Making a 1950's style double sided brake

Having read and enjoyed 'Shoestring Racer' and, with an assortment of Bantam parts lying about, I am thinking of making a replica 1950's Bantam racer. Apart from holding the assembly in a jig before welding to ensure spindle and spoke alignment, any other advice on making a double sided brake out of two half hubs?

Jim

Dont weld it.
Make sure you have two good hubs with equal diameter braking surfaces
Machine off the narrow hubs and make a ribbed hollowed spacer to fill the gap, then you can accurately rotate each brake drum to align spoke holes and screw it together.


Standard sort of advice:

Arrange levers so cams rotate in the opposite direction to the wheel rotation.
Weld up or grind cams so both shoes move the same amount
Get some of those laser cut 1/2" longer trials levers with splines
Make or buy some trials type D7 alloy brake plates, the d7 tinny ones flex too much.
It will look nice, but it is heavy.
I was going to turn mine into a Manx looking doubled sided TLS; but got a 160mm Bultaco for one bike and a 1960 Grimica for other.
4Kg lighter !

Good luck, let us know how you get on

John, many thanks for the clear technical explanation and photo. Not as simple as I thought!

Jim

Well remembered is The Wobbleyman (Colin Aldridge) Eastern Centre nineteen-sixty-something-or-other in front of me one moment and then gone at Barn Corner Cadwell. He lost it and ended up in a pile of hay in the barn yard.

He had skimmed the front drum and then overtightened the spokes which had the drum exploade just at the right place -- it was why we gave hime the nickname: he´ll wobble a lot but always comes back upright....


Just reminiscing .. best of luck with your project Jimmie....

Cheer!
JayBee....

Brakes?! They only slow you down!

I`m not altogether convinced the twin drums were actual used in the 50s, certainly in the 60s, just semantics I suppose! I made one my self in about 64, but soon junked it and substituted some thing more appropriate and that actually worked.

Trevor

Right on John C... I like it ... I couldn´t understand why some riders braked where I didn´t....

Perhaps that is why my head aches now and again, my left shoulder, right knee and left ankle give me gyp in the cold and sometimes in the warm....

Sorry about that -- you serious bike makers!

Cheers!
JayBee

After reading the technicalities in making one (or should that be a pair), I think it would be better to keep it simple and perhaps convert a hub into a TLS arrangement! I assume that has been done at some time.

On another 'track', in building a parade Bantam racer how much porting (inlet and exhaust) can be done on a D14 cylinder before the transfer ports must be enlarged or any extra work becomes counterproductive?

Thanks

Jim

Jimmie, as no one else has responded to your post, it looks like you are stuck with me!

There is quite a lot you can do to a D14 barrel without carving into the transfers!
The (4.5hp) D1 that I, and dozens of others, prepared way back in the early 60s eventually produced around 275% more power than standard without any work being done to the transfers apart from a general tidy up and ensuring they were simultaneously timed and were positioned relative to the exhaust port centre line. Symmetry is essential for turbulence free gas flow that incurs minimum pressure energy losses. It also serves to illustrate that the D1 transfer ducts were pretty good for such an early design. Starting from such a low base with the old D1, gaining power was relatively easy, you won`t get that sort of percentage improvement from the 12.5 hp of a 175cc D14 barrel, realistically about 50% if you are only concerned about parading and require user friendly engine characteristics!
To be able to more accurately answer your query it might be useful to know what sort of hardware you already have, and propose to use!
For instance, there is no point in carving out the exhaust port width if you intend to use a standard piston, the rings won`t survive. I`ve seen plenty of barrels that have an inappropriate, miss-match of timings, where the exhaust is for 10,000rpm, transfers for 8,000rpm and the inlet timing for a roadster, but sporting a huge diameter carb?
You will always be up against the cooling problems associated with an iron barrel, so an efficient cylinder head is essential, one that allows for the free, fore and aft movement of cooling air through the fins right down their roots where they blend onto the combustion chamber skull cap, the hottest part of the head.
With a bit more information your questions can be more specifically addressed.

