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DIY: Overhauling the distributor of my Premier Padmini (Fiat 1100D)

28th October 2024, 14:43 by Utkarsh Chaudhary

The main motive for removing the distributor was to fix an electronic ignition kit. The stock distributor in the car is a Lucas which I honestly doubt is original.

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Prologue

This is a thread that documents the overhauling of the distributor (Delco in Indian mechanic parlance) on my Fiat 1100D.

What exactly is a distributor however and why is it needed? The distributor in a non-ECM equipped car is responsible for distributing sparks to each of the cylinders at the correct time & is driven directly off the camshaft. A delco has to not only allow each spark plug to fire at just the right time, but it also has to ‘advance’ timing by accounting for an increase in engine rpm.

Distributor timing in a nutshell denotes when the spark plug fires wrt the first piston. The reference point here is top dead centre (TDC) of cylinder 1. Theoretically, the spark plug should always fire at TDC in an ICE engine (when both intake & exhaust valves close), however, there is a caveat here.

In the real world, the air-fuel mixture takes time to burn completely and this delay needs to be accounted for. Thus, the plug is to be fired slightly before TDC. Two other terms you will often hear wrt distributors are advancing and retarding. Advancing is when the distributor timing is set earlier in relation to what it is currently (in the direction before TDC), while retarding is when the plug is set to fire later (direction after TDC). The delco timing is to be set manually at idle (called static advance) by rotating it clockwise or anti-clockwise.

The main motive for removing the distributor was to fix an electronic ignition kit. The stock distributor in the car is a Lucas which I honestly doubt is original. Most if not all Presidents came with a Magneti Marelli distributor, but the quality of points was pathetic & it would often leave one stranded. Hence, most owners switched to a Lucas make for ease of maintenance, reliability & parts availability.

Even in the Lucas make, there are different series depending on the amount of advance offered and the type of advance. However, for the sake of simplicity, I will only talk about 2 of them. The 23D4 and the 25D4. The 23D4 is what my car and most of the early 1100Ds, Presidents & even Padminis had. The 23D4 uses a centrifugal advance while the 25D4 uses a vacuum advance.

The advancing mechanisms change or advance timing as the revvs climb. I won’t go into too much detail on how they work, but here is a video for those who are interested.

Removal

With the working established, it’s time to remove the delco. First thing to do is to bring the engine to TDC using marks on the crank pulley, note the position of the delco rotor (by popping the cap off) and then move on to actually removing it.

The Delco is clamped onto the engine block with a 10mm nut and bolt combination at the very bottom. You will simply need two 10mm spanners or ratchets to break it loose and take them off.

Before actually removing it, unplug all 4 plug wires and the main wire going into it from the ignition coil. Also, unplug the black wire attached to it on the side which goes from the points mechanism to the -ve of the coil. It’s held by an 8mm nut

That’s it. Pull the delco out now.

With it on the bench, take the cap off and work on removing the points mechanism. The points mechanism includes a capacitor, a contact breaker and a spring mechanism. The connect points and capacitor are held in place by 2 flathead screws. The spring mechanism pivots on a pin which is attached to the delco top plate.

Once the points and condenser are out, you can actually work on removing the top plate. Again, only two screws hold it but they are flathead screws and very easy to strip. Someone had already had a go at removing them before and stripped them partly.

After removing the flathead screws, the top plate comes off, revealing the advance mechanism. There is a set of 2 weights and springs here. If you do want to dismantle the delco further, it is to be kept in mind that each of the weights and springs are different. The 23D4 advances the timing at two distinct points in the revv range, hence the two different spring-weight combinations. It goes without saying that they will need to go back in exactly as they came out else the advancing mechanism won’t work as intended.

Also, there is tonnes of grease in here as is visible. This is simply the wrong way of doing things. Apart from gunking up the insides, the grease adds to the effective mass of the centrifugal weights and doesn’t allow them to fly apart at higher RPMs and alter timing. The most lubrication this mechanism should see is some sewing machine oil on the delco base and weights or some engine oil.

I simply cleaned all of this without dismantling it using petrol and a rag. It took me about 40-45 minutes and 3-4 rounds of cleaning to get it back to acceptable shape. There isn’t really any technique to clean it, just good old elbow grease and ensuring that you don’t accidentally pop off the advance springs.

Another very important point to note is that the delco body has two drain holes at the very bottom. Any lubricant poured (sewing machine oil or engine oil) should be able to exit the body via these holes. If not, it might eventually make its way up onto the contact breaker (in the case of a point-condenser system) and cause misfiring.

After unplugging the holes from grease using a thick needle, I proceeded to very lightly lube the weights and base with engine oil. The excess amount simply escaped through the drain holes as intended.

The top plate then went back on. Post this, the electronic ignition module was fixed. The module uses only the pivot pin and one flathead screw as opposed to the point condenser mechanism which needed two screws & the pivot pin.

The sensing ring then pops onto the rotor shaft (it’s a simple friction fit) and then on top goes the rotor arm. Check and alter the position of the ignition module such that the distance between the sensing ring and module is about 1mm and the gap is equal at all points. A slightly wider gap is not an issue, but the two shouldn’t touch

Wiring

There is a slight change in wiring too. As opposed to the points mechanism which only had one wire going to the coil negative, the electronic ignition has two. There is an additional positive to actually power the module. The most important thing to keep in mind is to ONLY power the module via a ballast resistor and not directly via the coil. Attempting to directly power it from the coil positive will fry it within a few minutes.

Install

Reinstall is easy. Position the rotor arm exactly where it was when you removed the delco, ensure the engine is at TDC and insert the delco. Complete the wiring as indicated above. Don’t tighten the delco completely in place. Put the cap back on and plug wires in the correct order (1-3-4-2) clockwise.

Fire the engine up. The car should atleast start. If it doesn’t slightly advance and then try. Get a timing gun and time the engine to be around 5-10BTDC. If you don’t have one, advance the timing till the engine starts to ping very slightly, then retard it just a bit so that the pinging stops.

Conclusion

This pretty much sums up my shenanigans with the ignition system. The electronic ignition kit should theoretically perform better (stronger spark), be zero maintenance (no need to adjust point gap or replace the points) and have better reliability (points can misbehave in moisture laden conditions). However, I never take things at face value. I plan to keep the stock points and condenser with me in case the worst happens.

A pic of the stamping on the delco for reference. The 23D4 is used on many MGs and Minis from the 70s and 80s. Unfortunately, it doesn't have vaccum advance which offers load based timing advance as opposed to only RPM based advance. I won't be able to install one either since my current carburettor doesn't have a vaccum port needed for the job.