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 Heavy Crankshaft....

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john bass

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PostSubject: Hi Trevor...   Wed Jun 15, 2011 2:20 am

Hi Trevor!
The bikers did it that way, as in the Moments of inertia (J or I) being mr²/2 when it really should have been -- J or I for a pipe section or tube as in
J = m.R²+r²/2. "R" being outside radius at tyre edge and `r´ in side effective inner radius -- somewhere down below the wheel rim along the spokes....

--er well!? I think it should??

Now you are on, does The crankshaft assy the lads are speaking of include the effective rotating bits of B/E bearing and con-rod? I think 2/3 of the conrod weight should be included.

But getting away from that for a moment I think it rather a fuss about a little that cannot effect Bantam racing very much -- except, perhaps in the way of deep-seated pyschological difficulties one or two of them might be tending towards in their longings to be star Isle of Man racers. I mean, if going by the way I had to scream Icarus-I´s nuts-off to get it to kick-in at all I´d think they´d always be slipping their clutches at some high revs where all the calculations go to pot anyway because of the slipping clutch....

Besides Rossi on a big 4-stroker with an excuse to make to the press is quite different from sweet-talking Bantam racers on resonant exhaust pipe 2-strokers.
As far as I can see (repeating myself here) there´s more advantage for a Bantam to have a light crankshaft because the time to get the revs onto the pipe will be quicker....

Perhaps you´d do me a favour -- would you have a look at these figures to see if I am right or have I forgotten something? Derek mentioned a Bantam crank of 96mm dia and 2.31kg weight

I ran thro´ some calcs for the amount of kg.m per 1000rpm´s for a Bantam flywheels of 96mm dia weighing 2.31kg.... and the following are what I obtained:--

-- in kg.m/per 1000s of revs:-

6.0 kg.m at 2,000rpm
13.3 kg.m at 3,000rpm
....; missed 4,000...?
37kg.m at 5,000 "
65 " 6,000 "
73 " at 7,000 "
.... Missed 8,000 also?? (who is nuts!?)
116 " at 8,500 "
120 " at 9,000 "
149 " at 10,000 "
180 " at 11,000 "
218 " at 12,000 "

I haven´t got my "scanning/picture-sending technique" working properly so I can´t show the curve -- it is quite smooth...

All the best,
Cheers!
John.
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john bass

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PostSubject: PS to Trevor...!   Wed Jun 15, 2011 3:48 am

PS - Trevor,

They start something off on here and then digress or vanish -- which I think is attributable to the psycho-whatisits they have -- they´ll be alright after they have been to Cadwell -- unless another Gearbox has blown up or another layshaft has broken....

Should be interesting -- whatever happens!!

Cheers
JayBee.
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john bass

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PostSubject: Avatar...   Wed Jun 15, 2011 9:23 pm

Ey oop!
See that picture of a prancing naked Bantam there...
That is me rounding Mansfield on my way to winning my first Novice Bantam Race.
33 years ago it were -- my tyres were Continental Sports Front and Continental Racing rear ....
Clutch oil was boiling and I had cramp in the fingers of my left hand ...
What a feeling -- whoopee!

And that after having to renew all clutch bits between practice & race: -- plates and springs were all kaput!

If it weren´t for the hill up to Charlies I´d have called Cadwell my favourite circuit.

Cheers!
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PostSubject: Quickie for Young Derek...   Thu Jun 16, 2011 3:04 am

Something stuck in my mind from earlier and didn´t go away -- it just snoozed in my mind for a while until it popped back in the form of Derek´s question about engine friction losses.
I had always thought it was a square law of the engine speed and checking in "Air Cooled Automotive Engines" the author, Czech Auto Engineer Mackerle confirms it positively.
If it weren´t for crankshaft energy increasing with speed, on a similar curve, these losses would not be overcome. The maximum engine speed (no load) is fixed at the speed where mechanical friction loss coincides with suction loss. Where the full load speed -- which is the final extension of the horsepower curve -- meets that loss curve is the max load speed. An advantage of a heavy crankshaft mass is that it helps overcome the losses and the engine will "run-on" to a higher max load speed.
Mackerle also states that pistons & conn-rods contribute 56%*** of the total friction losses thro´out and also, very interesting, was 3% to crankshaft sealing.
The latter had me immediately thinking of Mike´s photo and comments re seals.

