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D1Bantam/CB125 Rework
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trialsstar3
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March 21, 2020 - 11:10 am
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Hello all I'm a brand new forum member. I've been meaning to join after buying my first Bantam probably 4 years ago now. November last year I got round to doing my CBT and getting my D1 bantam on the road. I rapidly found my bantam not very enjoyable to ride, I wasn't comfortable and it's lack of speed almost felt dangerous. Last night I decided to get my bike on the ramp to start it's transformation. I felt this was the right time to join the forum. 

I look forward to getting to know you all. 

👍😊

Paul

20200320_223423_copy_806x605.jpg20200307_190320_copy_774x588.jpg20200320_231412_copy_677x455.jpg

All things Engineery 

1958 BSA Bantam D1

1980 Porsche 911 SC

1989 Mazda MX5

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Blue Heeler
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March 21, 2020 - 12:03 pm
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Welcome Paul, to all things Bantam. Nice shot against the riveted ironwork.

What performance were you getting out of your D1 engine....assuming it`s not a 150 motor?

Blue

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sunny
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March 21, 2020 - 12:59 pm
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well  done  Paul     we  see  by  the  bottom  photo   your   thinking   outside   the  box    a  very  nive  project      in  deed    as  long   as it  gets  you  out   &  thinking     its   good   

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NeilB
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March 21, 2020 - 1:38 pm
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Blue Heeler said
Welcome Paul, to all things Bantam. Nice shot against the riveted ironwork.

What performance were you getting out of your D1 engine....assuming it`s not a 150 motor?

Blue  

Assuming as he's stuck on a CBT, it will be the 125 motor.

Welcome to the site and forum, the D1 was never a speed machine, but getting it running 100% right (and fitting the crack plates) should improve things to at least a safe and useable level. The D1 motor was only ever around 4-5bhp however, so if you're comparing it to your CBT bike (which would probably have had around 10bhp) then it's never going to seem great.

Neil

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cocorico
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March 21, 2020 - 2:01 pm
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Hello Paul and welcome. I know what you mean about not feeling very comfortable  (or safe) on an old Bantam - that's the thing though, they're old! I don't ride mine very much, but I do find it fascinating and too good looking to sell. It's nearly as old as me.

It looks as though you have transplanted a new heart into it - Honda? If so, that's a quite common modification, popular with a few forum members. If you look in the 'Hybrid' section of the forum you should be able to find some examples.

 

 
 

 

1956 D3 running, lights to sort. 7 other bikes in the Barn. 1950 D1 engine now running.

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trialsstar3
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March 21, 2020 - 6:29 pm
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Blue Heeler said
Welcome Paul, to all things Bantam. Nice shot against the riveted ironwork.

What performance were you getting out of your D1 engine....assuming it`s not a 150 motor?

Blue  

Hi Blue, 

Thanks its a huge iron viaduct near to me. Well worth a visit if you're ever in the Nottingham area. 

I had the old girl on the Dyno last weekend but sadly she wasn't really powerful enough for me to even bother turning the computer on to take readings.  😂 

Its the original 125cc with a rex conrod & piston and full Electrex World electronic ignition.

Top speed on the flat was about 45mph... 

I have a Todd center plug cylinder head for it but decided to go the engine swap route. 

20200321_181139.jpg

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All things Engineery 

1958 BSA Bantam D1

1980 Porsche 911 SC

1989 Mazda MX5

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trialsstar3
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March 21, 2020 - 6:41 pm
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sunny said
well  done  Paul     we  see  by  the  bottom  photo   your   thinking   outside   the  box    a  very  nive  project      in  deed    as  long   as it  gets  you  out   &  thinking     its   good     

Thanks Sunny 👍 

I will be doing the conversion as sympathetically as possible, so the original engine can be reinstated at any point. I'm also going to try to make the CB125 engine fitment look as "factory" as possible. 

All things Engineery 

1958 BSA Bantam D1

1980 Porsche 911 SC

1989 Mazda MX5

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March 21, 2020 - 8:00 pm
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trialsstar3 said

Thanks Sunny 👍 

I will be doing the conversion as sympathetically as possible, so the original engine can be reinstated at any point. I'm also going to try to make the CB125 engine fitment look as "factory" as possible.   

Perhaps worth engineering a new intake to bring the carb lower and more level? Nice to hear you're not chopping up a nice bike and should be able to refit the old engine at a later date thumbs-up

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trialsstar3
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March 21, 2020 - 8:18 pm
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NeilB said

Assuming as he's stuck on a CBT, it will be the 125 motor.

Welcome to the site and forum, the D1 was never a speed machine, but getting it running 100% right (and fitting the crack plates) should improve things to at least a safe and useable level. The D1 motor was only ever around 4-5bhp however, so if you're comparing it to your CBT bike (which would probably have had around 10bhp) then it's never going to seem great.

Neil  

Hi Neil, I am indeed "stuck on a CBT" 😂

I took my CBT on this little bantam 👍 It was an eventful day with about half hour of my road test involving me cleaning out my carb at the side of the road... 

I'll probably do a full rework on the 2 stroke while the engine is out then re-install once I've got myself something like a Sunbeam S7 or similar 😍😍😍

I'm hoping with this engine in I'll be able to get much more riding experience in before moving on to something bigger.  It also means I can jump on one of the learner bikes for my full test without the shock of having the gears and brakes on the wrong sides. 

