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 Terry Beckett Chat.

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KISS



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PostSubject: Terry Beckett Chat   Sun May 03, 2015 1:38 am

Sorry folks. I used the term convex to describe the departure from pure triangular in `Squish bands and compression ratios`. It should have been concave, of course. The appearance is that of a gentle dome.
I`m no good at drawings and even if I were I would have great difficulty getting them onto `Chat`. Terry
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PostSubject: Does anyone ever mention...   Sun May 03, 2015 5:23 am

Does anyone ever mention "Dynamic Compression Ratio" as versus "Static Measured Compression Ratio". I mention this because the resonant exhaust system in punching (for want of a better word) the charge back into the chamber which must increase the dynamic CR  before TDC ...??

Or am I speaking garbage?

I spoke with a good tuner who reckoned a realtively low static CR helps with getting max revs  higher and  getting the "breathing"  right keeps the dynamic CR high...  

I still wonder why the Walsh Bantam was such a success using an open megaphone pipe -- I know the CR was 16:1 and it was on a methanol fuel but Bill Lomas reckoned it "...revved on and on..."
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Trevor Amos



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PostSubject: Re: Terry Beckett Chat.   Sun May 03, 2015 9:12 am

Strange thing John, you never read about the concept of dynamic comp in any of the tuning books from the past, or for that matter not too much about delivery ratio or trapping efficiency.
The defining factors of the dynamic compression ratio are those that are created by the addition of static ratio, delivery ratio and trapping efficiency. The higher of s/r and d/r the less static that the engine will tolerate, short of the onset of detonation. So perhaps high comp ratio as we used to know them are not the way to go. However, modern ignition systems that automatically adjust their timing can control heat and cylinder pressures very efficiently, play a vital role here.
But you are quite right in suggesting that high comp ratio are a mixed blessing, what we require now are adjusting cylinder heads that work in concert with ignition and self adjusting pipe action. That way we could maximise overall efficiency and minimise negative work prior to the commencement of the ignition burn.
Pie in the sky I know, but we have to thankful for the advances we enjoy, don`t want to go back to contact breaker points and all that old stuff.

Found my old slide rules and log tables the other day, my youngest daughter who was visiting, thought I had got them from an antique shop, cheeky young thing! I tried to explain that aircraft were designed by using these things, she thought it was all a big hoot!!!

Trevor

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PostSubject: Re: Terry Beckett Chat.   Mon May 04, 2015 8:36 pm

I know I keep saying it but it is worth repeating; A two stoke is only a two stroke. All the years of progress have left many unanswered questions. All we have done , in this respect, is change the way we ignite the charge. A real challenge was how to do it with points. Later, in the 80s Yamaha made changes to the ignition system that could possibly have affected my porting arrangements. So I shot over to see David Hunter at Micron to see if we could detect anything on his ultra modern electronic dyno. We eventually had to do it the hard way; ridden standard and modified with special attention to my usual modest change to the c.r. and any sign of heat. Whatever it was complimented what I was doing. Incidentally, you`ve no idea how much on track testing we did to reduce the c.r. and retain the usual result. It looks as though the boundaries have been pushed now and it is time to reflect again. Some of the latest Moto X machinery is a good place to look. Mind you, the objective I set for production machines was for the rider to have a good, reliable season of racing. If he could ride it he could win with it. Any modifications we made in development were incorporated in any machine thereafter. As they were mostly for short circuit racing the needs were obvious; lots of torque, out of the corners and half way down the straight before the revvers could get it on. Reliability: with advanced ignition systems and carbs that worked and respect for what the general motor strength could stand.(an assumption)
I must remember to preface my next bit with a tribute to David Hunter, a really exceptional tuner who was up, running, setting lap records and producing championship winning machinery for his brother when I was still standing, looking, asking and wondering. His great inventiveness will be reflected in `Transfer Ports`. Terry.
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PostSubject: ............*WISE WORDS TERRY*............   Mon May 04, 2015 8:49 pm

Good Morning Terry,

Thank you for the input and a glimpse of the old days!

Dave Hunter was indeed an ace tuner/rider and helped me a lot with the learning also!

I am sure we are all looking forward to more gems from the transfers article!...............Very Happy

Take Care!