Another question: are the flywheels in the D7 and the D14 the the same OD -- 200mm -- 7.87"??

*** I mentioned this before -- no matter I am alwaysrepeating myself....

Humble apologies for being boring!
Cheers!
JayBee.
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PostSubject: Re: Heavy Crankshaft....   Thu Jun 16, 2011 11:19 am

deliberate mistake john / MR Merckl, what engine speed were these taken at ?
friction is exponential, its rate increases with surface speed. ?

regds Derek
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PostSubject: Fings are going hup & dahn and round and round...   Thu Jun 16, 2011 9:00 pm

Hi Derek!
It is as you say. The level of friction of all the parts increases thro´out the engine speed range from slowest speed to the fastest speed. The brake horsepower curve dips (away from its max...) and meets the friction-curve coming up and the speed at which they meet is the Full-Load, max-speed of the engine...

The reason I quoted Merckel is because he wrote about Air-Cooled Engines. We did the same exercise with all our engine development at Ford Dunton and at KHD Canada Inc... To ensure a satisfactory oil-conumption the rings HAVE to be those with lots of lovely friction which is not so with race bits..

As I said before, I cannot at the moment send text or pics and I´d like to send the curve of Friction-effort versus engine speed -- it is a N² (rpm²) law when N is engine rpm.
The Propeller Law is similar -- it is a gradual increase, which increases more rapidly the faster the engine or propeller rotates...

With only the piston in the barrel -- which is already fixed to something rigid -- you then hang weights onto the gudgeon-pin and can measure COLD friction to move the piston.
But that is "stiction" and not the true friction of a moving piston which is slightly less than the "static-rest" friction just measured. So:
Having found the weight that just moves the piston you hang a slightly lighter weight on the pin and stand small weights on the piston crown until it repeats. Its old fashioned guess-work (or should I say Old Hat??!!) of course, but as long as you stick rigidly to the rules you should be able to compare piston-ring differences and also compare with hot conditions by playing a blow-lamp flame on the whole kebang making sure the piston DOES get as warm the barrel.

NB!! There must be oil there, of course, and if you happen to use 2-stroke mix don´t blame me if it stinks and divorce ensues -- or even burns your shed down and your neighbour´s too !.

These sort of tests are probably unnecessary because information is being bandied around all the time -- and if it isn´t it´s an easy thing to spy it out...

I ran off some calcs last night for a D7 -- 3.8kg crankshaft -- using the same dimesion of flywheel as I did earlier and now think that must be too small -- 96mm??

That probably doesen´t matter so much -- even if my calculations are wrong*** -- because the comparison is valid and the difference, very obvious:-

...2.3kg Wt:- c/s at 2000rpm the K.E. is 6.0kg.m & at 12,000rpm is 218kg.m
...3.8kg Wt:- c/s at 2000rpm the K.E. is 9.8kg.m & at 12,000 rpm is 353kg.m

Comparing 2.3kg & 3.8kg crankshafts & looking at those values in a pragmatic way, the 65% increase in weight of the crankshaft shows in 63% increase in stored engergy at 2000rpm and 62% at 12000rpm.
63% increase on all points on the previous figures given could give an idea of how the available torque at the rear wheel must vary from lowish to higher speed according to crankshaft weight.

What I had wanted to do was calculate the effort required to accelerate a typical Bantam & rider from speed `x´ to speed `y´ in a typical curve and got myself diverted onto this bit WITHOUT getting all the information I needed--

NOW I THINK I HAVE USED the wrong info for the above in taking 96mm as flywheel dia ...

On top of which there were no replies to the request for data re bike weight and rider -- fully-togged weight -- plus rear wheel weight SO PERHAPS THE WHOLE THING HAS BLOWN OVER & the Interest has WANED.

