Author Topic: Not BSA. 5TA in the cave.  (Read 355 times)

Offline A10 JWO

  • Resident Legend
  • *****
  • Join Date: Oct 2012
  • Posts: 730
  • Karma: 2
Not BSA. 5TA in the cave.
« on: 19.04. 2019 18:01 »
Parked next to my BSA is a new little Triumph 5TA 1963 version with a distributor sharing the spark. It has a Pazon Mark 8 ignition system with a Kirby Rowbotham distributor conversion. I took the tank off today and was surprised to only see only one coil. Is this a parallel twin. To me the engine note sounds like the Bonnie with twin coils. Can someone explain the firing order as I have not had time to get a manual. The Triumph forums are almost useless, thank you.   

Offline Swarfcut

  • Wise & Enlightened
  • *
  • Join Date: Oct 2018
  • Posts: 1321
  • Karma: 19
Re: Not BSA. 5TA in the cave.
« Reply #1 on: 19.04. 2019 19:13 »
  Back in the mists of time, before the advent of Brightspark replacement condensers, if your magneto failed you were in the hands of the Magneto Men and getting a maggy fixed was expensive and generally a bit of a gamble.

 Kirby Rowbotham, an enlightened engineer from Rugely, Staffordshire, England gave this a bit of thought and spotted a gap in the market. He designed and manufactured a distributor body, which used readily obtainable ignition parts to complete  the ensemble. Namely a set of points from a Ford Cortina, plus a distributor cap and rotor from a Fiat 500, (a 2 cylinder car engine), together with a standard ignition coil. This enabled a magneto system to be cheaply changed to  conventional coil ignition.
 This meant the failing magneto could be discarded and completely replaced by the coil ignition  KR System. In event of trouble on the road the KR set up was quick, simple and cheap to fix, and every corner motor spares shop had the parts. An inspired piece of engineering, back in the day. It was also a good substitute for a troublesome or worn standard Lucas Motorcycle Distributor.

 As now the weakness was that you still needed a good charging system and battery to power the ignition. Over time, the system was improved by the addition of electronic switching.  In early standard form, it used a single coil, one set of points and the distributor cap, rotor and leads to  fire each cylinder in turn. Just like a conventional car ignition system. It looks as if you have a later electronic version.

 What you may have, if there is no conventional insulated cap, is actually the standard body, but with a single electronically switched output feeding a double ended coil. In other words it fires two sparks at the same time. One spark to the cylinder on compression, plus another  spark to the other cylinder which is just finishing its exhaust stroke, a so called "dead spark." Both pistons rise and fall at the same time. The advantage here is simplicity, easy adjustment and identical spark timing in each cylinder.

 Have a look at the coil, good chance it has two plug leads, and it does not matter which lead goes to which cylinder.


Offline Sluggo

  • Serial Hoarder, or Eccentric Collector depending on viewpoint
  • Resident Legend
  • *****
  • Join Date: Jun 2017
  • Posts: 639
  • Karma: 11
Re: Not BSA. 5TA in the cave.
« Reply #2 on: 19.04. 2019 22:21 »
 I have a bunch of early 500 unit Triumphs and know a thing or 2 about them,  The gooseneck frame and frame bracing and the tank issue is a topic in itself. 
These have been languishing in storage and plan to make a few interesting projects out of them but plan to sell them to fund other projects.

5T speed twin, T100SC and other variants.  There is a real authority associated with the VMCC who I need to contact as he is the guru on these before I proceed much further..(Some of mine are matching #s but most are orphan bits collected over the years)

So before I go off on a tangent, The distributor grew from some of the 6T preunits and on the 500 sprouts from a cast boss off the intake came with a toothed gear on the cams.  I have worked with a number of people with these dizzies on early BSA unit motors (B40) several unit & preunit Triumphs and some Matchless use these as well.

My opinion??? The Dizzies on these are rubbish.  Never had any luck with successful running and tuning.  Im sure someone will regale with lurid tales of wild success, but I never had any.  IMHO there is too much slop in the gears and too little adjustment and range in the Dizzies.  On Garys Bikini T100SS, We could get it to start and idle, but any revs its a dog, Tune for mid and upper RPM and you cant start the bugger.
So, for those who want originality appearance the advice has been to fit a kit like yours.  Tobin had good success with his Matchy G12 after doing the digital conversion, So did Hal.

As the other poster noted, Its a car type distributor so only one coil needed.   Now,, I wont run one, I have enough parts I use the later timing covers and cams and run the EI inside the Points housing driven off the Exh cam. 

## FUN FACT,, Its not  super easy, but it IS possible to swap cams on a unit 500 without splitting the cases.     

If you want the parts to convert, I think I have enough left down in storage.

This page and sub-pages off of it has a wealth of info on the early unit twins. Not just the 350s so dont let the link title fool you...

On mine, since most is just orphan parts or already modified (Some are old race machines) there is not a lot of value in restoring them, However flat track and desert sled styled bikes are huge right now in the US so my plan is to largely customize mine, right now theres 5 projects, and plan is 3 rigids and 2 swing arms.
Ill include a pix of a Gary Nixon tribute bike of what mine will evolve into...
(I do have a T100SC I could part with if someone wants to take it on, good buddy price?  These are super rare but very obscure)

Remember that any advice received on a free internet forum is generally worth about 1/2 of what you paid for it.
We overcharge every 3rd customer to pass the savings onto you.
You can have High Quality, Low price, and fast turnaround. Pick any 2, Never all 3 at the same time.

Offline A10 JWO

  • Resident Legend
  • *****
  • Join Date: Oct 2012
  • Posts: 730
  • Karma: 2
Re: Not BSA. 5TA in the cave.
« Reply #3 on: 23.04. 2019 16:20 »
Thank you for comprehensive replies lads. This week I found a phone number for Kirby Rowbotham amongst my papers. He actually answered the phone and enlightened me about the system I have on my bike.He has been retired a few years but was fixing a mates bike when I called. He is stating that my distributor should outlive me as it only contains two magnets. I have only got one HT lead leaving the only coil so the distributor is sharing the spark. Whoever did the wiring on the bike did a top job, so that should last as well. I now have a black and white brochure that Kirby produced covering Vincents and other BSA's with the KF2. Was a privilege talking to this Grand Master.   

Online muskrat

  • Global Moderator
  • Wise & Enlightened
  • **
  • Join Date: Jul 2009
  • Posts: 8624
  • Karma: 112
  • Lithgow NSW Oz
    • Shoalhaven Classic Motorcycle Club Inc
Re: Not BSA. 5TA in the cave.
« Reply #4 on: 23.04. 2019 21:17 »
G'day JWO.
I bought my first mag replacement electric ignition in the early 90's from Kirby. Before I had internet so had to wait till 2am to phone him. Great bloke.
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Muskys Plunger A7