Rex
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KISS



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PostSubject: Terry Beckett Chat.   Wed May 06, 2015 2:30 am

Preface to Transfer Ports etc.: David Hunter deserves a special mention here. If you can find his article on Bantam Tuning you will learn something quite special. David was kind enough to take over my business when I was delegated the responsibility for the nursing services of five hospitals, all in the turmoil that large reorganisations create. He had retained the famous old cylinder and, in a loose moment, decide to mould the transfers. I couldn`t believe how many assumptions went out of the window that day. The factories took an age to catch up and use the technique.
The taper factor was preserved by leaving the inner wall contour alone. The rear wall was matched to the c/case as was the outer wall, larger than standard and followed through to the port mouth. The inner wall (nearest the exhaust port)was removed about as much as the metal could tolerate down to the port mouth creating what he calls the deflector which was about a 1/4" deep behind the port mouth. Needless to say, the port could then be widened significantly but retaining the deflector. I thought the speed was to do with the port size and the deflector, over exuberance with a right angled cutter until (1) I came in possession of a flow bench and (2) the need to find torque in a very top-endy Go-Kart motor. The results are described below. Almost incidentally, David`s work enabled three Bantam championships plus lap records etc. A fabulously innovative man.
I didn`t use the deflector technique in production machines simply because I didn`t think I could reproduce it accurately from one machine to another. But anywhere torque was needed, trials, scrambles, endures, Go-Karts etc. Terry
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PostSubject: Re: Terry Beckett Chat.   Wed May 06, 2015 3:39 am

Hello Terry,
Thank you for posting you experiences and thoughts on combustion chamber profiles and the direction that it took you in. They form an historic insight into a formative period of two stroke engine development that few active Bantam racers experienced, or at the time were perhaps not even interested in.
However, exposure for you to modern concepts will provide for a wider perspective that reflects the new reality of 21st century two stroke race engine performance. Some of the following revelations may even surprise you!
Development of GP 2t engines effectively stopped when only 4ts were allowed to compete, we should leave aside the politics of that decision! The Karting world is now where most current work is done, together with enthusiastic, private ventures.
The exemplar engine of 125cc capacity, and multiples thereof, is the Italian Aprilia, having bore and stroke dimensions of 54mm x 54.5mm. With 54hp available at the gear box output sprocket at 13,000rpm, and 16bar BMEP, it was overwhelmingly the most powerful engine in it`s class, ever!
Below are a few of the more significant engine stats:

Compression ratio; 15.5:1 running on unleaded race fuel.
Squish band area of 50% of bore, giving a width of 7.91mm.
Squish band clearance, static, of 1.28% of stroke with a linear dimension of .7mm.
During dynamic running this reduces .4mm.
Maximum dynamic cylinder pressure of 62bar occurs at 18*ATDC with maximum temperature of 2504*K at 32* ATDC.
The last two stats show that with the piston well down from TDC, the cylinder pressure is clearly seen be exerted over the entirety of the crown surface, and not just a small central part of the piston!

Way back in back in 1960, Jack Williams was struggling to get the 350 7R AJS to combust efficiently. Ignition advance of 38*was necessary to complete the process. The team then hit on the notion of employing squish to invigorate and speed up the combustion process, experiments concluded with a squish area .030”shy of the piston. This modification was so effective that ignition advance could be reduced to 33*, detonation was eliminated and the piston crown and combustion chamber surfaces were exposed for a shorter period of heat absorption. This modification also allowed a small but beneficial rise in compression ratio.
So, squish has been with us for at the very least 55years, it is one of the agencies by which turbulence is created and without turbulence combustion would collapse to a far more leisurely, laminar burn.
In a 2t engine there are a variety of turbulence inducing features that can be identified. Piston motion, creating a reducing chamber volume, transfer scavenge stream action that converts velocity to pressure, returning wave action from the exhaust pipe entering the cylinder prior to exhaust port closure. By far the most important of these events, however, is squish activity. Typically in a race engine, mixture is ejected from the narrow clearance gap between cylinder head and piston crown at a velocity of 35mtrs/sec, directly into the now burning mixture. This action in turn speeds flame propagation, which then in turn leads to a quicker and far more complete burn in the finite time scale available. Intrinsic to all of this is an ignition timing that retards towards peak torque revs and then more so into the over-rev band. With much more combustion taking place ATDC the exhaust gas is hotter and so heats the pipe to maintain effective torque well past peak revs!

Trevor
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PostSubject: ...................*TRANSFER*...............   Wed May 06, 2015 7:17 pm

Hi Terry,

Thank you for taking the time to give your ideas on transfers and how it was proven with actual results!

It must have been a big step forward to you and Dave!.................... Very Happy

We are all looking forward to more of this!

Take Care!

Rex
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KISS



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PostSubject: Terry Beckett Chat.   Wed May 06, 2015 8:55 pm

Thank you Trevor. I did a comprehensive reply and on the last line it all disappeared before I could send it. It must be around somewhere but I don`t know where to look. Help !! Terry.
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PostSubject: Re: Terry Beckett Chat.   Wed May 06, 2015 10:21 pm

Commiserations Terry, I guess we have all done the same in the past, pressed the wrong button, you are in good company!
I always now type my articles in Word, then copy and paste into the forum page. At least that way I still have a copy to hand as a fall back source of reference!

