Lucas Dk4 rotors

[Robert Foreman]

A friend has asked me to post a photograph of two dk4 rotors with the question what difference does the tail length make?


  Rotor arms.jpg (Size: 39.63 KB / Downloads: 376)  

[John Cornforth]

According to Lucas, the tail is to prevent back running.

[Bob Culver]

The tail is to accomodate the centrifugal auto advance range. Cras with little or no auto advance require no long tail.  More insulator materiel assists balance.
(For decades I have run a 1964 Minx. For most of that time the car was not easy to start idled poorly and did not slow run smoothly. It rapidly eroded the cap studs. eventually the rotaor sprked through. It transpired the spark was firong beyond the end of the brass. Everything was stock although the conatcts had been repeatedly restored by stoning so these and the rubbing block were much reduced. Remedied by attention to the vac advance adj and all much improved)

With most ignition systems spark duration is several degrees of revolution so some wdith/length is desirable. (I presume this explains why cars with failing igniton run with reduced power but not actually missing. The effective firing occurs late)

[Robert Foreman]

Thanks John for the information. 
  Poor running with a Dk4 is almost always due to wear in the bushes for the rotor shaft.

[Chris KC]

Which in turn may have something to do with how few people seem to re-drill the oil hole after fitting new ones!

[Graham Barker]

Hi Chris, not sure what you mean by fitting new ones. Did you mean after fitting a new rotor shaft?
Graham Barker.

[Chris KC]

Bushes