Engine Opinions

Well we have all the bits back so hopefully put the engine back together this weeknd and see what happens.


Eddie

Hey Eddie,
Saw there was a personal message for me but couldn´t open the box.

Re the pics -- this is the second time I have seen -- and known of... -- a needle roller small end. Every racing motor cycle -- including JAP 500cc/350cc Speedway & Grass Track engines -- had phosphor-bronze plain bearings in the con-rod small end... In fact, John Surtees is reputed to have replaced a main bearing, a ball bearing in his Vincent HRD Comet engine with a plain-bearing; which, he raced with much subsequent success and relaibility.
--
Can you explain WHY a needle roller small end? Lubrication reason at much reduced PetrOil mixture, perhaps?
--
In my experience it is the piston gudgeon pin bore that suffers. In fact my efforts to get Icarus-2 to be reliable when revving at around 11,000 rpm -- using standard long stroke -- failed miserably. That problem was the piston stretching itself such that the piston crown was clouting the cylinder head. Since the `Bump´ clearance was set at 40 thou (1mm) -- with the resulting piston (temperature) expansion -- or `thermal stretch´ -- in the order of 20thou there must have been a 20thou increase in gudgeon pin clearance -- ONLY up & down!!! ...
...
-- I mean, one could only laugh at seeing gudgeon-pin bores (in the piston) with perfect ovality -- and enormous gap twixt gudgeon-pin and its bore.

I never questioned why MY engine-man-cum-mentor never went to short-stroke [at the time every Bantam body (I knew in the late 60s...) was doing it so as to achieve reliable high max-revs] because he did the engine work as a hobby without charge -- In any case my own scrappy engine tuning was dismal (never enough time, my excuse). Big point, you know already, I guess -- is the stresses on the piston increase exponentially with increasing engine speed -- which we so-called engineers would call dy/dx-cubed --
"Pulsed" which is the acceleration of an already accelerated force!!
Cheers!
John.

Hi John,


Not to worry, it was only a message to say if you got stuck and you wanted help putting up pics then i would talk you through how i do it.


Interesting reading, in all honesty i bought the bike complete so it came with the needle roller small end, im sure somebody on here would be able to say if its right or wrong as they have lots more knowledge than i do in these things and i have bought the wrong type of things in the past so wouldnt be the first!


Regards


Eddie

john bass wrote:

Hey Eddie,
Saw there was a personal message for me but couldn´t open the box.

Re the pics -- this is the second time I have seen -- and known of... -- a needle roller small end. Every racing motor cycle -- including JAP 500cc/350cc Speedway & Grass Track engines -- had phosphor-bronze plain bearings in the con-rod small end... In fact, John Surtees is reputed to have replaced a main bearing, a ball bearing in his Vincent HRD Comet engine with a plain-bearing; which, he raced with much subsequent success and relaibility.
--
Can you explain WHY a needle roller small end? Lubrication reason at much reduced PetrOil mixture, perhaps?
--
In my experience it is the piston gudgeon pin bore that suffers. In fact my efforts to get Icarus-2 to be reliable when revving at around 11,000 rpm -- using standard long stroke -- failed miserably. That problem was the piston stretching itself such that the piston crown was clouting the cylinder head. Since the `Bump´ clearance was set at 40 thou (1mm) -- with the resulting piston (temperature) expansion -- or `thermal stretch´ -- in the order of 20thou there must have been a 20thou increase in gudgeon pin clearance -- ONLY up & down!!! ...
...
-- I mean, one could only laugh at seeing gudgeon-pin bores (in the piston) with perfect ovality -- and enormous gap twixt gudgeon-pin and its bore.

I never questioned why MY engine-man-cum-mentor never went to short-stroke [at the time every Bantam body (I knew in the late 60s...) was doing it so as to achieve reliable high max-revs] because he did the engine work as a hobby without charge -- In any case my own scrappy engine tuning was dismal (never enough time, my excuse). Big point, you know already, I guess -- is the stresses on the piston increase exponentially with increasing engine speed -- which we so-called engineers would call dy/dx-cubed --
"Pulsed" which is the acceleration of an already accelerated force!!
Cheers!
John.

Interesting subject, John. Being used to modern, well, mid-seventies, Japanese two-strokes, I tend to think only in terms of needle roller small ends. Truth be told I'm no engine man, but thinking on it further I can't see why they're necessarily superior, after all isn't the load in a straight line and with just a rocking motion? As you say, though, modern trends demand a reduced petroil ratio; so maybe it's a lube thing, and in that case wouldn't long-stroke engines with their high piston speeds perhaps benefit from needle rollers?

Anyway it's far easier just to pop in a new needle roller, rather than faffing about with all that reaming malarky!

Incidentally, do people still race long stroke Bantams or have those days disappeared into the mists of time?

