[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked)

Oh, don't apologize Josh! It wasn't my intention to make you feel bad in any way. Sorry if it looked like so.
Cheers

carefull in buying that because typical 4 stroke car det frequencies are lower around 5kHz and a 125cc 2 stroke is more like 10kHz.
So maybe worth to ask,if that circuit is analog like the one I have,it's just a matter of changing a few capacitors to move the filter's bandwdith center and the seller could do it for you?
Also learn all you can because i suspect that will not be just plug and play.
here's a link to choose freq.based on bore size: [Vous devez être inscrit et connecté pour voir ce lien]

motoholic71 a écrit:

carefull in buying that because typical 4 stroke car det frequencies are lower around 5kHz and a 125cc 2 stroke is more like 10kHz.
So maybe worth to ask,if that circuit is analog like the one I have,it's just a matter of changing a few capacitors to move the filter's bandwdith center and the seller could do it for you?
Also learn all you can because i suspect that will not be just plug and play.
here's a link to choose freq.based on bore size: [Vous devez être inscrit et connecté pour voir ce lien]

It is interesting that you quote that very site! Quite some time ago I found that same calculator, and when I entered in my piston diameter of 47.6, I seem to remember it giving me some message about the frequency being "out of parameter". It seems that now it works just fine! Interesting.

Either way, I must be able to easily detect detonation or I fear my 2013 race season will cost me many pistons. It take some time before I can post the results of experienc, but when I can, I will be sure to keep you good people informed.

Kind Regards,

~Josh

Well if the calculator breakes down or something use this 900/(Pi * r)
r is bore rad
Anyway I'd like to offer whatever help I can,I built a circuit but unforseen circunstances forced me to stop all development(got sacked)
I'm an electronic techn.please I'm very interested on your results since I think my circuit is similar.
At first glance I see poor suply filtering and a few others that make the thing so economic but can be solved.
Good luck and please don't forget us.

I have a question to Frits :
If I have look right on some pictures, you're using roll bearing on the crank instead ball bearing. I'm interested in the kind of bearing. I'm just rebuilding a 2 Stroke mx engine and I had the idea to swap the ball bearing with roll bearing. I had the idea a few year ago, but the bearing only manged to go up to 11000 rpm.(the one I found)
Do you know the manufacturer of the crank bearing ? Du to the incread friction of the bearing, is there any performance lost ? If I can't find some, I would use hybrid bearing.

Thanks in advance

Zash239 a écrit:

I have a question to Frits :
If I have look right on some pictures, you're using roll bearing on the crank instead ball bearing. I'm interested in the kind of bearing. I'm just rebuilding a 2 Stroke mx engine and I had the idea to swap the ball bearing with roll bearing. I had the idea a few year ago, but the bearing only manged to go up to 11000 rpm.(the one I found)
Do you know the manufacturer of the crank bearing ? Du to the incread friction of the bearing, is there any performance lost ? If I can't find some, I would use hybrid bearing.

You can find it all here, Zash:

[Vous devez être inscrit et connecté pour voir ce lien] and Manuals/02_2-stroke

There is no increased friction. On the contrary, because of the larger axial clearance (0,4 mm) there is less friction than with ball bearings.
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BC1_1442BA

Of course there is only less friction if there is enough radial clearance.
About 0,05mm clearance was needed.
Many bearings had to be modified by grinding.
The crankshaft needs to have a very free axial movement!

Zash239, I think that you also have to fit a straight cut primary gear because I think that the MX engine have an helicoidal gear that don't work with roller bearings due to axial effort.

Jan or Frits, can you tell us how the axial movement is stopped with roller bearings? (between the tracks and rollers or other way?)

Thank you for your answers

julien #41 a écrit:

Zash239, I think that you also have to fit a straight cut primary gear because I think that the MX engine have an helicoidal gear

Already by the mid '70's, MX engines had straight-cut gears...

Ok Graham, sorry for this mistake, I thought that because some road two strokes engine still have helicoidal gears.

julien #41 a écrit:

... can you tell us how the axial movement is stopped with roller bearings? (between the tracks and rollers or other way?)

Just take a look at the bearing picture on the previous page. The outer bearing race has a recessed path for the rollers, and there is a collar ring on one side of the inner race.

Thank you Frits, I asked that because on the RSW manual on Aprilia website the collar is another part and on your first picture the collar is built on the inner race.

julien #41 a écrit:

I asked that because on the RSW manual on Aprilia website the collar is another part and on your first picture the collar is built on the inner race.