All things Engineery 

1958 BSA Bantam D1

1980 Porsche 911 SC

1989 Mazda MX5

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trialsstar3
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March 21, 2020 - 8:34 pm
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cocorico said
Hello Paul and welcome. I know what you mean about not feeling very comfortable  (or safe) on an old Bantam - that's the thing though, they're old! I don't ride mine very much, but I do find it fascinating and too good looking to sell. It's nearly as old as me.

It looks as though you have transplanted a new heart into it - Honda? If so, that's a quite common modification, popular with a few forum members. If you look in the 'Hybrid' section of the forum you should be able to find some examples.

Hi ✋ thanks so much 😊
I was really not enjoying going out for rides so had to do something. And a new bike was never going to cut it for me. I felt it had to be a Bantam as my Dad had loads of em when he was a lad. He sold his last 7!!! About 10 years ago as a job lot... 😳 I didn't find out for a few years! 
Yup its a 1976 Honda CB125s engine should be good for about 11bhp 
I'll check out the others on here 👍 ill be needing some help and advice too. 20200321_203330_copy_754x845.jpg
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All things Engineery 

1958 BSA Bantam D1

1980 Porsche 911 SC

1989 Mazda MX5

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trialsstar3
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March 21, 2020 - 8:41 pm
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NeilB said

Perhaps worth engineering a new intake to bring the carb lower and more level? Nice to hear you're not chopping up a nice bike and should be able to refit the old engine at a later date thumbs-up  

Certainly will be looking at this as it's currently stopping the tank from sitting all the way down. 

All things Engineery 

1958 BSA Bantam D1

1980 Porsche 911 SC

1989 Mazda MX5

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Blue Heeler
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March 21, 2020 - 9:37 pm
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NeilB said

Assuming as he's stuck on a CBT, it will be the 125 motor. 

As it turns out, yes, but many D1 owners fitted the 150 for bit of extra oomph. Some on the forum have that set up.

Paul, you perhaps know that any Bantam engine slots straight in, incl the later 13hp 175s. Then there`s the 185cc conversion...

Blue

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March 21, 2020 - 10:22 pm
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Blue Heeler said

NeilB said

Assuming as he's stuck on a CBT, it will be the 125 motor. 

As it turns out, yes, but many D1 owners fitted the 150 for bit of extra oomph. Some on the forum have that set up.

Paul, you perhaps know that any Bantam engine slots straight in, incl the later 13hp 175s. Then there`s the 185cc conversion...

Blue  

Not legal on a cbt and would result in driving ban, lots of points, and large fine. Shame that the 125 limit isn't ignored for classic bikes in lieu of just the 14.6bhp limit as it would allow riders to have a classic bike like a bantam without having to suffer with less bhp than my lawnmower! 

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March 21, 2020 - 10:34 pm
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Got a sleeved down D14 cylinder and 125cc piston here, that`d flummox your legal bods Neil.

Engine`ll  have better porting/breathing/exhaust/4 gears, just modify a cyl head to suit and you`re away Paul 🙂

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March 21, 2020 - 11:22 pm
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Unfortunately the "legal bods" have a habit of just ignoring you and could take and then crush your bike because you can't prove otherwise. Either way, a 4 speed 125 bantam mongrel is still going to be far slower then a modern 125 even if it is legal, and a non-standard engine will likely make it more expensive to insure than a much faster modern bike, but it's been done now so is kind of a moot point dunno

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March 22, 2020 - 10:21 am
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NeilB said
Unfortunately the "legal bods" have a habit of just ignoring you and could take and then crush your bike because you can't prove otherwise. Either way, a 4 speed 125 bantam mongrel is still going to be far slower then a modern 125 even if it is legal, and a non-standard engine will likely make it more expensive to insure than a much faster modern bike, but it's been done now so is kind of a moot point dunno  

No bikes will be crushed during my watch I can assure you. 

Just so Paul gets the correct info.... insuring a Bantam with a Bantam engine would not prove more difficult than insuring a Bantam with "a much faster modern engine in it", let us stay real eh....and conversion isn`t "done" yet. Pulls up chair.

Good luck Paul 🙂

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bantammad
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March 22, 2020 - 11:27 am
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Hi bantammad ere well the so called legal boffins at the department of transport would like you to sit in a corner with your mouth shut as they would have it. Well for one l shall build bikes that are a bit hybrid. For example at one time I built a trials 125cc tiger cub for a friend’s daughter to use to be fair it’s performance was about the same as a terrier. Lovely little bike from the shed Les 

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mike p5xbx
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March 22, 2020 - 4:18 pm
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The only real problems with doing that is it would not now be eligible for MOT exemption
I have a 10bhp 4 speed D1 mongrel and believe me the standard D1 brakes are really not upto the speed it can do, its really not safe.
It does now have a D5 front hub/wheel which makes it slightly better

D? - D10- D14 Bantams 350 AJS -500 Triumph http://bsanotru.....lfire.com/

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trialsstar3
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March 22, 2020 - 5:48 pm
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mike p5xbx said
The only real problems with doing that is it would not now be eligible for MOT exemption
I have a 10bhp 4 speed D1 mongrel and believe me the standard D1 brakes are really not upto the speed it can do, its really not safe.
It does now have a D5 front hub/wheel which makes it slightly better  

Front brake is also up for a rework, might try making a twin drum front hub, then have a play with twin/quad leading edge shoe setup. 👍

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1958 BSA Bantam D1

1980 Porsche 911 SC

1989 Mazda MX5

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bantammad
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March 22, 2020 - 6:35 pm
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Hi bantammad ere have a look at my profile photo see my D5 twin drum brake.one l made years ago works well l might add good modification from the shed Les 

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