Crankcase compression debate

I tend to agree with you Trevor on the inlet set up that suits a bantam, that being piston ported and inlet tract reed. But why do you think a crankcase reed is unsuitable? I had a case reed bantam in 90/91 but it was a bit too radical featuring 2 reed blocks that delivered the inlet charge into the transfers it wasn't very good and I soon reverted to the previous motor ; However also rode the Andy Moulden/Paul Jurassi case reed motor which went like a rocket! So i think case reeds may still have a part to play??

Regards Mike

mjpowell wrote:

I tend to agree with you Trevor on the inlet set up that suits a bantam, that being piston ported and inlet tract reed.

How I read it, this is not what Trevor is saying Mike"

I have a picture of your interesting engine with the alloy water cooled cylinder, same as John marks, I actually like this idea shame it never worked, lack of enthusiasum or time, or possible better results and easier to get from other engine layouts,

I feel any set up will work, as well as any other (bantam only), we are limited by the iron cylinder unless you run exotic fuels -

I just feel the piston Port as Mick scutt has said, is possibly a bit easier to set up and tune, but the poor clutch and revs you guys are doing, ! I have at last had chance to look at why my crank reed motot it is now well under way, that we had so many problems with liner, my notes are a bit poor but its all down to fuel and a few mistakes along with a steep learning curve.

finishing off "I too would like to know what Trevor thinks on your question, this is a very interesting subject or me.

my theory is we are not all pumping out 35 hp because we are all still piston ported or inlet reed, these are just so much easier to do.

But I see no reason why a 175 should not be doing this, I think its just time. .

regards Derek

The 175 (which is usually bigger than 175ccs) with a "long" rod has a lot more VOLUME underneath the piston than a 125 (which is often less tahn 125ccs) so the maximum-possible crankcase padding is probably essential for the "175" whereas the 125 could be less padded depending on the tuner´s whim....

I have a 1953 article*** about the Hogan head where it is said crankcase padding was not really necesssary when the Hogan 9:1 CR head was fitted.... I was scrambling at that time and using pure benzine mixed, 50:50 with Pool petrol because the Pool petrol was about 78 octane.

I wonder what fuel the Hogan brothers were using with their fast Bantams of that era. Their Bantams were often quicker than any of the Italians or Spanish 125s.... That was the time of Maurice Quincey on the Walsh 123cc Bantam beating up the 250 racers witha megaphone pipe!!! on doped Methanol, of course.

*** I really must look for that article its somewhere in unpacked `Household Possessions´ from Canada.

Cheerrs!
JayBee.

Hello again ,
Lest anyone should be in any doubt , a correctly proportioned and advantageously installed crankcase reed will out perform anything , except
a similarly designed disc valve , in a full house race engine !
Within that sentence is one reason i didn`t include , for a Bantam race engine , the case reed set up in my post , one other being the sheer
volume of engineering work involved , very few can do it . Executed well it works ok , done poorly it can be a real dog.
Perhaps the biggest downside is the direction the inlet charge is compelled to take . By necessity and to be able to install the carb , the inlet duct
has a serious downward inclination , incoming charge smashes into the crank discs and huge amounts of turbulence ensues . Turbulence kills
gas flow and the breathing capacity of the engine is compromised from the start . A well thought out cylinder reed has similar problems but to
a much reduced degree . It is no coincidence that all of the last 125 GP reedvalve engines had the gear box almost under the crankcase allowing
room for the carb and an upward inclination to the reed housing where inlet charge can be aimed directly at the transfer ducts , and thence
to the cylinder . The route taken being the shortest , in it`s time frame , and as turbulent free as is possible and the crank discs are not
intrusive . There can be one potential advantage to a case reed and that is in the rear , "C" port , a far more efficient duct can be installed , but will
it flow any better in it`s turbulent environment , just can`t tell , suffice to say , i won`t be doing one !
So what can we take from all of this , does a cylinder reed do the job efficiently ...... ask Nick B !

