de'saxe engine configuration

who knows about this subject, could anyone give an opinion please.

And
1) has it been done on a bantam?,
2) what are the main advantages?
3) which way is best the barrel forwards or to the rear? (considering all bantam cranks run anti clockwise looking from timing side

4) if you were going to try this - by how much would you suggest its offset, 1.0- 3.0 or 5.0mm ? or more?

5) what are the disadvantages ?.

if some one knows please tell us all. ?

regards Derek

Hi Derek what an interesting subject? My opinion on the topic is nearly no-one what
it is you are talking about - hence the lack of responce!! I've raced a bike featuring
a de'saxe' engine and written an article on it in 'Classic Racer' magazine in 2005.
I suppose you could say the idea is 'old hat' (not JB) with the bike in question being
a Scott! I suggest people goggle de'saxe' (french for un-balanced) engines and have
a read, the latest ZX10 kwack features a de'saxe' set up so Kawasaki thinks there's an
advantage??

Ref your questions
1 yes it has been done on a bantam
2 main advantage reducing the thrust on the inlet cylinder wall/piston
3 forwards?
4 not sure.....
5 manufacture

Another point some pistons have an offset gudion pin - so have a small amount of de'saxe' anyway?
word of warning putting a piston in the wrong way wrong, may put more thrust on the inlet side...

Mike
p.s. Mick/Trevor will mota do de'saxe' calc's?

No one knows about it ! really.

reduces thrust load on down stroke" so mike does it increase on the upward cycle then. ?

the offset can be upto 20% of the stroke length ?
approx 11.0mm ?

We actually tried this by mistake, in about 1989/90, I'm sure the offset was either 3.5mm or 5.5mm and was forwards, I will check my notes,
from memory (22/23 years ago) I was rushing at the time trying to do it all over a late nightshift, I made a mistake taking too big a cut, and the cases rotated backwards I did see this after the first cut, but due to time, I decided to leave it, and had yet to do the proper barrel that was to be watercooled, I would correct this after the next meeting which I did.

The only difference from memory, was I could sence it was excellerating better in top gear, sadly it siezed just before going across the line at snetterton" I put this down to the extra friction on the thrust face, but iam not sure it was all down to this, ???

I agree we you that it could be a great subject to discuss "if others joined in who know about this,

Whats happened to JB lately.

you seen the photo's on GeTe facebook page today,and more yet to come.
I Notice the expansion tail pipe diameter, and the size of the C/Section seems very similar to what I get off motas, I just dont get large diameter pipes, biggest 87mm to 90mm center section.

Good luck with the show this comming weekend,

I hope to pop along at some point.

Derek

Hi Derek
If I remember correctly the standard Ariel Arrow pistons were offset. (eccentric gudgen pin). But I dont think this type of piston was used for racing ( see Herman Meyer ) Hope this helps. Barry.

Hi All

TZ pistons have the gudeon pin offset 1mm towards the front of the piston which amounts to much the same thing as an offsetting the barrel..

Is there an advantage ? Yamaha must have thought so but not all manufacturers do it.

Maximum cylinder pressure will occur somewhere around 20 deg after tdc so if you imagine the angle of the conrod at this point you will see that with this offset the angle of the conrod from the vertical is slightly less so there is less piston thrust towards the rear of the cylinder and more of the thrust directed downwards to rotate the crank. (sounds good!)

When the piston is approaching tdc the conrod angle is steeper and piston thrust is increased but since the pressure above the piston is only a fraction of that after tdc you lose less than you might gain after tdc.

Port timings are altered due to the offset piston moving more slowly around bottom and top dead centre.
The effect is to slightly increase the port time-areas at the expense of higher piston acceleration and higher maximum piston speed but we are talking about very small differences - at least with a 1mm offset.

Phil Irving *** says "If the offset is forwards and about 15% of the stroke (the usual figure) the exhaust and transfer ports will open later by about 4 degrees (depending on the con rod/crank ratio) and close later by about the same amount, which seems to be the wrong way, but the inlet port will open later and close earlier which is correct."

If you use Mota you can enter a gudeon pin offset and see the timing, area and acceleration changes in the .per file but Mota seem to disagree with Phil Irving and shows the inlet port also closing later - anybody got the time to work this out and check it?