Take another look at the picture, Julien. On the complete bearing the collar is lying on the inner race; on the right you can see the inner race and the separate collar.
Nevertheless yours is a good question: originally Aprilia used bearings where the collars were part of the inner race, but these collars would sometimes break. After switching to separate collars the problem was gone.

Gyro effect=tons
cranks with a ball and a cylindric bearing like most Ktm where the ball is responsible for axial lock on the drive side.That's an affordable way,a C4 ball brg.with polyamide or brass cage for the drive side and a c3 cylindrical roller with the same cage type for the other.Will endure hi rpm use.
Either way I don't think Aprilia RS crank bearings exist in standard sizes with that "loose"ring design.
I think there was a few MX bikes still using helical primaries in the '70s,those which were modified street engines?

motoholic71 a écrit:

I think there was a few MX bikes still using helical primaries in the '70s,those which were modified street engines?

Yes, when for instance the Yamaha MX bike was the DT-1 with the lights taken off. But once Honda brought out the "Elsinore" CR125 & 250 in... 72? 73? everyone got a bit more serious and built MX specific motors without the oil pumps and helical gears. Not sure about the European bikes of the era like the Bultaco Pursang, pretty sure the Maico's had straight-cut.

I was only born in 62, so I wasn't so involved in the early 70's

GrahamB a écrit:

everyone got a bit more serious and built MX specific motors without the oil pumps and helical gears. Not sure about the European bikes of the era like the Bultaco Pursang, pretty sure the Maico's had straight-cut.

I wish. Those Bultacos and Maicos still had a primary chain. I used the first Bultaco MX-engine with primary gears, the 360 cc Bandido, as a basis for my 500 cc roadracer. O, the joy of crankshaft bearings moving sideways....
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Thanks for all you replies
Luckily my primary gear are cut straight

GrahamB a écrit:

motoholic71 a écrit:

I think there was a few MX bikes still using helical primaries in the '70s,those which were modified street engines?

Yes, when for instance the Yamaha MX bike was the DT-1 with the lights taken off. But once Honda brought out the "Elsinore" CR125 & 250 in... 72? 73? everyone got a bit more serious and built MX specific motors without the oil pumps and helical gears. Not sure about the European bikes of the era like the Bultaco Pursang, pretty sure the Maico's had straight-cut.

I was only born in 62, so I wasn't so involved in the early 70's

1962 was an excellent year !

Good evening to all two stroke lovers!
Let me start by saying that I love to read this epic topic, thank you Jan, Fritz, and all the others that so kindly share your awesome knowledge.

I have a pair of doubts, that would like to ear some opinions, so let me start.
This two photos show an yamaha dt lcde crank-case, it is a 50cc engine, that is going to be a bit modified, with a 43mm stroke crankshaft, 84mm con-rod(should be longer, but the owner doesn't want to buy a longer con-rod, and a 46mm cylinder.
What I would like to know is if there is any benefit in mounting the reed-cage with the reeds opening in the vertical, instead of the more traditional horizontal, I took that idea from a couple 100cc kart engines that use reed cages almost as tall as the entire crankcase, and from the high-end aerox/scooter engines where its very common to see the reeds mounted in the vertical, in my head it makes sense, due to the crankcase shape:
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So, is there any advantage, or its a mater of only testing will reveal the true results, or maybe some already outdated/bad idea?
My other doubt is about this post(abbreviated, hope there is no problem in doing that):

Frits Overmars a écrit:

The picture below shows the Aprilia RSA125's blow-down angle.area and transfer angle.area. If you divide these values by the 124,8 cc cubic capacity plus the 8,6 cc combustion volume, and by the 12.500 rpm at which this engines develops its maximum torque, you will find the optimum specific time.areas for blow-down (8,72°mm² per cc per 1000 rpm) and transfer (66,16°mm² per cc per 1000 rpm) .
Your engine should meet these same specific time.area values, so if you know its angle.areas, its cubic capacity and its combustion volume, you can calculate the rpm of maximum torque.
It may be necessary to raise the exhaust timing beyond 190° in order to get the required blow-down angle.area for the rpm determined by the transfers (that is the reason for the RSA's 202° exhaust timing).
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I have another project that involves a 1990 yz 80 engine, 45.6mm stroke with 94mm con-rod, that I will adapt an Yamaha dt 80 italkit cylinder, the cylinder as a 54mm bore(a long way from a square engine I know..), to extract the most from this engine I would like to apply the suggest time areas that Fritz referred in the above cited post, but I think I'm missing something, the engine will have about 104cc, just to make the maths shorter.
The suggested exhaust blow-down time area is 8,72°mm² per cc per 1000 rpm, this leads to:
8.72*104*12 = 10882,56

