[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 3) (Locked)

fpayart a écrit:

La pression appliquée sur le liquide de refroidissement est destinée à retarder l'apparition de la cavitation dans certaines zones.

 
Cavitation can be caused by two events: high flow velocities around tight bends, and engine vibration.
When an engine vibrates, the metal surfaces move away from the liquid occasionally. Because of the inertia of the liquid, underpressure will occur between the liquid and the metal and this underpressure can cause local boiling of the liquid.
A pressurized cooling system will suppress this boiling and can make the cooling much more effective.

Vortex a écrit:

Manuel Rainer a écrit:

Vortex a écrit:

Sorry Manuel,
But how can you reach a compression ratio of 16:1 with a kartengine with a min. volume of 11cc with a in this engine normaly used mainexhaust diagramm of something between 195 and mabe 197 degree?
The corrected one is for sure under 10:1!
For me Mr. Thiel is right when he wrote; The fresh mixture did not reach the spark plug anymore.
Maybe too much turbulences?

hi

i am not driving official races. there is no limitation of head volume.

i got to 16:1 in my 125 TM KV95 rotary valve engine, with a head volume of 8,3 cc. ex on 197° squis gab 0,8. in this case the engine not want to rev over 13800.

Hi,
Ok that changes everything.
How much advance do you use?
Did you try more squish?
Which exhaust temp. do you reach?

hi

i have 0,9mm before TDC it is about 13,3° advance. in all tests the same.
the head is made like the one of the RSA.

i have tried 0,7 squish where i think the compression is near 17:1 the engine dont rev over 13500.
i have tried 1,0 squish where i think the compression is near 14:1 the engine revs over 14300.
i dont have different heads to test only the squish an let the compression. in my tests i change always 2 things. compression and squish. i know the right way is to cange always only 1 thing and see, but i dont have the posibility to do that. an for this was my question if the compression also can let an engine dont rev as much as with less compression.

i dont have a EGT. so i dont know the es temperatur.

thanks Riley i gonna see if i can get one.

Manuel

hey manuel,

you can fairly easy check the volume with a CAD program - just draw a negative including squish and then go to properties.

On my 50cc Derbi (with Conti cylinder and Conti insert) I made the experience that with a squish of 0,5 mm it just stopped revving at 13.500, had no overrev and detonated the sh*t out of the piston. After adjusting squish to 0,7 it was much nicer to drive and had plenty overrev.

Next step was to fabricate some custom inserts acc. to Frits/Jan/RSA guideline with different volumes, now I can lower the squish to 0,5 and maintain the overrev. Those inserts made quite a big improvement on band width and peak. So you might want to get inserts with different radii manufactured and test them...

Voici la traduction, merci Frits c'est exactement de quoi je voulais parler, en plus du début d’ébullition causer par les bouchons tarer à 0,9 bar.

La cavitation peut être causée par deux événements: des vitesses d'écoulement élevées virages serrés autour, et les vibrations du moteur.
Lorsqu'un moteur vibre, les surfaces métalliques s'éloignent du liquide de temps en temps. En raison de l'inertie du liquide, une dépression se produit entre le liquide et le métal, et cette sous-pression peut provoquer l'ébullition locale du liquide.
Un système de refroidissement sous pression permet de réprimer cette ébullition et peut rendre le refroidissement beaucoup plus efficace.


  

Merci Emmanuel  .

Your reaction makes me happy for more than one reason. Although I love this topic, it concerns me that it becomes more and more English (my own fault) and less and less French, and I feel somewhat guilty vis-à-vis my French hosts.

Frits, nous lisons pas à pas ce qui se dit ici.
Quand je dis "nous", je parle des passionnés du 2tps au sens large, qu'ils soient francophone ou bien anglophone !
Nous sommes plusieurs à porter ce qui se dit dans ce topic dans nos moteurs.
Cela prend un peu de temps, à l'échelle d'un passionné pas forcément "riche".
Il est vrai aussi que peu de monde est enclin à modifier la géométrie de leur moteur ... question de moyens, de finances, de compétences ...
Même si il est certain que l'anglais écrit ralenti la compréhension pour la majorité des français,nous prive de détails, nous y sommes un peu habitués ... dans la vie de tous les jours.

Une chose est certaine, ce que vous et Jan communiquez dans ce topic, en terme de connaissances technique est fabuleux pour ceux dont ce n'est pas le métier mais certainement la passion d'une vie et en cela vous avez nos remerciements !!!!!

