Time,timing,time area ?

Courtesy & Property Of Mike Powell.

The diagram above is the cylinder rolled out flat and is from a pencil rubbing from around 2003 its the same liner that's in it now some of the ports are a little bit bigger now.

This barrel at its best produced 24plus bhp with a retard ignition and a big fat pipe.

Its 'sister' engine was Tom first (?) Reed valve motor that Ned ran and was a simple
1exhaust 2transfer 1boost with inlet which made 20bhp with .065" btbc fixed ignition
and a skinny pipe.. this is the engine Phil Betty uses now and Mick Potter before but with a retard ignition. Mick didn't you get more out of on a dyno?

Just thinking NIck Bramley won the champioship last with a simular but highly
developed (P.Tibbitts) engine layout but an air-cooled cast iron barrel.

I'll post Phil Bettys cylinder layout via Edward later..

Regards Mike

The single observation I would make is how big those transfers are, "area Great" but 14 and 15mm high? that seems too me to be tall, bust for sure the areas are wonderful, what about the blow down.

like to see the other you talk of and Mick Potters results with the retard ignition.

an excellent post well done.

Derek

Hi Mike and all Bantameers,

By retarding the ignition timing (it is impotant to know that the ignition fitted is a Honda item and therfore not nesiserily ideal for a Bantam) and also fitting a carb 2mm smaller in diameter peak power was increased from 19 bhp to 21 bhp (Every dyno will give diferant bhp figers so every dyno can only be compared with it's self as barometric pressure, altitude, humidity ect have to be taken into acount). Optamising what you have is unfortuatly not straightforward a lot of trile and error went into what was eventualy a significant increase in power.

Mick.

The GT 186 , with a 62mm stroke , had transfer ports at 14.5mm high, who ever thought that transfers of that height for a 54 stroke could ever be suitable was seriously in error . I should think that the motor would struggle to make much power under 9,000rpm, and as Mike says difficult to ride !

Trevor

Courtesy & Property Of Mike Powell.

Interesting porting diagrams, Mike,
A lot of almost counter thinking going on here with these transfer ports in their respective barrels. On the one hand a tiny 11mm wide port, on the other a massive 35mm wide port ! Assuming that both engines have similar crankcase geometry and that the pipes are doing their job at a similar time, and why wouldn`t they be, then the resulting flow distribution is going to be massively different, and yet designed to perform the same task ? Taking an educated guess, that both driving and differential pressures are roughly comparable, then transferred mix from the 11mm port will have the velocity of an Exocet missile and the 35mm port will be sluggish, and directionally unstable. At opening, that big port/duct will contain a lot of inert gas and to get it moving, to deliver meaningful fresh charge,will take a long time and a lot of energy to reach its natural max. flow frequency. Bantams have little energy to spare on wasteful endeavours, that`s the very reason why they don`t produce 30bhp.........yet ! Mind you, 22bhp at 10,500rpm and 20 at 8,000 will out perform any current engine !

Catch you all again, later. Trevor

All interesting stuff Trevor ? I don't know the in's and out's in design of the cylinders
but the simple 4 port Phil Betty motor worked well on a straight ignition and it would
appear better on a honda ignition and originally built in a week in Tom's old shed in
1983. It has raced every year since I believe - are there a couple of pointers for Phil?
Perhaps make the widths smaller on the transfers and even them up?

The multi-ported version is a bit of a mix and match of ideas as it was an unfinished
Piston port barrel 6transfer which I turned into a Reed valve 4transfer barrel which
then had a liner by Fahron engineering with a free hand to make it work! The one
thing they couldn't change however was the bridge between A & B ports?

So your could say the thinking was done by two different parties.. and the funny thing is to ride they are both very similar.. not a lot at low rev's. But they have both been successful winning bantam championships?

Your last comment is so true.. and therefore folk should be catching up anytime soon

Regards Mike

Congratulations Mike you've established yet another record, albeit a pyrrhic one at best ?
After ploughing through my Porting Analysis file of both Bantams and all other race 125s, the 35x14 transfer port depicted in the second drawing you posted has been established as the largest single port recorded when balanced against power output, even exceeding that of the GT186 62x62 engine !

Could there be a lesson to be learned here ?

Cheers, Trevor

Excellent!! that is good news or is it? I need to know what pyrrhic means I suppose? Anyway that's Phil's baby now..

