a new member and new builder plus progress so far

Very interesting Dan, if your riding and race speed is as radical as your engineering then the top order will need to re-appraise their own efforts...

that made me laugh!

im under no illusion, i've got some bantam riding to learn,

just always seem to be chasing about with things and ideas,only said to robbie the other day that i was a little bored having built the bike and missed the lydden test/track day.

mike its interesting you mention two other bike have removable plates on the other side, it seem to be easiest to make the side behind the clutch come off as this way i dont have to make it oil tight and fitting the layshaft is easy this way as the fixed gear is at the bottom as you fit it in and not the other way with the free wheeling 28 tooth gear free to fall off , id like to see the other way though have you any pictures?

just an idea to get some oil flow through the bearing of the the layshaft , kind of what we spoke about yesterday robbie.

just thought i'd bring my post a little more upto date, here you can see the new barrel i used at lydden last year and the pipe i made too, since then subframe has been made lower and with the seat back and foot rests lower too, the photos don't show the barrel finished though lots more was done on shaping and matching left and right transfers,

i now have a race licence .... and i'm not afraid to use it!! lol

in this first video we can see what might be a reason the gears can jump, the flexing plate that must be able to move in order to make the gears select, however the design of the selector plate means it can move in the opposite way its meant to, making a jumping gear a distinct possibility




this second video shows after a mod to the plate, this lets the selector plate move in one direction only(the one we want it to move in) and a picture to




hope these show in a more understandable way les

https://2img.net/h/i238.photobucket.com/albums/ff278/dansofield86/temporary_zpsldka8k48.jpg
https://2img.net/h/i238.photobucket.com/albums/ff278/dansofield86/temporary_zpszes4fwrm.jpg
Just a few photos of work in progress
https://2img.net/h/i238.photobucket.com/albums/ff278/dansofield86/temporary_zpshdqhpcwj.jpg

Wünderbar Danso...

Did you use a program to design your pipe Dan and if so which one? I have my new motor from Brian which is a 175 and I need to build a pipe. Any ideas would be helpful.

www.torqsoft.net%2Fexhaust-design.html&h=MAQGmtaSk&s=1 see here Edward,lots of goodies to read and some of it free,

Thanks Dan really appreciated. I will let you know how I get on.

Hi Dan

If its ok I have a few questions, I am sure they are silly.

The exhaust design calculator refers to crankcase compression ratio, how did you calculate that? I know the CR is on the new engine is 8.8:1??

I have some information on the timing Exhaust 97 Transfer 65 Inlet 90. Can I calculate the port duration with this information?

I suppose its easy when you have done it once!?

Any help much appreciated

http://lambretta-images.com/archive/porttiming.php

this is a really useful page, lots of info to input and give easy answers etc,crank case comp is a hard one to calculate see here http://www.dragonfly75.com/motorbike/PCR.html, its involved

Thanks Dan

I am already involved, my sole motivation in life is now pipe design and high temperature gas flows.

Even going on a welding course next week!

don't advertise that! you'll be up to your neck in orders!

Edward,
Am I reading you correctly here, is the exhaust pipe design calculator you are referring to really asking you to factor in the case compression ratio in order to arrive at a suitable pipe dimensions, if that is what is being asked then it is certainly news to me? In messing about with just about every two stroke exhaust pipe calculator and simulation software available, case compression ratio has never been required, and is not a factor! The primary determinate for pipe design is acoustic wave speed and that is a function of temperature and time, not case volume, if you would like to know more just ask.
With symmetrical port timings, just double the timing and you have the duration, ie,194*ex, 130*trans, and 180* inlet, all are pretty much on the money, well done!

Trevor

Thank you so much for your post Trevor.

I am a relative newbie to 2 strokes, I did ok last season and I am really enjoying the riding but I felt it was about time I learnt more about the theory. The web site I am using for my calculations is www.torqsoft.net its the one Dan uses and lots of other bantam racers and it requires crank case CR. I don't know if that is a factor of the equation used or if it gives better / different results?

I am afraid I can claim no credit for the port timings the engine was built by BTW but its good to know you approve and thank you for the help with making sense of the numbers.

