Heavy Crankshaft....

I see in MCN that Rossi requires a heavier crankshaft to make the Ducati work to his liking...

So its quite appt. that that some banty runners have already stubbled across the benifits of either heavy cranks or greater inertia cranks...

Mike

Interesting point Mike -- If the rider is keeping the revs up -- as is needed in racing with a Bantam then I suppose it works OK anyway but more important is the bumpy torque curve which point Slick was always making with Ducati engineering when he was with Carl Fogarty. Later when Slick was doing his own thing he often reduced the static compression ratio*** thus increasing the max revs which means the idea of high inertia fits in there because the increased piston acceleration/deceleration forces have to be countered with increased balance masses.

PS -- *** the measured CR ... With well tuned air flow the static CR is increased.

Second thoughts:- Rossi has been used to higher revving motors -- hasn´t he?
It must take some rehabilitation time to go from a buzzer to a plonker...?
I know of one WSB rider(not Fogarty) who Slick prepared the engine for who preferred Slick´s tuning over another tuner´s because with Slick´s motor the power came in at a `controlled rate´ (more `gradual´ the rider said) whereas with the other tuner´s engine there was a sudden surge of power which the WSB rider said caused him to lose control and fall ....

John Rossi' prob is light crank spinning up easy up no 'guts and grunt' out of corners - like a 125 bant??
Where as Yam M1 heavy crank lots of interia out of corners - like a 175 bant??

Well almost ......

heres my crank our idea before rossi!!!

Rob your crank looks the same size as my 003 crank?? Yours gets you off the line quick or is it your greater cubes??

And here is a lightweight crank half - low inertia...

this is a very good thread, interesting sbject, inertia - but Mike ? "forgive me" for saying that aint' one of your cranks' all your cranks have got big chamfered corners on them. ?

why are you showing this one, I have to say it is a nice looking crank half through, why not show the other view assembled looking from the top rod on tdc. !

regards Derek.

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....

20 years mike its only 10

derek

Hi, Robbie and Mike,

Any chance of getting values for diameter and weight for your respective crank assemblies ?
I can then do some maths and make an informed judgement on this whole ,interesting,crank debate .
However , i fully understand if you both wish to keep your "secrets" to yourselves .

Regards , Trevor

Interesting features of the pic of Robby´s parts -- particularly the gudgeon pin -- looks gigantic, never seen one so big
and a ball bearing in there too-- got me wondering about balancing if the revs are high?? And the `ring at the top looks ´
odd too?

cheers!

Trevor

001crank is 96mm diameter and 2.3kg...

Mike

Good topic and always useful to see other riders components, I've ran small 125 and big 175 flywheels, though can't really give useful feedback but felt the bottom end more from the large flywheels

Wow this blog sounds like its going to get interesting - come on Rob weigh your crank, and tell us the diameters too.

we fitted a large weight on the rear of the clutch, it took ages to pick up speed compared to without, but once there it did however hold a taller gear better while changing, we did this just for croft CRMC race of year 2001/or 2. it was raining all weekend. ?

Regards Derek

Can´t say I could compare the Bantam´s pick up -- as a RACING machine -- with anything except the 500JAP grass bike of 9 years grass-tracking & Speedway practice in earlier times. With a max revs of 8400 on Icarus-1, Bantam I was always at around those revs, slipping the clutch like crazy to keep up with the other Bantams before they vanished way ahead -- the feel of engine inertia response having been lost in high revs and clutch slip...
The JAP engine on grass, (5000 revs max) spun the rearwheel a lot so that was much like clutch slip but in terms of `FEEL´ it was like being kicked up the back by many bulls (or horses) whereas the Bantam felt as if I was setting forth to visit Grandma for Sunday afternoon tea. The JAP had very light flywheels and an alloy rod. .
...
Silly statement, most of above but reading what has gone on here with Bantam Race Machine development I realise we -- as a team of 2 & a half -- never really got into it like you fellows have. I reckon Les, our machinist as half because he did a lot at the beginning and hardly anything towards the end. Derek did the engine, which I took back to him several times a season, but after the fisrt season I seem to remember seeing very little of him... But I must add that Icarus was very reliable.

Uh oh! I forgot Andy´s 250 ABS -- that did pick up quickly although the flywheel LOOKED heavy.