Trevor
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PostSubject: Re: Terry Beckett Chat.   Thu May 07, 2015 3:43 am

Thanks Trevor. I must admit I was the victim of enthusiasm this am and typed it straight onto the site. But this was the gist of it.
You will appreciate the struggle to stay on the doughnut and not get lost in the hole. I do appreciate what you are saying about the RS but I see that as an exercise, a toy for engineers, to progress happily until the boundary pushing has to stop. I see the information and analysis as a luxury to be enjoyed now. There was no such facility available to me before simply because I could hardly release such sensitive stuff in my business at the time. But I am not dealing with such a device. I really have to wonder about the future. The bubble of enthusiasm in the paddock over very highly developed but old 125s. The numbers on the grid go with my preoccupation with the 175, although obsolete. Is it so primitive or incredible to have a class for 175s, genuinely el cheapo governed by the same kind of rules as for the early Bantams that would encourage people to enjoy what is so absorbing and happiness producing. My thoughts about the 175 are purely devoted to the perpetuation of the species and on the site, sharing experiences to that end. Where else is there to go ? Well for you it must be disc valve inlet and some really adventurous porting ? I have some good assumptions about that. Terry
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PostSubject: Terry Beckett Chat   Thu May 07, 2015 5:19 am

I have to preface my chat about transfer ports yet again, with some concerns and codicils, which means I am some assumptions missing.
Broadly speaking, I found the main transfers did all the work and controlled the direction of flow. I came to see supplementary ports as lazy ports that followed on or mopped up. (They are taking the gas from the same source as the highly important and hard working main transfer.) That assumption was supported by a cylinder I saw recently that had a second transfer window and immediately under it another the same size. The piston had a 3 or 4mm hole adjacent to the gudgeon pin, feeding the lower window and so transferred the hot under piston gas. Now that is different, not unlike Walter K`s piston fed rear port.(aided by disc inlet) That is why the majority of other supplementary ports, in my experience, just do not work. If you measure the capacity of your transfers, in a 125 you will probably find that the port passages hold 125cc. Question ? How much c/case space do we lose with a supplementary port? What effect does that have on the main transfer? What would it take to make them work properly, that is, if they are needed. How does that relate to the sophisticated porting in a 186.? Engineer please. !
In the early days it was presumed that the transfers should be aimed to meet at a point just behind the centre of the piston where they would develop the power together to resist any attraction from the exhaust port. Probably still lingers on in the hearts of special builders. But do you think that a supplementary port would dilute that power ?
The c/case volume has a value to the transfer of gas. Although I estimate it in a cavalier fashion because my assumption is that they are quite flexible(forgivable). Tiny space: 12,000, Bantam untreated, 7 at a push, 350 P/vave 8,500 - 10. That is to say I don`t expect unanswered complications from that quarter. I still guard it though. The TZ didn`t bother with c/case matching and I can quite see why but customers like it although possibly detrimental. I will chat about that later. My assumption has to be that until enough gas is being passed undisturbed (by the exhaust, still getting organised) the engine is inefficient. When it is efficient it becomes a `resonator` The resonator then develops its own degree of efficiency or otherwise, within the powerband and, in my book, these factors must result in a machine that is quick, reliable and perhaps the most important, ridable. The reduction of the inefficient period therefore, has to be an important aim.. 60% of the work will be done by the combination of exhaust and transfer porting.
Terry
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PostSubject: Re: Terry Beckett Chat.   Thu May 07, 2015 8:35 am


Terry,
Have a look at these two sets of transfer duct mouldings, one Aprilia, one Honda, as you can see, both have 5 transfer ports. In both cases the circumference of the bore is pretty well occupied by transfers! ports!

Trevor
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PostSubject: Re: Terry Beckett Chat.   Thu May 07, 2015 11:45 pm

A lot of questions Terry, so I will try and address just a few of them.

If you introduce an extra pair of ports to a cylinder that communicates with the crank-case, and nothing else changes, then you will not lose space, you will gain it.

When in the power band rpm, modern engines do not rely on case pressure to move mixture into the cylinder. This is now the task of the exhaust diffuser. Reverse sign waves pull mixture from the case at transfer opening where there is little effective pressure. Maximum “suck” in both magnitude and duration from the pipe needs to be available when the port is fully open as the piston moves around BDC, correct pipe dimensioning is crucial to achieve this.
The Aprilia engine at transfer opening has a case volume of 570cc, there is little pressure available from there?