Hi Undy... and thanks -- Eddie also -- thank-you for the replies. NO! The phosphor bronze plain bearing DID NOT suffer from piston impacting head nor from the same violence of piston high-speed stressing that the piston did.
...
That´s why I questioned the needle roller small end. The Japanese would have surely considered that the extra weight of the larger con-rod eye and bearing itself -- even if only for balance of reciprocating mass which would have to be countered at the crankshaft counter-weights.
Comes back to having a heavy crankshaft ...??
...
The point of going short-stroke is that the maximum piston acceleration/deceleration allows for higher revs and hence more power by increased max engine speed. Keeping to the standard Bantam `long´ stroke means that going over around 9,000 rpm means the piston is being subjected to stresses close to the material´s*** maximum tensile stress & destruction. There´s a lot of technology in piston material and method of production.
In the 60s´ the stronger pistons were reckoned to be those that were "Squeeze-Cast" which meant that as cast, before the alloy began to solidify the casting was squeezed. This was a form of forging which gave the marterial added strength over just cast or just forged...
...
I am out of date -- which does mean that it is a good idea to find out about pistons, their material
and method of manufacture. Certainly the standard Bantam piston was never good enough for high speed racing....
...
***the standard Bantam piston was designed for about 5,000 max revs -- I should think.

Hi John & Undred,

Very interesting reading and info from you both. With piston process and materials i think Derek Betts would be the main for explaining processes.


Regards


Eddie

undredseesee wrote:

john bass wrote:

Hey Eddie,
Saw there was a personal message for me but couldn´t open the box.

Re the pics -- this is the second time I have seen -- and known of... -- a needle roller small end. Every racing motor cycle -- including JAP 500cc/350cc Speedway & Grass Track engines -- had phosphor-bronze plain bearings in the con-rod small end... In fact, John Surtees is reputed to have replaced a main bearing, a ball bearing in his Vincent HRD Comet engine with a plain-bearing; which, he raced with much subsequent success and relaibility.
--
Can you explain WHY a needle roller small end? Lubrication reason at much reduced PetrOil mixture, perhaps?
--
In my experience it is the piston gudgeon pin bore that suffers. In fact my efforts to get Icarus-2 to be reliable when revving at around 11,000 rpm -- using standard long stroke -- failed miserably. That problem was the piston stretching itself such that the piston crown was clouting the cylinder head. Since the `Bump´ clearance was set at 40 thou (1mm) -- with the resulting piston (temperature) expansion -- or `thermal stretch´ -- in the order of 20thou there must have been a 20thou increase in gudgeon pin clearance -- ONLY up & down!!! ...
...
-- I mean, one could only laugh at seeing gudgeon-pin bores (in the piston) with perfect ovality -- and enormous gap twixt gudgeon-pin and its bore.

I never questioned why MY engine-man-cum-mentor never went to short-stroke [at the time every Bantam body (I knew in the late 60s...) was doing it so as to achieve reliable high max-revs] because he did the engine work as a hobby without charge -- In any case my own scrappy engine tuning was dismal (never enough time, my excuse). Big point, you know already, I guess -- is the stresses on the piston increase exponentially with increasing engine speed -- which we so-called engineers would call dy/dx-cubed --
"Pulsed" which is the acceleration of an already accelerated force!!
Cheers!
John.

Interesting subject, John. Being used to modern, well, mid-seventies, Japanese two-strokes, I tend to think only in terms of needle roller small ends. Truth be told I'm no engine man, but thinking on it further I can't see why they're necessarily superior, after all isn't the load in a straight line and with just a rocking motion? As you say, though, modern trends demand a reduced petroil ratio; so maybe it's a lube thing, and in that case wouldn't long-stroke engines with their high piston speeds perhaps benefit from needle rollers?

Anyway it's far easier just to pop in a new needle roller, rather than faffing about with all that reaming malarky!

Incidentally, do people still race long stroke Bantams or have those days disappeared into the mists of time?

Hi Howard

Keep meaning to phone you current 175 bantams are mainly long stroke and most use crowded rollers think due to a miss match of Maico rod and suzuki piston.

more here

http://www.bsabantamracing.com/bikes/build175.html


I may be at Honington it's fathers day and that's want I want for fathers day a bit of peace and quite, interupted by noisy bikes only

Tony

ps ED love the pics of barrels IMO one of the barrels skirt looks very thin and fragile

Hi Tony,

Thanks for the information and the opinion, dad says he remembers talking to you at wroughton about six years ago when he was taking photos of your bantam and x7. I always have photos but i dont want to overload the site but would like to know why in your opinion why the skirt is thin and fragile just as a refernce and all information counts.



kind Regards


Eddie

Hi john - GOT YOUR pm many thanks for those very kind words, glad to hear that -

and Blimey another subject I can properly contribute and comment on.

