• Radman
    15 September 2015 at 16:48 #51441

    I have a CE6 Form D2R magneto for sale. It has been stored for 50 years plus but appears in remarkably good order when stripped and produces a fat spark when flicked. Some photos at http://www.cmengines.co.uk
    Thought it was good for LG45 but not sure now…offers invited….

    Colin M34
    16 September 2015 at 08:55 #51444

    The BTH CE6 magneto is a very nice unit, often fitted to the Meadows engine in an M45.

    However most LG45s used a pair of Scintilla vertex units in tandem. These are mounted on the nearside of the engine. So this CE6 unit would suit an M45 or Invicta, assuming it is a 3/4 engine speed unit not a 2/3 one used on a Three Litre.


    Richard Branch
    16 September 2015 at 10:30 #51445

    Going off at a tangent, how does a magneto running at 3/4 or 2/3 engine speed provide the spark at the right time? Or, doesn’t the magneto control the timing?

    David Bracey
    16 September 2015 at 13:40 #51446

    Good question Rich. I had always assumed that it was down to the worm gear on the end of the magneto shaft and that you would simply use a different gear. No?

    17 September 2015 at 18:04 #51450

    I think you will find that the 3/4 speed is achieved by the gearing inside the magneto – hence a 3 litre 3/4 engine speed magneto being of the “hens teeth” variety and value – the last one I saw was ?2500 I think !!
    With the greatest of respect Colin I think that the 3 litre engine magneto is 3/4 engine speed not 2/3 – at least it was on my 3 litre and every other 3 litre I came across !! The 3 litre used a “Scintilla MN6 -3/4” I think ??

    Alec Rivers-Bowerman
    18 September 2015 at 01:55 #51453

    My reprint of a Scintilla manual notes that the magnetos deliver two sparks per rev, so a six cylinder magneto has to be driven at 1.5 times engine speed. It also notes that for engines working on a two stroke cycle, twice as many sparks per revolution have to be delivered. They therefore made magnetos marked MN4 1/2, GN4 1/2, MN6 3/4, and GN6 3/4 with 4 sparks per rev, so they can be driven at the same engine speed as the conventional magnetos on four stroke engines. I suppose you could run one of these special magnetos on a four stroke – you would adding a spark just as the exhaust stroke was finishing, which I don’t think would do any harm.
    The gearing inside the magneto is to match the magneto speed to the distributing rotor, so it would be 2:1 on a four cylinder and 3:1 on a six.
    I’m getting this information from the manual – I don’t have a PN6 to look at as my car has a more modern Fairbanks-Morse.

    Alec Rivers-Bowerman
    18 September 2015 at 06:18 #51454

    It just occurred to me that the engine designer might have chosen to use the two-stroke type magneto (MN6 3/4) and run it at half the speed that a MN6 would need. I checked the club’s Vintage Lagonda Handbook, and it does state that the 3 litres did use the MN6 3/4 magnetos and that they run at 3/4 engine speed.

    Richard Branch
    18 September 2015 at 11:38 #51457

    Thanks for the explanations about speeds, it is all starting to make sense to me now! 🙂

Viewing 8 posts - 1 through 8 (of 8 total)

You must be logged in to reply to this topic.


Request to join the Lagonda Forum

To avoid rogue requests we are currently manually approving all forum applications. Please fill out your details below and we will forward a link and password to complete your application.