[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)

Nombre de messages : 105 Localisation : Biblis Date d'inscription : 14/01/2017

Hi Frits,
your results are very very close to what i calculated by hand.
Here is my first drawing for the cumbustion chamber. Seat for the spark plug isn´t right, that comes later.
I´m sorry for the milimeter paper, i don´t come by with my Solidworks on solid bodys. I can only construct plane objects with it.

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Squish radius 125mm. The squish band is set 0.6mm towards the piston (cylinder got 1,4mm overhang)
Gap 0,8mm.
The radius of the end of the squish is 53,75mm (76,00-(2x14,64% bore)
The radius of the spheric is 30,994mm with a high of 15,555mm. That makes a volume of 19,618cm³ in the spheric part.

Your combustion chamber looks very different. Do you think my one isn`t ok?

Thank you for your effort!
Best regards,

Bernd

Nombre de messages : 105 Localisation : Biblis Date d'inscription : 14/01/2017

Hi,
unfortunately i made a little fault with big effect. I wondered about your spheric to seem much bigger than mine.
I transposed two numbers while drawing. Sorry for that!
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Here a picture of the cumbustion chamber i calculated. What to you think about it?
All the measurement i mentioned above are right, just the drawing was wrong.

Best regards,

Bernd

Nombre de messages : 362 Localisation : Belgique Date d'inscription : 05/12/2011

what's the reason for the space between squish and bolt-holes ?

Nombre de messages : 94 Localisation : Hollande Date d'inscription : 10/09/2013

With a conventional lathe you can't machine a squish band with the radius. There is a much simpler and quicker way to do this . It's also possible to make auxiliary exhaust ports but you have to think practical and out of the box. Any experienced machinist can do this job. Give me a call on+31-40-2622009 between 19:00 and 23:00 Hrs and I'll tell yo how. Tada for now. Of course is this message only for Döllinger.

Nombre de messages : 105 Localisation : Biblis Date d'inscription : 14/01/2017

Hi,

the space is for a copper seal. It´s an aircooled machine. I have various other drawings for the cooling fins ect.. Too many measurements ect. to have all in one drawing.
The combustion chamber is the last drawing i need, and the most difficult for me.
@ Bob: That´s very kind! I`ve got someone with a CNC-lathe, who´s doing the job for me paying what i want. He´s a old fashioned man, who´s into that job.
Though i wish it was different i can´t do all work by myself. I´m repairing cars and do a lots of electric stuff. The day got only 24h.
Best regards,

Bernd

Nombre de messages : 94 Localisation : Hollande Date d'inscription : 10/09/2013

I do believe my way/effect is better. Got 60 years 2stroke experience. My dearest friend is a bloke by the name of Jan Thiel, he's 2 weeks older than me. We know each other already 60 years. How about that ? Don't forget that you can make auxiliary exhaust ports even with a barrel with studs. How ? Let me tell you. Einfach anrufen.Dann werde Ich dir die Auge öffnen.

Nombre de messages : 105 Localisation : Biblis Date d'inscription : 14/01/2017

Ok,

ich werde anrufen.

Döllinger a écrit:: Here a picture of the cumbustion chamber i calculated. What to you think about it?

The idea behind the classic hemispheric chamber in your drawing is that it should give the shortest flame path and thus the fastest combustion. But that theory was based on a stationary mixture, and flame speed in a stationary mixture is far too slow for our purposes.
For a really fast combustion we need turbulence that spreads fragments of burning mixture, which become then new seats of fire, like a forest fire that spreads because of burning leafs that are carried by the wind into distant parts of the forest. And the best turbulence is generated by squish action in a combustion chamber as shown below.
[Vous devez être inscrit et connecté pour voir cette image]

Nombre de messages : 105 Localisation : Biblis Date d'inscription : 14/01/2017

Hi Frits,
thank you for your help. I had a very instructive talk to Bob yesterday. Great support in this forum! Even with my old stuff.
When i look to your drawing:
-Distance from 3 to 4 is 14,30mm
-The high of the dome is 15,56 (vertical line from point 4 in relation to a line from point 2 to 2.
-Rounding of the edges 11,31mm?(like in your drawing) Or 12,57? (22,87-14,30)

Is that correct for the combustion chamber you think it´s the right one for me? (The one in your drawing)
[Vous devez être inscrit et connecté pour voir cette image]

Best regards,

Bernd

PS: 12,5:1 is Ok or could i get a benefit in even higher combustion?

