midlands Centre

Good Afternoon All,

It is the intention to orgsanise another midlands meeting, we are possibly looking at the first or second weekend after bonfire night. It will hopefully be held in the skittle alley of a local pub in gloucester.

Anyone is more than welcome to attend, if anybody is interested they please can they let me know on here or by pm so we can have a rough idea of numbers and what date/days work for the most amount of people.

This time i think it would be good to have an agenda so that we have time to discuss things so please feel free to put forward ideas. If you want to bring bits you are working on or have questions on then that's not a problem either.


Regards


Eddie

Terrific Ed, been looking forward to another meeting, but as I have nothing that would interest anyone, it will just be me I`m afraid!

Regards, Trevor

Wish I could get over.

 Much like Trevor I feel sure I´d have nothing to offer. You fellows have done so much in 4 decades to advance the Bantam as a  racer it far exceeds anything I´ve done -- or tried to do -- except race a Bantam perhaps. I was always wanting to race not work on the bike.
.
  -- and there it is, I am sure if you tweaked Trevor in some way the info will flow out isometrically -- or whatever....

As I said, on here earlier, looking though old BRC magazines I acme across a lot about the Amos Brothers. Both were contributors of technical stuff and were always giving a helping hand to other Bantamites during their racing times. David(?) Amos on his 180cc Bantam had the 250 lads worried and wondering where they went wrong. If I remember correctly David finished well up in the BRC Club´s 250 Champiomnships -- did he win it one year, Trevor?


-- just tweak Trevor a bit...

Hope you have a good meeting.

CheerS!

John,
Brother David didn`t manage to win the 250 championship, as good as the 186 was it was asking too much to regularly beat the more powerful, full size 250s. He did manage to embarrass and infuriate quite a few riders however. One nice incident was at Cadwell using the old 1.5 mile circuit, after harassing a couple of guys on their 250s for the whole race distance they both came snooping around the paddock. Upon seeing the 186 one of them was heard to utter in despair, "It`s a f...in Bantam", they then trudged, disconsolately off, one up then for the Bantam boys that day!

I don`t really need tweaking John, just ask and I`ll respond, as always if there is any way I can help, I will, and do. The upcoming Midlands get together may be just an example, to ask costs nothing, the answer could prove to be priceless?

Cheers, Trevor

Good Morning All,

Just to keep you updated, the dates that are suggested are either Sunday 9th November or Sunday 16th November. If interested parties can let me know which date is more suitable i can book the venue and let you have details.


Kind Regards


Eddie

Ed,
Thank you for all of the hard work you put in in locating a suitable venue for our next meeting.
Both of those dates are fine for me, I`m happy to fit in with the majority, should be a lot of fun!

Trevor

Good Afternoon All,

Just to confirm the meeting will be on Sunday 16th November.

Details to follow.

Kind Regards

Eddie

Hi me Michael would of loved to come but its the Nec Classic bike show that Weekend my be we can make it next have a good one Robbie

Good Evening All,

Would help if I put the details up!

The Avenue Pub
Bristol Road
Gloucester

Meeting from noon.

Kind Regards


Eddie

Many thanks Ed, looking forward to meeting all of the attendees again.

I was wondering if I could ask a favour of the 175 runners who will be coming? I have an up-coming winter project and need to measure up the various lengths of some 63/64 mm diameter pistons. This will enable me to get the porting and combustion chamber drawings done, old or damaged will be fine, as diameters are not involved. Thanks in advance, it could be a very worthwhile gesture, as we might get chatting about the big brigade engines?

Trevor

Inlet side of piston is 54.5 , exhaust side 62.1,top of gudgeon pin to top cylinder part of piston 24.2 , all dims are to top of cylinder part by the way pin is 16mm, overall piston lengt from inlet cut out h with crown is 59.2

Thank you Dan, that is great information and will be very useful, I will be able to move forward now. If there is any way I can repay you for your kindness then please ask!

Regards, Trevor

Trevor Amos wrote:

Thank you Dan, that is great information and will be very useful, I will be able to move forward now. If there is any way I can repay you for your kindness then please ask!

Regards, Trevor

Good Morning Trevor,

Could you email me on info@rexcauntracing.com  ?

We have some drawings of our 64mm single ring and 62.0mm single ring you are welcome to study!....................

All the Best!..........Rex

Hello Rex,
             Thank you for that generous offer, made I`m sure in the very best tradition of information exchange that is the hall-mark of our Bantam fraternity. With yours and Dan`s help I can make progress with the 175 project.
You should have my reply email by now.

Trevor

Quid pro quo Dan.
In your recently posted photos I see you use a very acute bend in the header of the exhaust pipe. A turn of that small radius will cost you power. Exiting high speed gas will not like that, and will protest by slowing down and creating turbulence, costing energy that should be used to advantage further along the pipe. There is a very real danger than rubbish gas will lurk there to be collected by the returning pressure pulse. The acoustic ex. pulse will travel at the speed of sound as it prevails in your particular header pipe, and will be at sonic level initially. It will hit the outer wall of the pipe and send reflections back, far too early, to the cylinder messing with the next pulse and further robbing the diffuser of energy to work with. No where else in the engine will have gas flow at sonic level.
This is a classic case of not being able to make up for later what was missing in the first place. A nice smooth generous radius will guide gas flow every where with minimum losses, the straighter the better, and the exhaust pipe is no exception. The first tangible benefit will be a cooler running engine.
Once again grateful thanks for your assistance.

