Heavy Crankshaft....

I´ll try not to be, Derek -- (boring) -- you repeated where Mike said his crank lacked inertia (not in those words but that meaning) -- I would ask (either you or Mike) is that just a FEELING or something based on fact (or even calculations??)

And was it relative the 125 or the 175??

Since some of the flywheel energy -- its inertia -- overcomes some of the mechanical loss attributable to BORE size it is obvious the 175 needs a larger flywheel....

If you take the cause of most mechanical loss in an engine as 55% being attributable to piston and its ring(s) the 175 is disadvantaged by having the bigger (longer) piston circumference -- hence more surface area and more piston ring pressure against the cylinder wall to create friction loss.

For the piston ring (one only) I calculated this Friction Loss AT 4500rpm to be
9.54kg(21lbs) for the 125 and 13.4kg(29.5lbs) for the 175... -- even if the argument of different types and shapes of ring is brought in, the 175 disadavantage is positivly of the order of 18 to20% -- AT 4500rpm ... More at higher engine speed.

Which then leads into the argument: which is the better piston ring for racing...?
Andy´s 250 ABS had a single Dykes ring which gave a good performance and behaved well in terms of reliability.

If this is too boring or too much hot-air please let me know -- I´ll delete and tell you how I came to race a Bantam....

Cheers!

Your point 1 -- exhausts, Derek -- in my opinion the final `tuning´ is down to experimentation. Preferably on a dyno...
"Each identically specificationed engine had variations in its `breathing´. " ***.

All 3 racing 2-stroke motors with which I was personally involved were finished off by the `suck-it-&-see´ procedure on practice days at Brands Hatch. Needed considerable time and patience -- because we never used a dyno back then....

I mentioned it before, how we had a 2-piece and 3 piece exhaust system where the parallel portion telescoped to be `too long´ and `too short´ according to the prescribed theoretical length and the nozzles (as changeable attachments) had differing angles. Looked terribly crude -- massive circlips and bits of ally angle all over the place but the method worked...

***this statement came from a famous 1920s´ engine tuner (I´ve forgotten his name) who had 3 Works TT engines which were identical in all respects but each gave a different power curve performance....

PS -- I should have started by saying there is a need to start with a firm idea
of pipe dimensions.

We were lucky, Derek Neil my engine man & road-race mentor***
had a Bantam racing brother, Colin... who worked for Joe Ehrlich of EMC fame
who gave advice on the exhaust pipe for Icarus-1 -- which, as I say, still
needed `fine tuning´ at Brands even after the great Dr Ehrlich had spoken....

*** Derek N... reckoned there was nothing to be gained in trying too hard on
hairpin bends. That was after I´d fallen on Druids, several times (over a fair
period of time, races included)....!!
I wish I´d taken more notice of him because it dunn `arf ´urt on some cold
mornings now....

Many thanks to Bassy for showing me the detailed work on crankshaft weights and inertia figures including graphs!! at Cadwell at the weekend. Proving that sometimes a crank can be too light.. Thanks John for keeping this topic alive (if only just to irritate Derek)

Thanks Mike!
Truth will out.
Your comment (Cadwell 25th Sept) of "...the 175 won´t pull away at start from rest at all well ...*** " was supported by Brian White (Thatched House, Brentwood 28th Sept...10pm) saying much the same, "...the 175 has got to have the big flywhweels to get off the line at all ..." *** ...

So it was NOT really so much to do with Rossi and his difficulties as to why the hell have big flywheels got into the picture (at all) of a small two-stroke owner´s intention to rev its gutts-out to exceed all expectation . Andy Boyle -- to whom I am eternally grateful for providing fantastic excitement on his Alpha engined 250Special before I got too anacient -- argued the point this morning to such an extent that I gave it some more thought and I now know why the heavier flywheel (larger diameter and heavier -- of course) does what it does on the 175 and would be quite wrong to have on the 125 ---

-- but since I have already exceeded the two lines that limit the reading of some (MP?) and could be called bullshine by others (as Nick B...°°°) I shall leave it to a more opportune date to explain.

Truth is the 15days of rushing about Blighty -- and being with the Boiler -- have exhausted my flywheeling-energy.

Was great to see a bit of racing again and some (too few) of the old lads. Sorry I missed so many....

*** both comments might not be EXACT quotes but the meaning was that as above ...

°°°was nice meeting you Nick and I am only joking too. Pity I didn´t meet you Edd -- you could have taken my pic too -- but then that was lucky because your camera might well have exploded!!

