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jimmitchell

Bantam - 4 speed into 3 speed look-a-like?

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When up at the Two Day pre 65 Trial I saw some Bantams which looked 3 speeders but were definitely not. Am I correct in thinking it is a simple (!) case of fitting a 3 speed crank in a 4 speed c/case to get the ignition on the ‘correct’ side and using 3 speed outed casings?

Our son has a B175 based trials bike and we were thinking of converting a spare engine to a 3 speed look-a-like over the winter just for something to do.

Any suggestions on what to replace the old Amal carb with – make (Mikuni ?), bore etc? He will never be competing in any restricted specification events so no worry on that issue.

Jim

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Dont quite understand. The 4 speeds use electronic ignition mounted where the stator used to be and you just modify the relevant 3 speed outers to fit. You dont change the crank. B175 is much better crank anyway.

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I’m with you now. I assumed as there was no points cover on the clutch side, the c/shaft must be reversed to have them on the drive side as per 3 speeder. But, as you say with electronic ignition it just needs a trigger on one side of the crank to work. Stupid ould me.

Any experience with suitable carbs?

Many thanks, and apologies.

Jim

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22 hours ago, jimmitchell said:

I’m with you now. I assumed as there was no points cover on the clutch side, the c/shaft must be reversed to have them on the drive side as per 3 speeder. But, as you say with electronic ignition it just needs a trigger on one side of the crank to work. Stupid ould me.

Any experience with suitable carbs?

Many thanks, and apologies.

Jim

Running an Amal premier 26mm as wanted to keep it legal but a MK1 and a half some people will say is better. Price is about the same as a Mikuni or Dellorto but no hassle over eligibility so works for me. Think you might have to grind the cam mounting off the end on the crank, but it was a while ago, if you want to use a D7 clutch cover and of course if your engine is a B175 then the kickstart shaft hole needs boring out too. Bolt holes all line up. Cant post photos on here of mine sorry.

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And what  Bantam you have there!

Please, give us all details of frame, wheels, suspension, engine spec and so on!

(just thinking of starting a first D1 build myself, while I am getting used to trial for the second time in my life, now retired and riding an '81 SWM 320 .....) 

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50 minutes ago, turbohead said:

And what  Bantam you have there!

Please, give us all details of frame, wheels, suspension, engine spec and so on!

(just thinking of starting a first D1 build myself, while I am getting used to trial for the second time in my life, now retired and riding an '81 SWM 320 .....) 

Rob Homer frame. Hubs from Alan Whitton Racing billet aluminium Bantam copies with alloy back plates. Morad rims stainless spokes laced by myself. Suspension revalved Betor units. Engine is modified D14/4 with alloy barrel and custom casting one off head reworked crank and flywheels with PVL ignition and brass additional weight from Jim Pickering. Modified Yamaha clutch from Harry Stanistreet. Modified outer cases. Lower 2nd and 3rd gears from Jim Pickering. Smaller engine crank sprocket. Self built exhaust and silencer. Marzocchi forks in Norton sliders. Alloy and titanium spindles. Modified Billet alloy yokes etc etc etc Loads more but its an ongoing project. Not as trick as some.

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On 20/06/2018 at 6:50 PM, old trials fanatic said:

Many thanks for all replies, especially to otf. Thanks for the photos of a lovely looking bike - was that one of the Bantams up at Kinlockleven some weeks past?

jim

 

 

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