Reed Valve 125s

Hi , all.
Not quite sure where to start this , in crank rotational terms that is , but bdc is as good as any , to analyse a little more reed valve function.
At least as far as i understand it all , these numbers are from my engine , simulated at 10,000 rpm , and just as Mark raced at Cadwell , so
that visual track performance can be measured against the theory .

Shortly before bdc , crankcase pressure is down to .8atm as a result of tuning action coming from the exhaust diffuser , as the crank rotates
to around 10* after bdc , the pressure ratio across the reeds , with atmostpheric one side, and sub-atmostpheric the other , prompts the them to
start to open and gas begin to flow , creating an inlet pulse which reaches a peak of 1.2atm , the suction pulse from the diff is .4atm , and is the
returning exhaust pulse which was , initially , 1.7atm . Eventually cylinder pressure comes down to a tad under atmostpheric , and , with such a
high final pressure differential , gas flow in the transfer passages accelerates to a mach figure of .7 ! The reeds remain open untill the case
pressure and the inherent spring in the petals combine to snap them shut at 115* atdc . The open cycle then recomences and the procedure
repeats and repeats ad infinitum !

If you want to get really subtle you could tune the inlet duct and carb position to the 2nd harmonic , and , with crankcase pressure on the
outside of the reed petal and a superposition pressure on the inside , which is the sum pressure of left and right hand duct pulses where they
combine. This small , extra pressure , can aid both reed lift and duration . Don`t have a clue how to asses it but it does factor in to the
algorithum governing the simulation for the inlet cycle .

Have to go now my head aches . Reed to you again soon ! Trevor

Thanks Trevor...!

2nd harmonic? -- the petals behaving like tuning forks ...? singing, Oh my beloved father....

Sorry! just behaving badly again!

Trying to get a handle on why harmonics? -- the air pressure waves you mean as the petals flap up and down? with it happening at 167flaps per second I expect the air-fuel charge feels as if it does not stop-start but acts like a continuous flow? or is it that the stop-start causes a primary wave to rush along the air charge and the tuning you spoke of is the secondary wave....??

Dunno what I´m writing about -- just swimming in ignorance -- mumble mumble, gurgle gurgle glugg....!

I wish I had paid more attention during Thermodynamics classes but there was a girl student in Architects & Building department who wore a mini-skirt we called a "wide-belt" and she was always walking past during Thermo lessons....

Somebody´s been speaking of sub-sonics and confusing me still more.
Another thing that has me puzzled is the difference -- if any -- of the speed-of-sound in dry air compared with 15.02 air-fuel mixture with 20:1 (or more) ratio of petroil mix?? Like, its perhaps something to do with speed of sound in air-density? -- hhmmm!

Cheers!

blimey thats really interesting your head hurts, I had a mingrain after only reading the first paragraph, but of course I fully understand it !!
anyway Trevor the Reed does not snap shut? it can not move that quick, surley I seem to remember it closes and openes again above 8,000rpm as the rev rise and fall, but never shuts completly "well not above 8,000"

great Topic

Still waiting for ian williams on hte software.

regards Derek

Trevor,

I have a couple or three questions having not looked at your bike in any detail,

Are you using a case reed ?

Have you a windowed piston for 360 inlet or are you using "power ports" ?

What factors have you used to determine the size of the reed block and petals ?

Any input appreciated

Thanks

James

its not the size of the reed block that is important, my advice the bigger the block the better,to a point, any motor cross or Kart engine 125cc reed would be just fine - far more important the reed material, is much more significant.

as its all down the resonance, we played with this 20 years ago on a dyno at AE goetze with 250 and 350 twins with one cylinder hooked up, we used from small 2 pettle blocks from trials and big cr 250 reed blocks on a 125cc cylinder, pettles steel actulally works very welll, but is liable to break, usually with a constant High RPM resonance frequency(flutter).

