Heavy Crankshaft....

I take it this is what you are mentioning as hoseshoes or stuffers?


Eddie

Good pictures Ed -- can see it all clearly now -- yes that´s the Horseshoe. I am not so sure of "Stuffers"
because I´ve heard that some 2-stroke tuners are padding every available space above the crankcase
with some sort of foam material but I am not sure of that. and what is being usded..?

Can you do me a favour, please? -- I need the weight of a Bantam rear wheel -- I´ve guessed at it as 26lbs but I might be miles out.

Thanks!

Cheers!

JayBee.

Hi Johm,

Im sure i can try and do that, are we talking standard rear wheel though?


Eddie

Sorry, i meant John!

Hi ed!
The rear wheel of your Bantam will do -- if it is a racing Bantam better still.

What I aim to do is to show the difference of acceleration force -- ie Tractive Effort at rear wheel --
with a 125 Bantam (2.4kg & 96mm dia flywheels) and that of the 175 (3.8kg & 136mm dia flywheels)
which means having Rider-plus-Bike weight and the rearwheel weight to calculate the `Flywheel´ effect
of the rear wheel. I have Dunlop´s Rolling Radius as 11.4/12ft with KR75 WM1 rim -- so I want to get
the weight of a rear wheel that´s similar.
I have already guessed it, as I say, as 26lbs but I may be way off....
Thanks, Cheers!
John.

Hi john,

All the closest ones are attached to bikes, if i get a chance i will dig one out for you and weigh it.


Eddie

Hi derek,
Yeah!

Instead of JB I am now known as "Old Hat!"

Cheers!

OH.

I´m trying -- and failing -- to send text & curves I´ve done on this subject but there´s something incompatable with my PC & the BR web-site that doesn´t permit it happening.

What the calcs show (assuming no arithmetical mistakes...?) is that the 175(136mmdia flywheels & 3.8kg wt...) stores approximately 3 - 3.5 times the kinetic energy of the 125 (96dia flywheels & 2.4kgwt...) thro´´out the speed range 2,000rpm to 12,000rpm -- remembering that 175s probably only rev to 9,500 -- 10,000 but this is theoretical anyway....

... With the 175 at 9,000rpm -- the KE is 3,907 Kg.m sec²
... and the 125 at 12,000rpm -- the KE is 2180 Kg.m sec²

Which does mean when you shut down the throttle -- without declutching -- on the 175 there´s a third more stored energy to push you along than there is on the 125 -- and if your 175 piston has seized there´ll be more damge to your internals....
If you can get the 175 to rev to 12,000 the KE is 6943Kg.m/sec² -- (its a rapidly increasing curve at the top-end) -- and it then seizes the damage will be much more disastrous.
The fingers of my left hand still twitch from the time of Andy Boyles 250 seizing on the Old Norwich Straight at Snetterton.

However, I´ve got some crazy figures for acceleration of the whole plot and need to go over them again --- this exercise*** would be much easier with dyno data from both engines -- for the engine speed range, 2000rpm to max power rpm... The "Jimmy & Ian" curves only go from 7.5k to 9.5krpm ....

***Purely selfish -- I´m only doing this to invigorate my ancient brain cells and find I actually enjoy it!!

OH!

Hi john,

Sorry john dont get the point ur making on ford, besides still plenty of changes and developments going on, but behind very thick closed doors. (in 1987 F17's had been flying in mass formation 10 years when one was spotted making an emergency landing) developed in the 1950's - ? just imagine what they have now, but not operationg in our atmosphere.!

Anyway should'nt we be talking about Bantam's !

On 125 /175 cranks - stored energy - Dyslexic's don't need to calculate, to know the advantages proven in you calc's, - knowing the adbvantage, but its very interesting to see what happens if you spin a 175 to those speeds, the crancases are not strong enough, to offer enough support "dont you think" ? and look at the piston speed well above 50m

regds Derek

Hi Derek!

Take another look -- nowhere mentioned, were engine speeds in excess of what the Racing Bantams achieve currently -- except in theoretically having the 175 at 12,000 rpm for comparison of KE in the flywheels.

