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

romeuh80 a écrit:: Frits and Jan

Lastest years motocross 125cc bikes have come with ceramic or anodized? Dome pistons.
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why haven't the 125 gp adopted them even before the motocross?

My guess is, this piston will not absorb soo mutch heat/energy from the cumbustion, so with more heat the pressure will be higher and more energy will go throut the exhaust making better power, is this true?

Besides, if the piston doesn't heat soo muth it will need lower clearances and can suitable higher power and RPM?

Of course this was tried.
It did not seem to make any difference.
Normal piston clearance was 0,04
But 0,05 gave more power.
and 0,06 still the same!
Friction can cause power loss!

romeuh80 a écrit:: I have another question Regarding 125GP.

I hav read somewhere, maybe here, that Duck tape is used on the cylinder head to determine that the engine temperature is ideal to go..

Is there some strong indicator that the actual cooling system is insuficient? Without a termo sensor mounted on the cylinder head...

And if that could tell us the problem before piston seize inside the cylinder

What was the total volume of cooling liquid used on the RSA/RSW?

I see that less liquid and bigger radiators was the way the things develop...

We never measured this volume, so I do not know!
Less liquid and a big radiator is the way to go.
And the quicker the water flow, the better!

I was wondering if anyone could tell me for certain at what height section C-C sections at? Looking at Section A-A it should cut halfway through the cylinder correct? This doesn't make sense though since there is too much material between the A and B ports when entering the cylinder. While I've been modelling I've been experimenting with several different positions for section C-C and haven't come up with anything for certain so any clarification on C-C would be greatly appreciated as I believe it is an important depiction of the way the air should exit the port. Below is my interpretation of it so far. One other question...What are the corner radius's of the transfer ports? 3mm or less?

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Jan Thiel a écrit:

romeuh80 a écrit:: Frits and Jan

Lastest years motocross 125cc bikes have come with ceramic or anodized? Dome pistons.

why haven't the 125 gp adopted them even before the motocross?

My guess is, this piston will not absorb soo mutch heat/energy from the cumbustion, so with more heat the pressure will be higher and more energy will go throut the exhaust making better power, is this true?

Besides, if the piston doesn't heat soo muth it will need lower clearances and can suitable higher power and RPM?

Of course this was tried.
It did not seem to make any difference.
Normal piston clearance was 0,04
But 0,05 gave more power.
and 0,06 still the same!
Friction can cause power loss!

Ok, that's it, thank you.

I have measured piston diameter up from the ring to the top.
Here some examples

Namura KX 125 2005 STD 53.95 (ceramic top) -> ~53,65 mm
Mitaka YZ 125 1997-01 STD 53,94-> ~53,55 mm
Honda NSR 125 Vertex STD -> ~53.6 mm

Have any of you compared crankshafts that have holes in them to crankshafts that are completely filled? Was there a difference power wise? I would expect the filled crank to perform better from an aerodynamic point of view. A crank with weight reduction holes would also increase crankcase volume but that may be negligible.

Dernière édition par Jan Thiel le Mar 23 Oct 2012 - 10:58, édité 1 fois

PVO a écrit:: I was wondering if anyone could tell me for certain at what height section C-C sections at? Looking at Section A-A it should cut halfway through the cylinder correct? This doesn't make sense though since there is too much material between the A and B ports when entering the cylinder. While I've been modelling I've been experimenting with several different positions for section C-C and haven't come up with anything for certain so any clarification on C-C would be greatly appreciated as I believe it is an important depiction of the way the air should exit the port. Below is my interpretation of it so far. One other question...What are the corner radius's of the transfer ports? 3mm or less?

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I cannot reply to this question as I have no designs!
And the design that was once published is very old, 1996 I think
Maybe Frits? Or Francis Payard?
The corner radius was 3mm
The C-port was 15 mm wide.

PVO a écrit:: Have any of you compared crankshafts that have holes in them to crankshafts that are completely filled? Was there a difference power wise? I would expect the filled crank to perform better from an aerodynamic point of view. A crank with weight reduction holes would also increase crankcase volume but that may be negligible.

I have never done this test!

Jan, Frits, on the other first topic you had talked about the volume of exhaust duct, like the exhaust was working like a pump and the duct was the conection pipe (so smaller volume more efectiv)

How was this volume ideal calculated? Or was just grind off material and try?

I am asking this, beacause I notice that the Honda RS 125 cylinders Have more exhaust duck volume over the years.... And some aftermarket kits have this volume even bigger than stock NX cylinder

Thanks

romeuh80 a écrit:: Jan, Frits, on the other first topic you had talked about the volume of exhaust duct, like the exhaust was working like a pump and the duct was the conection pipe (so smaller volume more efectiv)

How was this volume ideal calculated? Or was just grind off material and try?

I am asking this, beacause I notice that the Honda RS 125 cylinders Have more exhaust duck volume over the years.... And some aftermarket kits have this volume even bigger than stock NX cylinder

Thanks

I would not know any way to calculate this!
Maybe Frits does?
It was done by 'just' grinding until the best result was obtained.
The best way in my opinion.
Because even if you calculate something you would still have to test it!
I would never trust 'just a calculation'!
And I have more trust in logical thinking!
Reducing exhaust duct volume was already done on 50c engines in the 70ies.
And 125 twins in the 80ies.
It always worked!
So it was the first thing I did when I started working for Aprilia!