I am interested to know which simulation or set of equations you use to design a pipe? As I said I am a novice so although I understand the basics I will struggle if the theory is too advanced.

Thank you again and I would really like to know more when you have time

Best wishes

Edward

Edward,
Its great that you are keen to learn, I`m the same, even after 50yrs of messing with Bantams, so its no hardship to offer assistance. I will get something done for you that will not be too taxing, but don`t underestimate yourself, I have an idea you are one smart fella!
Welding is a terrific asset to have so stick with it, as Dan says we`ll all be queuing for your services.

Be it in touch, Trevor

hi all, in the scheme of things how important is it to have an effective pipe ?
just wondering

Adam,
Simple answer...........absolutely critical to have the correctly proportioned exhaust system. Keep an eye on Edward`s topic the numbers to calculate one are coming up!

Trevor

mornin thanks trevor

Adam,
There is a nice story about Jan Thiel`s antics when he was at Aprilia. After completely removing the exhaust on one of the 125 engines that just happened to be still on the dyno, he got the thing running, optimised the settings and got just 17hp, and a lot of noise! With the pipe the hp was 52 so you could argue that a good pipe might be worth 200% of improvement!
Not sure if that will be replicated on a Bantam race engine however?

Trevor

One of these days I'd like to resurrect the "Large or Small Flywheels" debate which might be useful to any of the newcomers and maybe some of oldcomers too. Remembering correctly: it was never properly resolved.

From what we´ve -- and I´ve -- already said and seen:    in the main the successful 125 Bantam uses Small flywheels and the successful 175 has the  Large ....

In with this was the question why did Rossi have those bothers of Ducati power-surge (for the want of  better words) whilst accelerating through the curves which he did not have with the Yam...?   when one would expect the Yam... to be the more guilty one of the two -- more "snappy" perhaps the bettrer word here. .

Whilst we express engine speed in revs per minute and revs per second which suggsts regularly  smooth rotation   the cycle of one revolion is not uniform although the cyclic irregularity of the two stroke is better than the four stroke.

Any takers?

Cheers!

JayBee.

Always ready to oblige John, here is a crank from an Aprilia engine, small at 93mm diameter and the gap between the discs same as big end width , small radius of gyration but high inertia with all of that very heavy Mallory stuffed every where! The most potent 125 yet created, so must mean something?

Trevor

On the subject of exhausts, back at the dawn of time (around 1964, actually) I was running my racing Bantam on a short open pipe, but decided it was time to try one of those much vaunted "expansion chambers". I had a buddy who was a welder, and he knocked up a rudimentary adornment for my exhaust pipe, consisting of two cones and a short thin tailpipe. I started testing it on the end of a standard, full length, front pipe. The result was quite shocking!

The engine started up and ran OK, but issued forth billows of blue smoke, and very little urge. I proceded to reduce the length of the front pipe, in stages, and it gradually became less smoky, and to produce more power, until I arrived at a set up which gave no excessive smoking, and a useful increase in performance over the previous, plain pipe, arrangement. I thought it looked quite business-like, too.

It was a very crude experiment, but certainly convinced me of the potential for improvement, just from modifying the exhaust system.

Thanks Trevor!

I did a bit of an exercise on this many moons ago where the 125 Bantam had 96mm dia and 2.4kg and the 175 had 136mm dia and 3.8kg. I calculated 'J' as 0.002765kg.m² and 0.00879kg².m² respectively ... the latter -- in the 175 -- having more than three times the flywheel inertia of the 125 when plotted graph wise showed the 175 multiplies the difference by much more as speed increases. I calcuölated that the 175 would be slightly sluggish on acceleration as against the Bantam 125 and concluded that torque for torque this is balanced by having 4 gears instead of three which means the Tractive Effort versus Tractive Resistance can be equal with use of the optimum gear ratios ... In other words the 175 formula is not so adversed to the 125 as has been suggested.

Rossi on the other hand was just "out of sorts" at the time (in my opinion) because the Ducati would have been less twitchy than the Yamaha by virtue of the twin versus four geometry....

Er...Um!

Cheers!