During the last 35 years 125cc race engine power has increased by 50% with revs increasing by just 5%, and port timings have remained pretty well static. Modern electronic controls have contributed to this but overwhelmingly it is the understanding and development of the scavenge cycle that has been responsible.
Continual refining of the transfer duct profile and compound efflux angles of the port windows, in both radial and axial planes, have been the key elements. Each combination of ports has a specific task to perform and also maximize gas transference into the cylinder in a well-defined flow pattern that avoids turbulent mixing with spent exhaust gas.
All port flows join together to create as much coherent flow in the “loop” of the rear gas column moving up the rear of the cylinder wall toward the cylinder head. However, if the column moves too fast in relation to the mean piston velocity, there will be severe scavenge losses to the exhaust port. If it moves too slowly, the cylinder will not be completely scavenged. A fine balance to make!
So if we can create and maintain a coherent flow into the cylinder at a high Delivery Ratio and maintain that flow then Scavenge Efficiency will be high. Then if we can make the pipe work well then lots of power can follow.
186 engines are not very sophisticated when compared to the best of the 125 Bantam engines that sport; pumped water-cooling, reed-valve controlled induction, multi-porting, and electronic retarding ignition systems.

Reed valves are also sensitive to pipe influence, where piston ports cannot be. Around 15* ABDC with the piston moving upward the case goes negative. Atmospheric pressure on the opposing side of the reed petal moves the valve open, and flow can take place. And until rising case pressure ATDC closes the valve, flow is continuous, and can be 275* of crank rotation. If you have been very clever and tuned your inlet length to the 2nd harmonic you can augment that inlet pulse with a little extra pressure from wave velocity, further bumping up inlet efficiency!

Trevor
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PostSubject: Re: Terry Beckett Chat.   Fri May 08, 2015 10:35 pm

Thanks Trevor. I must admit I was the victim of enthusiasm this am and typed it straight onto the site. But this was the gist of it.
You will appreciate the struggle to stay on the doughnut and not get lost in the hole. I do appreciate what you are saying about the RS but I see that as an exercise, a toy for engineers, to progress happily until the boundary pushing has to stop. I see the information and analysis as a luxury to be enjoyed now. There was no such facility available to me before simply because I could hardly release such sensitive stuff in my business at the time. But I am not dealing with such a device. I really have to wonder about the future. The bubble of enthusiasm in the paddock over very highly developed but old 125s. The numbers on the grid go with my preoccupation with the 175, although obsolete. Is it so primitive or incredible to have a class for 175s, genuinely el cheapo governed by the same kind of rules as for the early Bantams that would encourage people to enjoy what is so absorbing and happiness producing. My thoughts about the 175 are purely devoted to the perpetuation of the species and on the site, sharing experiences to that end. Where else is there to go ? Well for you it must be disc valve inlet and some really adventurous porting ? I have some good assumtions about that. Terry

Many thanks Trevor. I must admit that I am well focussed on what happens pre powerband because I think that it will soon be time to be going the other way i.e. how to develop power at lower rpm. My concentration on that aspect has produced some great results. I think because I am looking at the class we`re racing in and the rider`s needs to win races. The c/case volume means I have to have assumptions about it which I have described but I do give it some more thought if I feel it is being changed or diluted in any way. This focus tends to cause blind spots highlighted by your post and it became obvious that the supplementary ports only do the business when the resonator kicks in. The resonator to me, it is worth repeating, is dependent on how quickly the exhaust and transfer streams become organised and I have assumptions about that as you know.
Now, steady on Trevor, we`re not at the inlet bit yet but reed valves and trombone experiments with inlets; Yes. Most interesting.
My thanks once Trevor. It helped my thinking to a degree. i.e. 1. Think about sup ports again. 2. Keep them out of the way until the cavalry arrives. 3. See if you can squeeze some precious info out of Trevor re: shape, direction, taper factors, anything unusual about the neck area, from the Honda mouldings. Strange, I had just viewed the red mouldings when my friend, ex member of “the band” Mick Argyle, dropped in a bag of red Vynamold. I always used the yellow. Terry
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PostSubject: Re: Terry Beckett Chat.   Sat May 09, 2015 2:03 am



Terry,
The reason I included the reed valve in my last piece was not to highlight induction, per se`, but because the reed inlet assembly connects directly to the cylinder via the rear, 5th transfer port. Indeed, at peak torque rpm, any point of crank rotation from the 15* abdc until transfer closure the engine is “open” from carb bell-mouth to silencer outlet! Pipe action, emanating from the last part of the diffuser assists directly in this process.
The 5th transfer port play a crucial role in that cool, dense, oxygen laden mixture taken directly from atmosphere, flows in an upward motion to propel the rear column of mixture towards the head. Hopefully, whilst doing so, pushing old exhaust gas ahead of it and eventually out of the exhaust port. The rear transfer port outflow plays significant role in the choreography of transfer port flow balance. Asymmetric positioning of port windows can produce axial swirl take takes precious mixture directly out of the exhaust port, to play no part in combustion!