I'm aiming for 30º blow-down, that gives a blow-down area of 362,7mm2 which seems a bit on the low side, and if I take the values from the image provided I get a strange blow down time :/
14543ºmm2 / 812mm2 = 17,9º

But the RSA has way more than just 17.9º of blow-down, could some one shed some light?

Best regards, and thanks again for all the information and help provided.

I see where you problem lies, Senso. Angle.area is not simply the total blowdown area multiplied by the total blowdown angle. It is the sum of a lot of small area steps, multiplied by the time during which each of these steps is open.

For example, let us assume that the exhaust port is a simple rectangle, 40 mm wide, that it opens 1 mm further for each degree of crankshaft rotation, and that the total blowdown angle is 30°.
Then the first degree of exhaust opening will open an area of 40 mm x 1 mm = 40 mm², and this area will be open during the whole 30° of blowdown period. That first area thus has an angle.area of 40 x 30 = 1200°mm².

When the crankshaft turns 1 degree further, an additional area of 40 mm² is opened. This second area will be open during 29°, so its angle.area is 40 x 29 = 1160°mm².

Repeat this calculation for each crank degree until the end of the blowdown phase, and add all the angle.area values; that will give you the total blowdown angle.area.

In reality this calculation is complicated by the fact that not every degree of crank angle gives the same port height difference, and even more by the fact that the exhaust port is not a simple rectangle. But you will understand the principle of angle.area.
One final remark: my first name is spelled Frits, not Fritz .

I'm so sorry for calling you the wrong name, I will not do it again.

I understand, I need to integrate the area, maths it not really my speciality but I think I can come up with the right numbers, I will open a post in the Technique part of the forum when I have more data and crazy ideas, so to not spam this topic, but thanks for the advices, its all that I need to keep me going in the right direction.
In the case of the italkit cylinder it is a W shaped exhaust port, that might be fun to integrate and arrive to the correct values.

Best regards Mr. Frits

Bonne leçon de logique dynamique, j'ai pris ma dose merci Frits :-) , je voulais revenir sur les temps d'ouvertures et fermeture du distributeur (valve rotative), je post des photos d'un moteur avec la position de la valve au PMH (TDC), la fermeture total du conduit est 86° ATDC

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TDC position

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86° ATDC

Ensuite je cherche à savoir comment relever l'autre valeur angulaire, et quelle méthode utiliser?
Merci pour vos réponses les amies, je me fait ici le porte parole de ceux, qui ne ne comprennent qu'une partie de la distribution rotative.

Je posterais d'autres photos si nécessaire

Emmanuel Laurentz a écrit:

Ensuite je cherche à savoir comment relever l'autre valeur angulaire, et quelle méthode utiliser?

Désolé Manu, je me sens plus bête que d'habitude cet ap. Qu'est-ce tu entends par "l'autre valeur angulaire" ?
C'est par rapport au début d'ouverture, début de ferméture... ou l'aire d'ouverture en fonction d'angle, dans le même sens que les calcules de blow-down ci-dessus ?

Chers amoureux du 2-tps,
Dear 2-stroke lovers,

Je viens de parcourir un nouveau topic qui pourrait vous intéresser, ici :
I just discovered a new topic that might be of interest for you, here :

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Il semble que ce soit seulement une introduction à ce qui sera un topic plus détaillé.
I understand this is only an introduction to what will be a more detailed topic later.


J'en profite pour vous remercier à nouveau de la qualité de vos échanges ici : même un béotien total comme moi prend plaisir à vous lire en apprenant quelques mots nouveaux et quelques débuts de bribes de notions :)

Tu sais les valeurs sont indiqués tel 86/136 (pour l'exemple), donc sur le moteur ci dessus j'ai effectivement 86° depuis le PMH jusqu’à la fermeture de l'admition ok mais que représente cet angle de 136° et à partir de quand ?

J'ai lu dès la page 24 et suivantes des valeurs de 95/150.

Q: 95° avant fermeture admission à partir du PMH ?
Q: 150° à partir de quand ?