Hi, Mike,
Thank you for that , however, i am confused with the numerical designation you give to your engines and machines .
Is 001 your current racer and/or engine ?
In the spirit of free exchange of information on the forum the following may be of interest to someone.
The RS Honda crank weighs 2.31 kg, and is 96mm in dia, they do vary slightly due to the nature of their construction. The
later spec engine cranks are 98mm in dia.
My w/c engine crank, made in 1996, weighs 2.57 kg and is 96mm in dia! I had a design weight figure in mind when i started
the engine , in around 94 , i didnt achieve it, but the end result seemed pretty reasonable . Working on the basis that you dont
fiddle when getting good results , its never been altered.

Regards to all, Trevor

Hi all - anyone see the similarity between Mikes Honda and Trev's comments of cranks weight 2.3/ 2.31kg and 96mm diam?.

anyway 001 i'm sure means the first one produced, nothing to do with current or past just in order of manufacture ?.

Hi Mike just wanted to say not heared from you on my pembrey request, i did also notice how nice and clean and shiney your screen looked ! (pembrey!!!!). I was going to put helmut here but think it sounded rude. "in your own time of course" !

kind regards Derek

up's my last comment should have read "Mikes bantam and a Honda ? sorry!

Derek

Trevor i've got 2 bikes
001- (ex Pete Styles simple and fast)
003- with new motor(2010, non so simple? and fast - work in progress)
both are current and won races last season...

What year RS are you talking about? Later run balance shafts etc etc..
(I'm sure you know) And what about added weight ref ignition rotor?
I know there 2 external rotor weights/sizes before they went to internal
rotor type?

Mike

Hi, all.
Any time an engine is accelerating, combustion energy is absorbed by the flywheel, when revs equalise to a
steady state, some of that energy is stored at the rim of the flywheel.This kinetic energy is then used to maintain
the rev rate untill the next firing point in the cycle of rotation, the whole process then begins again.
So , how much power could be absorbed by the crank in doing this? Lets use some arbitrary nos in a non engine
scenario by way of illustration.
One flywheel , 3 lbs in weight and 8 inches in dia , another , 1lb and 4 inches in dia , lets accelerate them from
3000-6000rpm in 3 secs . By my calculations, the big wheel absorbs 570 watts , the small 25 watts. Increasing
the dia at which all this happens brings a whole new dimention into play . I converted to watts as the bigger numbers
are easier to visualise , there are 746 watts to one hp.
In the light of all this i`ll leave you to consider the merits, or otherwise, of heavy crank assemblies where power
is limited, in engines of similar capacity, and the engine is continually on and off the throttle . Could be a damned good thread this !

Regards to you all, Trevor

Trevor! What about if you are keeping the revs above say 5000 (with a max at 8400 as was my first Bantam) and slipping the clutch to accelerate most of the time you were accelerating?
Cheers!
JayBee.

Hi trevor ? Do the losses increas as the inertia rises ?? or is it constant ?

I.E will a higher reving engine (11,000 -12,000 )lose moe with large flywheels ? , than a slower reving eniging, are the loses exponetial (rise pro rata with revs or increase as the revs rise), or do other forces come into this creating bigger effects. ?

"coukld be good thread" No - IS A GREAT subject, I FEEL.

Kind regards Derek

It's and interesting theortical thread but you have to ask the question how many racers have the resources, time and money to experiment with such things !

MM-Tribsa!
You are right. And time was my problem. I hadn´t intended to race Bantam -- poor little machine -- with me bloated on expenses but having done the cycle parts nicely at low cost -- and got it ready I experimented with resonant exhaust pipes at Brands on practice days until my mentor and engine man was happy. But I tell you, the last thing on my mind was whether we had too heavy a crankshaft -- getting pistons "Run-in" was an all day affair and getting used to the idea of slipping the clutch, so much, was something new for me.
As I said, grass racing a 500 JAP could not be any sort of comparison...
-- With the Bantam my impression was of wanting to get off and push -- but after doing three day sessions of practice at Brands and finding that I could get past several bigger bikes on tricky parts of Brands I had the notion to stop looking for a jockey and do the racing bit myself.
...
What I discovered, of course, was that just racing -- my mentor and engine man looking after the engine -- took up much more of my time than I could spare -- but I went ahead and did it (as much as I could) hardly ever bothering with engine tuning info.....