Just read in Classic Motor Cycle Mechanics - a piece by Stan Stephens ref 250lc production race porting, remembering that
an lc is a 54x54 motor. Port heights (from top of barrel)

Exhaust 26mm
A ports(est. 25mm wide)43.5mm
B ports(est. 13mm) plus boost 41mm

Regards Mike

Trevor "stop it" leave the poor lad alone,

I actually found it quite interesting, and there for sure is a lesson in here somewhere, but I cannot pin point what it is, perhaps its in your comments !

anyway I think they are great post Mike, I would like to have seen pictures of the barrels that we asked Trevor for and (never got) got half of them, suppose we just need to organise another "Midlands Bantam racing meeting" and hope either Mike or Trevor will bring along their respective barrels, now isn't that a good idea,

seriously its great debating this type of information shame other loking in don't do the same, but perhaps a bit of encourangement and less leg pulling may help this !!!!!

kind regards to all

Derek

Derek,
Yes the lessons are there in most of the posts on this subject, and it`s not too difficult to see the short comings with this layout and their consequences . The ports themselves differ in cross sectional area by over 50sq mm , more seriously is the lack of symmetry of the fuel/air mix being transfered, and with the two ports having different velocities the ensuing rear gas column will be badly formed and subsequent scavenging will suffer.
View the large t.port at low rpm, with the pipe not working any sense, inducted air will be in short supply hence port gas transfer will be low, and that huge port is expect to maintain some form of control over lazy flow over a long duration period . There will be a lot of mixing of fresh charge with combustion deposits, rather than the old stuff being forced out ! Subsequent combustion will be with less than pure charge and power will suffer, things improve with higher rpm but the real penalty is felt with a lack of power band width and a tricky bike to ride and lap times suffer .
The real lesson is that there is a far better way to make a sweet running engine than that offered by these obsolescent designs, the moving hand has writ and has moved on!

Cheers, Trevor

Trevor, Do you think it best to delete these port designs so new starters don't make the same mistakes?
(still 4 wins at Lydden last month)
Well at least they no what not to do? But I still don't think they know what to do!

I think I can answer your question - Why don't bantam tuners post info on to this site? Well I feel its due
to unwanted comments for other people on the site.

I don't know if you have noticed but current bantam racers rarely come onto the site. If you go on the
memberlist you will see the last 20 signed in people, 3 at most currently race a bantam.

Derek, not coming to Cadwell then? you still up for 'pistols at dawn' at a rolling road somewhere??
And did you sort a 'John Sawer Trophy' for the Midland boys?

Must get in the garage now, for Cadwell race prep .. Mike

Pyro-Putty 2400 bonds tenaciously to cast iron and steel and stainless steel, and is easy to apply, cure, machine and clean. Can be applied up to 3/8" thick. Air sets in 2-4 hours. Heat cure at 200F for 2-4 hours.

Pyro-Putty 2400

This high temperature ceramic and stainless steel metal-filled paste is ideal for repairing defects in manifolds, headers, exhaust pipes, mufflers, and more. Withstands temps up to 2000F

PYRO25 Pyro-Putty 2400  £48.81
By Phone: Call +44 (0) 1420 474961 between 9:00AM - 17:00PM GMT. Monday to Thursday and 09.00 to 12.00 on Friday and we'll be happy to assist you.

looks like the reprofiling of the cast iron barrel exhaust port may be easier than i thought.... anybody used this product.      

( info kindly given by husberg from kiwi biker forum)

Hi Nigel dammed good job mate, where did you find this one, never heard of it.

Hi Mike
a change of heart !!!!

like many things, perhaps people give up because its so difficult to compete, no point in flogging a dead horse!!!,
actually No i don't think you should delete the information on the porting post but it would be good to say how it performed ! compared to the bike/engine you normally race, 10 seconds a lap slower at least?

back to current status quo, sometimes you just got to admit defeat and move on, lots of people understand this,  but lots of people come and even stay a while then move on,

"WHY", like Trevor said the answers are in here somewhere.

What I feel you need to do is make a few changes to even things up, them perhaps people will come and stay to play a while longer, than they are doing, i have even offered a few suggestion what to do, sadly this seems to wind a few up rather than look at what is being said, we are all human sadly taking it personal as an error we all make from time to time.

Almost forgotten, Mike pistols at dawn !!!! shall we have a wager, who ever looses pays for the dyno of both bikes my bike verse yours ! think about it and get back to me, i recon we need an independent dyno, as on mine you would def lose. !

regards Derek

No Derek, you said you would pay! So that's a No.. your idea anyhow!
Plus I expect my bike to lose on torque and bhp!
Its the rider that makes it competitive as this years championship shows.
In fact its been unbeaten all year when its finished a race its won!(1dns 1dnf)
Its having a bit of a rest at Cadwell with Jack Scrivener giving it a ride out.
I'm concentrating on the Seeley G50 as I'm in with a shout of winning the 500 Specials
championship too.

