Heavy Crankshaft....

Hi, John, Ed ,
Sorry if i abandoned you ,but you did`nt need me John as your balancing post was spot on, nothing i can really add ,
another authoritive piece of work !
Returning to fluctuating velocity , it might go some way toward explaining why ex pipes don`t always function
in their predicted fashion . The calcs are done using constant velocity , time and temperature at , usually , peak
rpm. If, however ,a returning plugging pulse is 500 or more rpm out , the results will be poor . I suppose thats the time
the hacksaw comes out , what can be done, nothing really , as " garden shed " tuners can`t test for it .

Ed, never stop asking questions , no matter how trivial you think they may be , they will always be answered , and , we
will all be the better for it ! I got so nostalgic doing some of the crank work referenced from decades back, that i almost got my
Slide Rule and Log Tables out , now thats pretty sad don`t you think?

Happy tuning all , regards Trevor

Hi Trevor/John,

Many thanks for the information, i certainly will keep on asking questions as i feel there is a wealth of knowledge on this site and when there are topics like crank stuffers, small and large cranks, 125/175 pipes i can pop into the next room or upstairs and physically go and look at what is being discussed.

Regards


Eddie

Subject closed I guess -- for all of you -- not me.

Just in case I get blocked again -- racers and helpers alike, have a good time next weekend at Ladden...
Cheers!
JayBee.

Just came across "The Motorcycle" mag (The Blue `Un as they used to say) for 11th June 1953 . There´s a picture of Fergus Anderson on a Moto Guzzi (he finished 3rd on it in the Junior TT) which has an external flywheel that looks to be 10inches in diameter. Being of large dia the engine would have more inertia to contend with than an internal flywheel half that size yet that 320cc Guzzi was very competitive in those days....

Ah! just remembered! this subject is closed -- ennitt!??

BIG flywheels to you too....

I asked this question before -- in Brian White´s article about his BTW tuning: the flywheel looks VERY BIG -- is it like that in racing trim?? No answer................!?
--
Like I said before, perhaps Brian has a secret he has been keeping from you ALL!
--
Perhaps his motors run on to higher revvs because of a heavier flywheel??????

Yaaaawwwwnnnn!!

With an appropriate design, you obtain more angle-area for the transfer ports, but less for the exhaust... You really must utilize both sides of the cylinder for exhausts if you want to raise the maximum rpm for optimal scavenging. And with opposite exhausts you need symmetrical transfers that create a stable central scavenging column, otherwise a great deal of the fresh charge will short-circuit into one of these exhausts.

The pictures below show the effective port areas and the angle-areas for the ??? RSA with conventional ports and for with symmetrical ports.
The ratio between the two transfer angle-areas gives an impression of the rpm that should be attainable...

The transfer timing is about the same for both cylinders and the exhaust timing of the FOS is lower than that of the RSA; the RSA-exhaust timing is a compromise between a timing that is too high for optimum resonance and an angle-area that is too small for the rpm that the transfer ports permit.

With the FOS-system I do not need to compromise because I have 23 % more exhaust blow-down area and 33 % more blow down angle-area, even with the lower timing. And all of the exhaust area is above the transfer ports, contrary to the RSA where 1/3 of the exhaust area is situated too low to be of any use for the exhaust blow down phase.

Another advantage: because the cylinder is symmetrical, it will not distort under temperature influences. This makes the piston very happy .

hope you find this interesting

Hey Derek,

Pardon my ignorance, but what is the RSA (In NZ that is the Returned Servicemans Association = British Legion) and FOS ?

You mentioned below, but we didn't see any pictures.

Hi Derek,
Fritz Overmarrs, by any chance ?

Trevor.

Perhaps we should start a new thread on this topic and also include the work being done as the Foekema Symmetric Twostroke, I did read about someone drilling 18 exhaust holes to atmosphere on a Go Kart engine with some interesting "on pipe" performance increases

James

Hi James!
No one answers my questions -- what do you think of the BIG flywheels in the BTW tuning article -- is there some secret there?
And Trevor? what are you on about??
I must have missed something somewhere?

All I am going to say it works for me

John,

The big flywheels bring a different set of characteristics and I have them in my 175 , I cant really comment beyond that because to date we have not been able to get the gearbox working due to issues with second, that may be related to the big flywheels of course, as Alans 125 which I have been riding has as near as can be the same gearbox setup and small flywheels and the gearbox has not missed a beat in seven races.

What do you think ?

James

My gearbox is ok now all gears

Hi Robbie,


What was it in the end?


Eddie

Hi, John, and all ,
Go to Pit-Lane.biz , click on Aprillia/Derbi section, then page 21, and all shall be revealed.
Looks like Derek lifted his post directly from here , but why is it on Heavy Crankshaft ?
Happy hunting !

Regards Trevor.

Dunno James. Might be cyclic irregularities (Trevor´s quote of 500rpm variation during one cycle of the crank means passing through a `negative´ point ... ) are less with big flywheels and that being so there´s no `free´ gap where everything is `loose´ regarding the gear change -- i.e. the flywheel energy keeps everything under strain) simultaneously, a bit of drag from the clutch -- and the gears won´t mate cleanly. If I remember aright, Icarus-1 (125 of course) had big-flywheels (I don´t think I ever saw them...!) and I had no bother changing gear. Sometimes -- during racing -- even changing without the clutch, which was a dreadful habit which came from grass racing where I only used the clutch at the start. There´s a momentary pause of strained drive if the shut-off matches the mass-inertia --- something (bullshine) like that!!?????