  



edit : je ne connais pas de forum où on ne parle pas de ce qui se dit ici, je ne sais pas si vous imaginez la porté que celà peut avoir ... je connais des personnes ( dont je ne donnerai pas le nom  ) qui ont imprimé les deux topics afin de les relire dans leur lit  

Frits, no complaints here for the English, I'm sure there are many many many others out there whom appreciate not only the topic but also the language, you have reached far and wide to all edges of the globe by doing so
Thank you

Frits, even french speaking people here is happy that you dont use your native language... and happy also than Jan doensn't write in Thaï.

ขอขอบคุณในเดือนมกราคม, Dank je Frits.

Hello Again.

Been some time I didn't came here. I see some questions had been "reposted" or the level of questions had fall to the very beginner level. Unfortunely I have to respost a little too, because I can't find the info in this the long long thread.

Just to little questions. Frits, if you can answer please, many thanks.

About the ring clearance between his edges, if I remember it was said that 0,5mm was the minimun, and 0,4 seized, is that right?

Also, If a ring as a cooper/bronze side, this side will be up? Towards the piston crown, to prevent some detonation or even transfer heat a bit better?

Many Thanks  

romeuh80 a écrit:

About the ring clearance between his edges, if I remember it was said that 0,5mm was the minimun, and 0,4 seized, is that right?

No, it's not. The minimum safe ring gap clearance is 0,5 % of the cylinder bore.

Citation :

If a ring as a cooper/bronze side, this side will be up? Towards the piston crown, to prevent some detonation or even transfer heat a bit better?

If a ring has only one coated side, I would put it on the underside to minimize the friction in the ring groove.
If you have removed a ring and can't remember which side was down, put the shiny, polished side down.

That's is 0,27mm.

So I was forgoted and wrong it seems.... glad to came here.

Thanks

koenich a écrit:

hey manuel,

you can fairly easy check the volume with a CAD program - just draw a negative including squish and then go to properties.

On my 50cc Derbi (with Conti cylinder and Conti insert) I made the experience that with a squish of 0,5 mm it just stopped revving at 13.500, had no overrev and detonated the sh*t out of the piston. After adjusting squish to 0,7 it was much nicer to drive and had plenty overrev.

Next step was to fabricate some custom inserts acc. to Frits/Jan/RSA guideline with different volumes, now I can lower the squish to 0,5 and maintain the overrev. Those inserts made quite a big improvement on band width and peak. So you might want to get inserts with different radii manufactured and test them...

hi koenich

did your engine dont rev and detonate of the fact of too high compression or because it has a different shape?

i have checked the volume with Inventor i only was not remembering the precis value an i cant get mi notices.


thanks Manuel

Hi Mr. Jan, Mr. Frits and everybody.
Sorry for the question, I know you do not like air-cooled engines, but the reglament prevent us from using water cooling ...
The question: We use a Bultaco 250 engine with aluminum cylinder and iron cast sleeve. Can I mount a aluminium sleeve and apply nikasil?
I have not ever made and do not know if anyone will have any experience with this, what do you think?
If yes, what type of aluminum would be suitable for the sleeve?

Thank you for sharing your knowledge

Yes Piquer, using an aluminium sleeve with nikasil is a very good idea. There are many types of aluminium with good mechanical properties, but not all of them are suitable for nikasil treatment. It is advisable to check with the firm that will be applying the nikasil.

Frits Overmars a écrit:

Yes Piquer, using an aluminium sleeve with nikasil is a very good idea. There are many types of aluminium with good mechanical properties, but not all of them are suitable for nikasil treatment. It is advisable to check with the firm that will be applying the nikasil.

thank you very much Mr. Frits.
As aluminum has a higher dilation coefficient than iron cast, I would have left a less tolerance, it's correct?

Frits Overmars a écrit:

Yes Piquer, using an aluminium sleeve with nikasil is a very good idea. There are many types of aluminium with good mechanical properties, but not all of them are suitable for nikasil treatment. It is advisable to check with the firm that will be applying the nikasil.

Thank you very much Mr. Frits.
As aluminum has a higher dilation coefficient than iron cast, I would have left a less tolerance between the cylinder and the sleeve, it's correct?

This is for this vehicle: [Vous devez être inscrit et connecté pour voir ce lien]

-------

[Vous devez être inscrit et connecté pour voir ce lien]