Jan Thiel a écrit:: ...I would not know any way to calculate this! Maybe Frits does?
It was done by 'just' grinding until the best result was obtained. The best way in my opinion. Because even if you calculate something you would still have to test it! I would never trust 'just a calculation'! And I have more trust in logical thinking!

Yes, I like to think I do. But it is not something I will explain here; gas dynamics are too complicated to 'teach' via a forum.
Like Jan, I am very much aware of the limitations of any theory. Before you start calculating, try logic.
I used the analogy of the bicycle pump that Romeuh80 refers to, as an example to help you imagine what happens in an exhaust pipe. You do not need any calculation skills to understand that, just a bit of logical thinking.

this is the design of my cylinder, the exhaust port is oval shaped and 13mm large in the minimum section...

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Thank you for sharing!

1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 15 771973

1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 15 771973

Marc a écrit:: Thank you for sharing!

X2, Thanks for your help.

Great, thanks Wink

Jan, Frits, How mutch losses are there in chain transmission?

Is there mutch difference between one 520 and a 420 chain? Besides the reduced wheight?

And from 420 to 415, still worth the change?

Thanks

Nombre de messages : 112 Localisation : Germany Date d'inscription : 07/02/2012

@SB07: for which engine is this cylinder?

Nombre de messages : 9 Localisation : Croatia Date d'inscription : 15/06/2011

Hi (again :),

by reading some informations few weeks ago by Mr. Thiel, he wrote that:

- they produced cca 300 cylinders per year. Why so many? How many bikes were supported? By considering fact that there was no much interest (or money) for development (team wins already), and other fact that there were no or little seizures (normal wear could be compensated by piston size - far cheaper than cylinder), it would be intresting to know why so many cylinders per year? And, speaking of cylinders, what was "life" of cylinder and why they were replaced (excluding seizures)?

- replating was almost never good as original one: have you considered why? due to fact that replating factory is not good, or thermal characteristic was not same, or something else?

Thanks,
Tomi

koenich a écrit:: @SB07: for which engine is this cylinder?

Minibike engine 1973 - [GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 2) (Locked) - Page 15 771973

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Tomi a écrit:: Hi (again :),

by reading some informations few weeks ago by Mr. Thiel, he wrote that:

- they produced cca 300 cylinders per year. Why so many? How many bikes were supported? By considering fact that there was no much interest (or money) for development (team wins already), and other fact that there were no or little seizures (normal wear could be compensated by piston size - far cheaper than cylinder), it would be intresting to know why so many cylinders per year? And, speaking of cylinders, what was "life" of cylinder and why they were replaced (excluding seizures)?

- replating was almost never good as original one: have you considered why? due to fact that replating factory is not good, or thermal characteristic was not same, or something else?

Thanks,
Tomi

A 125 rider had 2 bikes and 2 spare cylinders, that makes 4 cylinders per rider.
There were about 20 Aprilia riders in GP's, that makes 80
A 250 rider had 2 bikes and 3 spare cylinders, 7 per rider.
With 20 riders that means 140 cylinders.
Now we are already at 220.
Then there were various national championships in many countries.
We could never make enough cylinders!
Plating and replating was always done by the same factory, called Tecnol.
Removing the old nikasil causes some aluminium to be removed also, not good!
So the more often a cylinder is replated the worse it becomes.
The 'life' of a cylinder depends on how it is treated, it can be more than 2 years.
But some teams, mostly the slowest, had many seizures.
The best 'crew chiefs', Brazzi and Sandi, never had any seizures!
Development was continuous.
Cylinders from works riders were sometimes replaced by better ones.

Dear Frits, Jan, Grahamb and Friends!

I’m Balázs from Hungary and I have been tuning Simson 2T engines for a few years as a hobby. I'm glad to be here, and if you don't mind I would ask some questions, as I need some technical advice. Hope you are willing to help! Thanks in advance!

B.

I'll do what I can, but I don't deserve to be put in the same line as Frits and Jan ! lol!

GrahamB a écrit:: I'll do what I can, but I don't deserve to be put in the same line as Frits and Jan !

Hello GrahamB!

Thank you very much for the answer. I would start with my latest problem. There are exhaust auxiliary ports and they have their own angle which will define the direction of the exhaust gas's flow, in other words the real surface of the auxiliary port. I attach some drawing. On the A and B drawing you can see that the width of the auxiliary ports are the same, but the direction of them are different, so the width of the flow is also different.

All of these are important because they influence the 'time-area' of the auxiliary port, and also determine the sizing of the auxiliary passage. My problem is that if the area of the auxiliary passage is smaller than the auxiliary port's flow area then what will be the real area (or capacity) of the auxiliary port? (C drawing)

Hope you can understand what I'm tring to say, but my professional vocabulary is a little bit poor, excause me about it.

B.

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Dernière édition par Jan Thiel le Jeu 1 Nov 2012 - 5:30, édité 1 fois

Solution A is the worst, and B the best.
But sometimes C is the only possibility, due to the cylinder stud holes.
You can try to make the passage a little bit higher internally.
So that you maintain the same surface.
But this may be limited due to the transfers.
Sometimes it is really better to have a central bridge.
Surely auxiliary ports gives the best HP!
But only if you can make them as big as necessary!

Nombre de messages : 60 Localisation : australia Date d'inscription : 01/06/2012

Im sorry if this has been asked before but what gearbox oil did you run and did you dyno test other oils to arrive at your choice of oil. The same question regarding two stroke oil

We used AGIP fuel and oil.
But many other makes were tested.
There were no big differences.

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