King Bantam Special

Dave I found them :-





I'm just glad we stuck to a simple set of cheap rules in Britain as an engineering excercise it must of been great! So did it ever run? and backwards at that to get your back wheel going forwards? Well Interesting...

Well await your comments....

Mike

wow

This was the assembled motor , when it ran well it was magic but the D10 case were crap ,just as was stated in the early Bantam Tuning Manual
(blue cover early or mid 1986). If I had stuck to the good cases it would probably been my current engine ,but seeing your new evo cases it got me
planning another go at it.

I see the cylinder is reversed -pipe out the back. Did the engine run the opersite way round? Just wondering how the primary drive assy coped with that? Perhaps counter rotating straight cut primary gears is an option space and maths alowing ??

Mike

I,ll slip the gear cluster in one half of the crankcase to refresh my memory it,s just sitting on top of a storage shelf....more later.
Dave

dave holding my breath ------- "we are waiting? with great interest"

rgds Derek

Dave is that a YZ125 gear set ? and gear or chain primary drive ?

Damn a evenings delay had to finish rebuilding a friends yz250 crank,whilst my every move was been scruitinised

Dave

Slippped the gear cluster into left hand crankcase ,damn its a good fit.Okay ,yes the engine was running in reverse ,I used a acetal chain guide to control any unwanted chain throw.
There was a couple of reasons why I stopped tuning ,the weakened crankcases ,missed gears,the on going problems with then Boyer Bransden anologue ignition.The rules also changed for running specials and at that stage I hadn,t have proof of the Ashby Bantam so reverted to the old faithful piston port.
Ended up building a couple of other bikes for racing 1969 kawasaki a1r 250cc ,and a 1967 bridgestone bs125cc yes both rotary disc engines. These are my real bikes as the Bantam is my fun toy.

John,
The gears was brought as a1977 yz80 ,I still have the cases so I could retrieve the numbers to confirm year.
regards Dave

Hi Dave love the Kawasaki Samuria A1 with its steel disc valves and that jolly interesting bore and stroke, so is an A1R a racing one? Strange Kawasaki went to piston ported triples thereafter???

Mike

Dave simons won world title with kawasaki on this base engine they have always been on the cutting edge Remember Kork ballington. ?

great stuff Dave.

regards Derek

Dave simons won world title with kawasaki on this base engine they have always been on the cutting edge Remember Kork ballington. ?

great stuff Dave.

regards Derek

Very interesting thread, good stuff, find the gearbox more fascinating than the disc valve does/did it hold up?

Hello Tony"- answer to your question did it hold up, No he had more trouble with in than we do, better off sticking with Bantam 3 speed less trouble, more reliable, simpler with only three gears what could possibly go wrong. !

I have some photo's of our kids you know its nearly ten years since you came over with them.!! they grow up quick


site livened up" yes a little, there are a few trying, but sadly just can not get some of them to post, or join in ? would be better if more posted, there are plenty looking in, we know ? " make it much more interesting if they made a little contribution every now and then,? especially for all comers, new builders, and potential newcomers.

Sad to here your not coming out to play this year, will be other years tony, once a Bantam Racer you can not get away from it, frustrating /painful as it can be - just nothing like it.

Derek

Not really Derek,I had more trouble with the Admin in Austrailia when the rule changes came into practice.So I had to back track into 4 speed gearbox which just blows a 3 speed set up away ,there is no comparisson.

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 ?