*** in his book Two-stroke Power Units

Mick

Scott engine crank is 3/8" forward of cylinder centreline. It would be interesting to have info on max pressures on piston on both sides of TDC and calculate side reaction on to cylinder walls. This however has altered greatly as we all improve top end filling by modifying inlet and using resonant exhausts. Working on a humped piston Day cycle engine means you are on your own a bit as regards development. I am not convinced of the merit of offset gudgeon pins as it seems logical to think that the piston will try and heel over if the load is not centrally supported. Rather like a rod that skates right then left if the axis of the G Pin is not perfect and thus shorten big end life drastically. I shim rod LE's in pistons to control stance and this enables BE to take more load and last longer. I still use premium unleaded but last year had detonation and seizures with exactly the same set up as the previous year. I think the additional ethanol content tipped it over the edge, so I tried 4 star leaded with NF octane booster and it ran just fine. I must be on the edge with combustion pressures. Normal Scott 19bhp main jet 190 ignition 35BTDC Carb 25mm My bike 45bhp main jet 570 ignition 21 degrees, home made 38mm carb but then I made my own head etc
I admire what you do with Bantams. It would be easy if we had the cash to go out and buy a fast bike, but to get more out of what you have is a real achievement worthy of genuine respect. Kindest Regards Roger Moss

Hi all,
Mick gave us some good all round info on this old chestnut and the Phil Irvine piece from the late 60s is spot on ,as far as it goes .
To get bang up to date, some investigative work done to the Aprilia RSA125 engine suggests that the concept is not worth the hassle.
There is no question that rod angles become assymetric , but the benefit is negligible on this engine so a Bantam would`nt feel it !
Less obvious is the increase in piston stroke against the crank stroke indicating that from tdc to bdc is more than 180* and from bdc to
tdc is less than 180* . This then begs the question , just where is tdc ? All of this was arrived at using an offset of 10% of the 54.5 stroke .

Confused ? So am i .

Have a good 2012 , regards Trevor

I seem to remember a Bradbury engine that somehow lengthened the expansion stroke -anyone know anything of that??-

The late Dr Joe Erhlich made an engine with articulated con-rod whereby the AFTER TDC expansion was enhanced. i.e. At the time of the peak combustion pressure the con-rod lengthened itself and thus the torque was increased ... I think it was called the e-3 engine -- it made the news a few years back and then vanished. Someone said GM had bought the patent. I did not like it because how the heck could you rev an engine to some decent speed with an articulated con-rod.

And then there was a French abortion witha sort of rack-&-pinion arragement trying to do the same...

Anyone got any news on Doc Erhlich´s motor? -- the French one is somewhere on the net...

I have a completely different idea on how to achieve the same which my dear ex ABS sponsor, Andrew, laughed at -- but unless I get a sponsor it will pop-its-clogs with me... Ahh! -- they all sigh with the wet eye.... Ahhhh!

Shame really -- the Bantam 125 formula ought to include engine management microprocessors and direct-injection injectors -- and progress would be made.

Great to see what people think about this topic, the good thing is everybody
now knows about it! Will be having a chat with 'Scott' man Roger Moss at the
Newark show tomorrow..
Mike

not sure what you are trying to tell us Mike, but before we move on from this subject,I would like to clarify what we are saying


it does not produce any more power ?

more importantly it does make better or more effective use of the current power you are producing ? .

adding one point to the RSA 125 point trevor noted, an aquantance of mine said they only dropped it because they were told to! and it was somthing to do with the increased friction at higher RPM apparently needed to much cost /time - and the potential that it cancells out the advantages at higher rpm because of the extra friction.

! But he who should be listened to, said there are possibilities for engines only running to 10,000 and with a low number of gears. !

regards Derek

Roger! -- still using hump pistons on your Scott -- what shape is the combustion chamber? and where was the detonation occuring in that shape??

Thanks,

JayBee.

'Mr Scott' Roger Moss explained to Robbie the virtues of De'Saxe' configuration
engines. I think Robbie was a little un-sure?? Great to see you....