*** I´ve asked Trevor to check my calcs on that list I produced above and now I think the biggest mistake was using 96mm for dia of the flywheels -- not Bantam -- surely? It will be the radius which makes my calcs wrong because I was using 0.048m but the characteristic effect is there.
as the radius....
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Trevor Amos



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PostSubject: Re: Heavy Crankshaft....   Fri Jun 17, 2011 12:23 am

Hi, John.
You`ve really got an angry tiger by the tail on this one ! All great stuff, though i share your fear that no one else
really cares any more. Yes , a large dia- high moment of inertia, crank will store a lot of energy, the down side is
accelerating it up to the chosen rpm, and a lighter , smaller dia crank will absorb less torque in doing so. I`ve done the
calcs comparing a D7 and my crank and the results show that the physics, maths and my own experience running
with both, that, heavy, large dia cranks are at a clear disadvantage .
Factor in also that you have use energy to slow and stop the big crank twice per rev, then ,spin it up again twice per rev .
A long dwell at tdc and bdc, such as happens with the 175 boys , further uses energy , and ,if you employ a long
con rod, acceleration away from both stationary positions will be sluggish. Again ,depending on stroke and rod length ,
will depend the pistons max point of velocity, and as crank rotation is not symetrical more rotation is spent slowing down
than accelerating, again, absorbing energy The consequences in doing all this is that the more torque that is absorbed in rotating
the crank the less there is to accelerate the bike .Not forgeting that there is only one brief spell of torque production per rev,
so, from about 20 degrees atdc torque is inexorably being used up. Quite depressing really !

Hope this makes some sense, if not i`ll just give up !
Regards all, Trevor
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PostSubject: Thanks Trevor ...   Fri Jun 17, 2011 2:11 am

What you said all makes sense -- particularly the bit about it all fading away.

They finish a race all relaxed, after having exhausted all their adrenaline which leaves them in a state of euphoria mixed with anxiety that perhaps someone has put in a protest against them and then remembering they´d done nothing wrong ... get quite exciteable and if someone mentions a new Gizzmo that improves acceleration by 2% they go ape about it and all concentration is then on the new gadget. Must have one -- echoes down the oil-stained walls...

Much like Rossi and his moaning about his Ducati. He could NOT blame the way he chopped off Stoner onto his Ducati´s skittishness -- it was just a "Do or die attempt" to beat Stoner thro´the bend and such riding tactics -- even by a Monster-God-Star of the sport -- is not sporting. I say unnecessarilly Dangerous! He should have been punished for it.... .

"Everybody´s going short-stroke" I said, in 1968, to Derek N..., who did my Icarus-1 engine, "Why duun´ we? Everybody´s go--- "
"Not likely!, said Derek N..., "With your weight a long-stroke motor is necessary."
He was probably right!! It had a lot of pull at 5000....
Enoughto get the skin off a rice pudding, at least!
Only joking Derek N... if you are reading this -- I never did thank you enough...

I remember when fairings were first talked about --- ON CHEAP RACING BANTAMS NEVER! went the cry from a lot of die-hards ....

I like your point, Trevor about short period of torque-production and of course it happens when the conn-rod is at its disadvantageous angle and also a lot of power is lost to the commencement of combustion before TDC.
On our new diesel engine in Canada, I worked on that aspect with our diesel engine. By fenaging the diesel fuel injection to have a small-fine squirt before TDC to get the fire going and then a massive squirt at TDC -- with a well developed combustion bowl in the piston -- a higher BEMEP was achieved with lower peak combustion pressure at TDC. At that time we could only do it at one speed in lab-controlled conditions but with the intro of engine.management systems electronic control it was finally achieved and The system is used in the Ford diesel engine....

What I was hoping (a few years back) was to improve on this notion a different way using a small 2-stroke engine (like a Bantam) to make the combustion period happen at a better time -- much like the e-3 engine(4-stroke) the late Joe Erhlich got into experimental phase with -- that now seems to have vanished. My criticism of this was that the articulated conn-rod was far too heavy and hence the engine
rated speed would be limited to low speeds.

Any road up I am going to have another go at the Bantam flywheel using the correct diameter -- if I ever get it -- and with Rear Wheel and all the other data: like weight-of-bike-and-rider and then try to work out the acceleration differences with different weight flywheels.

If I don´t get the info I´ll still do it -- FOR MYSELF -- because I think it might help with keeping dementia at bay...

Sorry this is so long ...
Cheers!
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PostSubject: Talking of seeing a shrink...   Fri Jun 17, 2011 5:00 am

I am beginning to wonder ...

Here I was talking about Bantam racers getting high on euphoria of racing and here I am bemused by numbers such that I am wondering if it is me that needs a psychologist....

I am sure I saw the figure of 200mm for the diameter of a Bantam´s flywheels somewhere in this web site but when I look again its not there. In inches that is 7.874" which seems about right.

