few, so quality control just isn't there/

I did buy the seals and bearings and rebuilt the old one and it sits in my trunk, juts in case.

geo

[maxm50]

Wow Geo, that must have made one helluva bang! Thanks for the warning. Glad to hear that AR took care of it even after warranty. I will definitely hang onto my original for rebuildable parts, if it’s not too far gone.

Max