Thin reeds were seen as better responding, on the lower curve, but when too thin would kill top end, (ok trials)just as it started to flutter out of controll / resonance harmonics, (or uncontrolable frequency) - we had two engines with high speed cameras, taking Photo's, the main object was to develop a camera to see piston /reeds and the waves yoiu get inside the inlet venture as yiou can see a sea of waves as they bounce back and forthe like sea spray, a colaberation with karl schmitt and Uni in germany, the main engineer was a guy call "Oliver Karl", German, who is currently looking at my new toy, he actually worked as part of a govement paid team of engineer working on reeds for the then 250cc squad that Helmet Bradle ( could you imagine the uk goverment doing this, why we have no longer any 250cc champions) "and yes the dad of current moto 2 champion", This is how I know reeds do not close, at all" above a certain RPM thresh hold.

anyway thicker material are more stable at high rpm, but can surpress power under (peek power) like thay are inflexable /unable to cope with flexing enough to open far or big / too thick to open as quick as required - that was shown to surpress the torque curve below peek, appearing
thin reeds better especially just as it comes on the pipe, soffens (not sure Im using the correct terminology here) our current reeds are too thick, our bike is pipe and the top end is surpressed, this is because the material is too thick and the reed could do with being another material

but ultimatly its how they are responding to the expansion chamber we currently have, and the strength size and shape of the current resonante waves that it creates, when the exhaust port opens ???.

what a great subject this could be.

for thou's who are interested "back then we started with variouse materials 4 or 5 matal to plastic carbon fiberglass , etc all thick and tested at each stage by putting them on a jig on the surface grinder and taking 0.002 thou off at a time!, a cur was printed we have expansion boxes max torque was 10400 for the 250 and 9300 for the 350 - its not easy to take 0.002 thou off a carbon reed, eventually we always got down to a sixe between 1.15mm to 1,35mm but my god it was so boring a stask and the end result - you could not say without testing hundreads of different materials, there was very little differece to actual top end power, only on occasions with carbon that never broke, but pettle thickness
made a significat affect on the power curve below the range and as it cam on the pipe to the middle of the power curve. top end was nearly always the same, Blimey a topic I have some actual dyno experience with.

My opinion is "if" you want to tinker, tinker with a 125, "leave the 175 class alone""175 are easier to build, for beginners to cut their teeth on, none of you can disagree we have a great deal of Brains / knowledge / experience in or little class as much as you would find on any grid lets not spoit it.

so if you want to be creative "do it with a 125 Bantam", if you dont agree with this please say so.

Very Best regards to you all.

Derek Betts

Mike,

Out of curiosity, were reeds only permitted on Bantams from 84, I seemed to think they started to appear around 1972 did the rules stop their use in Bantam racing or was it a case of no one had tried it ?

Who had the first Reed Valve bantam ?

James

PS. Derek, you are too late 175's are already special have you seen Tom Snow or Robbie Brown and all within the rules.Click here for Rules. There was a proposal for a "road" 175 class but no takers

Very intersting Derek -- I had thought all along (by what I saw and heard of reeds, which weren´t much `cos I was diesel oriented) that they WOULD clap shut at low engine speed but stay open at high speed -- because at 12,000rpm they are opening and shutting at 200 times per second and to be right-clappers at 1,200rpm (20 waggles per sec...) they´d have to be well engineered to do the same at 12,000rpm(waggling ten times as quick) .

If they don´t clap shut at 12,000rpm then the pulsing, to cause reflecting sound waves in the air-fuel charge must surely come from the transfers opening and shutting -- OR AM I WAY OUT???

It might surprise some on here -- I have a very simple mind!! Scientific explanation and mathematical formula do not convince me until the thing looks right in my mind as well... so I just cannot see these thin blades opening and clapping shut at 200times every second!
Plus the reed valve assembly resembles a fatigue test rig where the tester is trying to break the reeds.

The "Water Hammer" phenomonen is where the shutting off of a water valve completely & QUICKLY causes a pressure wave to travel backwards in the pipe and its reflection to then move quickly forward at the speed-of-sound -- such that if you now open a vertical pipe at the place of your shut-off valve the water will shoot up to a height much heigher than the flowing-water´s pressure head....