Any numbers anybody -- diameter of a Bantam flywheel please?
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PostSubject: Re: Heavy Crankshaft....   Fri Jun 17, 2011 5:40 am

Hi John,

i find this all very interesting although i dont understand it or am i technically minded with regard to engines.


Eddie
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PostSubject: Re: Heavy Crankshaft....   Fri Jun 17, 2011 6:19 am

Hi Trevor - John

prefer the friction topic John - more to it than this, anyway Blimey this crank stuff is interesting especially the bit on small is best for reduced energy losses (quicker acceleration)? I think this is what Trevor is saying,

I would like to ask a question on a 175cc pulling a much larger gear, will it therefore slow down less during gear changes, as a result of its increased inertia, one the next gear when releasing the clutch to accelerate again, it will have a greater mass ? I think there is more to this subject.

so what your both saying is - a short stroke 125 revving to 11/12k, then the small light flywheel has a big advantage over a larger heavier one, advantage is quicker acceleration

but on a large 175cc pulling much taller gearing going up the box, as its power is produced at lower RPM, for sure this is reasoning i think your saying, the inertia stored in a large fly wheel will give it an advantage on gear changing speed drop ? especially with only three gears, (the large fly wheel 175 bantam "KER'S")

any one spot any spelling mistakes found out how to use the spell checker ?

Regards Derek
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PostSubject: Re: Heavy Crankshaft....   Fri Jun 17, 2011 6:40 am

Hi Derek,

Spelling spot on as far as i can see, interesting comments on 175.


Eddie.
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PostSubject: Who started this?   Fri Jun 17, 2011 2:13 pm

Will this never stop! -- rather foreboding pair of figures, wearing white coats coming thro´ the door -- I´m just doing a runner...

Phwew! I´m back....

It´s not an easy thing to grasp Ed and more difficult to calculate since the (flywheel) radius of gyration is squared as is the tangential acceleration -- in radians/sec² -- of the flywheel rim, which leads into expressions involving a lot of long numbers-squashing to get correct.
I ought to delete that -- enough to confuse the one above...

Point is the I.C. petrol engine is only 25% efficient*** at its best. Most cars on the road are operating at about 16% of the energy potential of their fuel.

For the vehicle to accelerate there must be more tractive effort (TE) than tractive resistance (TR) -- i.e. when TE = TR the vehicle is at constant speed. A tremendous amount of energy exists in a rotating flywheel as can be seen in the figures I presented previously, some of which is used to combat engine friction, some to get the air-fuel mixture into the engine, some to go as waste heat into the atmosphere (some to burn the rider´s leg) some to vanish via radiation and a bit to go to the rear wheel(s).

I feel sure Trevor agrees with me -- a light flywheel has more advantages with a Bantam where the rider needs to get the revs up to where the resonant-pipe comes into effect as quickly as possible. The 175 probably gains with its heavier flywheel in that the engine will rev on (to higher revs) against the engine losses although the maximum rpm possible doesen´t seem much more than 10,000 with a 175... Brilliant really when you think the original max rpm for a Bantam was 5000....

Transposing the 175 power curve shown on here recently (the torque curve seemed to be suffering from St Viatus Dance!) shows a bumpy torque curve with a maximum of 13lbsft -- plus a little bit -- which, for the crudity of the formula (compared with 125), is in my opinion good.

With a larger 4-stroke engine the light flywheel must give that feel one can generate with a Bantam in jocular moments showing off to the Gallery.

This actually happened in the Pits at Brands where the ground was sloping and the rider was poodling across the fall-line. The rider suddenly disengaged clutch, increased the revs to about 12000rpm, let in the clutch and instead if doing a vertical wheelie he wheelied off-course at an acute angle to horizontal and almost demolished two other racebikes. Asked why he did it he grinned and said it hadn´t been done before. He had to fork out quite a bit of cash for his efforts.

But it probably was what Rossi was bleating about -- that sudden unexpected surge thrust similar the above. It is possible to do much the same with a Bantam --although I could never wheelie Icarus-1. It is that poodling along at say 10mph, the clutch is disengaged and the freed engine revved really hard and then the clutch lever let fly -- the rear wheel flips the bike sideways, especially if the stomach is full of spagetti & vino. Obvious really, I suppose, ... .


*** heat energy in -- into the tank -- to energy at rear wheel(s)...

Cheers!


