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 ref Photo's some transfer,scavenging phase, 1 of John bass.

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Derek

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Number of posts : 1065
Age : 56
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Registration date : 2007-06-15

PostSubject: ref Photo's some transfer,scavenging phase, 1 of John bass.   Sun Mar 31, 2013 6:58 am

for ref only -

I will pop along at some point and explain what some of these are.

most self explanatory, or perhaps our resident experts may wish to comment.
some reason John Bass Photo not come out, John your in a new/old book about BSA BANTAMs and quite a few pages on racing no one from the lastest people other than MICK Scutt gets a mention, but great reading lots of alloy barrel bikes from the scottish 6 day trials, etc.
from the 70's also topic in another on P.C. Clive Dodds, and the guy I first met when I was just 10 years of age, Inever new half the Neil Andrew and quite a few more all very interesting reading by Owen wright. and a picture of my Bike as it was in about 68'ish owned and raced by the then John Danks.

Nigel included for you, a picture of someone talking to you at the midlands do! lol.will be along soon to add some more,

[img][/img]
a bit out of date but effective to show what actually happens ?
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john bass

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PostSubject: Fascinating!   Sun Mar 31, 2013 9:47 pm

Fascinating pictures Derek, thank-you.

Fascinating to have my name in print again -- NOT with "WANTED dead or alive..." attached....

If it was a pic of me it must be from yonks ago when I had hair & teeth as was chased by lots of loose women... Ah --oh! Sigh! If it were a pic of me racing I am glad it didn´t come out, because for sure as hell I´d have had a foot on the road. At short circuits like Llandow I´d forget it was tarmac and broadside paddock Bend -- in the rain, of course.

Most of the fellows looked cold but it looks like you Midlands Wallahs have some good technical stuff going. Wish I WAS there ... !!!???

What about that pic of a clutch? -- looked unusual -- tell us more about it....?? Bigger the clutch with more plates and springs and the Torque Conversion multiplies itself enormously ...

I retire and stop thinking about loose women.

Well done the Midlands -- definitely ahead ....

Cheers!

JayBee for John-Boy....
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Derek

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PostSubject: Re: ref Photo's some transfer,scavenging phase, 1 of John bass.   Sun Mar 31, 2013 10:15 pm

Hi John at last some time to add some content.

first to load your picture ans another you may like or wish to comment on.

The clutch I have no comment on as the cloth hides a secret Im keeping.!

unusually no one commented on my barrel, at our midlands bash, Ithink there was too much being said no time to look, just listen, really amazing stuff, Ihave a long list of things I need to try and one item already given me a little bit more, Im almost there, taking into consideration my extra weight I was wondering what difference round a race track a bike excellerationg that is three or four stone lighter than a bike of equal power and torque would make to lap times.

now heres your picture John, for reference the new books in the national motorcysle museum are great, many new one's on the Bantam.


regards Derek




if some one could or would perhaps comment on what this image is showing - please.
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Derek

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PostSubject: john bass   Sun Mar 31, 2013 11:08 pm

john
I was just studdying your picture,!!! seems your back wheel appears huge compared to the front, that looks like small(a 16inch perhaps)and if ever there was a reason to extend the wheel base, (moving the back wheel backwards, can be seen as clearly the only way, surely your position on the bike shows this and the limitations of the riding/weight/position on a racing Bantam.

insidently when Mick Nash "d"villia helped me build a Frame, he suggested to make a much longer swingarm, some 75 or 80mm longer Ithink he made it. I did load some photo's on here, but the bike can be seen in the pictures page on here anyway.

A lot of talk about chassis, and some realy interesting stuff, but in reality, I dont think having a great rolling chassis is the most important thing to start a bantam racing or project, as long as the brakes work and its safe as all you need to start, I think its better to spend time on the engine development first, then turn to the chassis after you cannot hold the same line/speed through corners as others.

