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

Sorry to disturb you, I just found that in one of my hard drive...

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J’y vois un 2tps avec la boîte sous le moteur,une valve rotative à l’échappement,allumage en bout de vilo. Y-a de la place pour des clapets ?ou un disque ?

Pour moi c'est un disque AR pas de doute.
Dan

Adco a écrit:

J’y vois un 2tps avec la boîte sous le moteur,une valve rotative à l’échappement,allumage en bout de vilo. Y-a de la place pour des clapets ?ou un disque ?

je vois le moteur d'un RSA

belle photo....

Frits
I have spent most of the day trying all kinds of angles on the ports(I used modelling clay) and have settled on the best combination(and turns out to be the simplest):
1. Curved the inner duct wall at the port floor, this made a big difference on axial flow and symmetry. As it was originally, it had about 3mm of almost flat and then started the curve from about an 80 angle.
2. Re-angled the A-Ports at 25 degrees axial, this helps to push the flow down onto the piston from the middle of the piston to the boost port and the flow became more symmetrical there too.

JanBros a écrit:

Adco a écrit:

J’y vois un 2tps avec la boîte sous le moteur,une valve rotative à l’échappement,allumage en bout de vilo. Y-a de la place pour des clapets ?ou un disque ?

je vois le moteur d'un RSA

Et bien voilà! Je me coucherai moins bête ce soir. Je lis  ce sujet par curiosité technique depuis que je suis sur ce forum.....et je n’ai jamais vu la moindre photo du moteur en question !

Adco a écrit:

Et bien voilà! Je me coucherai moins bête ce soir. Je lis  ce sujet par curiosité technique depuis que je suis sur ce forum.....et je n’ai jamais vu la moindre photo du moteur en question !

Adco, your comment initially surprised me, but when I checked it, I noticed that indeed there are not that many pictures of the RSA125 here.
I consider it my duty to ensure that all Pit-Lane forum members can enjoy a carefree night's sleep; maybe this will help.[Vous devez être inscrit et connecté pour voir cette image]

Merci Frits ça c'est beau !

Thank you Frits!

2 choses m'interpellent:
- le diagramme du distributeur rotatif!
- la qualité visuelle des fonderies!
Bref, sacré moteur!

fullgazlolo a écrit:

2 choses m'interpellent:
- le diagramme du distributeur rotatif!
- la qualité visuelle des fonderies!
Bref, sacré moteur!

Lolo, the castings look so nice for a very simple reason: they were not cast. Only the cylinder and the coolant pump housing were cast; all other alloy engine parts were milled from solid.
The pictures below show the very first milled prototype, when the intention still was to use an electric coolant pump. But because the capacity of the then available electric pumps was nowhere near large enough, a mechanical pump was finally fitted. That is the reason this pump looks like an afterthought.

Whenever an RSA engine was opened, paparazzi were lurking with their cameras. Sometimes the mechanics fitted an inlet disc with  a ridiculous timing, after which they 'forgot' to cover the engine. The real RSA inlet disc began to open 142.5° before TDC and closed 88° after TDC.
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Thanks Frits !

Thank you Frits for the pictures.
Can you explain how exacetely the disc rotor and the balancing shaft are driven ?
Best regards, Bernd

Frits, I have also saw the inlet disc diagram ; what do you think about 152-88° ?
Do you think -considering rotation speed- it would be working without disc !! ?
(my father, Yves Le Toumelin, told me an anecdote about MZ 125 1960's Kaaden Degner without disc : they forgot it... motor was very difficult to start but working normaly after...)
About your RSA crankcase photo, the cooling system around crankshaft case is it independant and separate, of the main cooling systeme, with radiator and water pomp separate from cylinder cooling circuit ? Stéphane Le Toumelin

what is the use of the little alloy tube behind the primary case ?

Thank you for the timing explanation!
For the distributor, I had heard of things like that in kart ... crowns with a number of teeth engraved different from the number machined!
It remains a beautiful object, anyway!

Döllinger a écrit:

Thank you Frits for the pictures. Can you explain how exacetely the disc rotor and the balancing shaft are driven ?

The balance shaft is driven directly from the crankshaft, as usual, via a couple of gears at the right-hand side of the engine.
The left-hand side of the balance shaft drives the shaft for the inlet disc via a set of bevel gears.
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Hi, how this system is "oiled" ? by oil of gearbox, without pressure ?

SLT a écrit:

Frits, I have also saw the inlet disc diagram ; what do you think about 152-88° ?

In theory the inlet should start opening as soon as the pressure in the crankcase had dropped to the pressure level upstream of the inlet disc.
In other words, when the pressure difference over the disc is zero. Then we will have the maximum time available for the inlet phase, and the crankcase pressure, which is dropping anyway because of the inertia of the mixture flow from the case to the cylinder, and also a little because of the rising piston after BDC, will not drop quite so strongly, and the flow through the transfer ducts will not be slowed down quite so much.

At the rpm of maximum torque the zero pressure difference over the inlet disc occurs at approximately 20° after BDC. But opening the disc when the pressure difference is zero, means that there will be a very weak pressure signal to the carburetor. This will make carburation tuning rather difficult. In a fuel-injected engine this problem would not exist and in that case I would definitely open the disc soon after BDC.

Citation :

Do you think -considering rotation speed- it would be working without disc  !!  ? My father, Yves Le Toumelin, told me an anecdote about MZ 125 1960's   Kaaden Degner without disc : they forgot it... motor was very difficult to start but working normaly after...)

I had the same experience with the home-built rotary-valve 500cc two-stroke  that I raced in the early 70's.  Once the inlet disc stuck open when the hexagon in the disc centre ripped apart. Thanks to the suction from the exhaust pipe the engine kept running as long as I stayed in the powerband (this gave me the idea for my 24/7 inlet principle) but of course the carburation was much too rich, because it was never intended to function with a 360° inlet timing. And the same will be the case for the Aprilia RSA: for a 24/7 system to function it would need a rather different combination of carburation settings, inlet tract diameter and length, and crankcase volume.

Citation :

About your RSA crankcase photo, the cooling system around crankshaft case is it independant and separate, of the main cooling systeme, with radiator and water pomp separate from cylinder cooling circuit ? Stéphane Le Toumelin

There is only one cooling system with everything in series, Stéphane. Separate systems would only make sense if they had different working temperatures. But a radiator with a lower working temperature is less efficient, so it is better to use all available frontal area for one big radiator.

Adco a écrit:

what is the use of the little alloy tube behind the primary case ?

desmofr16 a écrit:

Hi, how this system is "oiled" ? by oil of gearbox, without pressure ?

That little alloy tube is the return line to the oil pump that you can see at the left in the picture below. It lubricates the gearbox via oil jets from a gallery above the gears and it also provides lubrication for the balance shaft and the inlet shaft bevel drive. The crankshaft and the piston are lubricated via the usual fuel/oil mixture.
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Merci Frits apparemment ce petit rappel était bienvenu :superbe moteur!

Frits Overmars a écrit:

all other alloy engine parts were milled from solid.]

In Italy ?

Gorgeous ! Thank you Frits !

But please, stop laughing at paparazzi !