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PostSubject: Daft or stupid??   Sat Jun 18, 2011 4:54 am

I ask myself if I am daft or just stupid...?

96millimetres = 3.8inches -- as the Diameter???

Seems very small...???

Now you can call me stupid because I now have this urge to calculate the Tractive Effort at the rear wheel of a typical Bantam & its rider.
Just for myself...

So I do need as factual data as is possible to get -- relative the Bantam.

If not I´ll guess at things like the rider weight plus bike weight being 150lbs + 250lbs ...??????? Nice round figure 0f 400lbs.

Could do it for different rider weights anyway...

This difference of crankshaft weight effect is not as simple as it might first appear and I think this -- in conjunction with those other values of stored flywheel and rear wheel energy -- will show more clearly the effect if shown as lbs or kgs force at the rear wheel -- for a range of engine speeds...

...Cheers!

.



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PostSubject: Re: Heavy Crankshaft....   Sat Jun 18, 2011 11:45 am

JohnB, my D14 standard flywheels are 136mm.

Seems we made the mistake of rebuilding Brownies old crank assuming it had the lighter D7 wheels. Oh well, it might work well in a 4 speed trials motor !

Now got to find the old Lionel Howell spare crank with turned down outer diameters, that might be a good compromise for the 3 speed 185 motor.

D14 flywheels cause a lot of overrun on slow corners.
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PostSubject: Hey JohnS...   Sat Jun 18, 2011 3:25 pm

Thanks JohnS,
But am I still missing something??

... A 136mm --5.354" -- is DIAMETER ? it is still small according my memory of Bantam flywheels.

Yes, when the flywheel is heavy there is the tendency when changing down -- particularly with the Bantam & 2-stroker -- for it to be the reverse of what we call "engine braking" on larger 4-stroke engines. The feeling is as if another change down is necessary.

I am using an old crib for the RR -- Rollong Radius -- of the rear wheel: -- 11.4"
when using KR73 WM1 rim for the calcs ...

Could you please send the weight of this 136mm flywheel??

Stay cool!
Cheers!
JayBEe.

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PostSubject: PS --   Sat Jun 18, 2011 4:33 pm

PS -- if standard 175, that´s 3.8kg -- isn´t it?

My memory stirs -- to reduce crankcase volume we fitted "Horseshoes"*** into the crankcase to take up the space outside the flywheel rims -- am I right?
Also referred to as "Stuffers" -- aluminium hoop with a section cut out for conn-rod action ...?? Or were stuffers in the flywheel recesses?
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PostSubject: "J" as the Mass Moments of Inertia...   Sat Jun 18, 2011 9:10 pm

Inertia is defined as when JayBee cannot out of bed in the morning or when he has eventually started on something he cannot be stopped and goes on and on...

Like this ridiculous exercise brought about by a Tempermental Spagetti nosher who needed excuses for his poor performance on the motorcycle race track.

For a 2,31kg and 96mm dia flywheel-crank assembly -- ignoring the 2/3 of connrod weight rule & big-end... I calculate the `J´ (Mass moment of inertia) as 0.00266kg.m/sec² which looks terribly small compared with the crank´s stored energy I showed earlier.
... That´s because the other part of the formula involves (radians/sec²)² (squared yet again) which is for example -- at 5,000rpm:-
... {(2Pi x 5,000/60)² x 1/2)} which as a BIG number when multipled by the little number above -- still comes out at 365kg.m/sec² of energy...

A large flywheel spinning in a vacuum is a tremendous source of energy -- good for a "kinetic energy recovery" arrangement....

To bring the 365kg.m/sec² back to understandable units of measure it is necessary to divide by the force of gravity (remember Big-G? I warned you about? that lurks around Cadwell...?? particularly at the S bend below Park Corner...?) which is 9.806m/sec² gives 37kg.m which as a Torque value, is probably easier to accept.

Of course I might have forgotten to divide by 2 somewhere but it is something to think about!!

The formula for the energy of a pair of rotating discs is:-
... (m.r²/2).(2Pi x N/60)²/2 Where m is the weight, r is radius and N is the speed in rpm & of course, Pi = 3.142 -- so check it out for mistakes.