I was in this position at cadwell park a great circuit to develp a chassis, especially through chriss curve and the goose-neck, I noticed two in front i was catching, but both were pulling away from me through here, but i was considerably quicker up the hill and down the straight to park, at the last cadwell meeting.


Derek
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Colin Hall

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PostSubject: Re: ref Photo's some transfer,scavenging phase, 1 of John bass.   Mon Apr 01, 2013 3:00 am

Derek,

You ask what the diagram shows; it is straight out of the Jante SAE paper.

It refers to the diagram higher up on this page (fig. 9.2.4) showing four patterns of flow produced by the motoring method. The left hand drawing above gives a possible scenario that would produce the ‘tongue pattern’ shown as figure (a). The transfers are angled too far towards the rear of the cylinder wall were they meet up at 9 o’clock. The combined flow moves across the piston crow towards the exhaust port. The pattern produces high levels of fresh and exhaust gas residual mixing – not good.

The right hand drawing shows in effect the opposite where the transfers are angled excessively towards the centre of the cylinder. When the flow streams combine, the flow heads towards the rear wall at which point it splits hugging the walls producing the ‘wall pattern’ figure (b). This leaves a large central core of exhaust gas residuals – not good.

The lower diagrams in the set of four show real target velocity profiles – what you will produce if you follow the method. The one I aimed for and achieved fairly well was a combination of figures (c and d). The transition boundary 12 o’clock/6 o’clock, splits the cylinder into two halves. The rear half of the cylinder (on the left) has a vertical velocity gradient increasing from 0 at the transition boundary to ~20/23m/s at the wall - the wall side of charge has to travel further.

With multiple transfer ports the whole thing gets more interactive hence my original suggestion for how you would tackle this. It helps if you have a feel for where the stagnation point is (the point where the opposing flow streams interact and the local velocity is zero).

Colin
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john bass

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PostSubject: Optical illúsion Derek   Mon Apr 01, 2013 4:37 am

When approaching the speed of light even the wheelbase of a Bantam gets distorted Derek...

Much more likely is that the cameraman made a BU of it.

Both wheels were original Bantam, shod with those fantastic racing tyres from Continential Sports (French, I think?). See my avatar where I am really belting it around Mansfield in the process of winning my first ever road race -- almost the same pic... -- A Novice event where the clutch burned out -- yet again -- but stayed together long enoug....

Fond memory ....

Yaaawwwnnn! Oh! how boring!!

Cheers!
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Trevor Amos



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PostSubject: Re: ref Photo's some transfer,scavenging phase, 1 of John bass.   Mon Apr 01, 2013 8:10 am

I thought you guys might be interested in the follow precis of an article i read explaining transfer theory .

" Static pressure at the foot of the central column can have some adverse effects . Too high a pressure will impair the flow , because the the higher this pressure is , the smaller will be the pressure differential that accelerates the charge through the transfer ducts . Aiming the transfer ducts axially a little will improve the flow , just like it does over the piston crown . Slightly axially-aimed transfer streams will provide for less violent , not completely head-on collision . The central column can be controlled this way , and the transfer streams will keep the axial component of their velocity, so the central column need not start it`s journey to the cylinder wilth zero velocity . So the axial column speed can be controlled as well as by the axial transfer angles "

The physicist who wrote this article , co-developed the 125cc , 55bhp Aprilia engine , not someone , whose experience , you could really argue with !

Trevor
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Derek

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PostSubject: Re: ref Photo's some transfer,scavenging phase, 1 of John bass.   Mon Apr 01, 2013 8:53 am

Hi Trevor pressure differential from where to where, the charge into the cylinder, or pressure in the cylinder or incomming fresh charge towards the transfers port base, ?

surely the higher the pressure in the transfer base the greater the differential as the cylinder should be at a lower pressure ?, I have always understood that if the transfers erupt too violent into the cylinder they increase the potential for uncontrolled turbulence ? increasing the potential of mixing with the outgoing exhaust charge.

I had assumed there to be a lower pressure area in the cylinder, because of the exhaust, so puzzeled that I may not fully understand this critical aspect of the delivery charge, information.

