Technical Fiat 124 Electronic distributor

[malcolmbird]

Hi All,

New guy here. Has anyone rebuilt a Fiat distributor before? or have any instructions on how to do it...?

I don't think my centrifugal advance is working. It seems to be seized in the advanced position.

Thanks - Malcolm

 

[F123C]

Welcome to FiatForum!

I'm familiar with the points type distributor but not with the electronic type. But afaik:-

The centrifugal advance unit is inside the distributor body under the plate carrying the magnetic? pick-ups. To remove the advance unit, use a pin punch to drive out the roll pin holding the drive gear onto the distributor shaft and withdraw the shaft and advance unit. Alternatively, you might be able to free off the sticking advance unit in situ using a penetrating oil spray.

What makes you think that your advance unit is seized in the fully advanced position? You do know that the ignition timing is automatically advanced to about 10*btdc by one of the magnetic pick-ups for cold starts and reverts to normal timing when the engine reaches c. 50F?

Hth,

Al.

 

[malcolmbird]

Hi Al,

Thanks for the reply.

I think the advance plate is seized because you cannot turn it agains the springs. Also, the counterweights are loose and not under any tension from the springs.

regards - Malcolm

 

[varesecrazy]

Hi All,

New guy here. Has anyone rebuilt a Fiat distributor before? or have any instructions on how to do it...?

I don't think my centrifugal advance is working. It seems to be seized in the advanced position.

Thanks - Malcolm

maybe this post, and similar - in the classic spider section will be of help,
https://www.fiatforum.com/spider/439505-pertronix-ignition-77-spider.html

Charlie

 

[F123C]

Hi Al,

Thanks for the reply.

I think the advance plate is seized because you cannot turn it agains the springs. Also, the counterweights are loose and not under any tension from the springs.

regards - Malcolm

I'm wondering if the advance unit was previously dismantled and not correctly re-assembled. Iirc it may? be possible to do this and end up with the above symptoms.

In my experience, advance units usually seize up in the fully retarded position, especially if the vehicle has been laid-up.

If you have a timing light, you can easily check if the advance unit is working by watching the timing mark move as you rev up the engine.

I don't know if you've ever worked on car ignition distributors before but just so you know :- The advance unit springs are usually different strengths/lengths. The stronger spring will appear too long and loose on the mounting pins. This is normal, do not tighten the spring ends/loops to eradicate this. It's necessary to give an advance curve instead of a straightline advance in the ignition timing. The lighter spring controls the initial amount of advance, then the stronger/longer spring comes into play slowing down the rate of advance, resulting in a curved advance when plotted as a graph.

I still think you might be able to check/free out the advance unit with the distributor in situ on the engine.

Al.

 

[malcolmbird]

Hi Al,

It's as if the weights where thrown out to their max extension by high rpm and then jammed there.

But there is another reason i'm going to take it apart. I have am intermittent 'squeal' coming from the vicinity of the distributor - typically above 3000rpm - t's hard to pinpoint, but it sounds like a dry bearing. Each time these squeals happen, the tach needle jumps about 1500-2000rpm.

So hopefully 3 birds with one stone....

Malcolm

 

[malcolmbird]

Hi All,

Well, I took the bus by the horns and pulled the distributor and took it apart. Despite the teeth gnashing, it was pretty straightforward. Getting the drive pin out was the trickiest.

What I found was that the upper bearing was in the process of disintegrating and the lower one was partially seized. The centrifugal advance plate was seized on the distributor shaft, so I had no centrifugal advance.

Everything went back together so this will hopefully cure the intermittent squealing and attendant tachometer bouncing. Not to mention that it's no going to explode on me at any moment and do god knows what damage in the process..

So if you have noisy bearings, or fluttering tach needle - check your bearings. As it turns out, it's a cheap and easy fix.

 

[Charlie124]

On a tangent to this discussion, is there an easy way to tell if the ignition advance is working? I just got a '77 124, and it runs pretty rough for at least 5 minutes, and eventually runs pretty good. By rough I mean hesitation when trying accelerate and an occasional mis-fire.

 

[F123C]

The only way I can think of to check if the ignition timing is being advanced is to connect up a Timing Light (Lamp) and watch the timing marks on the crankshaft front pulley and timing belt cover move further apart as you increase the engine speed from idle to about 3000 rpm (or whichever engine speed corresponds to full ignition advance).

As regards your engine running roughly etc. for the 1st 5 minutes and then smoothing out?

I'm assuming because of the age of your car that it's running on a carb.
In which case, I'd check out the choke operation. You are using the choke when starting from cold? Also there's a mechanism built into the carb to pull off some choke as the throttle is opened, to prevent over-choking. With the air cleaner removed and engine stopped, pull out the choke knob (down beside the steering column, near the ignition switch?), look into the carb top, the choke flap should be fully closed. Push on the flap, it should be possible to partly open the choke flap (against light spring pressure).

Start the engine, depending on temperature, you may need to back off the choke a bit as soon as the engine starts (you don't need full choke unless it's freezing). Try operating the throttle or have someone press the accelerator pedal. As the engine is revved-up, the choke flap should partly open (as described above).

Try the above, if relevant and report back.

I don't think there's much that could be wrong with your ignition system, given that your engine runs well when it's warmed up. So I'd leave it alone for the moment and concentrate on the carb and choke first.

If you do decide to investigate the ignition system, check out my post above re:- the two sets of contact breaker points inside the distributor (unless you have electronic ignition) which alter the ignition timing depending on engine temperature. Might be related to your poor cold running? if the cold start c/b points were dirty/burnt/ incorrectly adjusted etc.