Döllinger a écrit:: When i look to your drawing:
-Distance from 3 to 4 is 14,30mm
-The high of the dome is 15,56 (vertical line from point 4 in relation to a line from point 2 to 2.
-Rounding of the edges 11,31mm?(like in your drawing) Or 12,57? (22,87-14,30)
Is that correct for the combustion chamber you think it´s the right one for me? (The one in your drawing)
PS: 12,5:1 is Ok or could i get a benefit in even higher combustion?

The drawing on the previous page was specifically meant for your engine. The X-values are diameters, as is customary in CNC lathe-work; the Z-values are heights. These values contain all the necessary for a CNC-operator.
If you go higher than 12,5 with the compression ratio, you will probably lose power, unless your exhaust pipe is very inefficient.

Nombre de messages : 105 Localisation : Biblis Date d'inscription : 14/01/2017

Hi Frits,

now i understand! Sorry, not my métier...
Thank you for your support. I will send a picture as soon as the 2 heads are ready.

Best regards,

Bernd

PS: Found a method to define the overhang of the cylinder exactely. So only one operation on the lathe is necessary.

Bob van der Zijden a écrit:: With a conventional lathe you can't machine a squish band with the radius. There is a much simpler and quicker way to do this . It's also possible to make auxiliary exhaust ports but you have to think practical and out of the box. Any experienced machinist can do this job. Give me a call on+31-40-2622009 between 19:00 and 23:00 Hrs and I'll tell yo how. Tada for now. Of course is this message only for Döllinger.

A bar with 2 points machined to the radius of the squish you want, positioned on the centerline of the tailstock and the cross slide. With 2 hands winding the cross slide and the traverse in the saddle , keeping moderate pressure on the bar, the tool will cut the radius. That was how things were done pre-cnc Wink

Nombre de messages : 94 Localisation : Hollande Date d'inscription : 10/09/2013

Why the radius if you can machine two parallel sides, on on the piston crown and one in the cyinder head? Cheaper and quicker.

Nombre de messages : 105 Localisation : Biblis Date d'inscription : 14/01/2017

Hallo,

tomorrow this block of alloy will get to my CNC-operator. Thank you your help.
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Best regards,

Bernd

Nombre de messages : 690 Localisation : Auvergne Date d'inscription : 14/11/2010

Frits Overmars a écrit:: For a really fast combustion we need turbulence that spreads fragments of burning mixture, which become then new seats of fire, like a forest fire that spreads because of burning leafs that are carried by the wind into distant parts of the forest. And the best turbulence is generated by squish action in a combustion chamber as shown below.
[Vous devez être inscrit et connecté pour voir cette image]

What do you think about toroidal head ??? seems that it works like your drawing - more complicated, less efficient ???

pascaltz a écrit:: What do you think about toroidal head ??? seems that it works like your drawing - more complicated, less efficient ???

The squish action in a toroidal head is identical to the squish action in my head, which by the way I call a flat-toroide.
But tests by Jan Thiel have shown that the toroide with intruding spark plug, as shown in the pictures below, does not produce the same power as a flat-toroide. The reason could be that the intruding spark plug creates a scavenging shadow; a zone where old combustion gases are not completely washed away by the incoming fresh mixture.
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Nombre de messages : 690 Localisation : Auvergne Date d'inscription : 14/11/2010

Thanks Frits;I like the "flat-toroide": easier to turn and better !!! I keep all your "tips" in mind for my TZ ... [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 13 980796

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 13 980796

Your drawings show a domed piston; on my 89 [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 13 177154

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 13 177154

reverse 250 TZ I have domed pistons and I planed to put TZ V2 flat top pistons which fit perfect ... with new heads !

Domed are better than flat headed pistons ??? which pistons on the Aprilia's ?

pascaltz a écrit:: which pistons on the Aprilia's ?

Domed pistons with radius = 190 mm ; dome height = 1,93 mm ; edge angle = 8,17°.[Vous devez être inscrit et connecté pour voir cette image]

Nombre de messages : 690 Localisation : Auvergne Date d'inscription : 14/11/2010

Thanks Frits for that well-documented answer !
I see little "oil tanks" feeded by little holes on the opposite side of exhaust - extra lubrication to reduce friction ?; we usually see little holes to lubricate - cool ? - exhaust port "barettes".