Is there a current 175 achieving 12,000rpm?

Piston speeds are unaffected by KE of the flywheels -- only by engine speeds -- of which I think you aware....

Of course -- if the crankcases did break up for some other reason the flywheel energy therein would show itself quite dramatically. I have seen

I changed the energy units from Joules I used previously to Kg.m sec² because I thought the units look more easilly understandable. Turned in kW would look different again.

I didn´t get your point about dyxlecic -- and think its time for me to quit on being clever with calcs --

-- in any case Trevor was invited (or volunteered) by Mike -- NOT ME!

Cheers!

Hi John
l like the post, "interetsing for a change" ! LOL.

I have just JUST spent over an hour, writting a mission on converting liner forces to rotational forces, (without using any calculations) in addition saying I would go for a light weight crank in a 125,
heav'ery on a 175cc-
discussed the bearings flex - and the lack of strength / ability of a bantam crancases to hold a 175 crank 3.8 kg @ 12000.rpm ??? effectively enough for the process to convert the forces generated from linear to rotation energy, without massive energy loss, (the flex in the crank and crankcases, at at these speeds) - and all done without cals -

Dyslexic's" can do this John. - but please feel free to proff the theory, as I always find the cals stuff on here interetsting and im sure others do to.

Also i feel Trevoe has already commented on this and you have to agree with his cal's and theory, commented on when you would want a lighter /

when would you need a heaver crank - thruxton/croft/silverstone. and why " a 125 bantam reving to 12000.
a 175 reving to 9,500, 10,000. would require a much taller gear to go at the same speed of a 125 bantam reving to 12000.


I think i worked out - top gear no matter what gear ratio, - 1000 rpm would equal approx 10mph, so you need to pull taller gears.

a 175 neesd to pull a larger gear to compete as they do! against the higher reving 125 bantams,

175- will as a result of "natural size weight (3.8kg????) excellerate slower, and need more energy when changing gear,(also lose more of the energy through trasposition of linear to rotational energy as a result of flex in the larger crank and cases,

To keep the bike going forwards with a taller gear a heavy crank is good in the instance of changing gear, so has advantages especially with only three gears, so will have much greater advantages pulling taller gears over a smaller lighter crank pulling the same gear, cancelling out the advantages spoken about, at some point on here, "but not only on gear changing".

But after writting a mission on this, I have not the time to re write it all again -- so kept it brief here.

great topic "energy transition"

I also made specific reference to John to go ahead and proff the cals on the gearchanging /linear energy convertion to rotation energy transition, especially between 2nd and top, as i'm sure it will be very interesting.

Best Regards Derek

Absolutely right, Derek!
It does not need a titled Professor or Doctor of Science to have a "feel" for machines but the calculations do prove a point on a function that cannot be seen or felt.

My son Slick is like that.
Wobbleyman, Colin Aldridge took Slick on before he´d left school as his GoFer and handed him over to be apprenticed to Jimmy Wells with the words, "He has no time for fancy words but he´s got magic hands."

Something that cannot be easilly assimilated is the energy build up in a flywheel. Even when
the engine is running free of load there is very high flywheel energy realtive its diameter & weight.


At last, with the TT over, I managed to have words on the phone with son Slick -- we got onto Heavy Crankshafts and he recalled the Foggy dillema with Ducati -- flywheels too light and Ducati engineers sticking to their ideas --
...and Terry Rymer complaining of "...nothing happening on part throttle opening -- then just a tweak more and all hell lets loose at the back wheel." With that temperamental engine in his SuperBike Terry had dropped it because of that problem...
So Slick gave him an engine he´d tuned with a lot of torque back-up (same flywheels & crank) and Terry went out and had success.

So I come back to what I said earlier, a good torque curve can overcome the difficulty Rossi has BUT SUCH IS NOT SO WITH A BANTAM -- the torque curve on a 4-stroke is much easier to modify....

Getting back to the energy of a flywheel associated with a Bantam:-

Running the engine free -- no load -- the energy levels I stated eralier are still there. Whether you like my calculations or not, Derek! there´s a well established formula for flywheel energy which I shall
give -- if you want it....

