History Opinion

Good Morning All,

Was looking at a few things and just wanted people opinions:

No sump plug and post area ground back and plugged, any reason?

Running three surflex and two metal, typical in the early days?

Square front exhaust post with adapter and spring held complete with expansion pipe but no silencer - any idea?

Amal TT Carb, popular mod in early days?


Eddie

Eddie ,
My take on your list are:
think the sump plug boss gets in the way of the exhaust (low level pipes)
i still run this on the water cooled (needs constant inspection but no metal bits in the oil)
Front pipe flange ,every bike seems different i guess it come down to whats easy for you to make.got to be silenced real good or you wont be racing(simples)
finally on the carb dont know much about the amal tt bet it was the (b------s) in its day ! cheers Nick

TT carbs were not really suited to Racing Bantams in my experience. I tried to improve mine with a Terry Beckett float chamber. This was an SU (BMC Mini) chamber suitably modified and suspended by a threaded (for height adjustment) rod mounted in a sprung diaphragm made from inner tube rubber. Final development of my 1st Banatam kept this float chamber but ran a Gardner carb, much more responsive, and allowed last minute mixture changes on the grid, even with a gloved hand.

Good Morning,


Many thanks for the replies, i can imagine the tt carb was probably a pain to set up, with regards to the sump plug you could be right nick and maybe it had a low level befor instead of a high level, how do you drain the oil though? with regards to the exhaust it may have had a bolt on silencer at some point if you couldnt run them unsilenced.


Eddie

Hi, all,
Ah , TT carbs what joy ! When i joined the BRC , in 1964, SU float chambers were in common use.a popular
mounting rubber was from the Gold Star. I can`t be certain when Terry came on the scene but i`m sure it was post this period.
It must be remembered that TTs and GPs were about all we had available , unlike the situation today!
TTs did have one good feature in that mixture strength could be adjusted , during a race , by a clip on mounted lever actiating
a slide on the carb body.
TTs a pain to set up , maybe , but Fred Launchbury, who was a multi champion , had impecably sorted carburation with his set up
Oh , and for those who like these things, 14.5 bhp at 9500 rpm.

Thanks Trevor - I had quite forgotten the air lever on the TT carbs. If I now remember correctly the TT carb main jet size could be varied by as much as 3 sizes, whereas the GP carbs you only got 1 to 2 sizes?

Also, I know the GP2 is a remote needle instrument, but was the TT similar, or did it have a needle at the centre of the slide?

Well clutch all cleaned out of old oil and now working again, tank to get looked at and strip and service the carb and see what happens, is the lever similar to a choke?.


Eddie

Hi Eddie,
just to clarify is your list how your bike is at the moment ?

Hi Nick,

Sorry i have probably got confusing, my dad is building a 175 bantam to race for himself, my questions and bits are regarding one of the projects im working on to keep the mind going as it were while waiting for bits for my dads.


Eddie

Hi , Peter,
A little more info. The TT had a central needle , the GP had it`s needle to one side in the choke and fuel entered by an inclined
spray tube.The RN , as the initials imply , had a remote needle position in a chamber to one side of the carb body.
From memory , Sam Benn used a GP to good effect on his , all red , bike , but he was about the only one to do so .
Hope this helps a little .

Hi Trevor.
I bought your Longstroke engine complete with TT carburetor, (early 1970s) I needed a reliable engine to back up the 56x50 I built as it only finished a few races. We tuned our engines very differently then, packing the crankcase fitting 4''flywheels and then filling the balance holes. We believed that Pump efficiency was what we needed. Your small fin long-stroke even had piston stuffers. It was a good reliable engine, that gave me many more enjoyable finishes than my short-stroke,(overheating and narrow powerband) You told me that the crank was made by Alpha (mainshaft and flywheel cut from one piece). Have you any more information about the crank, as I believe Alpha made cranks for other twostrokes (250 Starmaker)but have not read anything about Alpha cranks For the bantam.

Once upon a time there was a formula printed in the Club Magazine for designing an expansion chamber that I used to find a starting point before experimenting. It possibly originated from Dave Hunter. I honestly believe that the issues in developing the ideal expansion chamber are so complex that experimentation is the only way. At school (in the 1950s) I was taught that the speed of sound and the speed of light were fixed absolutes. Now finding that the speed of sound also depends on the temperature of the gasses it passes through, and knowing that the temperature inside the exhaust varies extensively. I am left knowing little more than that it takes less time for the echo to come back in a short tunnel than a long one.
[b][u][/size[size=18]]Barry Golding

Yo "Barry" another heavy weight coming out !

a gracious welcome aboard to you "sir."

we are all holding our breath in antisipation of ! and for Trevor's post in response to you.

but Trevor please don't forget my post response to the - "tail pipe diameter outlet " please respond soon on this thanks.

kind regards Derek

Hi ,Barry,
Good to hear from you.
Indeed the crank was made by Alpha . In late 1967 i approached Alpha to see if they would be interested in making
three 4 inch cranks with integral shafts . One was for me , one for brother David and one for Chris Jarvis , they agreed,
so i sent off my drawings, all was approved ,and ,would it be alright if they were made from Ariel Arrow forgings !
A delivery date of 6-8 weeks was quoted , and, sure enough they duly arrived.
The engine was first run in March 68 . As to the cost , £30-5s each ! Less than £100 for three beautifiul cranks , makes you think !
Your teachers were correct , the speed of sound at , air standard conditions, is absolute at 340.6 mtrs/ sec , at say 600 degrees c
it becomes 590 mtrs/sec .The problem with speed of sound calculation in an exhaust system is that you have to factor in
the specific ratio of heat at 1.33 , the universal gas constant at 8.314 j/mol k ,and the molecular weight of the exhaust gas ,at
0.2896 kg/ mol and temperature in k . After that it`s not too bad!