As a small indicator of the work required to produce a winning engine , Jan Thiel , admitted that from the time he was given the job at Aprilia
untill his departure , over 200 exhausts , 40 types of transfer ports /ducts and 100 cylinder heads were tried ! So get your winter development
schedule mapped out now , you could be busy in the garden shed and at the dyno .

Here is a nice over view to contribute to the on going ccr debate , it comes from a guy whose credentials are beyond question , a real been there ,
done that engineer . However , he has no experience of Bantams and regards them as a source of great mirth !!

" In general , high bmep engines that by design have good transfer port/duct geometry can have a case volume down towards 1.3 , lower performance ,
or rubbish transfer/duct design engines will perform better up at 1.4 . A small case vol speeds up flow at lower rpm keeping carburation clean and
widening the power band but a bigger case vol gives the pipe something to pull on at high rpm to make power " ." Get the pipe wrong at either end
of this range and it all turns to s..t " !


Be back later , Trevor

Same thoughts hear Trevor... on a bantam there isn't the room to get an effective case reed in. Tract reed delivers inlet charge on top
of the sheltered crank wheels (use of packing rings) where as on a case reed- inlet charge pointing at the crankshaft. Out of interest whats
your thoughts on a disc valve as not in the ideal place only being on one side of the engine? (I know Exactweld had 2 disc valves/carbs per
cylinder and of course Aprilia RSA had the one at the back.)

Cheers Mike

How I wish we´d had something like this source of technical information way back, 44 years ago. I´d have found time to get into Bantam engine tuning instead of just looking after the bicycle parts and making excuses I was too busy for ought else.

Never mind -- it was a fantastic -- fun(eh, painful sometimes) time, well worth doing.

I don´t say this very often -- I wish I were 30 years younger. No, make that 40.

I found that 1953 article about the Hogan Head and had Luke Filewalker clear me of virus contamination so if young Edward Pickering doesn´t object I shall send him the copy.

But then its really only Old Hat and sickening nostalgia.

Cheers!

JayBee -- John Boy trying to behave!!

Hi John,

No objections, just send it to the yahoo account rather than work one so I can get it across quicker.


Kind Regards


Eddie

Hi all
Have measured the ccv and it took 385 cc so that comes out at 1.47 to 1 is this any good for a 175 ?

Hey John ,
I got going in 64 , there was practically no info available then , just a re-hashing of existing practice and virtually no pioneering
development . But i`m still here doing techno stuff so the bug bit deep !
Any chance John , that the Hogan article could be posted here for me and others to enjoy , the brothers were truely enthusiastic
Bantam boys ?

Cheers for now , Trevor

Morning Trevor,

As soon as John sends me the Hogan info I will put it on the forum.


Kind Regards


Eddie

Hi Robbie ,
That volume will work just fine with the bigger capacity , most of the number range quoted come from 125 engines and their multiples ,
250 twins , 500 fours and so on. When you stop and think , the crankcase is really a non dimentional chamber , subject to continually
changing pressure and temperature . To simplify its function to a basic geometric ratio , that takes no account of it`s max , min or
transitory contents , serves to under state it`s complex nature . We all love a specific number , dial it in and you get " x " performance ,
sadly things are rarely that simple !
The larger cylinder volume will take longer to fill than a 125 of 54 bore , is your bore up around 64mm , pumping that bit harder helps
to get the job done in the time available ?
Do you have just two transfer ports , if so then the gas flow regime will differ from that of a 3,4,5,6 or 7 port arrangement , and so too
will overall turbulence in the combustion chamber at trapping .
After saying that , two ports having correct duct proportions and optimum efflux angles will out perform c..p multiple ones . Carefull choice
of exhaust system proportions will also pay dividends , but you may have to wield the calculator, hacksaw and welding torch to get things
just right ! As they say , there are no free lunches when playing with " simple " twostrokes , and the self limiting nature of Bantams !

Hope that helps in some small way , regards Trevor

Morning Ed and John b ,

Many thanks for that offer , i just love this historic stuff , helps fill the gaps in Bantam race development and provides for
a perspective of then and now !