The above cylinder cross section drawing of the Aprilia engine, the upper of the two mouldings, might fill in some details of duct dimensioning for you?

Trevor
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PostSubject: Re: Terry Beckett Chat.   Sat May 09, 2015 10:57 pm

It is gratifying to be at the cutting edge of this technology. I do have experience of double and triple supplementary ports and could see the angles of entry which I thought theoretically great, including the LC series and Suzuki 750s. In all these cylinders I devoted my efforts to the main, exhaust side transfer and made sure they all opened together. The rear ports other than cleaning them out were left strictly alone, angled sharply upwards to open some degrees after he mains and liable to get in the way. There is a lot more to this drawing, albeit in Italian, and I will respond to it but I am in fear of getting caught up in this interesting hole and losing sight of the doughnut again. But I mean, introducing fresh air into the cylinder, albeit a puff, and while the transfers are still open. It sure is innovative - and frightening. But my thanks once again Trevor. Early next week. Transfer ports.
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PostSubject: ....*PLEASE RESPOND AFTER THE TRANSFER PORTS EPISODE!*....   Sun May 10, 2015 4:09 pm

Good Morning Terry,

Great to get your information and insights of results with your LC's etc!....................... Very Happy

It would appear that your engines had more flexibility and would suit the average newcomer/beginner?

You might also have knowledge on piston inlet porting and tuning for fixed ignition timing?

Do you think these ideas might give newcomers a clue of possibilities?

Have a Great Weekend!

Rex
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PostSubject: Re: Terry Beckett Chat.   Mon May 11, 2015 3:01 am

I`m sure it seems that way Rex. But in those golden days when riders could afford to race and there was a choice of machinery to do it with, the competition was fierce. My primary aim was to win races, try hard for the flexibility you mention but also the longevity. Development of power with the least rpm and in safety was a real challenge. That is not to mention the specials such as the SAAB which I will come to - eventually. These challenges remain today especially with Bantams. I love the cutting edge and the analyses from Trevor. They are a real eye opener and serve extremely well to confirm or eliminate my precious assumptions. It all leads to the question; Why do you do that? and the answer; Because it works. Always nice to hear from you Rex. Terry. p.s. In case it appears that rpm concerns me; The 50cc class was prolific at one time and 14000 was not at all unusual. I didn`t have time to think about flexibility then. It`s only that I`m not looking in that direction for a 175 Bantam at present.
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PostSubject: Terry Beckett Chat   Mon May 11, 2015 9:51 pm