But I just want to (correct you) "put you right" so with squeeze castings and the main benefits, there is more than one benefit.

In fact so many, one is metal integrity - forgings, are good ! but a forging is only as good as the material lump it starts with!??, this may have inclusions in it when forged, these will then be week points in the forging after forging.

squeeze cast pistons don't have these issues, molecular structure are completely different, far more reliable than forging. with close to the same strength. (without aids - but far higher with) As a squeeze cast piston is pored into a metal die (another correction John) its then squeezed while its still molten and continues to do so during the solidification process.

Also unlike forgings the dies can be 5 or 7 piece meaning much more control of the internal shape /profile, strength, meaning a lot less metal and therefore less weight. ? metal density is higher so they are not much lighter.

But the biggest advantage is what you can put in the die, (aids) that will end up inside the aluminium, before you poor molten metal in and this ant the "old hat steel or titanium supports skelling-ton structures, Im talking about far more exzotec materials, in all different densities.

Our Bantam engines raced by me with our own squeeze cast pistons, that were squeezed at over 300 tons PSI back in the day - 1987/8/9/90 - but it did not have an aluminium crown and was in more than two pieces. "if only".

regards Derek

Hi Ed I like your quotes, - i see where your going with this, and make the following comments.

Some people Know some don't - "those that can - do" those that can not moan, these also look on "learnt information as power? - I have a different opinion, - for me people with this opinion are small minded and betraying mankind.

Only by passing on information will we continue to expand out knowledge, to improve our way of life, only a very small minded group, usually very educated, but with no common cense!, but "sadly the small minded community does seem to "pre-vale".

may be they are here for the same reason.? !! - certainly why there are so many swear words, I learnt about.

I like your previous information ed", and some great quote, hope everyone seen these.

regards Derek

Crikey! I really like this site, but it makes me feel as though my engineering experience and scientific knowlege is akin to that of an amoeba that's just failed the entrance exam for Single Cell Elementary School.

Welcome to my world plus minus the knowledge and experience! , everytime derek's dad comes round i probably make his head hurt with too many questions!

Eddie

ER'M ed how many bantams have you and your dad got. ???

Oh and it looks a beauty.

regds Derek

A few plus spares...

Thanks for that, its the one your dad has looked at the barrel and piston on and asked you a few things.




Eddie

Wow!

A NAKED Racing Bantam??

I´m seeing things...

Shades of the past -- when Roy Bacon wrote, "Racing On The Cheap!"

Don´t put a Skirt on it Ed, fairings multiply all the engine rattles, squeaks and grunts.
Without a fairing you get a wonderful feeling of freedom!!!

Old Hat hath spoken....

Hi John,

Dont you worry, it never came with one and i think it looks better without.



Eddie

hi eddie ,nice one that red bantam is as john said a thing of beauty, it reminds me of some pictures i saw some where of some aussie racing bantams can't remember where i saw them,might have been on here in the archive, they had a carb on the side of the crankcase and the exhaust coming out of the inlet on the barrel. cheers adam.

Hi Adam,

Thanks for the comments, yeah i do like it too. Might be completely off the mark but that could be the King Bantam Special you are on about.



Eddie

Good Evening all,

When we have eventually got the little red bantam before i have had to almost completely cover the bellmouth to get it started, is this a sign that we need to reduce the air mixture?




kind Regards


Eddie

this usually means one of a few things but not limitd to

1) carb too week on btm end pilot system
2) you openning throttle to soon or not enough when bump starting
3) inlect timing to large - no suction to start the system off-
4) doggy coild
5) doggy ignition
6) wrong ignition timing.
7) duff plug
wrong plug cap
9) an air leek on the crancases
10) an air leek between carb and barrel.
I'm sure there are more.

first simply try increasing the pilot jet, or turning in the pilot air screw at an angle at the rear of the carb.

for others to read - actually Ed sent me a very nice post off line, on about there should be more technical posts and more interetsting items like the crank one trevor and John has so diligently responded to, that I critisized, on reflection with this, I actually agree with Ed, we should have more technical information being posted and written, and i may have been a little over crital and out of line with what our forum needs for others to look in and find interesting enough to stay and may be join in longer term, I stand corrected for my errors, on this subject.

best regards Derek

Good Morning Derek,

Many thanks for the pointers, will get dad to look at the list and check back on the notes, it could well be the carb needs adjusting as its a tt with a power jet, may also try and source a plug as is a shorts reach and i only have new sets of long reach race plugs. Will also check the igniton but we have had a good spark and as i say it has run but was a pig to keep running on lower revs.


Kind Regards



Eddie

will try the pointers tomorrow and providing it doesnt ran will get the borrowed rollers out and see if we can start it again.



Eddie

Scratch that idea, lets take the clutch apart AGAIN, i must of done something wrong in a past life................