By the way Ed , did my email , of yesterday , with pics , get through to you ok , these things have a habit of going astray ?

Cheers , Trevor

No problem Trevor,

Can't beat nostalgia, sorted my email nightmare so they will be up shortly.


Kind Regards


Eddie

Courtesy & Property Of Trevor Amos

Thank you for that Ed ,
Were it that everything in life was as dependable as Ed !

These two pictures are of the RS case reed set up , in the first , the path to the transfers is direct and reasonably uncluttered even with
the piston at bdc , impossible to achieve on a Bantam . On the Gilera, Derbi and ktm clones ( Honda copies ) the reed block to cylinder
axis angle is increased to provide an even more direct path. The crank discs interfere minimally with the incomming charge , but ultimately
it is the reed block that limits the engine , you can only lift the reeds so far with the energy levels available , the disc rsw has no such
problems, a huge uncluttered port at the rear with a 42mm carb feeding it !
The second pic is another view of the same , but the reed housing can be seen to approximate a 90* angle with the cylinder axis , tilt
the reed down hill a touch and things improve aerodynamically , and the flow is even less distracted by the crank .

Going slightly off topic , take a look at the ratio between crank disc and main bearing dias , just one reason why a 175 with a big crank
and std dia bearings mysteriously doesn`t make the power !

Great topic this , keep it running guys , regards Trevor

Hi All,
The debate is very interesing but I bet there are a lot of Bantam members out there that have not a clue what you guys are talking about so
I would like to poke my nose in. It has been many years since I've been involved but I seem to remember the formula for CCR is fill the engine
(with crank in place) with piston at TDC- this includes the volume of transfer ports and induction track, and measure the volume, let's say for
this equation the volume being 385cc, now reduce the stroke so the piston is about to open the transfer port then take this volume let's say 256cc
then dived 385 by 256 and you will get for what it's worth 1.49. Now, if you want to know if your motor will run better then take out the packing
rings, if you find your Bantam is faster then stick with it if not revert to experimentation , for what it's worth JS2 runs about 1,5. but I'm working
on a new pipe.
Les 2012.

The "suck it and see" sort of development is awful & soul-destroying. Having a dyno and sticking to one change at a time is the right
way and wonderful way to do engine development.
With no dyno and rushing off to a test track every so often is a long-winded way of getting the job done. Plus, if the change didn´t
work a whole day of the "Two day flu" ***would have been wasted.

***We had what was known as "Two & Three day flu" at Ford Dunton -- no mediacl certificate needed -- and I was frequently at
Brands feeling dreadful. Not because of flu -- because the change didn´t bring expected improvement.

Cheers!

Aint that the truth John !
Every time I see you post one of your formulas I think. You as a Ford engineer and me as a Ford fitter mechanic both know. Ford coined the phrase 'Teething trouble' when their engineers found theory and practice didn't always coincide
Pulled a few sickys as well John, I only found out my supervisors son was a biker when my supervisor told me how he knew I was in the IOM while I was off sick

Hi Trevor
I could not resist this one, trevor you use the words Impossible ! my own personal feeling is nothing is imporssible, a little difficult may be but not impossible. love the photo;s I bet no one has spotted what I have, the other thing having work for some considerble time in afoundry and machining casting its amazing the technology in making these cases and barrels, not just std casting process these are precision investment cores not just normal silica sand these are very high cost items.

2) the other think on you point about the fly wheels as they are travelling in the same direction as the gas flow what differenece does this have sure this will improve what your talking about.

3) I have tilted my barrel forwards 15mm to improve this aspect, Im quite please my think was correct then, I was also onto the inner ducts but not to the level or knowledge we have know. but I did do this well DAD did in about 1985/6 it was some years later before it appeared at a race track 90, in it first face it seized just starting the last lap, I think whch was about the time I solid my current bike/engine to Keith Andrew.

