[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked)

Beau schoot,mais quand est t'il avec la guillotine en place !!!!Sacre RSA il m'a bien fait saliver cet hivert avant l'arrivee de nos Maitres Jan et Frits sur ce genial forum.Amitiees et a Dijon.Zeze

One wants the pressure wave coming back into the cilinder but NOT the burned gases that are hot and can cause detonation!

Thank you, Jan!

Great Jan Thank you for this explanation about preventing the burnt gases from coming back inside the cylinder.

But what about the fresh gases escaping from the exhaust port -maybe due to short circuiting or overscavenging-? We want them to come back into the cylinder ?

Maybe these fresh gases are very close to the exhaust port : inside the port duct of the cylinder?

Yes, ideally the escaped fresh gases remain in the exhaust duct and get pushed
back into the cylinder by the positive pressure pulse that is reflected by the rear
end of the exhaust pipe.

Jan Thiel a écrit:

Yes, ideally the escaped fresh gases remain in the exhaust duct and get pushed
back into the cylinder by the positive pressure pulse that is reflected by the rear
end of the exhaust pipe.

Thanks for your reply

Stephane a écrit:

oui c'est ca.
ca permet de réduire l'angle que forme la bielle par rapport à l'axe du cylindre au moment ou la tête de celle-ci est la plus écartée de l'axe de l'axe du vilebrequin
(en fait quand les 3 points - axe de piston / axe de tete de bielle / axe du vilo - forment un angle droit)

parmi les avantages évidents il y a en effet ceux cités par janpol.

autre avantage moins connu, plus la bielle est longue et plus la cinématique de l'ensemble bielle manivelle fait que (principalement) le diagramme de transfert augmente pour une même hauteur de lumière.

en clair : si on augmente la longueur de la bielle sur un moteur donné, ca va augmenter son diagramme de transfert.
ou
à diagramme égal, on a une lumière moins haute, donc un meilleur guidage du piston (fiabilité)




selon les derniers renseignements que j'ai pu glaner, la bielle du 125 Aprilia ferait 118 mm.

nsfman a écrit:

comme a l'époque sur les g3 bidalot , mais le soucis est le démontage de l'axe après échauffement

étonnant, car ca se prévoit facilement à la conception et - a posteriori- ca se corrige facilement à la la fabrication

bonjour Stéphane, moi c'est Stéphane lol

je lisais ce superbe post et je suis tombé sur ton explication de diagramme fonction de longueur de bielle. Sauf erreur (il faudrait m'expliquer shématiquement le truc) pour moi, plus la longueur de bielle est importante, moins une lumière donnée a un diagramme élevée, un simple petit shéma que l'on fait avec des longueur volontairement "hors norme" pour que la différence soit flagrante, nous donne bien ce résultat... allez, j'en fait un vite fait...


Alors, ça nous donne:

vilebrequin course 80mm
bielle 100mm
pour 90° parcouru, nous obtenons 31mm de course

vilebrequin course 80mm
bielle 80mm (oui je sais, c'est impossible, mais sur un shéma, je fais ça quoi je veut!! nah!!)
pour 90° parcouru, cette fois, nous obtenons 29mm de course

(les données ne sont que shématique, rien n'est super précis, mais nous avons un ecart de 2mm quand meme)

autrement dit, pour un diagrame de 180° a l'echap, avec une bielle de 80mm et une course de 80mm, nous devons avoir une lumière de 29mm de haut et pour la meme configuration moteur avec une bielle, cette fois de 100mm, nous devrions avoir une lumière de 31mm de haut...

PS: que l'on me corrige si j'ai merdé :)

STEPH a bien sur raison .....

Hi everybody,

I am by honored reading posts from such important persons in Aprilia (and generally 125 GP racing) history, as Mr. Overmars and Mr. Thiel. So many informations, so many data, so many explanations. It is nice to see a lifetime experience shared on public forum, you do not see that every day..

As trying to find information about 125 GP racing, maybe this is place to get some answers from people that have all the credits in the world on this subject Smile.

1. Nikasil (Nicasil ?) or steel barrel?
2. steel or carbon reed petals?
3. why are GP pistons (at least asso werke that is in my hand) has sides of piston "rough" (they are definitely not smooth nor polished, as head of piston? To keep oil on piston?
4. On that same piston there are two small holes (i believe on inlet side, cca 1 mm in diamter), why? to ensure better lubrification of small end?

Thanks,
Tomi

Tomi a écrit:

.

1. Nikasil (Nicasil ?) or steel barrel?
2. steel or carbon reed petals?
3. why are GP pistons (at least asso werke that is in my hand) has sides of piston "rough" (they are definitely not smooth nor polished, as head of piston? To keep oil on piston?
4. On that same piston there are two small holes (i believe on inlet side, cca 1 mm in diamter), why? to ensure better lubrification of small end?

Thanks,
Tomi

no need to worry Mr Thiel or Overmars
1 Nicasyl
2 Carbon
3 To keep oil
4 To keep oil / lub fonction between piston and cylinder wall

Thanks for replay :).