For Aprilia it's domed pistons ! Standard pistons for reverse TZ were domed and kit pistons were flat then all the V2 had flat top pistons. I know ... Aprilia's are better than Yamaha's ... [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 13 921866

[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 13 921866

Can you give us the + and - of domed and flat pistons ?

Do you know the type of pistons mounted on the lasts V2 - V4 factory bikes ?

pascaltz a écrit:: Do you know the type of pistons mounted on the lasts V2 - V4 factory bikes ?

Which V2 - V4 factory bikes do you mean?

Nombre de messages : 690 Localisation : Auvergne Date d'inscription : 14/11/2010

All of them: NSR, YZR, RGV, ... to see if all the Japanese factories went the same way than you.
I will have a look at the FPR topic to see their choice.

Nombre de messages : 5 Localisation : Hungary Date d'inscription : 22/04/2017

Hi!
My name is Laszlo, and have been reading this thread since months and at last I managed to catch up with the last post :) I am from Hungary and I am a teacher of engineering and currently developing a valve concept for foul-strokes as my Phd.

First of all I have to say thank you to all the contributors of this thread and especially to Mr. Overmars and to Mr. Thiel to share their knowledge so freely with others.

I try not to ask questions that have already been answered.

What I am eager to know why have not you streamlined the divider wall at the entrance between the A and B transfer ports on the RSA cylinder?

Laci a écrit:: Hi! My name is Laszlo... I am from Hungary and I am a teacher of engineering and currently developing a valve concept for foul-strokes as my Phd.
First of all I have to say thank you to all the contributors of this thread and especially to Mr. Overmars and to Mr. Thiel to share their knowledge so freely with others.
What I am eager to know why have not you streamlined the divider wall at the entrance between the A and B transfer ports on the RSA cylinder?

fogadtatás Laszlo, and thank you for your kind words.
Streamlining that divider has of course been tried and tested, and the result was negative.
Streamlining would mainly improve the inflow from the crankcase into the B-ducts, whose lower entry areas are rather small compared to their upper B-window areas, but apparently this 'improvement' would upset the scavenging balance:
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Nombre de messages : 5 Localisation : Hungary Date d'inscription : 22/04/2017

Thank you for your answer! [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5) - Page 13 771973

During reading the topic one contradiction always kept creeping back: Since the expansion chamber restrictor raises the outflow to sonic why has Mr. Thiel reported that the end pipe + silencer still had an effect on deto+power? This same result was drawn a couple of pages ago by a forum member (I do not know his name maybe he is from OZ) with an RSW 250 (or maybe RSA) when he changed the length/diameter of the silencer.

And I also would like to know whether the two small holes (+ the groove) on the piston side facing the C port wall in the cylinder serve purely lubrication purposes or has some more magic behind ? :)

Why is that you are all Dutchmen in an Italian factory? Has it something to do with a specific school in Holland? What was your role beside Mr. Thiel?

Laci a écrit:: one contradiction always kept creeping back: Since the expansion chamber restrictor raises the outflow to sonic why has Mr. Thiel reported that the end pipe + silencer still had an effect on deto+power?

If the flow through the restrictor is sonic during most, but not all, of the cycle, the components further downstream can still play a role, especially when the inner silencer diameter is close to the restrictor diameter.
Therefore I prefer an inner silencer diameter much bigger than the restrictor diameter. It not only makes the restrictor effect more dominant, which simplifies tuning, but it also helps silencing. This may sound weird, but a large-diameter perforated tube in the silencer gives better attenuation than a small-diameter perforated tube.

Citation :: I also would like to know whether the two small holes (+ the groove) on the piston side facing the C port wall in the cylinder serve purely lubrication purposes or has some more magic behind ?

No magic, just lubrication.

Citation :: Why is that you are all Dutchmen in an Italian factory? Has it something to do with a specific school in Holland? What was your role beside Mr. Thiel?

There is no specific school in Holland; we just liked to play with our mopeds (doesn't every kid?).
My role was talking, drinking, listening to music and brainstorming about two-strokes together with Jan, performing physics calculations and developing computer programs; not for Bultaco, Garelli or Aprilia, but for Jan personally.

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