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post-war engine, which has Lucas Part No. 420196. Some of the pre-war cars around 1933/34 were


fitted with the earlier Rotax distributor, which is a totally different design to Lucas, but can be retrofitted with the DK4A unit. The problem with many distributors on pre-war


cars is that they are generally worn out, usually resulting in variation in point actuation and the centrifugal advance being next to useless, causing poor engine operation. There are companies refurbishing Lucas units, but


this can be expensive and experience has shown that the quality can be seriously lacking. New 'old stock' Lucas DK4A unit fitted Tony


Talking Distributors by David Freeth


Recent servicing of my 4ADT Roadster highlighted that, due to serious pitting and piling, there was the need to replace the contact breaker points. Having collected numerous sets over the years, I assumed that I had a suitable replacement. How wrong can you be? Of all the types onmy shelf, none was the correct pattern. A visit to a local ignition component company drew a blank but served to highlight the many different types made by Lucas. Fortunately I was able to obtain two of the correct sets at this year's Beaulieu Autojumble. Coincidentally, Tony Perkins was also having


Perkins' 1936 Le Mans has transformed engine performance. What about the advance curve, you may be


thinking? On 9, 4A, 4AB, 12 and SM cars, advance curves are similar and all are fully advanced within plus or minus 2 degrees, at around 2,500 to 3,000 engine rpm. Advance curves on other makes of car fitted with this unit are not too far off these figures. So, for ultimate power, a few degrees may have some influence on all-out performance but, what is most important, is an advanced mechanism working correctly, i.e., that it does not go fully advanced at around 1,000 rpm which happens on worn-out units. Also variations in contact operation can cause havoc with the smooth running. So, if you are not too worried about absolute


ignition problems on his '36 Le Mans with a non- standard worn-out Rotax unit. Realising how little information is generally


4ADT Roadsters all operate in a clockwise direction, again viewed from the distributor drive end (or reverse, of course, if looking down the top of the distributor). So, if you are purchasing replacements, make sure they are of the correct rotation. Most have an arrow showing direction. Two types of distributor are fitted to 1500cc


Lucas distributor is fitted to all post-war cars except those with twin carbs, however minor differences exist, dependent on rotation and the Singer model. Of more interest, this distributor will also fit all pre- war 4-cylinder cars back to 1933. It also appears that the same type of points, Lucas PartNo. 407050, will fit allmodels, again except the twin-carb 1500cc


32


clockwise cars. Single-carburettor have the standard unit. Twin-carburettor have the unit with the addition of vacuum advance and retard operating from the front carburettor. Investigation has shown that the DK4A model


anticlockwise direction,viewing from the distributor drive end. (or reverse, of course, if looking down on top of the distributor). Post-war 9, 10 and 12 hp cars are the same SM1500, Hunter Saloons, together with 4AD and


available on the Lucas distributors fitted to Singers I did some investigation to establish what parts and units fit the variousmodels and this resulted in some interesting data which I hope will prove useful to members who have problems with ignition systems on their cars. The following information covers all 4- cylinder cars from1933 to 1956. No 6-cylinder cars were produced after 1937. Distributor rotation on pre-war cars is in an


originality on pre-war cars, go for the later DK4A distributor, which should improve engine performance and smooth running throughout the speed range, but make sure that the bearings and advance mechanism are in good condition. You may be lucky to obtain a new unit since they are more available than the early units as most early post-war makes had this unit fitted. The following Lucas instruction on point setting


may be useful:- "After fitting a replacement contact breaker set,


most of the 'bedding down' of the contact breaker heel occurs after a few hundred miles and it is necessary to check, and if required, to reset the gap between the contacts. To do this, remove the moulded distributor cap and turn the engine over by hand until the contacts are separated fully. Check the gap using a feeler gauge of appropriate thickness (see below). If the gap varies from the gauge, the contacts must be adjusted. To do this ,keep the engine in the position giving maximum opening of the contacts and slacken the screws securing the plate carrying the fixed contact. Move the plate until the gap is set to the thickness of the gauge and then tighten the locking screws.


advisable to recheck the gap to ensure that no movement has taken place while tightening the screws. "The width of contact breaker gaps required in


It is


service will, due to the difference in cam design, depend on the year in which the distributor was manufactured. After 500 miles running, the gap of distributors made prior to 1952 must be reset and maintained at between 0.010 and 0.012 of an inch, whilst the gap of distributors made during and since 1952 should be between 0.014 and 0.016 of an inch. If, with a pre-1952 distributor, it is found that there is a tendency for excessive "pitting and piling" of the


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