Sod’s Law with Respect to Ignition

I don’t know if it has happened to you, but I find that my T-Type invariably breaks down at the most inopportune moment, usually it is raining hard, or it is dark, or worse – both! Over the years I have developed a quick diagnostic technique for breakdowns, I carry a cheap yellow plastic spark plug tester in the driver’s side door pocket. Up with the bonnet, pull off a plug lead, insert the spark tester in circuit, turn the ignition on and pull the starter knob. If the plug tester flashes yellow, then it’s not the ignition, but most likely the good old SU fuel pump. However if the spark plug tester does not flash it indicates an ignition problem. More often than not I have found that the most likely culprit is the rotor arm, so the first thing to do is replace the rotor arm with a new spare, this usually fixes the problem, if not it is most likely the CB points or the condenser.

Now that I am in the latter throes of middle age (OK, I am an old age pensioner but reluctant to accept it!) my eyesight is not what it used to be, nor are my fingers as nimble! When changing points and/or condenser at the side of the road (in the wet/dark) it is very trying. It is all too easy to drop one of the little screws, washers or spacers, and never to be seen again you end up stranded. So a few years ago I came up with a plan to help me in these situations and purchased a new distributor base plate complete with new points and condenser (see photo 1).

Distributor Base Plate
Photo 1 – new distributor base plate, complete with new points and condenser with plug tester in the foreground.

I fitted the new base plate, complete with new points and condenser, to my TA and adjusted the CB points gap to the correct 12 thou setting and ran the car to check everything was OK. I then removed the new distributor base, and replaced it with the original one. The new one is then stored in my tool box along with a new rotor arm in a re- sealable plastic bag ready for instant use. If I break down now and the fault is in the ignition, I can change the complete points/condenser/rotor arm unit in minutes, with no set-up required. Just remove the LT wire (secured to the distributor with an old SU petrol pump screw cap), remove the cap and rotor arm, undo two screws securing the base and swap the distributor base for the new one.

The distributor base for the TA is different from that required for an XPAG, but all are readily available on eBay or from Moss etc.

Now once you are back home with the car safely in the garage, it’s time to find out what failed and replace the faulty component, and set up the distributor base for next time. I find that working on the distributor in situ is not easy, mainly because of eyesight and bending down problems. I find it is much easier to remove the distributor complete from the engine, and work on it on the workbench.

Now for tip number 2, to help you make it easy to remove and replace the distributor without losing the timing. This is much easier if your distributor is fitted with a micro-adjuster attachment.

This is how I do it……………

Firstly remove the distributor cap and leads, and move them out of the way. Make sure the car is not in gear and then turn the engine over with the starting handle until the brass tip of the rotor arm is pointing to one of the distributor cap holding clips (see photo 2), and then remove the starting handle. Raise the two cap securing straps vertically and secure the two with an elastic band as in photo 2.

Photo 2 – shows the elastic band attached to the two distributor cap holding clips.

Then remove the bolt that secures the micro- adjuster to the engine block (see photo 3).

Photo 3 – shows the bolt which secures the micro-adjuster to the block.

Carefully pull the distributor out of the block, noting that the rotor will turn slightly anti-clockwise until the distributor is free. Make a mental note of how far the rotor moved, as you will need this info when replacing the distributor.

You can now take the distributor to your workbench, clean it, replace the required components and adjust the CB points gap easily (see photo 4).

Photo 4 – shows the distributor on the bench for ease of maintenance.

When you are ready to replace the distributor in the car, refit the rotor arm, refit the rubber band to the two cap securing straps and turn the rotor arm until it is between the rubber band and with the brass tip pointing as in photograph 2. Then carefully turn the rotor slightly anti-clockwise a small amount (as noted earlier when you removed it) and push the distributor back into the block. Finally, check that the rotor arm is in the correct position (between the rubber band), and replace the bolt securing the micro–adjuster to the block. Remove the rubber band, replace the distributor cap and start the engine to make sure it runs OK.

If you follow the above procedure carefully you will not have to retime the ignition as long as you have not moved or removed the micro-adjuster from the distributor, and you have not turned the engine over whilst working on the distributor. I have removed my distributor many times using this method without any problems.

The Lucas part numbers for the TA distributor base are as follows:

• Distributor base (complete) 400164 or a bare base is 400001
• Contact breaker points are 400415 and the condenser is 400308

If you look around at autojumbles you can often buy and old base plate with worn components for around £5. This will provide you with the wire link and LT connector for your new base, or you can make one with black wire and a couple of spade connectors.

For an XPAG engine it is best to buy a kit of parts that includes a new base plate with a non-soldered new condenser. If you search on eBay there is a seller called automobileelectrics who trades as Classic Automobile Electrics Ltd of Scunthorpe, U.K. He sells a ’distributor base plate repair kit MG TC TD TF’ for £35 which looks good value to me.

Brian Rainbow

4 thoughts on “Sod’s Law with Respect to Ignition

  1. Neil Hatfield says:

    So obvious, so easy, Why didn’t I think of it. Have always worried about dropping that little screw back into the distributor or worse into the grass. Many thanks

  2. John Mitchell says:

    Hi Brian,

    Thanks for article – some useful information, but please throw away what looks to be an aftermarket rotor arm, with a rivet fixing! There have been so many ignition failures in classic cars due to the widespread use of these ‘rivet rotors’, which are of poor quality, and tend to short out through the rivet itself.

    Original UK made Lucas rotors had the brass conductor fastened within the male plastic moulding of the rotor itself, thereby largely eliminating the shorting out problem.

    Over the years I’ve collected quite a few original S/H Lucas rotors, which I still use. Eventually the tips of the brss conductors wear back, but with the mileage most classic cars do, this will take many years. Also beware of so called ‘Lucas’ rotors in bright shiny boxes. These are made in various parts of the world and are of varying quality! Remember Lucas have not made car electrical equipment for many years, but the use of their labelling on many electrical components is widespread.

    I understand a good quality ‘red rotor’ is now avalable, without the notorious rivet, and to avoid unnecessary breakdowns I would advise all owners to check what rotor is on their cars. If it’s got a rivet seriously consider changing as soon as possible!



    • JOHN JAMES says:

      Brian Rainbow has commented as follows:

      “The rotor arms in my photo are genuine Lucas ones, part number DRB101C which I purchased from the Lucas Service Centre in Warwick about 5 years ago. There are lots of pattern rotor arms around that are of inferior quality. I purchased a couple of new so-called red rotor arms from H&H at MG Live, and have one spare in my TA, and have fitted the other one to my MGB GT. I am perfectly happy with the ones currently in my TA, the one in use has done about 15K miles now and will get changed eventually.”

  3. Martin Moore says:

    Hi Brian,
    What areally sensible idea I have all the spare bits but not set up as you suggest for simple replacement, will set about doig just that .
    The “Law of Sod ” certainly applies I missed the first day of the Devon weekend in 2011 as the TA stopped on the main A386 out of Plmouth en- route for The Moorland Links Hotel (condenser failure ) but I had to get the car rapidly removed as it was in a dangerous and causing a serious jam ! On this years Atlantic Coast Express run the condenser failed again very quickly diagnosed and replaced by youn and nimble fingered Steve Lovegrove . Will chat to soon re the importance of measuring everything before replacing the last head skim allowed the pistons to hit the cylinder head !
    Best regards Martin .

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