Transfer Ports. Broadly speaking I found the main transfer did all the work and controlled the direction. I came to see the supplementary ports as lazy ports that followed on or mopped up. I also had problems thinking about the space they added to the c/case. To that end I looked at a cylinder recently that had a second transfer and immediately below it a second, the same size. The piston had a 5/6mm hole adjacent to the g/pin obviously feeding the cylinder with some of the hot under piston gas. I think that measurement is very important If you measure the capacity of the transfers you will probably find (in a 125 that is what the transfers will hold. If you mould them you will have a good idea of what taper factors there are and the possibilities for widening the port. In the early days it was presumed that the combination of the transfer streams produced a power that could resist the fast moving, exiting, exhaust gases by meeting somewhere just behind the centre point of the bore. Walter Kaaden came up with a supplementary port in the rear of the cylinder which must have been aided by a piston port and a disc inlet. I thought at the time, that this fed more gas into the cylinder which aided the direction of the rapidly expanding existing gas as well. It didn`t occur to me that such a valuable charge would be wasted on scavenging. However, his drawings showed the same traditional configuration for the two main transfers. It gave rise to many supplementary port experiments. (I`ll chat about the Suzuki 750 sidecar motor another time) It was a mistake to assume that this port was the only contributor to the kind of power that won Grand Prix or that supplementary ports were bound to work whatever and remember, he was also working with two main transfers. However, years later I decided to experiment with, firstly, the window size(width) then altered the front wall to go straight down to about an 1/8” to the exhaust side of the window creating what appeared to be a part blocked window. I exaggerated that with a 5mm ball cutter and blended it into the wall just beyond the neck. It enabled the window on the exhaust side to be widened. The upper leading edge, close to the the exhaust port, was radiused (I understood that gas didn`t cope very well with square holes and this particular hole had real work to do, at least the leading edge did) No fear of contamination from the exhaust, I had a bullet proof assumption about that (remember Jack Machin`s oversize, very effective exhaust port all those years ago)
Much later I was fortunate to acquire, from an innovative engineer from Derby, a flow bench that worked with a series of manometers.(about 10 but I only used 2) The maker was four stroke man- poor soul. Like the computer, I didn`t really understand it but used it effectively in my own narrow way. One of the first and most important things I found was that the air ignored the base of the transfer window whilst negotiating the curve into the cylinder. It provided a very valuable pointer. It meant that I could drop the cylinder with no ill effect and turn a low revver into a much better revver with a little help from the exhaust port. That is not to raise it but increase the effective opening time from 30 to 60% if necessary in fact, anything rather that limit the precious power stroke. You will remember that other changes are needed I also found, among other things, that David Hunter`s deflector had quite a dramatic effect. I couldn`t believe the result. The flows stuck to the cylinder wall and met up at the back. There was no activity in the cylinder centre. Tried it out on a GoKart motor. The Dad wouldn`t let me even look at it when I suggested development and the kid didn’t want to lose his newfound winning ways. Something of a loss. Of course, I am aware that there must be a significant difference in the behaviour of hot gas ( is it hot or just expanding?) at 9000 + rpm in the cylinder but the results raise questions yet again. I was just content with the results. My friend, Andrew Wakefield, who worked for me, used the same technique on model aircraft engines after I retired and rapidly became overworked with work, most from the USA, until the fad faded. I didn`t use the technique on production machines of any kind because I didn`t think I could repeat it accurately from one machine to another. but Go Karts, scramblers, enduros, In fact, anywhere where the torque was elusive. The results were quite satisfying.
Lessons and questions: Try to preserve the power stroke. Lifting the exhaust gives rpm without useable power. To fill the power gap the transfers must be made to pass more gas usually by raising them or as above. Check; is the neck of the port able to pass more gas for the larger window? Is there a value to be gained by matching the cylinder to the C/case? I thought so until I measured the first of the TZ. I wouldn`t have bothered too much after that but the customers liked it, probably to some detriment. It suggests that the transfer taper design is more flexible that I assumed. Does c/case volume matter? I thought it did but got so I could be satisfied with the assumption that; this is good for about 9000+ or, in a Bantam: It would be helpful if you were shareholders in Devcon or plan to get by with 7,500 at a push.
Philosophy. Keep asking questions, measure things, try to overcome the human tendency to loose sight of the doughnut and get lost in the hole. e.g. In the early days a young flier named Jack Machin was kind enough to let me look at his cylinder. I could have fallen down the exhaust port. But despite his success it took me years to appreciate just what it meant. It was because I was obsessed with the theory that the exhaust would contaminate the mix and should be separated at all costs and failed to think a little further.
To be continued. I did reply to Trevor`s last helpful explanation of the sup transfer ports but I must have forgotten to label it TBChat Terry
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PostSubject: Terry Beckett Chat   Tue May 12, 2015 10:57 pm

Transfer Ports Contd.

Port timing; Transfers v Exhaust. I place more importance on these two to create what we know as the blowdown period than anything else although, as you know, everything else plays its part and has to be changed to compliment whatever these two demand. Let us think 8,500+ operating rpm. and I am thinking 175/186 with suitably reduced c/case space. (engineers and Devcon) plus the right bottom end gear for reliability at 9. Enter a codicil: I do not know the 186 alloy cylinder port timing, the taper factors or anything about the port characteristics including the supplementary ports. But keep your eye on the doughnut ! it is only a twostroke after all. Let`s treat it as such. Needless to say, as you would expect, I would measure the transfers carefully and mould them for sure I would want to know what cc they held, any taper features, any restrictions, especially around the neck etc.etc. So we`ll start with and try to get the maximum from 23%(about 13.5 mm) of the stroke and go from there. It would almost certainly need more if the port size increases still failed to reach our target. We will have made full use of the deflector, widened the main and adjusted the passage to suit. The idea is a useable powerband width and good power to 9000rpm. If we have maximised the width, the difficult bit, then all we have to do is to raise the window but keeping the trajectory low. But remember, we would be dealing in very small increments here. The reason I would start with 23% is to find how much of the powerstroke I can get away with. For 9000rpm I may need 13/14mm of blowdown. Add 27mm for the exhaust height and we have a happiness producing 31 or 32mm of powerstroke. So we would start with 30% of the exhaust port opening simultaneously and be prepared to go to 60% with the usual radii and chamfers. So we have good power but not enough, say. We will shave the transfers (all together now) and raise the exhaust twice the transfer lift. It will open over slightly less of a % but that`s OK. And so on. The pipe has been designed on the modest side, an overall length for 9k( about 920mm incl. a 150mm tail pipe @ 23 dia. and a parallel section not exceeding a diameter of 96/8 mm, length about 55/60mm giving us a terminal cone about 175mm long. To achieve the twin aims of keeping the primary pipe reasonably shallow and the given parallel section dia, a supplementary cone can be inserted on the end of the primary cone (about 75mm long to adjust it, just deduct that from the primary pipe length.) The inlet: we are stuck with an unencumbered inlet port (hopefully) with its own unknown resonator(keep it short for higher rpm etc..) but with some physical difficulties (kinks) employing a carb of 32mm. The inlet timing has never seemed critical to me if adequate providing it was given additional breathing and observation of pistons and rings. Lots of drawings to look at for width etc. And now the c.r. Keep it on the modest side until we are close to target elsewhere. I`ll settle for 9.5:1. with an appropriate ignition spark. This will increase to 10.5 + probably, if the plug chops look OK. At that time we`ll give the head some more detail consideration. The `chop` can tell you a lot more than the mixture as you know. Just a thought: its rarely on full bore that the problems occur, its when you knock it off.
Development is confined to: adjustment of the transfer height coupled with exhaust height/ effectiveness. Again leave the c.r. until necessary. Doubtful if the pipe will need to be adjusted but I would give it a lick or two if I thought it was being unhelpful.
It is necessary to warn that when digging behind the main transfer window to create the deflector, try and ensure there is enough meat there to do it. It is hell`s own job to repair if you break through.
Additional ports and such exotica I`ll have to chat about next time. Terry.
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KISS



