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

Manuel Rainer a écrit:

hi

Frits or Jan what is the best surface for a con rod? polished, grinded, grinded and than sandblasted, only machined?
how was the RSA cod?

and what was the optimal water temprature for the RSA

thanks Manuel

Aprilia conrods were polished.
We tried lowering the temperature to 45°.
That gave the best result.
Lower temperatures would have been better I am convinced.
But they were not tried.
We tried from 90° to 45°
Every 10° lower meant about +1 HP

hi jan. i dont know much of con rods but i see most standard rods are shotpeened. is that not necesarry or polishing is good enough ?

Dear Jan,

In regards with temperature and cooling system i remember that you said didn't find a good enough pomp : How did you determine the flow you need ?

Thank you for all you do for the 2 strokes addicts   

Anyone have an idea why thrust washers breaking/coming apart.
Seems it doesnt matter if there is .55mm of crank float or
.2mm. Some do not seem to be getting that hot.
Left side always looks new, right side is always literally gone
most times spread thru out engine.





After looking into this some more it has more heat on this side than I thought.

Whats the best clearance from the washers to the rod ?

Hello Jan,

it's been great to read yours and others experiences regarding twostroke tuning.

Although the Aprilia's were considered the standard which others were judged by, Honda did win the final 250 season with Aoyama. I was personally rooting for him big time, but any thoughts to that season?

Was it a case of Honda building a bike that rivalled the Aprilia, each having their own strengths? Or was the Honda outclassed in handling, power characteristics and Aoyama just rode really well?

scottydog a écrit:

Hello Jan,

it's been great to read yours and others experiences regarding twostroke tuning.

Although the Aprilia's were considered the standard which others were judged by, Honda did win the final 250 season with Aoyama. I was personally rooting for him big time, but any thoughts to that season?

Was it a case of Honda building a bike that rivalled the Aprilia, each having their own strengths? Or was the Honda outclassed in handling, power characteristics and Aoyama just rode really well?

Aprilia riders crashed too many times, that's all.
Especially Bautista!
If I remember well he crashed no less than 5 times.
And Simoncelli started the season with a broken wrist.

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In this drawing is visible a restriction, something like a de Laval nozzle, I presume. What is the impact of this restriction on the operation of the engine? To understand. This type of restriction only improves the high revs only or even the middle revs? Thanks in advance for any response.

{mRk} a écrit:

In this drawing is visible a restriction, something like a de Laval nozzle, I presume. What is the impact of this restriction on the operation of the engine? This type of restriction only improves the high revs only or even the middle revs?

The 23,25 mm restrictor between the end cone and the tailpipe serves to close the reflector area as much as possible for a more effective pulse reflection. The tailpipe and the perforated silencer tube are wider than the restrictor, so the influence of bends, dents and carbon deposits in these tubes is reduced.
The restrictor diameter also influences the average pressure in the exhaust pipe. A larger diameter gives a lower average pressure, hence more expansion of the exhaust gas, a lower gas temperature, a lower velocity of sound and a lower resonance frequency that is suitable for lower engine revs.
I designed a variable flow restriction but it was never used because two-strokes were banned from GP racing.

Thanks, the explanation is clear and precise.
I will start to experiment with de Laval inserts. I will use the exhaust that I have already realized increasing the internal diameter of the tailpipe from 24mm to 26mm.
In addition, I will work on the energy of spark, perhaps reducing the spark energy will help me improve the high revs extension after the maximum power.

if you want more over rev, i'll have to reduce the advance to keep more heat in your pipe

[When the radial clearance of a conrod is not enough the rod Always tends to move to 1 side, 2stroke or 4stroke.
Enlarging this radial play solves this problem. The only proper way to do so is by honing the bore of the conrod somewhat larger.
For a high revving 125 I prefer a radial clearnce of at least 50 mu. I also favour the so called top guiding of the rod in the piston. Machining the rod width inside the piston can be achieved by milling on a vertical mill. The needle bearin needs positioning by means of washers/shims of high grade aluminium like 7075/ T6.
This means that no more side washers are required on the bigend. Also here the bigend needle cage needs positioning in order to prevent the cage from walking.
Summary :

less friction because of rubbing and consequently a lower bearing temperature.





quote="mxer"]Anyone have an idea why thrust washers breaking/coming apart.
Seems it doesnt matter if there is .55mm of crank float or
.2mm. Some do not seem to be getting that hot.
Left side always looks new, right side is always literally gone
most times spread thru out engine.





After looking into this some more it has more heat on this side than I thought.

Whats the best clearance from the washers to the rod ?[/quote]

Stephane a écrit:

if you want more over rev, i'll have to reduce the advance to keep more heat in your pipe

Thanks, I know this. Thanks, I know this. I use several Zeeltronic programmable CDI, advances ignition are ok.
But I want to try other ways, I want to do even better. I want to work first with the inserts de Laval. I'll tell you how it goes.

