Lucas DKX2A Distributor.

[twolitre]

For some time I have been searching for a DKX2A Distributor for my 5T Triumph Speed Twin. It is NOT the same as 6T Thunderbirds, which only have 12.5 degrees of advance and have a very different number.
  I have found one bearing the correct number (40352), but with the suffix letter 'B' instead of 'D' (i.e. the correct number is 40352D).
  Can anyone tell me the significance of that letter please?  Does the letter signify some small update on essentially the same (15 degree advance) distributor I need?
  I am starting to get rather desperate for a suitable unit.  It seems I might be better looking for hens teeth or that unicorn stuff.
  I do know that Triumph Twin Spares advertise one 'for Triumph Twins', but they do not respond to requests for more info.  I have given up on that.

[L.A.B.]

According to the information here:http://www.starchak.ca/tech/pdfs/lucas.pdf

The DKX2A 40352D & E apparently had a 14° advance range, compared to the 40352A & B (B = "1956 Triumph motorbike - 5TAC & 6TAC") that were both 10° advance types.

All four were apparently superseded by the DKX2A 40449 A & B with 12.5° advance range.

And no...I don't know what an "ECM curve" is!

[twolitre]

Thanks L.A.B.  I never would have found that info!
  However.......  My info. came from a parts book dated 1955 which lists the numbers I quoted (the Lucas info does say + or - 1 degree).
  The bike was exported, unregistered in 1957, and the T.O.M.C.C. provided a dating certificate for 1957.  The engine (and frame) number is 08275, which to me seems rather low for 1957 because the parts book says "Starting with engine number 70930".  The petrol tank holes for the (missing) badges look to me to be for striped band trim, which I believe had been superseded by 1957.
  Presumably the 5TAC and 6TAC mark the conversion to alternator, which this bike has.
  Do you think the above suggests the bike is really an earlier product which should have the 'B' suffix distributor?
  I am (was) a well qualified Motor Engineer, but my practical experience has been almost solely on four (or more) wheeled vehicles, having given up biking in 1960 and having only been recently re-born.  Of course the engineering principles are familiar, but the applications are not.  I must rely on others to help me out in cases such as this.
  Incidentally the same parts book lists the 40449A for the 6T.
Regards and Thanks,

Oh! And I do not know what an ECM Curve is either!  Though I have produced plenty of advance curve graphs for engines on Brake Tests.

[L.A.B.]

 Presumably the 5TAC and 6TAC mark the conversion to alternator, which this bike has.

Yes, the Lucas records do confirm that.

I think maybe we discussed it before, but the '54, '55 &'56 5TAC had the DKX2A 40352D distributor, the '57 & '58 had a 40352E according to the Lucas service sheets.
I had to go back to the Lucas '51-'53 general list to find a 40352B.

[twolitre]

Thanks L.A.B.,

Since the 'D' and 'E' types have the same maximum advance and hopefully the same advance curve (ECM?), either of these should not produce a timing issue.
  I was worried that insufficient advance would cause overheating at the top-end, along with excessive pipe blueing, possibly valve burning and certainly loss of power.  Too much advance would cause pinking and possibly holes in piston(s) along with big end failure etc.
  It seems best to forget the B variant and settle for D or E if I can find one.
  Many thanks, I think I owe you more than one!
  Jim.

[L.A.B.]

It's been quite a while since I've had anything to do with any type of motorcycle distributor, so I don't really know if it would be possible to increase the advance range of a DKX2A somehow, by filing any bob-weight slots or stops?

Even if a distributor was used that didn't quite have the recommended advance range then it should work if the distributor was set correctly at the recommended full advance?
If that resulted in the ignition timing being a few degrees too far advanced at lower RPM that may not cause any problems?

[twolitre]

  I did get to look inside a DKX2A unit with 10 degrees advance.  The bob weights throw out to within thous. of the casing - no way that could be increased - and I could see no other way of doing it except by manufacturing new pivot links.  I could not work out what shape they would have to be.
  I think what must be remembered is that we are talking distributor degrees.  The effect on the crankshaft is twice that, and any discrepancy starts to sound much more serious.

[douglas]

As long as it is timed to max advance i cant see an issue for idle or low speed running. Remember bikes with manual advance maggy's are usually just left on full advance once running. I run a single 500cc with fixed advance for starting and running because i'm too tight to buy the right end housing and cable!! In the past i was happy to find and use any lucas dizzy that would fit ie. Triumph , Norton,  BSA without a problem. Most of the advance mechanisms are worn enough to give or take a few degrees. I understand your need for originality but if it's a henstooth i would grab anything that comes my way. Douglas