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PostSubject: Trry Beckett Chat   Wed May 20, 2015 3:18 am

It seems an age since I was chatting about transfer ports and perhaps we can expand upon that. I now appreciate that because I had no assumptions about the supplementary pots I tended to ignore them, perhaps for the best. But now I think about it differently and have to go back to basics. What are we trying to do? We are trying to get as much fresh gas into the head as is possible. You already know my assumptions about exhaust gas behaviour and how to control it (to an extent) Trevor`s experiences with the Aprilia go to show just how much effort has gone into `scavenging` in order to achieve that basic objective. I have always thought that what was left of the exhaust gas after the blowdown period was pretty harmless. I can see that careful design of the rear transfers could aid the objective once the resonator was in operation. But I am not dealing with 12,000 rm + with unlimited development resources. However, the thought is there and I would certainly give more thought should the opportunity arise. Incidentally, should I be asked to `tune` such a device I would ask the usual questions that I ask all riders. “What do you want ?” I would then give the motor to my engineer, ask that I get to know about any anomalies, have it put together properly and give it back to the rider… I didn`t cater for beginners as such. If someone wants to race they want the same spec as the Champion and that is what they got. I once did a motor for a miner from north Notts, his name was Mark Ordige. I heard he was being overtaken and the usual rider exaggerations at Snetterton at the week-end. I asked who did the winning “Oh, Mark” they said. I asked Mark during the week what had happened and he, man of few words, said “I warn`t rushing but I got fed up wi `em an` cleared off.” What do you say?
As we were talking about transfers I should mention a Suzuki 750 we prepared for sidecar racing. Michael Argyle suggested that as we were using three Gardener carbs it would be helpful if we could have reed valves. He cast the housings in aluminium, a hell of a nice job but I cannot remember how we fitted them now. It gave me the idea of some rear supplementary ports that I don`t think worked because I should have used a piston port to feed them. However, the plot went to the satisfaction of the two young enthusiasts but with a fatal error in the design. We used, at their suggestion, Wiell`s rings from a Hillman Imp instead of head gaskets and they just did not work. Something took them out of the scene and a great development opportunity was lost.
With regard to supplementary ports: As you know I thought their effect, if at all, was negligible. This was simply because no fresh gas was introduced. What was required was a feed of the under piston gas into the cylinder (aka Walter Kaden MZ) the effects of which were quite dramatic as the spurt of fresh gas also helped the scavenge. He hadn`t discovered the deflector at that time. The same goes today because the hot underpiston gas works harder and has more than one function. I realised this phenomenon later on and didn`t have time to develop anything.
Mind you, other than the race kit transfer device I described to you last time, I am aware that a piston ported inlet is not the tool for the job. Talking about tools for the job and “What do you want” One, John Dady came in with an early post-war James Cadet engine, 80cc I think, a ghastly lump of cast iron with exhausts protruding from each side etc. What did he want? The power to be doubled, to be absolutely reliable and to be used for a charity run from Lands End to you know where. Well, we did that and he did that. A wonderfully generous man. He lives near Derby, is a meticulous restorer of bikes and motor bikes and I go to see him just to eat his wife Anne`s cake and take in the smell and ambience of the workshop. Another one, a champions champion, Dale Ward, the SAAB, a work of genius, the Garelli 50 et al. Chat about it next time. Terry
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PostSubject: Re: Terry Beckett Chat.   Wed Jun 10, 2015 2:08 am

I've enjoyed reading this thread, I remember the Suzuki 750 Kettle you mention above and all the work you put into it, it was a beast but so beautiful when you'd finished it, the only other engine I remember that was as huge was the 3 litre V6 Yamaha F1 boat engines we did.