Hi Trevor

all dependant on Temp then, "mind you, lots of hot air on here too!

Now please look at your "outlet diameter" post for me, and do the next installement for all our budding listeners /posters and the like "young guns ! in the design of the expansion chamber
Also we need to try and keep it all on the same post, if we can, will make it easier to keep track, especially people reading/ looking back at old posts for help in the future, etc.

from memory I think I asked you about the length of outlet pipe - is it formula for a ratio or mathmatical calculation based on hot air movment / also we need to work on the first taper in the box ? and the length's "o" and not forgetting the revers cone.

whats your take on "Gordon Jennings" formulas for expasion chamber design.

we are all reading up on this - whilst "hold our breath" and waiting for you

Hope your well, keep posting and see if we can pull out a few more budding heavy weights from hibernation,

I'm convinced stat's!!! -they are all reading these posts, just waiting for the opportunity to have their say.

Its a shame they don't, I have considered reasons why, "too old","trouble reading" you see when your past it - its usually the eye's that go first, then the memory". !!!


Best regards Derek

Hi all

When i get the chance i will post photos of what i was on about from the original post.



Eddie

i did get the chance to put pics up as this was all related to the yellow one and went under the new learner part, all very confusing!


Eddie

blimey you can not sleep then ? you should be out in the shed.
"i would be if i was at home" lots to do.

regds Derek

Hi Derek,

im alway up early and come on here on my phone. Bikes are in the house so no wet shed for us!


Dads home today so will probably be attacking another seat loop!



Eddie

hi ed

I like the front wheel looks the business, wouldimage that would still be good today, and the cylinder head I have been after GT 100 A to finish off an original fred launchbury engine I picked up some time ago.

also its on backwards the pointed end should be at the back

also can see you been working on this as it has a nice polished ignition cover. my son edwards Bike has a D5 frame, I believe they are lighter, and been told but not sure this is true, that they areold more prone to cracking just above the rear engine mounts.

regards Derek

Hi Derek,


I did all of this a while ago, was just juggling pictures to get the in the right topic, no idea what the brake is off, maybe someone will know but yes it is a good one. Well i always thought it it looked back to front but the thing came complete and the head was that way round? I must admit it is light but the fairing weighs a ton!


Yeah i know about the polishing, i do like to do that but dad says im strange...............................



Regards


Eddie

just spotted seems you have x2 GT100 A as in one picture the head has a cutaway in the other it appears as though it does not. ! just an observation,

you seem to have so many, bikes we had a issue our selves with this, we planned to have three Bikes we have one completed and racing,

I have found its difficult to make progress on the others when its like this, it just seems to take an age.
eds shortstroke is a 50x56 the frame still needs lots of work to finish it.
i have another bike Iwould like to finish its undergoing frame changes as we sprinted with it, it needs lots of work, at the same time as all this I want to do and try so many things with the current bike.

its knowing what to concentrate on, trouble is i'm not sure what to focus on first, I found at first we ended up doing loads on both bikes and engines, but with little progress, to finish either, we only finished my bike because we adopted the method of only working on one engine or bike at one time, i recon when they are both completed, i'm hoping it will be easire, we are still finishing off bits from eds top end, I finished machining it tonight - off the subject - I just dont know how this hobby can be done at home without a small lathe, I finished fitting the head and machined the squish on the head that came from Ted, ED'S engine is now ready to go back in the frame, we still have an exhaust and some bit's bob's and brackets to finalise.

we have spoke to a few about how long it takes to develop a bantam, to a point its competertive, Ultimatley the answers comming back are it takes at least two years of racing to development a fast Bantam, this is after it has been built.

I was told this by a guy called Ernie Barr, as a boy of 10 years old at cadwell park in 1971.

Our aim next year is to catch the group in front, but we also need to be able to ride faster so need a little more practice, stopping for long periods, you loose your speed both entry and mid corner speed, this affects the speed down the straights, this makes you bike appear slower than it actually is.

regards Derek

Hi Derek,

Not sure where you are looking as there is only one head for this one and its only been off once.

No such thing as too many bikes, but yes i agree you can fiddle with too many at once. Dad is doing his own bike and im just doing history tinkering with bits and pieces so dad can finish his.

Unless you are in "the know" with people who have access to tooling then it maybe hard, i have a few things i want to do and dad has a few bits e wants made so we are gonna give it a whirl.

Good to hear that Ed's bike is coming along.



Eddie

Hi Ed

You can always ask my dad, for machining changing squish clearences, he has in tyhe past been able to do allsorts of things, now his machine are much smaller so on bigger items like a barrel or liner or gear box best to just ask Brian or Tom- if they can help, Im sure they will do it but as for machining heads and pits and pieces I would get a small lathe they are so cheap at the moment nothing like making a part then it working ok or even increasing your performance!.

Tom Miller without a doubt makes the best cranks I have seen/used they are turbine smooth too, we have been using one in old faithfull for I think it was 6 years no issues! just change the big end cage.

For big or major items (in the off season), I'm sure both will be willing to help they dont charge a lot either, Im sure would be willing to help, just got to brave enough tom pick up the phone and ask.

Hi Derek,


I have a lot of time for your dad, he has been over many a time to look at things and explain them to us, plus he is good company and has great stories.

Brian White i know we have met many times at races and him and his brother always say hello and chat to dad. Never met Tom Miller, but i know he does alot to help people out racing.


We already have a lathe and your dad has offered to help us when we go wrong or if we need advice.


Eddie