4) I hear those disregarding this layout for a fast bantam, I completly disagree with this, Andy Moldens bike went resonbly well, as Mike says, but ours was a lot stronger in all area except perhaps handling. I still intend to push on with as my winter project for next year, even though this engine/bike, dimmed the light for me and ended my passion for tuning and racing my Bantams, just too many issues to resolve, with a lack of knowledge / understanding / no time and perhaps a lack of experience, to resolve them. I had the best machine shop, we re machined the cases on a newall jig borer at lucas aero, things are different now, but the dyno readings proved it had loads of power all through the rev range and torque it had such a wide spread.

the crank reed engine is not dead, its just in the que in the shed waiting behind a few parts to be sorted, along with a few other bits and pieces, for my new bike and eds Bike and the sprinter looks like its comming out next year too, along with my twin disc set up, for me 175, I always wanted to do this, hopfully this will also be out soon, not sure about you guys but it taks loads off effort to do things with limited resources, in not having a full machine shop to hand, so its a trip off to the local eng shops or down to dads when somthing needs doing I cannot at home.

well thats what Im working on so what are you guys working on and doing now or next year lets see some pictures.

Derek

Hi Derek ,
Just a couple of points , the flywheels , themselves present few problems , it`s what comes off their periphery that is the problem .
Any rotating disc will move air , if that air contains petrol and oil it will have mass and density , a rooster tail of gas will centrifuge
off the disc and , in the case of the RS , collide with the inlet charge flowing through the reed block , turbulence ensues, bulk flow
falls and consequently , power drops . Covering the crank has proven to assist flow , but you have to balance this with lubricating
the various bearings , so take your pick !

I have never , and would never , suggest that Bantam case reeds doesn`t work ! What they do bring is a huge amount of work
needing specialist machining facilities and so on . What they don`t bring , so far , is any advantage over the much simpler alternative
of a cylinder reed , eventually the whole set up is compromised by poor gas flow , and dodgy carb installation ! However , i wish you well
with your personal project and look forward to seeing it on the track .

The project i am working on may interest you , it is based on a BTW barrel and head . The inlet port has been filled to accomodate a
correctly positioned duct alligned with the reed valve and is a development of current practice . The exhaust duct has had a multi bore
run up it and a sleeve with tripple ex ports shrunk in , a second sleeve forming a new bore incorpoates more of the tripple ex port
arrangement , the inner transfer duct profiling and port angles , with , the last part of the inlet tract . The original barrel, which is little
more than a finned sleeve , has had some judicious in- fill of weld , awaits cnc milling of the outer transfer ducts and subsequent heat
treatment . when the whole lot is assembled , treated , and final machining done , the bore will be Nicasil plated . Other things like stud
position , extra case screws , gearbox bearings , clutch basket and so on will be upgraded , i may go for an inserted head with a torroidal
chamber , a watercooled head is also a consideration . Thinking long term , a modified near side gear box mod with a detatchable insert
housing could offer extra , sleeve gear , output support and complete gearbox removal with the engine in situ . The whole project is
designed to produce power with relibility , the time scale is open ended and is determined more by funds than much else !

Sorry Mike P , i have just re- read the whole topic and realised you asked a question and i have failed to reply , i will get down on that !

Cheers to you all , Trevor

PS , you are very quiet on this Allan , any thing to add , after all you are the instigator and perhaps the main beneficiary ?

T

Hi all, Dereck you mis-quote me I said ' Andy Moulden bike goes like a rocket!'

Its also faster than mine and if the motor had been in my frame the exhaust would not of decked out and races would of been won and lap records would of fallen I feel?!

Trevor , no worries ref post just interested on your take on the(disc) subject. Also my next bantam motor is a BTW cylinder/head featuring inlet tract reed, some parts have been acquired but not a lot of thinking/work has gone into it yet. Going air-cooled to save weight - no rad/water/pump/battery - hope to get it down to 72kg dry!

Regards Mike

Hi Ned!
I knew Ford engineers before Dunton and it was a Dunton Supervisor who guided me into
taking interest in Bantam racing, then making a Bantam racer. I have described my time there in Testing Operations as the most boring 4 years of my life. But if I´d not gone to Rainham (before Dunton) I´d have never have known Bantam racing nor road-raced at all and would have the missed the fabulous experience of actually RACING the ABS 250 against Greeves Silverstones and the like.