Maybe your clutch drags a bit...

One for Trevor*** -- when the rider behind gets too close to the geezer in front and his front wheel collides with the rearwheel (of the bike in front) the moment of momentum really takes over and is it, "Impact?", "Impulse?" or "Conservation of Momentum?" that causes all the subsequent bother?

It happened to me at Cadwell -- bloke in front put his brakes on where no JayBee had NEVER braked before!! Small wonder I am having physiotherapy for my poor shoulders!!

***All welcome ....

Sorry this is so long as the Bishop said to the actress!!

PS... at the moment of contact the rear wheel tyre patch is going upwards and the front wheel is going downwards ....????

john bass wrote:

I had no bother changing gear. Sometimes -- during racing -- even changing without the clutch, which was a dreadful habit which came from grass racing

And there was me thinking you got into the habit because you had to take your hands off the bars to change gear when you started biking.

Hi Trevor

Correct trevor "cut and pasted.

but read on the next topic ! inertia - weight in flywheels ?.

Derek

Trevor

To answer you, I first met said person in Milton Keynes uk 2002, but again in 2004. initially I happend to spot a cylinder casting and as usual asked lots of questions, I was to purchase a machine tool for de buring valve ports, for aero device, not allowed to say - official secrets, he was there to view same machine, he was very talkative, open and spoke excellent English.

Derek

John - BTW crank is a heavy one for 175 use. That is the answer to your question!!

Derek/Trevor Great site Pit-Lane.biz

Derek are you going to make the first bantam FOS engine?? Can't wait!

Thanks Mike!
Calculations show there´s a big difference in a 200mm dia flywheel´s energy storage from that of a 96mm*** dia ... but when compared with the max power output is negligble... Without proof I´d reckon the bigger flywheel would aid the engine´s ability to rev-on to higher max-rpm....

Whilst I´m on -- how is your short layshaft? have you crack-detected lately?

**Calcs DO show:- The larger dia flywheel of same weight stores more engergy than the smaller -- which you knew anway, without the calcs -- but interestingly the larger flywheel of less weight can also store more energy....

Cheers!

Hi Mike

No absolutely not, I have enough to do thanks,

Ed's bike is taking a while to get finished, my bike is about there from the cadwel breakdown, and next i want to make a new barrel for my old motor crank reed motor, especially with my better understanding of hot air. !

Derek

mjpowell wrote:

Derek in the 20yrs?? you were away from bantam racing I have changed my cranks

The chamfered cranks were replaced about 10yrs ago - the inertia was to low

This is my 001 crank(half) was in bits hence no rod etc on it....

Hi mike
now i've been thinking !!!!!! you know I like a bit of controvosey.

as i was been reading through a few of the topics on this forum, i came across the one above again, i feel some important aspects missing, anyway this one has really been throttled to a point it started off great, and to begin with, a really interesting topic, but now to a point' dare i say its becoming boring reading.

i feel some fresh topics are required, as the current items don't help me or give me ideas to improve my bike.

i'm already trying to arrange what i will be doing next year, so that i may attend more meetings and hopefully have more fun.

I was therefore disappointed to only finish one race at the Cadwell meeting, i have taken some steps to improve this area, but i need a number of issues sorted to be able to do this.

For this reason i have been spending a great deal of time "too much time" reading, and just can not help but comment to the following of what i have read to our engineering specialists on here.

so please forgive my layman's view, but this is how i read and see other comments, they suggest the following,

1) exhaust, Pipes the only way to develop a chamber properly is by experimenting, seems you can get formulas pipe's that never perform as calculated items, that are purely a guide, constructed of a great deal off guess work, and never accurate. one said he never come across a formula for pipes or ports that works any good, ? he even mentions some of the highly respected developed software systems with contempt.
2) he says port timings and experimenting with them is useless and irrelevant in the quest for power, (just to a point - some where near is good enough)
3) port timings ratio's of "angle area" is completely irrelevant, again at logger heads to some of the comments made on this forum.
4) he say's power and its quest for more comes from the transfers (see 5)ports entry into the cylinder and the exhausts ability to evacuate the cylinder.
5) breathing efficiency gas flow and good scavenging comes from the transfer ports and exhaust, but much more impotantly - not from there size or timings which are irrelevant, but comes from from there shape and direction and how they control the way the mixture streams before and while it enters the cylinder, also vital is it's traversing the transfer ducts, speed is unimportant in fact the desired effect seems to be, to slow down the streams as they enter the cylinder.
5) torque and Power come from experimenting with these factors, others have such minor influences, exhaust pipe/cones/lengths and the shape and direction of the transfer streams as they are directed into the cylinder.
6) one of the reasons ignition timing has/can have such a profound effect in this area seems to be because they way it affects the exhaust resonance and so evacuation phases.

i found some of the aspects just great, and more impotantly absolutely no boring calculations, but all great reading and very different, but at the same time, very open with no sarcastic or hidden
un-informities/no secrets as they know it does not matter what they tell you, as they suggest "you can only find the best/improvements by experimenting to evaluate and consider what works.

so to recap - power comes from the pipe and transfer ports.

This is how i have read it, so where does reliability come from ?
meticulas preparation? "some would say", not for me -

i feel those with developed bikes seem to show more reliability than those who experiment so try new things, in an attempt to make there bikes quicker, there is an exception but it seems to be ? few.

not sure this is how others would see it !.

regards Derek