One word of caution. When removing the air cleaner body (not the top lid/cover), it's all too easy to drop one on the 8mm nuts (5mm thread) down the carb venturis. If the throttle is then opened, the nut can find it's way into one of the engine cylinders. (the nut can't get past the carb butterfly valves until the throttle is opened). So account for all 4 nuts!

Al.

 

[F123C]

On a tangent to this discussion, is there an easy way to tell if the ignition advance is working? I just got a '77 124, and it runs pretty rough for at least 5 minutes, and eventually runs pretty good. By rough I mean hesitation when trying accelerate and an occasional mis-fire.

Just had another thought re engine running rough for 5 minutes then running ok.

Some Fiats had an adjustable air intake on the air cleaner so that hot air was drawn in in winter and cold air in summer, this was in the days before thermostatically controlled air intakes became commonplace. Your Spider being a '77 might have the old system.

Fiat used 2 types of air cleaner adjustment depending on model.

Iirc on the twin cams the air cleaner intake spout was spring located and could be swivelled to pointing towards the front on the car (cold air setting for warm weather use) or swivelled to pointing down towards the exhaust manifold (hot air setting for cold weather use.

On other Fiats, the air cleaner adjustment for hot or cold weather use was inside the air cleaner. It consisted of a blanking-off section attached to the lid of the air cleaner. This lid could be fitted in 3? ways. In one position, hot air was drawn into the engine, 2nd position, cold air drawn, 3rd position hot and cold air drawn in. There are alignment marks stamped into the lid and body of the air cleaner. An arrow and iirc an I for winter (It. inverno?) and E for summer (It. estate?). This info used to be in all the owner's handbooks.

Running a Fiat in cold weather with the air cleaner set to summer (cold air) can give exactly the poor running problems you're having for the first 5 minutes.

Hth,

Al.

 

[g8rpi]

Just had another thought re engine running rough for 5 minutes then running ok.

Some Fiats had an adjustable air intake on the air cleaner so that hot air was drawn in in winter and cold air in summer, this was in the days before thermostatically controlled air intakes became commonplace. Your Spider being a '77 might have the old system.

Fiat used 2 types of air cleaner adjustment depending on model.

Iirc on the twin cams the air cleaner intake spout was spring located and could be swivelled to pointing towards the front on the car (cold air setting for warm weather use) or swivelled to pointing down towards the exhaust manifold (hot air setting for cold weather use.

On other Fiats, the air cleaner adjustment for hot or cold weather use was inside the air cleaner. It consisted of a blanking-off section attached to the lid of the air cleaner. This lid could be fitted in 3? ways. In one position, hot air was drawn into the engine, 2nd position, cold air drawn, 3rd position hot and cold air drawn in. There are alignment marks stamped into the lid and body of the air cleaner. An arrow and iirc an I for winter (It. inverno?) and E for summer (It. estate?). This info used to be in all the owner's handbooks.

Running a Fiat in cold weather with the air cleaner set to summer (cold air) can give exactly the poor running problems you're having for the first 5 minutes.

Hth,

Al.

Hi,
Interesting thought, but as the engine is cold, the intake position won't make any difference for the first five minutes. The warm air intake is to prevent ice forming in the carburettor venturi. The reduction in pressure and latent heat of evaporation of the fuel lower the temperature enough to cause moisture in the air to freeze in the venturi. This causes a loss of power. Most commonly happens at part throttle. The effect is insidious, the driver compensates by opening the throttle more until eventually they run out of throttle or the engine stops.
Well known problem on light aircraft, but still kills people every year.


Robert G8RPI.

 

[F123C]

Hi,
Interesting thought, but as the engine is cold, the intake position won't make any difference for the first five minutes. The warm air intake is to prevent ice forming in the carburettor venturi. The reduction in pressure and latent heat of evaporation of the fuel lower the temperature enough to cause moisture in the air to freeze in the venturi. This causes a loss of power. Most commonly happens at part throttle. The effect is insidious, the driver compensates by opening the throttle more until eventually they run out of throttle or the engine stops.
Well known problem on light aircraft, but still kills people every year.


Robert G8RPI.

Hi Robert,

I accept what you're saying about carburettor icing, having experienced it myself on Fiats on a few rare occasions (when the air cleaner intake was set incorrectly! or the car run without the air cleaner in place) but I still think that the warm/hot air intake setting does have an effect on how the engine runs during the first 5 minutes.

Remember that although the engine is cold, the exhaust manifold surface, over which the intake air is being drawn, will quickly rise in temperature. This warm air being drawn into the carburettor assists with fuel vaporisation and mixing of the fuel and air.

The main reason that a rich mixture is supplied to a cold engine (by using either a choke to restrict the quantity of air relative to fuel or an enrichment device to increase the quantity of fuel relative to the air) is to get enough fuel to mix with the air and thus burn well. Some of this excess fuel drops out/condenses on cool internal surfaces within the engine, manifold and intake ports etc. so doesn't get burned until it too is drawn into the cylinder.

Some say that it's this excess, unburnt fuel from excessive running on choke/short runs not getting the engine up to normal operating temperature that causes the abnormal wear on top piston rings/grooves/top piston lands/top section of cylinder bores.

[As an aside, I was just thinking about 'quench zones', small areas within the combustion chamber where combustion cannot take place. Anyone ever notice how some small areas of the combustion chamber don't seem to have carbon build-up??? ]

In conclusion I feel that Fiat put adjustable air intakes on their air cleaners for good reason and included instructions about same in their Owner's Handbook and Workshop Manuals for good reason. I suspect this was to allow the engine to run better than it might do without having such choice of intake air temperature available. Later cars had thermostatically controlled air intakes on the air cleaners so no manual adjustment needed. (just check that it's working!!).

Al.