Like I said, I was talking it over with Slick and he is keen to have the curves and the formulae
so I shall be doing it in any case.

Oh! and he has promised me the name & address of a contact within the Jurby Race Circuit Organisation -- hopefully sometime this week,

Cheers!

John B,
If you look on the main web site under bikes and bantam racer articles on page 10. You can see a typical 125 bantam race crank, there are also some views on pages 2 and 3.
Note that I got rid of the crankcase stuffers not long after finishing the articles and now run a BIG crankcase volume, and do not suffer any disadvantage.
Also if you look further through the articles I have dumped the big carb in favour of a considerably smaller TM1 Mikuni which I run to this day on the motor.
The bike is a front ish runner on a good day! and I have won 250 classic races with other clubs on this bike so it is fairly modern in its build.
The crank is 100mm diameter, but I have no idea of the weight though!
This to add to your knowledge.
Cheers
Alan

Hi Alan!
Thanks!
Thought you might have drummed me out by now -- for digressing too much on here.

Now you introduce yet another variant of Bantam flywheel & crankcase -- sort of in between size:- 100mm... 96mm for 125 & 136mm for 175) and unknown weight... and then you throw away the supposed essential of the Bantam´s 2-stroke efficiency the crankcase-volume-reducers....

In any case I proved to myself with Icarus-2 Bantam that my Bantam tuning was awful. My excuse is/was that I was 4-days a week away from home for my job and time at home had to be shared with the family as well as bike preparation (Andy Boyle´s 250 as well...)....

As Derek just pointed out none of us really needs figures when we can FEEL the difference ...

My eternal problem is that where many can see such in their mind´s eye I need numbers -- or, most particularly, curves -- to convince myself of advantage or disadvantage of differences.

If anyone is still interested I am generating curves of Flywheel Energy versus Engine Speed -- for my Son Slick in the IoM -- which do show enormous differences which are, of course, only theoretical and represent a freely -- not loaded -- accelerating engine speed. Bantam 125 & 175 included.

Cheers!

Hi John
"will some give this man a "bone".

Derek

Hi, John,
Just been reading an interesting article about cranks and the World super bike antics of the Yamaha team.
Yamaha provided full convertion kits including lighter cranks, and ,whilst these were an improvment over
the OEM jobs the engines still could not match the low to mid range acceleration of the big Ducatis .
It seems that the large dia crank webs, needed for primary balance, were impeding acceleration,
the crank weight was`nt the problem so much as an unfavourable MOI. The web dia was reduced ,
and primary balance was restored by inserting Densamet slugs in the crank at the most advantageous
position from the rotational axis. When tested , this crank then became first choice for Haga, Hayden and Hislop,
the backroom engineer who came up with this was later seconded to the MGP set up and Snr,Rossi went on
to be world champ!
So taking this example and that of our two Bantam cranks ,its safe to conclude that, even with two cranks having the
same mass if one has a larger dia it will absorb more energy than its smaller counterpart in reving up to the desired
rpm level.
I dont know about anyone else but i recon this has been the most thought provoking topic ever on the site , and
we all have you to thank for that John ! keep it going , must be more great stuff to come .

Regards Trevor.

Hi Derek!
Fix me up with a trip to Robby´s Thunderstrip or whatever it is...

Curves & more curves...

--- & thighs... it´s me what´s going blind!!

So, Ive just got back from escorting the missus to the eye surgeon which meant I was sat for two hours playing with numbers and drawing curves ...

Curves showing the trends...

I got sensible at last and plotted the flywheel stored energy as horsepower which shows the flywheel horsepower as just over 2 at 9,000rpm for the 175 (136mm dia & 3.8kg wt...)
-- whereas the 125 (96mmm dia & 2.4kg) is only 0.65horsepower (approx 5/8ths) at the same speed (9,000rpm) and at 12,000 is 1.2horsepower.