The Reed motor is 0.3sec slower (Cadwell) than the piston ported barrel you had in your
hand at the first Midland meet.

If you put your money where your mouth is Replay Scooters (Chalky) in Rothwell Northants is
a Dyno (Rex Gaunt uses him) in easy reach to us both and why not get all the bantams there?
one run only? Hightest Torque figure gets the John Sawer Trophy?

Something to think about... Regards Mike

Mike
I do not remember saying I would pay for the Dyno ! blimey thats so very generous "of me"!!.
"that offer expired on the 16th september at 11.0am,and the torque trophy Idea is poor taste "I decline".

The barrel you bought to the meeting was not your current item ? and it was you that told me it was 10 seconds a lap slower than your current bike. !

I have to say it appears so many bikes have been restored/built, there is a Forum of Technical information that you could only dream of when I started racing, its now so much easier with all this information to build and race a fast reliable-ish Formula Bantam Racer, there are many more new bikes being built. So why do you think the racing class seems to have died off again, to what it was 12/18 months ago".

Derek

I thought as much... please put your time limits in your posts in future..
I decline too then..

Derek things I definitely know about my 'current' championship winning bike
Is it uses the barrel I took to the first midland meeting and you had a good
Look at it and posted some pic's on line and on facebook under your female
alter-ego Bsa Bantam Racer. This bike 001 is a little faster than my reed valve
barrel 0.3 sec at Cadwell and my spare bike 003 is a second slower round Mallory.
Hope that sorts your memory out..

Shame you no longer race a bantam but I wish you luck with your racing at Assen
at the weekend and your racing exploits in the future

Mike

Time as in the GOOD OLD DAYS -- a lot of secrets were kept....


Wobbleyman acting the part of the "Vulture-with-a -Vernier" could be observed sneaking up behind  a desperate `Senior´ stoning off the scuff on his piston whilst  Wobbleyman was measuring his barrel.  As was said on here it was not until Don Eden published some info... in the Mag that riders shared their secrets -- sometimes not entirely factual, of course!

Colin Aldridge -- the original Wobbleyman -- did the ports on my Icarus-2 barrel (I had no time...) and in spite of what some said about his tuning being crap Icarus-2 motor revved to 11,000 rpm  where Icarus-1 was 8,400 with wind behind. However Icarus-2 was unreliable -- I was using BSA pistons which grew in length-- and with the steering geometry being somewhat special meant a constant crossing of the fingers of the right hand. That meant with three fingers of the left hand hovering over the clutch lever made it a pleasure to climb aboard Andy Boyle´s 250 ABS with 5 gears which had the legs of a Greeves Silverstone at that time.

That is my only  regret, I was just getting things sorted with the 250 ABS when the great offer came from Canada and I took it meaning that Andy didn´t get going -- properly -- again until a few years back. His Royal Enfield GP5 that is doing well now could have been making a name for him in the eighties  if he had kept going after those early to mid seventies but I think ambition with the job also got to him and he made a different name for himself in Germany and America for Ford.  

And I replaced motorbike racing with downhill ski-ing -- which needs similar skills and scrubbing off of speed in corners and am glad now that I had both experiences....

Good luck to you all...
Cheers!

JayBee....

just opened up an old damaged cast  barrel to see if the exhaust modifications were possible.i think if that if i opened up a little more an insert could be made which  could accomodate an exhaust stub aswell,  rather than using an epoxy type filler glue, although the latter would probably be quicker.

Hi Nigel/Mike, interesting this, is the object to resolve the duct shape/area inlet outlet formula, or to straighten it up "a little"- i recently cut the exht thread bit off our new water cooled cast cylinder, looking at it, its possible to re bore the port inwards going past the first bend up to the left side stud line, but not breaking through, on the left just the right side then grinding the fins back to get a better weld on, lots of work to make the wall thicknesses the same here, after this the port could be moved / correction the exh duct central line could be moved over, to a more central position so getting a better shorter central position, missing the down tube is then the next issue.


Mike both your diagrams show reed barrel engines, you have been on a piston port cylinder so too has ian, these are the new cylinders and take over from the old items Im assuming this of course, I know this as on both diagrams you can clearly see the rear transfer coming from the inlet - this is not possible on a none reed piston port engine, that you were using the last time I looked ????????, and you clearly remember you telling me the reed valved cylinder engine was 10 seconds a lap slower than your piston port motor.  lets get back to commenting on Nigel's photo's


Derek

you can make a sleeve that can be fitted in the exhaust and inlet this'll correct the swan neck type exhaust path

dan is this a 175 barrel? does it have a liner/sleeve in the barrel?

Yes and yes nobby

Yes and it sure goes well look forward to it being out on the track next year