I will have to read this topic several times in order to understand everything. Since in my lifetime I will never have a chance to test 125 GP engine (I had "in my hands" several GP 125 and 250 bikes (just to see them) and engines, but was never allowed to have detailed look :), am am playing with standard rotax 122.

However, as for theory and reed petals vs disc, I would like to know more:

- in max (or at least working) rpm are reed petals "breathing"? Like slightly moving as piston is moving, or they are constantly open (as theory 24/7 suggests) because mass of petals (although mass is minimal, maybe it is enough on 13 000 rpm?).
- since disc inlet has "fixed" timing (exclusively dependent on rpm because it is gear driven) maybe (as discussed before) better results can be achieved with electronically controlled reed valve? Now is reed valve dependent on pressure (under-pressure), but with little effort it can be rpm AND demand sensor (demand sensor = throttle = TPS = RideByWire) dependent. Or maybe, instead of rpm that key parameter is demand (throttle)?

And as Mr. Overmars wrote earlier that petals are there just to start engine, is there some topic or literature where I could find more?

Thanks,
Tomi

Tomi a écrit:

in max (or at least working) rpm are reed petals "breathing"? Like slightly moving as piston is moving, or they are constantly open (as theory 24/7 suggests)......
And as Mr. Overmars wrote earlier that petals are there just to start engine....

Bok Tomi,
In a normal reed valve engine the petals open and close with every crankshaft revolution until the rpm gets so high that the reeds must move at more than their natural frequency; they cannot do that and at that point the carburation gets messed up.
When I introduced my 24/7-system to this forum, I did not say the reeds of a normal engine are constantly open; I said they could be constantly open when the engine is running in the power band, provided the resonance frequency of the inlet system (intake tract & crankcase volume) is tuned to avoid backflow.
I also said that in the 24/7-system the reeds are there just to start the engine; in a normal engine the reeds are also there to prevent backflow while the engine is running in the power band.

Citation :

Bok Tomi,

I do remember earlier text about nice gesture about language, nice and thank you!

Citation :

In a normal reed valve engine the petals open and close with every crankshaft revolution until the rpm gets so high that the reeds must move at more than their natural frequency; they cannot do that and at that point the carburation gets messed up.
When I introduced my 24/7-system to this forum, I did not say the reeds of a normal engine are constantly open; I said they could be constantly open when the engine is running in the power band, provided the resonance frequency of the inlet system (intake tract & crankcase volume) is tuned to avoid backflow.
I also said that in the 24/7-system the reeds are there just to start the engine; in a normal engine the reeds are also there to prevent backflow while the engine is running in the power band.

All clear about this. Or, to be honest, I do not have sufficient knowledge to continue discussion on this level. First (ok, after reading with understanding what you have wrote) I will try to get more info and documentation form different sources about subject (last being racing department, very, very hard to get there, even for "inside" guy like me).
2 strokes are interesting and apparently endless subject, and it feels nice that there is a lot to say and develop in that field.
It is pity that (maybe) biggest reason for huge development of 2 strokes - MotoGP is turning away from it's own child.

Thanks,
Tomi

Frits Overmars a écrit:

When I introduced my 24/7-system to this forum, I did not say the reeds of a normal engine are constantly open; I said they could be constantly open when the engine is running in the power band, provided the resonance frequency of the inlet system (intake tract & crankcase volume) is tuned to avoid backflow.
I also said that in the 24/7-system the reeds are there just to start the engine; in a normal engine the reeds are also there to prevent backflow while the engine is running in the power band.

Frits are there any studies conducted to find out if the reed petals(clappets for Jarno) completely close when the engine is in phase?

Institute of TwoStrokes a écrit:

Frits are there any studies conducted to find out if the reed petals(clappets for Jarno) completely close when the engine is in phase?

There must be hundreds of such studies; just look at the list of SAE-papers. And in case you really want to know, it's not too difficult to do it yourself. Make an appropriate window and run the engine with a stroboscope for which you can move the phase, while leaving its flashing frequency governed by the ignition. That way you can scan all crankshaft positions in the running engine.

Un "aimable informateur" m'a fait parvenir ce document rarissime sur lequel apparaît notre ami Jan Thiel!

Qu'il en soit remercié!



PS: je vais modifier le smiley en conséquence...

En voyant cette photo de Jan THIEL la lime à la main,

je ne peux m' empècher de penser à cà : [Vous devez être inscrit et connecté pour voir cette image]

(cylindre Solex 6 transferts de Solexgump)

Le sens de l' humour de Maître Jan et de Marc me pardonneront ce

elles sont minuscules ?
Aurais-tu moyen d'augmenter la résolution de l'image ?

Lolo, tu nous fais ds la pornographie a nous montrer les dessous d'une dame comme çà.



superbe tes photos.

Hi everyone , this is the best two stroke topic on internet with serious fans and professional engineers involved.
It is sad that some motorcycle corporations are killing two strokes even in prototype racing where the most important are performance and competition.
Lets keep two strokes and this topic alive with great pictures, discussion and ideas

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Hi

Sorry for my english

I’m Stefano…
I’m working on the development minibike engine.
These bikes do not have the change ... have a similar range of use for karting 100

I'd like to build a plug to the jack that replaces Seeger

What do you think?

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