A point about this use of radians/sec² is that the formula is based on the fact that whilst the flywheels are rotating there is a constant urge for all its particles to fling themselves away fronm the centre. Thus at the radius-rim a constant outward push (we call centrigual force) along with the velocity of rotation results in a tangential acceleration as a force of the weight of the wheel trying to tear itself in bits away from its parent metal, all around the circumference, to cast them out into into space. Hence there is angular acceleration although the flywheels could be at constant speed...

In Montreal I had a test rig (under my office) for destroying Diesel flywheels that proved the above point -- a big bang when the cast-iron (cast steel also) flywheels broke up and flung their bits outwards ...

I shall carry on calculating....

Cheers!
JayBee.

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PostSubject: Re: Heavy Crankshaft....   Sun Jun 19, 2011 8:08 am

The D14 flywheels weigh 3.8Kg without any shafts.

Interestingly, the turned down 4.75" ones are 3.3kg complete with shafts and Omega rod.

An old 96mm short stroke crank with rod is 2.4Kg

John, stuffers may have been used around the outside diameter of smaller wheels, but usiually the old Todd practice was to fit a "horseshoe" in between them to fill the space outside of the big end rotating circle
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PostSubject: Robbie's crank   Sun Jun 19, 2011 8:29 am

This has been a long and intersting thread, I missed some of it.

So Robbie, your picture shows a nice crank, how wide are your flywheels ?

From Trevors calculations and experience, smaller wheels might be better on a 175 ?
But Mike suggests that is not the general experience ?
Curiouser and curiouser
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PostSubject: Walsh Bantams   Sun Jun 19, 2011 8:41 am

The other bit of the Heavy crank thread I passed was the topic of thin rings on the Walsh Bantams.

I have talk extensively to a number of Senior Aussie Bantam Racers and the styatements regarding the bike Bill Lomas rode are true. Amazing for that time and the technology they had. There is a DVD Spirit of Speed - The history of MC Racing in Australia hosted by Wayne Gardener, that describes a lot of it. A lot of credit should go to Bert Flood who worked for Finlay Bros. Their bikes had special thin light forged rods and pistons (new each meeting) and one thin spring steel ring replace every race. The later ones had finned alloy barrel muffs (there is a [picture in JBs article) and special high CR heads (15-18:1) running on Methanol. Special very small internal flywheel magnetos.
Apparently Walsh used to keep the bike covered up, like the Hailwood Honda 6 at scrutineering, but they all knew what he was upto and they would wind him up. Bert would put the wrong jets in a successful carb and give it too him !
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PostSubject: Walsh Bantam   Sun Jun 19, 2011 5:06 pm

Hi JohnS!
Thanks for that addition to my digression on Heavy Cranks. Fascinating Walsh Bantam but less fascinating when its known to be running on Meth -- Dope makes a big difference to power via improved thermal efficiency....

Seems the former (Heavy Cranks) has GONE AWAY anyway --
Cadwell next weekend -- of course!!.

-- I wanted to do some calcs showing the typical Bantam 125 and 175 advantages of lighter cranks when considering inertia of the whole plot to be moved: Rider + Bike plus the inertias with typical Bantam data -- and asked for real weights and data on Rider, bike and rear wheel weights but only your 136mm flywheel for 175 (without its weight!) and 96mm with 2.3 kg for 125 -- so far!! From somewhere came into my head that a 175 crank is either 3.8kg or 4.5kg so I worked on both just for the heck of keeping my ancient brain cells active.

Any road up -- its Cadwell next week so all these OTHER things have to be forgotten.

They are forgiven -- Cadwell -- Cadwell next weekend -- OMG I wish I were there...
Memories of the smell of boiling oil and burning clutch at Charleys... then the thrill of taking Mansfield Balls-Out -- well Icarus-1 was only good for 82mph downhill...!!

Broken Layshafts also!!! Also forgotten!!!!

This `light or heavy cranks´ has had me thinking quite a lot and calculating some fancy figures using on Guessed Numbers & Data -- plus a few bits I´ve found in long forgotten BRC papers.

Re the Heavy Crankshaft issue I think it essentail to look at the whole system.
The rear wheel of Rossi´s Ducati is acting as a much bigger flywheel than the rear wheel of a Bantam for example and the Ducati crankshaft similarly having a much
greater Mass-Moment of Inertia than a Bantam...