Trevor

i have looked at the bend myself a few times, it came from a gilera that made 26 hp, i used it as i had it to hand and have since kept it for no reason other that convenance ! i will be looking to change it however as with an off at brands it took some of the force and could make a mess of the engine if not tucked away a little better, but a bigger rad of exhaust must work better, the bike feels quick but you never where the powers lurking untapped !

Hi Trevor
There is a old 175 racing piston in the belly pan of Michaels bike at the NEC for you if any of your center lads are passing it there for you I wiil be there sat and sunday and hope to be there Friday afternoon
Robbie

Hi Robbie,
          That is a very kind gesture, were I able to be there I would have picked it up and had a nice chat to every one. If there is a chance that someone could get it to me or to the Midlands meeting I will be most grateful.
There must be a story behind carrying a spare piston secreted in the fairing, track-side repairs maybe? All joking apart, enjoy the NEC and I hope you can make a lot of converts to the Bantam cause.
However, there is going to be a deal of techno talk aimed specifically at the 175 engine at the Midlands meeting as this seems to be the growth area. So, being in Gloucester may be might be more rewarding for you both than Birmingham? Now there`s a choice for you!
Thank Michael for me and I hope we can all meet up some time.  

Regards,  Trevor

One of the many topics that was discussed at our get-together was transfer ducts and ports and their influence on performance.

At initial opening the mixture in the duct has zero velocity, and it is only the pressure difference at the cylinder exit compared to that at case entry that overcomes inertia and flow commences. Flow accelerates into the cylinder and ceases only when these two pressures equalise, the flow then is at maximum velocity. The mass of the gas column in the duct is, specific mass x duct length x cross sectional area. As we want to transfer that gas into the cylinder as rapidly as is possible, we will require a certain flow velocity. This velocity is inversely proportional to the duct cross sectional area, and, the required pressure differential is proportional to the square of this velocity!

So, are larger duct areas/volumes of any real benefit other than to satisfy the philosophy of, bigger is better?

Cylinders with transfer ports that are too high will derive no benefit from larger ducts, as is the case with Malcolm`s barrel!

Whilst we are here, could someone explain to me why bridged exhaust ports are a waste of time, particularly when the potential for increased time/area is so important and a bridged port can do just that with out increasing port timing?

Trevor

i would say a bridge isnt needed on a narrow exhaust port ,( unless the rings need it i guess)i would have thought it only robs the area,
if talking about Malcolm's engine, and ive only seen the photo of it id guess the transfer looks a little close to the exhaust and could be widened towards the inlet side by a fair amount , then reduce the height of the transfer giving a better blow down figure, just my layman's ideas of course, not backed by science or calculators but by my arse on a seat! , i had a barrel that look a bit like Malcolm's once, it didnt work very well, and having seen malc struggling with it guess there must be something not right ,

Thanks Eddie and Malcolm for setting up the meeting on sunday,  had a good day and again Trevor coming up with more valuble tuning information.  Just got to put all the theory into practice.

I arrived at the Avenue just after 12 noon, I left at 5:30 and we were chatting for over 5 hours, and was amazed when Malcolm told us what the time was! We could easily have gone on for another couple of hours such was the level of intense involvement.

Malcolm and Ed are perfect hosts and the venue was ideal, Derek had his rapid machine there ,which has progressed enormously over a very short time scale. Lots of parts and engines to handle, a vast photo montage and books, drawings both current and historic to pore over. A whole plethora of Bantam racing to see, with tea, coffee, beer and snacks at hand. As can be easily seen from the photos Derek took, we were all having an enjoyable time, and learning an awful lot from each other.

So where were you all ?!!

Very many thanks must go to Malcolm and Ed, for arranging the day to enable us to indulge ourselves!

Trevor

Spent a few minutes this afternoon scrutinising the published drawings of one of the Aprilia barrels. According to my maths, the "B" transfer port window area in the bore exceeds that at the barrel base/crankcase inlet by around 10%!
This flies in face of hitherto accepted wisdom that the, in, is always larger than the out, sometimes by an increment of up to 50%.

Working on the assumption that Jan and Frits knew perfectly well what they were doing at the time, and that this barrel can be regarded as an exemplar, is it US that are making the misguided assumptions and doing it all wrong? Is there a better way?

Trevor

i think this shows the kind of detail thats required around your transfers and also the a, b port sizes.

thought this was interesting, taken from the kiwi biker site

Originally Posted by wobbly View Post
When unleaded became mandatory in 98 most teams had a hell of a time keeping deto under control, having to run very rich and retarded.

The cylinders with the straighter pipes always gave a lot more grief, until a lowly dyno operator at Yamaha discovered that when he stuck a large pressure probe into the header, the deto went away.

They managed to keep this secret for a couple of years but when teams like WCM got hold of the bikes, and left pipes lying about as you see in the pics,word soon got around.

Click image for larger version.  Name: Det Button 2.jpg  Views: 5  Size: 38.3 KB  ID: 305353Click image for larger version.  Name: Det Button.jpg  Views: 7  Size: 79.1 KB  ID: 305354

The "things " intruding into the header take varying forms,but all do the same thing - the usually bottom "bent "pipes dont have the same issue, so dont need the so called deto buttons.