So if it is not the opening & shutting of the transfers when the reeds stay open
what causes the intake resonance??

Yyaaaawwwn!

thanks john
Derek

oi james the first engine with a reed valve "i seen in 1949 motor cycle picture, I think he copied a scott.
he's still a live and scott had them in the 1930's.

regards Derek

resonance of a "flask! ? john over to you could you explain sure you will do a better job then me

and the depression and wave created by the exhaust !

regards Derek

James bants had reeds from mid 70's? (think it went to agm one year) but were limited to inlet
tracts (but case reeds hadn't been thought of anyway, yet?) Eariest Reed - don't know ...

Tom Built Ned a reed top end for his motor in 82/83? Which became Rick Powells 84/85/86 - mine 87/95 -
Keith Woods95/02? - Mick Potters - Phil Bettys.

Martin Palmer built a reed motor 81/82? which was sold to Nick Turner -then Pete Tibbits (Pete put it in his Max Ridge frame)
- Nick Bramley

Derek some 175's have 4 transfers (and 2 exhausts 2 inlets!) however because of the 60/60 stud spacing and lack of
ally in the crankcase mouth and bridges (and studs) everything becomes restrictive - so its all self -policing. A motor with 2ex 4t 2in is a cylinder full of bridges not holes
The rules work just fine. At Cadwell Snowy lapped slower with 4 transfers than I did in 08 when the bike had 2 transfers?

I think best port layout for a 175 is 1exhaust 2transfers 1inlet...

Hi Mike

Many thank you for that very well presented case, I sure this type of case went on with the short stroke V long stroke, but you need to change this as its not accurate its not 4 trasnfers its two with a rib glued into them splitting the port, see my file on return to bantam racing page 8 brians sprint Barrel.!

Derek !!

Good one Derek!
Keep it fair...?? that´s how it all started-- Racing on The Cheap -- it was...

... {[... take a Bantam off the street, whittle all the uneccesary weight off, just tune the ports a bit (doesn´t cost much more than elbow grease), get a Todd head and close-ratio gears (frightfully costly! but a MUST!) -- install coil ignition with battery and CB points and use a total formula that generally puts a restriction on other parts to keep total cost down...)]}

Exactly what I have been saying -- have a Low-Cost formula -- might be slower racing and not so pretty -- no skirts -- but would give newcomers the start and would be a motivation to move on...***
...move on when they see the way clear to do their bit with the real (reed, skirt, doped fuel, tiny flywheel and fancy gear) thing...

NO! just not acceptable ... everyone has got used to Racing Bantams being somewhat special and that´s how its gotta be...

...and how that´s gotta be -- is that the number of Bantam Racers will equal zero in a few years time!!!

***Icarus-1 was low cost and I had fun in the Intermediate class but it was never competitive in Senior races but that did not stop me racing the b..... thing and entering as many races as possible (even Senior races).

Go well & keep well!!

Hi John great comment with a lot of sence - you always talk a great deal of sence john (especially when you agree with me) LOL.


Derek

I think for a starter if this is going to be a debate on the 175 class then atleast start it as a new topic, topic drifting all over the place makes it hard to find anything or if people want to comment they can never find where one starts and the next ends.



Eddie

OK Ed!+
For starters who is going to race Bantam -- you or your Dad?

...or both of you?

I saw you´d got a Greeves -- I know what I´d rather race...

Hello James,
Sorry for not responding to you earlier than this !
I`ve been experiencing some sort of glitch with the forum message box , no new messages were coming in , Ed`s been trying , as have
others , then suddenly , the log jam cleared and six new ones arrived at once . Since then i`ve been playing catch up !

Case reed . No , mine is a cylinder job , i did considder it at the design stage but the sheer volume of work involved , with no clear
advantage showing over the alternative i rejected that option . There are a lot of instalation and gas flow issues that i could better
overcome in a well executed cylinder reed , and as yet , i don`t think a competitive case engine features in the results . The engine
still uses the original exhaust, and it seems , for us at least , reed engines are less fussy than piston ported engines where exhausts are
concearned .



