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Bantamising my bits D1/D3/D7
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csx355
Penwith Cornwall
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August 10, 2020 - 8:33 pm
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Hi all - I have two Bantam Plunger frames,

Frame 1 - BD2s 4232X  - This frame is in good order and has been powder coated grey. So it's my current favourite!

and  

Frame 2 - BD2s5416X  - sound with very good forks and plunger units. 

I currently have three motors,  

  • a 125 with closely spaced studs which came with the first frame
  • a 150 BD3B and a 175  GD7 both of which came with the second.

My plan is to build the first frame with the 125 motor, apply for an age related number - there are no V5's,  and ultimately insert a 175 motor to make something tidy, light, traily and usable that can be towed on the back of a camper van as a fun punt-a-bout. 

I have no doubt that it would be more cost effective buying something complete but I like rescuing these things and I have built up and have registered a B44 and a B40 before so I have an inkling what is in store. Neither of my BSA's are show ponies but they are tidy enough, relatively original (give or take), ride nice and keep me happy. My intention is to completely rebuild the motors and see what's left over. 

So today whilst 'optimising' my little Bantam shaped treasure trove I found that the forks that came with the bikes are different. I have skinny little Bantam forks with Frame 1 and BEEFY pumped up Bantam forks with frame 2. Both are Bantam forks with the basic screw inny springs and the same lower leg drop outs, but Beefy set from frame 2 has fatter upper legs and lower yoke. 

And this got me thinking.

Ultimately I need the bike  to be 'original' in order to get an age related plate -

I'm not sure that anything I have is related -

I like the idea of the beefier front fork. Am I going to have hassle with the registration process if I go down the 'Beefy'  fork route? I seem to have loads of front hubs,  and front brake plates with a only a couple of ropey rear wheels. Building wheels is not an issue however selecting hubs might be as there seems to be a variety of brake anchoring / torque arm options!!   

IF anyone has tread this path before - I'm sure loads of you have - what tips and tricks do you have.  Many thanks - in advance.

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GlenAnderson
Dover
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August 12, 2020 - 9:56 am
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When dealing with the “authorities”, having as much as possible correct is the way to go. In your case, I’d go about it this way:

Rebuild the 125cc engine using as many of your existing parts as possible, and just prioritise getting it running.

Assemble a bike using the skinny forks, and as many of the bits you already have. 

Get a dating certificate from the club, and get the bike examined and registered. It doesn’t need to be 100% complete, or fit for a thousand mile trek; just a rideable condition. 

Once you have a V5 in hand for that one, strip the cycle parts of the first frame, and fit them to the second, wait a few months, and repeat the process. 

You can be refurbishing the other parts while this is going on, and working towards building the first bike as you want it. 

When you have the second V5 in hand, you can then do that bike. 

I’ve had an on/off affair with a 125cc D1 for more than 40 years. The engine is barely adequate for a skinny teenager and a lightweight rigid with no luggage. The extra power and torque of the 150 makes a surprising difference, and there’s very little in the way of visual clues it’s been done. My bike was nicest to live with when it had a D7 motor, but the bigger carb and air cleaner meant I had to do without a toolbox and fabricate a battery carrier.

My advice would be to aim for the D3 engine and skinny forks in the road one, and the D7 and heavy forks in the trail one. 

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csx355
Penwith Cornwall
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August 13, 2020 - 8:52 pm
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Many thanks Glen that's exactly the advice that I need. I'm not looking to 'put one over' just to rebuild the bikes, get them complete and road useable again and keep the one that suits my needs the most.  

I sort of feel though that the 4hp of a 125 is likely to be a tad asthmatic for use in todays traffic. (read my weight). I'd like to at least keep up with the tractors on our roads and not have them overtake me!

I have a number of bikes and am learning slowly that battery-less systems are preferable for me to have as I can't possibly ride any of them enough to prevent the battery from eating itself, which is irritating. The EWorld system with lighting coils seems to do the do and my plan was to fit one of those. 

 

I have started putting the frame / rolling chassis together and will start on the motor/s dreckly. 

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GlenAnderson
Dover
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August 13, 2020 - 10:40 pm
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Yes. Much though it pains me to say it, a standard D1 really is a bike that struggles once you’re out of the 30mph limit. I have tried pretty much every trick to squeeze a little more performance from my 53 D1 and it’s always “one step forward, one step back”. All the tuning tricks provide more power at the expense of flexibility, and only go on to expose the vast gulf between second and third gears. A standard D3 is a much nicer bike to ride than a tuned D1. If you can live with the aesthetic of the bigger carb/air cleaner needed, a D7 engine is probably the best “upgrade”, giving easy 50mph cruising and 60+ flat out downhill. The D10 and later engines are capable of propelling the earlier bikes well outside the capability envelope of their chassis’ and cycle parts. I had, for a long time, plans to fit a D14/4 engine to my D1, but it made it quite a handful and took away most of the enjoyment of riding it. That engine is now earmarked for my swingarm D3, who’s chassis is much more capable of the performance it can provide, and the D3 will donate its engine to the D1. 

A battery free solution is also quite sensible. I bought Rex Caunt’s cdi system and am very pleased with it, but I made a bit of an error and should have specced the version with no battery, because not only is a battery a big and conspicuous lump to have on an early bike, every time I want to use it I find the battery is flat. Life would have been so much easier if I’d not opted for it. 

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chickensoup
Bolton, Greater Manchester
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August 22, 2020 - 8:54 pm
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Hi, The 125cc lucas engine that came with my 1950 D1 needed a lot of money spending on it, so I am currently using a 175cc D5 direct electric engine. Its great, quite nippy round town and pulls 50 mph no problem. The only draw back is, even though the engine looks the part, because of the larger carburettor, I cannot fit the nifty tool box, so the bike looks a bit bare. 

The D1 is also a very small bike. I had to make some bracket alterations to the seat. It is now about 2 " further back and higher to fit my 6' 14.5 stone frame.

I also had no problems with the DVLA ( mixing D1 and D5 components ) I had no documentation at all when I got the bike, just frame and engine numbers. I got an age related number, dating from the youngest component ( D5 engine )

Good luck with your restorations, keep us all informed of your progress with photo's

Kind regards... Nick

1950 BSA D1 Plunger   242 UYW

1966 BSA D7  LBF 62 D

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