The 175 power curve published on here looks dreadful -- nothing below 7,000rpm -- just a short piece of power curve... 7krpm to 9k plus a bit... Taken from the Jimmy/Ian dyno plots shown on here... large fluctuations off the torque curve suggest something wrong with the pen-recoder -- damping gone wrong by the look of it -- engine torque does NOT fluctuate in that manner -- if it does then gearbox breakages could come from that...

On that graph the two Flywheel horsepower curves are close together up to 5,000rpm which suggests that neither 175 nor 125 cause any delay in accelerating up the effective-pipe-resonance-revs...

Hasn´t anybody ever checked out what the torque values are below
that speed 7000rpm?? both for 125 & 175.

What I have said above was not the point of the exercise -- what I REALLY WANT to do is show the acceleration differences of light to heavy flywheels -- and as I said -- having torque v speed data would make the job a lot easier.

Thanks Trevor!
Just read your message...
Thanks for your kind words...
I am really struggling -- the old brain cells keep wanting to shut down and I ain´t gonna let them.

I put Alan´s 100mm crankshaft -- for which Alan stated no weight -- in with an unrealistic figure of 4.5kg -- would make them too Chubby for the Bantam!!
I put its curve in with the two other curves and this 100mm dia x 4.5kg F/W curve sits in BETWEEN the higher, 175 --(136mm x 3.8kg) and lower, 125 -- 96mm dia and 2.4kg curves...

--- which conclusively proves your point that the bigger dia (although lighter) F/W absorbs more power than the heavier flywheel with smaller dia....
.
This exercise is neglecting the conn-rod & big end of course (far too complicated for me...) and is looking at it as two discs, attached together...

Gotta fix a blocked drain -- so more anon --- hopefully!!

I really envy the blokes being at Cadwell this weekend -- except for that bluddy hill it was my favourite circuit.

Thought Provoking Trevor!

Wretched subject had me hopping out of bed, two nights back, at 2.30a.m. ...

No! it is as you say -- and the more I look at it the more I see.
Cheers!

If you are going to Cadwell then I am JEALOUS!
Raving jealous...

Have a good weekend.

Cheers!

Hi Trevor. Have you been envolved with a heavy crankshaft for this weekends BHR bantam race's?

Its just I've seen who's racing at the weekend... thats all .....

Regards Mike

Hi, Mike,
I would never use a heavy crank in a Bantam engine, too much of a handicap, have you not read and digested
any of this topic ?

Enjoy the weekend !Trevor

Er?

I´d ask the question -- where has the one-who-raised-the-question been? this last month?
-- but that´s too rude a question to ask.
No doubt very busy preparing fo Cadwell....

But before the question I want to put -- is that the topic started off as Rossi´s grumble about the Ducati -- and I had thought he was complaining of it being too frisky after he cut Casey Stoner up in the corner....

Strictly Bantam -- I´ll just add another question to it:- Is it possible that there´s more lower-engine-speed-torque with the 175 Bantam (136mmdia x 3.8kg, flywheels) than the 125... (96mmdia x 2.4kg flywheels) which makes up for the increased inertia drag of the 175´s heavier flywheel -- making the whole question RELATIVE BANTAMS MUTE anyway??***

My memory of Bantam racing was of a lot of clutch slipping. Getting the engine & bike speeds up to the road speed where the clutch could be fully engaged.


***That is something I would like to prove by number crunching but without torque values for lower down speeds on both 125 and 175 engines some assumptions will have to be made -- anyway I´ll have a go and might surprise myself with the findings...

Cheers!

PS -- I´ve still got a blocked drain...JB.

Get off to Cadwell and put heavy flywheels out of mind. Number crunching does prove beyond doubt that acceleration of the whole plot is undermined by heavier
flywheels ...

I´m jealous as hell --- but all of you riders, watchers and helpers alike HAVE A GOOD WEEKEND...

Go well & keep well (old Malawian proverb),
Cheers,
JayBee -- (for John-Boy in his dreams).

PS-- Beware of Big-G....JB.

Like broken layshafts -- subject closed?

Yeah OK! so Cadwell got in the way ...

...Cheers!