During my time at Dunton the development engineers were "Component Engineers" which meant each one only worked and developed one component in conjuction with a new model´s other engineers. It was a cock-up in my opinion.

Did you ever hear of Alex Macfazdean? who went sidecar passengering and did some record breaking with his own home-made streamlined, cigar shaped special. He had a Norton-Wankel (rotary piston) engine in it at one time. Alex had "3 Day Flu" during which time he looped his record-breaking-special on Pendine Sands and poor -- now sick --
Alex had his disaster pictured on the middle page spread of the next edition ofMotor Cycle News whilst he was still off sick, nursing his bruises and concussion... I made my steel-boot sole (for Speedway practice) at Alex´s place and I cannot remember the name of it now. Anyway Alex was doing very well with his own engine recon business in 1986 when I saw him last. Can´t remember the Essex village now -- was south of Dunton....

Keep well,
JayBee...

Hi Mike ,
Sounds like a good project , i did a fair amount of number crunching on heat build up , the big problem could be assymetrical
cooling from the angled ex duct and lack of finning there . Heat saturation can build up very rapidly and cause real problems
with distortion . We will both have a problem there but i suspect you`ll be on the track befor me , best of luck . Can`t argue
with weight reduction aspect , that alone will reduce lap times . Strategic air ducting may help a lot here with shifting heat mass
but keep hot air away from the carb bell mouth , ingesting hot air is a real no no .

Good luck , Trevor

Hello JB
Yes I agree with you suck it and see is not the way to go, dyno is the way BUT!! what would you sugguest to anyone who has no
access to a 2 stroke dyno. How would you advise to test the changes?. How would you know if the idea's one had would work?.
I for one have no access to a dyno, I've checked in my area but only 4 strokes therfore I ask your advice. How can I evaluate
the changes made to JS2 without the use of a dyno?.Test days at Brands on the odd occasional visit,a race day with the club?.
please advise.

Les2012.

Its worse than going fishing Les -- a lot of patience needed if you develope just by track
testing. I´d set out with two others to get a Bantam racer made & on the track and so in being tester at Brands one & a half seasons didn´t seem too much. I just enjoyed the practising -- except for piston profiling which was a pain .. ... ....! ...As well as assessing what one-change-at-a-time meant there was the weather conditions to correct for and a
lot subjective feelings to cope with. Because I was far too overweight the effect of me
slimming down had to be taken into account -- I knocked off 3.5stones in 6 months which
probably accounts for my current longevity!!

I editted this at 11.03 (knowing that I had access again to the site...) -- The point above is very important -- if you are testing changes at the track they really have to be done on the same day (or correction factors applied, same as on dyno...). As the weather is this year (the temperature and humidity have had wild swings) a change for the better -- or worse -- could go unnoticed unless the performance was corrected and that comes down to sensible guessing because correcting is very difficult to do on the track.
I made a telescoping, parallel section for my first resonant pipe. With this I was able to get a good approximation of the length that worked the best -- with the particular transfer port shapes and all timings at taht moment... Then we made several small changes with ports and timings using that one pipe until the seeming optimum was reached and then repeated the lengthening & shortening exercise again... until I had a high torque motor, for my weight -- with reliabilty. With Brands practising on a Wednesday -- in those days -- there were 4, half-hour sessions during the day with cars and sidecars in the other 1/2 hours. This meant I could get enough testing in -- in one day -- to be relatively happy with the results.

I quite often enjoyed Brands-test-days more than race meetings because there was no fuss about scrutineering and so on -- you could do it at your own pace -- and there were always bigger street bikes to chase and beat up.
Better stop now or I´ll go on for ever....

However! The fact that I seemed to be going well at Brands -- particularly against Café Cowboys on Dommies and Big Triumphs had me thinking I´d be a Bantam Club champ... Not with an estimated (by timing the accelerations) 12 bhp ... No way!


Good luck"
Cheers!
JayBee = John-boy!