Thanks mike

While we should never set ourselves up as experts, if we are to make progress, we each need to try to understand the fascinating dynamic interrelationship of the various functions of our engines. What is then found, certainly with Scotts, is that after Scott left the company in 1917, the designers that came after him had very little understanding of gas flow. So we look at an engine where the inlet tract was very restricted in section and with bridges in the square inlet ports that performed the function of impeding gas flow very efficiently. Now we look at an inlet tract that has a floor, which is a cover over the central 9" flywheel and a roof between which you cannot pass your third finger! We look at the engine logically and understand that the cylinder block sits on top of the crankcase and ask ourselves WHY does the inlet tract need a ceiling? If we cut out the ceiling we can use the underside of the block as the roof of the inlet tract. Now we have added about 60% to the cross sectional area of the inlet tract. The trick is to want to understand everything and maybe if anything does not make sense, then it may well be rubbish regardless of the respect the originator may be held in. We are currently working redrawing some original Phil Irving drawings and he was obviously an enthusiastic inexperienced designer with little understanding of manufacturing realities. Certainly no GOD. Scott heads were rubbish so I make my own shaped to match the Scott piston but with a central pre chamber on Ricardo lines. Of course there are a lot of mods to get the maximum gas through in the shortest time and get the fastest burn as near to TDC as possible. Hence the reduction in timing on pump fuel from 35Deg BTDC to 21Deg BTDC. As regards De Saxe arrangements, I was pleased to show Mike the details and evidence and note how well his bike went later. Kindest Regards Roger PS of course for competition engines I make my own cases, Alum barrels, heads carbs, gearboxes, but it keeps me interested and out of the more expensive clutches of loose women!

Thank you Roger...

You answered my query over the odd Scott shape with that pre-chamber, Ricardo fashion. I spent a lot of my professional life trying to get the optimum combustion chamber shape right for performance, fuel economy and emissions to happen all together -- mostly in diesel pistons with bowl-in-piston and the chamber shape DOES make a hell of a difference to the performance, which can be seen in Heat Release diagrams showing the increase in degrees of crank angle with lower peak pressure (thus reducing NoX emmissions) achieveable by small changes of shape. The Bantams seem stuck -- currently -- with an accepted shape and I hesitate to say that it could be improved.

Wonderful engineer Ricardo but he too could slip up. He did with the 1927 Triumph Model TT engine where the inlet (cantilever) cam follower didn´t "follow" it dug in and wore the cam badly.

Cheers!

JayBee!

Hi JB. You never know who you are in contact with on these forums and as you indicated a long involvement with engines, I thought I would mention something I am involved in for your general interest.I have a friend you might know named Rob Collett, an ex GM engine designer and admirer of Ricardo. Rob has made several sleeve valve engines and runs about on a 500cc uniflow sleeve valve two stroke engined bike of his own manufacture. Rob had long had a notion that with a conventional two stroke, it was not possible to achieve optimum transfer timing. I was pleased to help make a test engine which is basically two Scott engines back to back like an early square four but with an intermediate gear so both cranks rotate the same way. The Scott engine was chosen for these tests for economy as this is a private project. The economy comes from the unique design feature of having the transfer duct as an external casting. The whole is built into a stretched wide line Domi frame and will go on the dyno with a set of fabricated ducts that transfer the charge from No 1 crankcase to No 1 cylinder typically in conventional way. Inlet via my old 1967 reed valve system direct into the cases. Record the output on a H&F water brake. Now remove transfer ducts and substitute a set of ducts that take No1 crankcase charge to No3 cylinder typically. The transfer is longer and at a more beneficial time. The inlet is almost 180 degrees rather than say 120 degrees conventionally. We then do dyno output tests with this system. and log data for comparative analysis. The third option is fun! According to flow layouts, it is quite possible that we could remove the valve plates out of the reed valve bodies and once we spin it over it will function without reeds. Rob has a nice square four drawn out based on Yamaha main components, but there is much more engineering to recreate the transfer ducts to the proposed system. We have to do what we can afford to evaluate the system. I have no knowledge of this system being used elsewhere. Another engineering adventure! I have no illusions about Scotts, but respect the vision and courage of Alfred Scott and so drawing out the underutilized potential is a nice challenge for a practical engineer and is mostly within my means. PS if anyone has knowledge of 3D laser printing for prototypes I would appreciate advice re making molds for investment casting of pistons for more economical low volume production Cheers Roger

Thanks Roger!