Derek
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Trevor Amos



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PostSubject: Re: ref Photo's some transfer,scavenging phase, 1 of John bass.   Mon Apr 01, 2013 10:37 pm

Derek ,
Spot on with your assesment as to what is happening , but with a couple of caveats to add . The pressure in the cylinder at transfer opening is almost entirely dependent on pipe action , with the diffuser returning continuous suction reflections that evacuate the cylinder of combustion deposits . The hope is that at transfer opening , the cylinder can be below atmostpheric pressure and a large enough pressure difference exists to promote strong flow from the crankcase , so far so good .
The problem is that the waiting transfer gas contains a lot of inertia and takes a good energy kick to get it moving , and long and or excessive area ducts make things worse , and as the gas accelerates to it`s maximum flow rate the piston is moving and case pressure is dropping . As long as the flow pressure is greater than cylinder pressure every thing goes along nicely , it is at the parity of the cylinder pressure and case pressure the flow velocity will be at it`s maximum and have a lot of kinetic energy , but as soon as cylinder pressure exceeds case pressure then flow reversal takes place ! So yes , the transfer streams do collide and excessive kinetic energy is converted to pressure energy and if the streams are angled to use that pressure to maintain column integrity up to the cylinder head and eventual exhaust port closure ,
you will have a high value trapping efficiency and combustable charge of high purity , and make lots of lovely power !

You might like to factor in the effects of the reed valve inlet dynamics where you have , just above atmostpheric pressure on the inside of the petals and just below on the other side which combine to lift the petals and allow a longer inlet period to lift potential case filling , which , comes just after BDC with the trasfers still open ! And at this point the engine has a free flow path from the carb bellmouth to the silencer outlet .

The gas dynamics of a Bantam engine are not simple , they only appear that way !

Is that piston crown pic one from your current engine , if so the heavy carbon build up at the front indicates short circuiting , where the oil is carbonised before combustion .
The remainder of the crown is pretty good.


Trevor
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Colin Hall

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PostSubject: Re: ref Photo's some transfer,scavenging phase, 1 of John bass.   Tue Apr 02, 2013 4:53 am

Trevor, Derek

This all sounds about right. I guess the real problem with the process is that of using language to describe complex three-dimensional flow - we know what we mean to say.

One thought that comes to mind is how the behaviour of a fluid is altered by the pressure field it encounters. It maybe easier to see this on an aircraft wing. The flow streams start to split ahead of the leading edge stagnation point – question how does the air ‘know’ that there is a wing coming towards it. Answer it does not, it cannot see the future, what it does ‘see’ is the pressure field that is created around the wing by the air already flowing around it. This pressure field extends well out side the wing surface. The direction a flow stream can take is in part governed by the pressure field flowing around it.

The same thing happens when the object is fixed i.e. your engine and a fluid is passing within it. Inertial forces are taking the flow in one direction but the pressure field is ‘sees’ within the cylinder will modify the process. It all gets a bit complicated.

Colin
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Derek

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PostSubject: Re: ref Photo's some transfer,scavenging phase, 1 of John bass.   Tue Apr 02, 2013 8:36 am

Hi Colin many thanks for your continued contributions here.
if this is difficult for you guys to explain three dimesional happenings, imagine what its like for guys like me and others to fully understand, I tried to understand this, to do this I got a large plastic bag added a small qty of water then blow on it, the air creates ripples in the water, yet no air touches or blows on the water !!!.
anyway be good to see what you guys would explain for a new strater what he should be doing with his cast barrel Transfers or what we should be trying to do with the transfers with all the limitations they offer.
a piece just like the items done in the Tuning Manual on sorting the barrel.
Derek
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Colin Hall

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PostSubject: Re: ref Photo's some transfer,scavenging phase, 1 of John bass.   Wed Apr 03, 2013 7:32 am

Derek,

Water in a bag? It's simply a matter of energy transfer........

Colin
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