, a lower gas temperature, a lower velocity of sound and a lower resonance frequency that is suitable for lower engine revs.
I designed a variable flow restriction but it was never used because two-strokes were banned from GP racing.[/quote]
Ciao Frits, modify gas temperature was the reason for shielding pipes with alutape?

hey frits let me ask something. i been reading of the coanda affect trying to understand it better. aparently the smoother the surface is the better the mixture can stick to the inner wall as it passes over it. do you know this to be true ? so what wall surface texture was used on the rsa125 transfer ducts ?  also do you know what the sharpest radius of the inner wall is, at the moment when detachment starts to happen or is there too many variables to say a exact answer ?  thnx

brokedown a écrit:

hey frits let me ask something. i been reading of the coanda affect trying to understand it better. aparently the smoother the surface is the better the mixture can stick to the inner wall as it passes over it. do you know this to be true ? so what wall surface texture was used on the rsa125 transfer ducts ?  also do you know what the sharpest radius of the inner wall is, at the moment when detachment starts to happen or is there too many variables to say a exact answer ?  thnx

Scalabroni explains Coanda

Filandro a écrit:

modify gas temperature was the reason for shielding pipes with alutape?

Yes. But the main purpose of the carbon heat shield around the upper part of the RSA125 exhaust was not to keep the heat in the pipe but to shield the crankcase from the exhaust heat.
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brokedown a écrit:

i been reading of the coanda affect trying to understand it better. apparently the smoother the surface is the better the mixture can stick to the inner wall as it passes over it. do you know this to be true ? so what wall surface texture was used on the rsa125 transfer ducts ?  also do you know what the sharpest radius of the inner wall is, at the moment when detachment starts to happen or is there too many variables to say a exact answer ?

The coanda effect depends on the fact that air cannot enter between the flow and the surface that it is flowing over. Then the atmospheric air pressure at the outside of the flow pushes the flow against the surface, even if that surface is bending away from the flow.
Ripples in the surface may cause a detachment of the flow and once that happens, air can enter the gap and the coanda effect is lost. So the most important aspect is a smooth surface without sudden steps or hollows; in short: where there is never a sharp deviation or a small radius anywhere. A high polish is not necessary.
I cannot tell you below which radius detachment starts to happen because flow density, flow velocity and pressure at the outside of the flow play a big role. If you want to delve deeper into this, you should talk to an airplane designer.

 

Like "Marc" +1.Thanks very,very a lot.Zeze

Hi
One question to the RSA Disc Valve

Jan or Frits, in the PDF from Aprilia called "Tracciatura e taglio valvola rotante" there is how to cut and set the disc valve of the RSW. the timings (Opens: 142,5 before T.D.C. Closes: 88 after T.D.C) are different then the (Opens: 146 before T.D.C.  Closes: 93 after T.D.C) from RSA.
are this only old informations, or where they always differend settings? and why?


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and have you ever tried to cut the closing part of the disc like in the photo? the timing is the same but der is a improvemend of opening area

thanks Manuel

Manuel,

We have gone to the longer disk valve timing with good results. It seems to me that this works well with the longer connecting rods now being used along with the increased exhaust port time area now being run.

Manuel Rainer a écrit:

Hi
One question to the RSA Disc Valve

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and have you ever tried to cut the closing part of the disc like in the photo? the timing is the same but der is a improvemend of opening area

thanks Manuel

This is clever. Has anyone tried it? I guess it would snap the port closed very suddenly compared with the square cut disc. Could this cause shock waves or other gas flow disturbance?

Hi everyone, I have been reading my bum off to get to this page.It has been great reading dispite the translator.
I have not seen much much discussion on disc valves and would like to understand if possible how the different shapes might influence h.p and torque.Max

Hello.

I've got a little question to brokedown, Ian Harrison, Dave Pearce and all the others who might have experiences with it.

Could you please tell me something about the durability of Devcon Aluminium Putty when used in transfer / exhaust ports? (several years?)

Thanks. Regards.

Daniel A. a écrit:

Hello.

I've got a little question to brokedown, Ian Harrison, Dave Pearce and all the others who might have experiences with it.

Could you please tell me something about the durability of Devcon Aluminium Putty when used in transfer / exhaust ports? (several years?)

Thanks. Regards.

Transfer ports are no probelms not so good in exhaust ports , Belzona might be better for that.

lodgernz a écrit:

Manuel Rainer a écrit:

Hi
One question to the RSA Disc Valve

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and have you ever tried to cut the closing part of the disc like in the photo? the timing is the same but der is a improvemend of opening area

thanks Manuel

This is clever. Has anyone tried it? I guess it would snap the port closed very suddenly compared with the square cut disc. Could this cause shock waves or other gas flow disturbance?

I tried this in 1970, but it did not give any advantage.