Cheers, Trevor

Hi Trevor

Many thanks for your informative reply. Over the next few days I will have a hoke about (local phrase for rummage through) and see what I can turn up. I know there are two non-BSA alloy heads - GT and ? but perhaps for 125 engines. Plus a few 'large' carbs. Ah dear, if life were only simple!

Regards

Jim

Jimmie,
About 35yrs ago I bought a D14/4 Bantam as a commuter bike, so it was a given that it would be `improved`. I bought a 10:1cr head from George and set about checking the factory compression ratio on the bike. BSA claimed that the cr was in fact 10:1, but my measurements had it at about 8.75:1. I removed the original head and the aluminium gasket, with the piston at TDC the crown edge was a good mill and a half down the bore. Small wonder the cr came out wrong, but more importantly the squish gap was so big as to be totally ineffectual! The barrel top was skimmed at work, and with the Todd head fitted, and a squish clearance of just under 1 mm the revised cr came out at almost 10.5:1. A mill was taken from the top and width of the exhaust port and the inlet timing was extended a few degrees. Nothing dramatic was done to the timings, but starting, acceleration and top speed were all improved. However, what really surprised me was the improved fuel consumption, it is this sort of effect that I was referring to when citing user friendly characteristics. But it is also shocking to me that BSA could have done just the same and produced a far better product, but their big four strokes took centre stage and their corporate attention but were to prove, ultimately, their down fall.
So if you have Todd head then you can`t do better than to use that!

Trevor

If only, my first bantam had the twin bantam brake and the only thing that slowed me down were the heels on my Lewis Leathers boots and a quick prayer, especially at the hairpin corner on the club circuit at Cadwell.

Hey there, David K. When I was Bantam racing there was a bloke by the name of Dave Kershaw hurtling around on a Bantam - are you he, by any chance?

Might be John, but I have a feeling that this particular DavidK is a Mr.Kingsnorth, as well as Bantams he campaigned a very special 250 Suzuki back in the day, remains to be seen, used to live not too far from me, and nearer still to Steve Hall!


Trevor

You are right Trevor, i think you lived just up the road in Findon and Steve lived in the same town as myself.. The bantam was the first one that i owned along with Neil Andrew, it was turned into quite a quick machine allowing Neil to become a "Senior" and myself to win a couple of senior races.If i remember correctly it had an Amos tank, probably the only item left from the original starting bantam from 1969.The original double sided brake was absolutely useless.We used to take it in turns to race the bike and at a Cadwell park meeting it was my turn. I managed to fall off in all my three races prompting the statement from the old Saint Johns sargent on the hairpin point to say "not you again".
I had out braked two tiger cubs into the short club hairpin corner, the brake simply stopped working and i realised i was going to torpedo the cubs so i put the bike onto opposite lock and went over the handlebars and slid up the road with the bike on top of me.Good fun , but as you say i moved onto the 250 class , with the occasional outing on a Bantam.

We all of us start somewhere, great picture this and is the prequel to a very successful racing history for both of you! What year would this be Dave, mid 60s?
The hairpin at Cadwell and in particular the 1.5 circuit where approach speeds were that bit higher than the 1.3, saw huge numbers of `brake fade` incidents. I remember with some horror the twin hub brake was good for about two seconds and then just zeroed out, a D7 was better, especially with green linings, but eventually had to be replaced as the bike and me got a bit quicker.
Actually Dave, I lived a short distance further along the A6 in Rushden but now reside in Somerset, still regularly in contact with Steve who now lives in Desborough  

Cheers Trevor

Trevor
What a photo, it would have been about 1968, the year before we started racing.
As we had to take the racing bantam to bits to fit in the boot of an old ford to save time Neil used to drop the engine into a nearly legal D1 road going frame to ride it up to the local air field.
The first time Neil rode it up to the drome the local lads on their various motorcycles decided to show the old motorcycle how to go, boy did they get a shock when Neil gave the engine a bit of throttle and left them in a smoke haze .

Jimmie: if you can send me a personal message with your e mail address, I can give you the details of how we have ported a D14 barrel for our pre 63 racing. It gets 17.7hP and 13.3 ft thingies / buckets of torque !

H John

PM sent. Many thanks.

Jim