MASCOT March 1984

THE ROADSTER FRONT - Distributors

Bill Haverly

There were four distributors used during the Roadster period, two of which span most of the years and cover the most common series. But before going into the details and specification of the types fitted, a few general comments about these Lucas units, plus some information on repairs and availability of spare parts will perhaps provide some useful background data. The first thing that needs saying is they are reliable, and unless you are very unlucky will not need any more than regular servicing during the life of an engine. Because they have a proven reliability, the current Lucas servicing covers only five items, cap, points, base plate, rotor and condenser. But with most of our Roadsters going through their second life, attention may well be needed to other working parts such as bushes, cams, shaft/action plates and auto advance weight assemblies. Lucas have some older stocks of these parts for factory overhauls of distributors of our period but these are not available over the counter. Nor do they commit themselves on the cost of reconditioning, preferring to price each job independently.

Each distributor should have a model/type serial followed by a part or Service number stamped into the casting of the main body as identification, a sample Roadster reference being DKY4A-BP75 40192. The DKY4A model was fitted to many British cars after the last war, and was used on all Roadsters (except twin Carb versions) until 1955. The serial DKY4A refers to the body shell and some of its main fittings, being Lucas coding for a distributor to fit 4-cylinder engines, with a large die cast body, pressed steel contact breaker plate, and auto advance weights. The rest of the parts in this model varied to suit the needs of a range of engines on which it was used, each model being given a specific part or service number which is the real identification of the individual unit, needed as a reference by the makers when replacement parts are required. Variables in distributors between one engine and the next are direction of drive (clock or anti-clock rotation), driving dogs and gears, rotors, and of course the advance weight/spring assemblies which govern the ignition advance range of the unit. None of this information is given for effect, but to point out the dangers of interchanging a distributor which appears externally to be the same as fitted to your Roadster but in fact is not suitable unless it bears the same model and service number. A case in point here is the 9 hp and 1500 cc Roadster distributors - both familiar as DKY4A's but not possible to swop as their rotation is opposite.

On the whole it is safer to recondition the original unit on the engine rather than chance your arm in attempting to modify even a new unit found somewhere in old stock or at an autojumble - unless you are fortunate enough to find one with the right service number.

Overhauling is mainly a matter of dismantling and reassembling, the only real work involved being in replacing top and bottom bushes, the parts most likely to need renewal, and even this is not difficult. The difficulties arise in trying to find the correct new parts to replace those worn items like bushes, weights, toggles and springs, etc., which are hidden below the base plate. Fortunately there are a few specialists in obsolete stock around - and one with a large assortment of Lucas spares who has helped me out in the past is Martin Peters, 19 Lucks Lanes Buckden, Huntingdon, Cambs. Tel. 0480 810440. Another, further south, who is also worth trying is ABC Spares of Holt Forest Farm, Wimborne, Dorset, Tel. 025884 309. 1 also have details of all the parts fitted in Roadster distributors, so can pass on the Lucas number of any item that might be required.

On the question of spares availability of the serviceable parts, there is no problem - they are still obtainable from Lucas agents. Distributor caps of the three types used vary in price from just under £8 for the pre-war Roadster down to £6.75 for the common 1946-55 version to less than £3 for the cars fitted with twin carb engines. Points average out at about £2.50 per set; 4AD rotors are fitted to many other modern cars and the earlier rotor fitted to the 1074 cc engine is still in the Lucas books for under £1. The condenser fitted to the first Roadster series is now obsolete but can be serviced by the later types which have the same capacity, differences being in size and means of attachment to the base plate. Prices vary from about £5.50 for the 'A -AD' condenser down to £1 for those lucky enough to have twin carb Roadsters.

Another point to take into account is the change in cam profile between 1949 and 1952 which affects the setting of the contact breaker gap. Full details of these developments were given in a Singer Service Bulletin in the November 1980 Magazine, but as they are relevant to the distributor's efficiency are summarized here. Symmetric cams were fitted up to 1949, when the asymmetric shape was introduced to reduce pitting on the points. Distributors with these two cam profiles have a points setting of .010 - .012" but to allow for bedding down of the contact heel on renewal, should initially be set at .014 - .016" and reset after 500 miles if necessary. Anyway that's what the makers recommend.

From 1952 there was another change - to the high lift cam, and distributors fitted with this profile should be set up to a .014 - .016" gap. The three cam profiles are shown below, but if there's any doubt that a high lift cam is fitted, this can be checked by-referring to the suffix letter after the service number stamped on the body. Details of suffix letter changes indicating use of the high lift cam are given after the General descriptions of the four types

Now for details of the four distributors:

'R' Series (1939) DK4A BP62.0 - 405543 Service No.(40062)

Similar in style to the Post war DKY4A described earlier, but with smaller cast iron body and a lower 'D' shaped cap, and distinguishable with the lid off by a. black moulded plastic base plate. The post war 9 Roadster can be substituted for this one if necessary. The same engine, after all., was used until early 1952 and the only drawback will be the loss of originality.

Cap 400135 (DB100); Points 400415 (DSB120); Condenser 400308. Rotation anti-clock from drive end; Ignition advance range 18 - 20 degrees. High lift cam introduced from Service No. 40062 E onwards (on replacement units).

4AB Series 1946 - 1952 DKYAA BP75 409461 Service No.(40192)

The larger 'D' shaped body cap and fittings as outlined in the main article. Differences from pre war model include pressed steel base plate, higher domed cap, different points and condenser. Of the serviceable parts only the rotor arm is interchangeable.

Cap 418888 (DDB111); Points 407050 (DSE122); Rotor 400052 (DRB105); Condenser 409613 (DCB108). Rotation anti-clock from drive end; Ignition advance range 16 - 18 degrees. High lift cam introduced from Service No 40192 D onwards.

4AD Series (1951 - 55) DKY4A BP86 40167 Service No.(40071)

The same body, cap, points, base plate, condenser and bushing as the post war 9 Roadsters, but not interchangeable because rotation is clockwise viewed from driving end - rotor arm therefore different.

Cap 418888 (DDB111); Points 407050 (DSB122); Rotor 400051 (DRB101); Condenser 409613 (DCB108). Rotation clockwise from drive end; Ignition advance range 20 - 23 degrees. High lift cam introduced from Service no. 40167 H onwards.

Twin curb. Roadsters (1952 - 56) DM2P4 40363 Service No.(40517)

A breakaway from all the earlier types which incorporated the developments taking place in the early fifties, having a vacuum unit working in conjunction with the auto-advance weights; the only common service part with the 4AD being the rotor.

Cap 418865 (DDB105); Points 420196 (DS13115); Rotor 400051 (DRB101); Condenser 423871 (DCB101). Rotation clockwise from drive end; Ignition advance range 16 - 18 degrees. High lift cam introduced from the outset at 40363 A.

The one item common to all .four Roadster units is the driving dog which engages the distributor with its drive shaft. It has an offset spade end and the part number is 410601 (422012 Part numbers in brackets have superseded the original Lucas numbers.