I find it very interesting reading Terry's notes and about the things that happened before I knew him (I'm Andrew Wakefield) I worked with him for a few years before he retired and enjoyed every moment of it he is the kindest and wisest person I have ever known, he taught me many lessons that I have used to help mould into my life.

I'm really looking forward to the SAAB, when you get time Terry it's something I know nothing about other than the success it achieved.
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KISS



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PostSubject: Terry Beckett Chat.   Wed Jun 10, 2015 9:06 pm

Hello Andrew. Glad you`re following some of this interesting Forum. It seems a long time. I can remember being very busy but there always seemed to be the time to accept these special projects. I was grateful for your help at the time and glad to hear from you now. Thank you for the reminders. I will get round to the SAAB soon but I`m engaged at a possible glimpse of the future responding to the Race Manual Preparation thread. The problem I have is: Who will it be for? and you can imagine I would be interested in that because my Bantam racing days must be numbered among my happiest. Terry Beckett.
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KISS



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PostSubject: Terry Beckett Chat   Thu Jun 11, 2015 5:03 am

I knew of Dale Ward only vaguely as a sidecar man of some repute with an IOM TT trophy in his cabinet. On the international circuit at that time was a young German Named Rudi Kurth his passenger was Dane Rowe. Some may remember. He raced an ultra modern, a very low, slinky sidecar outfit that was quite outstanding. I remember it was called the Cat and breathed through three blow holes like a whale underneath where his chest would be in flight. I think he used some sort of outboard triple for the power. Dale saw it and decided it was the type of device he wanted to race and set about it. It was early `71. And the power unit ? A three cylinder SAAB Sports unit. It was an incredibly primitive, terrible lump of cast iron that was different in that it had a multiple oil feed to the bearings etc. needless to say it would need the pipes and carbs to complement the package. The spec, necessarily, included very real torque and enough top end to do the business. In the meantime while I got on with the power business, Dale was working with Ray Petit, world class panel man, making the beautiful fairings in aluminium to mount on the innovative frame built by Dale himself. That frame was built on 2” blocks and the ultra low centre of gravity meant cornering par excellence. The pipes were encased below the sidecar floor and I can remember it stood up on its side at Croft and there was nothing to see. Poor scrutineer. It also had unusual suspension. No damper but a torsion bar fitted from a Douglas Dragonfly. It shouldn`t have workd but it was perfect. The motor`s new breating came from 3 Gardner carbs fed from a pair of SU float chambers and then a rail followed by a method I didn’t understand from Gardner himself. This was to cope with the problems trying to keep the three carbs fed whilst cornering hard. It resulted in `great on the circuit but hard to start.` In `72 it competed in 22 meetings and won 16 due to the starting problems. I had some doubts about it initially simply because I couldn`t see how it could survive in racing mode. I needn`t have bothered myself. It did all it need to do at 6000 and held together well. The electrics worked off three contact breakers and coils as opposed to the distributor I stand corrected about the cranks. It was only changed twice in its time. At the end of `72 a family problem upset plans for further development and the beautiful thing was sold to a local rider. I`m told I fitted reed valves to it later although I cannot remember it.
Then there was the Garelli. A standard 50cc motor but fitted with a 5 speed box. Requirement: To fly. I was helped by the 5 speeder and didn`t have to think so much about torque. I think the carb came off a Triumph Tina, reamed out to 19mm ? The package turned out OK straight off the bench, ridable and quick. It did the usual and flew for two laps and gradually lost it`s power. It had a little seize to show us it was unhappy and as a result Dale did some fin removal and welded on a neat little water jacket. The head remained air cooled. I can see Dale pouring hot water into the Le Velocette radiator from two thermos flasks now. He did some happy winning with the little device but someone pestered, first me and then Dale until it was sold. As is usual, once a motorcycle leaves your hands, no matter how successful, you never hear of it again.
I see Dale occasionally and wife Ruth who was a Ward Sister. He is still, always engaged in something ingenious, like a charabang for the grandkids to drive. We clear off to The Old Farts Club maybe twice a year to move in old familiar ways. If there are any vintage , or other riders come to that who live this way, make contact and show yer face. Contact Tony Spencer at tonezere@btinternet.com
Terry Beckett.
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