360*. When we raced the bike at Lydden , in 1997 , the engine included all of these features . Mark established the lap record and finished
22secs in front of the second place man after 12 laps. At Cadwell 2011 Mark finished 18secs in front of the same rider after 4 laps .
The hole in the piston skirt has gone , as have the extra ports , but the result was the same ! Within the operating range of the power
band as Mark uses it , these features gave no benefit that he could discern , so in favour of a less cluttered inlet duct they were
discontinued , there appears to be no down side at all as a result of this move !
The RS features two pairs of conventional transfer passages and a smaller fifth one , no extras , no gimmics but it does it`s job
supremely well . Sycronicity at it`s very best , a simple layout giving a lot of power with no fuss !

Reed block choice is very simple , RS,CR ,RM and so on , any of the six petal blocks will do the job as will choice of reeds. We have tried
them all , plastic , g/fibre , carbon fibre have given delamination problems but work well . Curently we run the same as in Steve`s RS
and they seem to opperate ok on the Bantam .

So , it seems be Mike , that you`ve got your answer by proxy , patience is still a commendable virtue !

Hope that helps a little James , Regards Trevor

Trevor,

Thank-you, certainly food for thought

James

Trevor many thanks for this great information.

do you weld the ports on to the barrel, do you weld, silver solder, or braze the exhaust on or do you do them differently, how much of the fine's do you remove.

We are currently building another barrel, and the last time we did this we had great results but it suffered huge distortion issue with regard to what we feel was down to the way we brazed the Exhaust and the Transfers onto a 125 Bantam barrel!

Theres another would you go 175 or 125 iron barrel, when building I'm presuming you have gone 175 as i think you talked about aligning with the liner! in a previous post, so the question is why this route.!

best regards

Derek Betts

hi trevor I spoke to you in about 1994 about my Bantam barrel you gave me via email variouse options, after Igave you the detals Ihave just posted we are currently in the process of fabricating a new barrel for that water cooled engine its about time we did somthing with it, so could you have another look at my last post on here please.

kind regards Derek

I'm currently re-building 001 as a reed motor as I feel it will be easier to ride than the
piston valve motor. (love the expression 'piston valve' as used in classic racer magazine
- funny really coz it means it hasn't got a valve!!)
I hope to have it running within the next month with a view to taking it for a few shake
down sessions at the festival of 1000 bikes.
I've changed a few things on it which i'm hoping will improve performance.
It would appear i'm now a heavy-weight at 12st in the bantam class - and as JB said if your too heavy - race
something else?! Perhaps I need to sit a lightweight on it...

You are going American Mike -- piston valve indeed -- try and behave. A ported barreled two-stroke is a "Piston-ported 2-stroke"....

Yeah well -- yew know -- chew chew chew -- and get chew!!!!

Why `enn yew racing, you know!? Get off your bum, yew know, and put it on a 250 yew knmow -- most of the time they have 5 gears and enough torque that constant clutch-slipping is unnecessary and make riding a lot more comfortable except for the amount of gear changing -- you know!

Cor blimey! & Cheers, you know!

12 stone you 12 stone ! you mean someone else is going to ride your bike dont keep us guessing Mike

I know you love a bit of intreage.


seems the other side has got you changing your ways

Americans have that effect on people I lived there for a while, its all about bullshine.

regds Derek

Agreed Derek, the world´s greatest circus -- would be a laugh if they didn´t keep going for Lost-Cause wars. I wonder when MP is going to be seen wears a stetson, spurs and calling his bike "The Lone Ranger" -- chewing terbaccy and gobbing into back-green, where-ever that is!?

I was at Warren, Michigan with TACOM*** watching GIs doing maintenance to an instruction book that had only pictures....

Uh oh! I think that gets me banned for R-Predudice yet it is the truth - yewknow!

*** during the HUMMVEE & HUMMER trials.

Hi John
i too lived in michigan but only for a while and while on business.

I can imagine you getting on really well there, the people are great especially in Chicargo, what a cold and "windy city"- they are completly different to the newYorkers "yanks".

regards Derek