I don´t know about the laser stuff but my old-ex-250ABS-sponsor makes his own molds for casting Alpha engne replica bits. Andy Boyle -- in Chelmsford -- do you know him? or of him,. Roger? He is working on an Alpha twin just now...!

Rob Collet rings a bell but I cannot put a face to the name...

What angers me is the GP organisers going anti 125-2-strokes. There´s much continuous development in this field and your comment re Ricardo, Collet and sleeve valves has me remembering (important aspect at the moment -- memory...!!) that a Ricardo sleeve valve (Vee) engine worked OK but didn´t get accepted -- had spherical prechamber -- something like that! intended for an aircraft originally. The sleeve rotated only few degrees, out and back. By cam action the sleeve reciprocated (whilst rotating those very few degrees) each sleeve in turn ....

I think the small two stroke can still be made to go better without the hefty complication of the Lotus Omnivere being invloved... Of course, Lotus are trying to prove stratified charge which Ricardo did in the late twenties....

Wünderbar! someone who knows a Heenan & Froude water dyno! These electronic, excitation controlled things really give me the pip. With an H&F you can halt the water flow to get an exact No-Load condition for comparison purposes without an electronic regulator swinging the load about ....

I am on this web-site because I feel like a floundered whale -- living in an apartment here in Germany with only an electric hand drill, hacksaw and a few files to play with: cut off from reality and life as it were. However, I made a model steam engine -- without its flywheel -- that ran at 1rpm and then used the bearings from it to make a model Tatham (I have corrected "Tattershall" -- different thing altogther) dynamometer that has since been turned into another (top secret) model....??

Tatham dyno was in the days of belt driven factories from a steam traction engine outside. To get an idea of how much power the machines were using this belt-transmission-dyno came into being. My model used an endless chain with four bicycle sprockets---

--You might laugh at that but the idea was to be able to measure the friction losses in an engine and I measured -- with this model -- the friction loss of my big Bosch hand drill merely by rotating the plot with a socket-hand-brace. I think it is all too practical mechanical to be taken seriously.
Son Slick in the IoM thought it a grand idea but he was far too busy to make such a device, plus his not having enough machining capablity put the mockers on the project.

Whilsst pre-chambers work very well, they are not as efficient as open chambers. The reason -- say the Professor-Doctor experts (usually Japanese!!) -- is that heat energy gets lost in the throat from the chamber to the expansion-space above the piston. Certainly, the heat-release diagram is excellent in that it starts the pressure on the piston at usually only a few degrees before TDC or even at TDC which means no combustion pressure opposing the upward piston travel which means that any precombustion -- or detonation only happens in the spherical combustion chamber where it does little harm....

In my infancy there was a bloke on a Scot (Squirrel, I think??) who came thro´our village every workday morning with a yowl that woke up the whole village: with goggles over a flat cap on back-to-front he looked really evil.
Its fixed in memory -- that picture! and My Dear Mum wringing Her hands and saying, "Poor man -- he´ll surely kill himself..." (Wow! the name has come back, Hap Lane). Well, Hap died in in his bed in his sleep -- probably a Happy Man from whence came his nickname.


I would question the current Bantam combustion chamber -- most popular at the moment -- as to whether it is the most efficient??

Cheers!

JayBee.

Just read a bit about the Honda Moto3 engine, spec bits (but not all) given away:-

84kg wet,78x52.2mm,inclined back 15degree, backwards exhaust exit, balance shaft,
semi-dry sump, desaxe' cylinder, separate gearbox/crankcase,air bleed overrun.
Claimed 47.6bhp@13'000rpm 20.7ft-lb@ 10'500.

He's back -

Hi mike welcome back from the wilderness, what was it like you abviously survived! great news well spotted, this is another bluff, just does not make any difference at all except for load underpower -torque is the same so is the power "however" according to the F1 boys it makes a significant difference to excelleration, this is mainly do to it being well past tdc PRIOR TO FULL COMPRESSION LOAD BEING APPLIED or simply it makes better use of the retarded Ignition timing that you not otherwise be able to use.

I copied and pasted this this from an email so the explanation not to Dyslexic. ! we are every where even in the F1 pit lane.

Are you riding at mallory or still in retirement ! good to see you back

cadwell i mean

regards Derek