Here´s a thing that probably hasn´t yet been considered which is again a disadvantage to the 175 competitor:-

When considering the acceleration of a geared system (which of course the motorcycle is as in engine-connected-to-rear-wheel...) there is an Equivalent Mass to be added to the Rider + Bike Weight which I have calculated with guessed numbers
for rear wheel weight (11.8kg -- 26lbs), RR*** and gear-ratio (7.002) which shows this:-

1. the 96mm flywheel, weight 2.3kg -- Mass Equvalent = 9.1kg -- 20lbs.
2. the 136mm flywheel, wt 3.8kg -- Me = 11.8kg -- 26lbs
3. the 136mm flywheel, wt 4.5kg -- Me = 14.5kg -- 32lbs.

So, as I see that bit above here -- which I had not considered at all when I started out on this exercise -- indicates that having a heavy flywheel means a disadvantage in total mass increase to be accelerated.

1.Instead of having 200kg (440lbs of rider & bike) to accelerate, in case 1. it´d be
209.1 (460lbs) to move along...

2. .... it would be 211.8kg (446lbs)...

3. .... it would be 214.5kg (472ilbs)....

So Rossi (he´s skinny enough already) lets up on the spaghetti and still has weight added to his frailty if he demands a heavier flywheel and having a lighter flywheel has a flightier (frivolous) or friskier mount beneath his knobbly knees.
I like the lad but he´s caused a lot of fuss generally and on here too.


***among my mess of old papers I found a page -- numbered at the top as "30", obviously from an old BRC mag which is titled, " RPM -- Gear Ratio to speed Chart for Bantams" from which I took (Rear wheel & G/Box sprockets) 47 x 15 -- Top Gear Ratio = 7.002 at 8,500rpm (wind behind Icarus-1!!) would be travelling at 82.7mph -- phwew!
Most important bit was a note at the bottom, "Dunlop gives the Rolling Radius as 11.4" and rolling circle of a KR73 WM1 Rim as 6 feet. Makes calcs of engine revs to mph very neat.


Last edited by john bass on Mon Jun 20, 2011 11:55 pm; edited 1 time in total
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PostSubject: Whoops!    Sun Jun 19, 2011 5:16 pm

Oh heck and whoops!

I missed the bits you put in JohnS -- but what I have written above should be of value as a comparison of heavy versus light cranks.

I must start all over again...

But you can see from the calcs I made (in the last post) that a 175 is disadvantaged by the increased size and weight of it crankshaft/flywheels ...

The bit of info that I used came from Thomas Bevan´s "The Theory Of Machines" which is Old Hat (as Derek might say) but was long ago approved by the IMechE for teaching to engineering students.

And re that Gear-Ratio to Road Speed Chart -- I guess you all have that or taht it is available within the circle....

Cheers!
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PostSubject: PS...   Sun Jun 19, 2011 5:26 pm

PS...
Look I am supposed to be out walkling with the missus...

... but I must add this -- Robbie did show a nice pic of his flywheels and I tried to scale the OD by comparing the piston dia with the flywheel dia ...

... Robbie doesn´t say Owt about his gearbox breaking either and I wondered what that was about.

No! -- mustn´t disturb Robbie -- Cadwell is a few days away -- but he really ought to tell us more about all those thighs -- the pair astride his bike and around his bike at the Thundersprint thing -- How do some blokes get ALL the luck?!

Don´t forget your spare layshaft at Cadwell -- have a good weekend -- you hear!!

cheers!
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PostSubject: Re: Heavy Crankshaft....   Sun Jun 19, 2011 9:21 pm

[quote="john bass"]Oh heck and whoops!

The bit of info that I used came from Thomas Bevan´s "The Theory Of Machines" which is Old Hat (as Derek might say) but was long ago approved by the IMechE for teaching to engineering students.
-----------------------------------------------------------------------------------------------------------------------------------------------------------------
Hi John have you ever asked the question, why has technology on the internal combustion engine and fuel types not changed for 80plus years ?? and why are we still teaching this in univercity, we are all just pawn's in a much bigger picture.

Brunell for his time a great industrialist, from 100 years ago, no matter what subject, technology has / is being controlled by the powers that be.

The petro chemical industry would never allow alternative technology, materials or fuel for the internal combustion engine to move it into the 21st century, especially one that covers 2-3rds of the worlds surface!!!. Technology threatens the current revenue stream, that all the current wealthy banks /goverments including our own, get there revenue streams infact all the world - so not trying to be contavercial "but this subject is "old hat " too.

Always good reading your posts, john.
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