King Bantam Special

This just gets better, Dave I think the work your doing is so interesting "fantastic", love' all your posts, and the photo's Dave, we are all interested in your preference for the 4 speed box.

BSA never actually produced the close ratio 4 speed gears the was some done for BSA comp shop for the scotish trials team, by an out side company, and I believe a set of 4 and 5 speeders, these managed to find there way into the bsa bantam racing fraternity in the uk. not sure who has these now. Dave Amos had some on his 190cc I'm sure, infact trevor has sent details of the ratios to Jhn senddle in newzeland. comments anyone.

Dave we are all really interested to know how you managed to get the std 4 speed box to work,
1) what have you done,
2) what type of mods,
3) the first gear std is so tall it overerevs 16 zillion rev's when you come down the box, how you coping with this
4) tried this loads of times on my 198cc sprinter, also can we see pictures and/or suggested mods to your selector mechanisum. you have done I will post the Tom Miller mods soon when we strip the box, thats unless anyone alse has picture they can do before me.


a big topic of conversion and mods in the uk is selectors, and as I have just lost the good cop compertition. ?

5) whats your thoughts on these Dave.

Kind regards

Derek

Sorry Mike missed your post ,my bike is a tuned Samuri a1 ,stroked down to 54 x 54 easier to get pistons ,rods.The original rotary discs made from tufnol explode at high revs,a hard lesson;replaced with s.s disc ,all good now.The gearbox is a pain low 1st ,5th is not much better,will be sorted on next gearbox(6speed).This picture was 1995 before fitting of the A1R fairing.

Derek,
So many bloody questions.It will take a few posts to explain the conversion of a d3 crankcase to 4 speed but it is very easy.I have found all my referance notes/drawings,but you have really grabbed my attention with 4sp cr 5 speed bantam boxes ......more info thanks.
I have an article written in January 29th 1966 (Motor Cycling Racer Test Todd Bantam) it claims a four speed all-light alloy engine ,in the specifications section it gets blurry and I don,t know if they quote the 4speed ratios
How can a search function be added to older posts because I,m sure all the good info has been on here or discussed at some point? any ideas anyone.
I cannot find my bantam gear page with part numbers ,I,ll search again but can anyone hoist a image just in case.With my current st 4 speed first gear is too low ,great wheelies off the line scares the vintage 250cc,350cc,into back off mode,then the hole between 1st and 2nd is were I abuse the clutch a little.The ratio,s 2,3,4 are fantastic but a 5th gear is worth 2 seconds a lap and when competing against bikes with 5 gears (125cc classic)you cannot compete.
I was told the 3 speed cr gearbox was designed for push starts,In Australia it,s all clutch starts ,
3speed cr just didn,t work.
regards Dave

just re reading through things and this is an interesting subject ......well to me anyhow,

have anyone any info on four speeders that have been used in the past?

I believe Trevor Amos has posted the Todd Amos 186 four speed gear teeth numbers here before. If he does not reply I am sure he would not mind me revealing, eh Trevor ?

I have read of a Close and Ultra Close set ups:

1: 17/20, 24/23, 21/26, 4: 27/20 gives: 1, 1:1.09, 1:1.294, 1:1.823

1: 21/26, 24/23, 4: 27/20 gives 1, 1.09, 1.294, 1:1.671

We have:

1: 19/28, 22/25, 25/22, 27/20 giving similar top 3 ratios as 3 sp CR
ie: 1, 1:188, 1:1.534, 1:1.989

built 19T MS by splining 3spCR 1st gear on standard shaft and pairing with a 28T LS 1st gears made and new 27/20 top gears giving a decent first gear for getting off line with high secondary gearing sprockets

That`s fine John, that information is now in the public domain any way!

Four speed 125 engines have been around for years, Fred Launchbury made a reference to the 4 speeder in the MCN racer test of the Todd BSA way back in early 1966.
I was at a BRC, Snetterton race meeting in the 60s when a tannoy announcement was made asking for permission from the other competitors for Fred to substitute the legal 3 speed engine for his illegal 4 speeder. No points that he may accrue would count towards the championship tally. The excuse made was that he had engine problems which he later confessed was just a ruse, but he still won anyway!

Back then BSA were into scooters and their offering had the D7 engine installed. In an effort to upgrade the overworked 175 engine it was thought that an extra gear and a bit more power would have more public appeal. The engine was forced-draft cooled, and the fan drained a lot of energy from the engine, hence the need for the upgrade. Experimental 4 speeders were made and Fred`s was believed to be one of these units but with closer ratios. Sadly for BSA the scooter project eventually failed, but the stronger D14 emerged from the ashes.

This is part of the tale of the 4 speeders as I have experienced and have been told, but it is all eminently plausible. That a 4 speeder existed is not in doubt, and intriguingly may still be out there? George might know, after all he worked for BSA before he went off the make ballistic missiles!

Trevor

As previously alluded:

the gears were: First: 19 - 28 25 - 22 23 - 24 Top: 26 - 21

Giving ratios of: 1, 1.187, 1.407, 1.825

Very similar to Bultaco TSSs at the time ?