-- and I hope Lord Essex forgives me for the above....

So! here´s hoping, that for 2011 your flywheel nuts don´t swell up too big and your layshafts don´t bend and go soggy (or should that be softy?) .

AhhhhMen!!!

PS -- that last bit should have been 2012 -- of course!
Senility joins up with Insanity -- or is it just Seniority...??

Big Flywheeling Fan -- see BWT Tuning ....

I have sussed it out -- Rossi was making poor starts and heard Brian White`s comment that a 175 Bantam with small flywheels couldn´t pull the skin off a
rice pudding so his Ducati ought to have heavy flywheels like what a 175 Bantam has...

Motorcycle racers are SO temperamental, little differences to THEIR normal ways upset them so much. And some boost their spirit with Winding-Up others --
ey Mike???

Should have guessed -- Welsh parentage!!

John,


You would of been more than welcome to of had you photo taken, was a a vey good weekend cadwell with people on top form including hearing about wobblyman!



Eddie

yes Ed - john should have been employed ON JACK AND NORRY he tells great stories.

regards Derek

Yeah Derek!
I had great & unforgettabler experiences including racing a Bantam and Andy Boyle´s 250 ABS. It was a last minute thing -- going to Cadwell on the Sunday I mean and many of the memories came back -- ouch!.

Thanks Ed,
It was a last minute thing and we got to Cadwell late
-- well just in time to see the first Bantam race on
Sunday.
We´ll do it next year -- me sitting on a suitably strong
Bantam...!

Hi John,

We probably walked past each other as apart from the regular racers i dont know who anyone is or what they look like!, cadwell was last minute for us too but having been caught out and missed the first bantam race at cadwell last time we left in plenty of tie and the last Lydden we got there about three hours early!


Eddie

During our trip to Blighty I was fortunate to meet up with the brothers,
Brian & John White, Ted Smith, Tom Miller & Russel Lee -- although I
didn´t get to talk to Rusty and not much to Ted & Tom since Andy Boyle
and I were sitting (somewhat squashed) at a pub²*** table with the
White Bros...

We got into the subject here and in the process I asked Brian how many
seconds would it be that he´d be slipping the clutch, with the engine revving
at 9000rpm, at the start from standstill. His reply was somewhat indignant.
I forget the exact words but something like his having a stopwatch somewhere
on, or up, his person ...? Tom said, "more like 11000..." so I assume a 175 revs
to 11000 on NO LOAD.

OK, so I am making a long story of this but bear with me...
Brian said something like " ... a 175 with small flywheels won´t pull the skin
off a rice-pudding. The 175 has to have the biggest flywheels possible..."
So there we are:-
Big (dia at 200mm?) flywheels revving at 11000 have considerable energy
(about 15000Joules***) whilst slipping the clutch -- of course the revvs
will drop back to nearer 9.5 under load but that extra energy is there and
being `tapped´ much as KERs is on Formula One cars.. This extra
energy added to the 12.1ftlbs***³ of torque contributes to getting the 175
moving.

So there it is -- PERHAPS the answer to the Rossi whinge. The Ducati with
slightly bigger flyweights on its crank might well get away quicker at the
start!?

With a Bantam, attaching weight to the clutch -- as Derek suggested -- would
probably do the same thing. Now! I wonder who might be the first to have an external flywheel -- á la early Guzzi -- on a Bantam???

***I´ve had a lot of bother with these units of energy -- in torque don´t
look so big but maybe big enough....!
***²Brentwood, 21hours 28thSept...
***³From the Jimmy/Ian figure Mike Powell published.

Overdue I´m thinking?

I was being very silly and have deleted my silliness...

Humble apologies ....

So JB, my mistake in using the heavier D14 crankwheels instead of the D7 ( ? 0.6Kg lighter) might not be a bad idea after all ?

Just need to get the pipe, carb and timing sorted.

Nice evasion critical question Young John --
Yes Young John! After speaking with Brian I have to agree: no mistake.
If the D14 flywheels -- are bigger than D7 -- and as you say, the D7 are lighter -- when used on a 175motor*** then according to Brian White you´ll be pulling away from standstill as fast as pulling the skin off a rice pudding. Brian was very emphatic about a 175 needing BIG flywheels for acceleration from start.
And Brian with his sprinting experience should know -- rather, does know....

Repeating what I´ve said before -- the flywheel energy during 10,000 to 11,000rpm clutch slipping (from start) counteracts the increased friction losses of the 175 that I say are attributable to the increased bore size...! As I said before, like having KERs....

*** probably one & the same, just to prove my ignorance of BSA Bantam coding.... D1 to D3 were all 125s? -- D4 was a 150? -- am I right????

-- Derek????

--still waiting for a response.

JB sorry for not replying earlier, we have 12 hour time difference.

Bantam models: D1 was 125, D3 150; D7, 10, 13, 14 and B175 were 175s

Thanks John...

Filling in time until someone explains how the heavier flywheel (that we now
know is necessary on the 175...) actually functions....?

...so what about KERs on a Bantam? -- if F1 cars can have Kinetic Energy Recovery Systems so can Bantams. Plenty of space for a big, heavy flywheel
above the Bantam cylinder head. Of course KERs could be achieved by using a generator charging up capacitors that when discharged drive an electric motor in the rear hub but that would come out heavier than the heaviest flywheel. Then there´s a compressed air system which could also be quite heavy...

Derek´s idea of Beefing-Up the clutch weight is easier but the clutch runs at
38/17 -- 2.235 times -- slower than the crankshaft so perhaps a flywheel
forward of the engine sprocket might do better -- particularly if it was
declutchable by computer control and used when at advantage to do so....

Hhhhmmmm!??

Hi all I know is my bike is the quickest off the line then it all goes down hill from there think its a age thing
anyway the crank weight is 4.9 kg[img][/img]

Wow Robbie! Your flywheels are BIG man! The inch rule suggests 14inches dia....??
If that´s the same 175 set-up you had at Lydden 2005 the way you joined the Parade
rather late backs Brian White comment, that a 175 gets going with big flywheels -- you
were that quick the ambulance driver couldn´t catch you -- he was backing into the Pit
Gate slot as you came out on full elbow and you missed each other by millimsetres!
(I´m sure it was you -- humble apologies if it weren´t.)
...
So I did a quick calculation and at 9,000 rpm your motor´s flywheels create 34,407Joules
per second of stored energy whereas my previous calcs of another (a) 175´s flywheels at
200mm(7.9") dia x 4.5Kg created 10,000 Joules/sec and then (b) a 125 engine with its
flywheels at 96mmdia x 2.4Kg gave 1,227Joules/sec at that same 9,000rpm speed.
Yours ...-- 3 times as much as another 175 -- and like, 28times?? as much as a 125 with
small and light crankshaft!!??
This is only theoretical, assuming the flywheels are plain discs and have no con-rod attached
but the results are satisfactory for comparison purposes...
...
That´s OK while the engine is revving at 9000rpm and you are slipping the clutch but the
story goes the opposite way when accelerating the engine from a low speed to say, 7000
rpm (to get onto the pipe). The engine is then using its energy output to create energy within
the flywheels and less is going to the drive-transmission than would be if the engine were
at a constant 9,000rpm. That is by virtue of the extra flywheel weight & diametrical size.
Admitted, this difference [of (a) & (b) above] is only by fractions of seconds but when
accelerating for some seconds between gear changes this (lagging behind) becomes a
considerable difference in distance on the road -- representing the difference of disaster+
from triumph for a racer.
...
Hence Robbie, your acceleration during racing might well be suffering more lagging-behind
because of the bigger/heavier flywheels than (b) above but not of (a)....??

I hope that makes sense!
I might be wrong -- of course -- and if so, maybe someone out there will please say so!
Lastly, all the best....
Cheers!

My god can we pick a subject that is little more interesting than a wet lettise,
BUT FOR MY PENNY - I recon as you only slip ur clutch once per lap, and off the start, Robbie (who is a great guy) is losing 2/3 seconds a lap and could be a lot higher up the grid with a smaller lighter crank ??? "my thoughts are wait for it" secret on this aspect.

Derek.

Funny! I seemed to have been slipping the clutch much more than that, I had to ... -- particularly at Cadwell -- to keep the engine revs up enough to be on the pipe ...

Boring subject? I thought there were others on here who wanted more of this...? I´ll gladly belt up if that is what THEY want?

And for my own interest --please yourself if you read any of this ...! -- I calculated the Moment of Inertia of
Rob´s Flywheels and compared that with a 125´s (MofI) and another 175 (MofI)and the difference is enormous
from both which means the acceleration from low to high speed -- without the slipping clutch -- is going to be sluggish.
It seems to suggest you can go too far with flywheel size....?

JayBee the BOF....

Boring Old Fart....