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

I have a query I would like to discuss.
On some two strokes the bottom of the transfer tunnel is flat then changes to go up the out side wall. So basically it goes straight out from the crankshaft and then does a 90 and goes up the transfers, Others go up at an angle straight off the cranks shaft, I can only think certain shapes are for different power spreads. Did you play with that much on the rsa engine ??

No, not at all!
The transfer passage in the crankcase has not so much importance.
So we made a nice big radius and never changed it!

We never broke any pistonrings!

Do you have a picture of the cases on the aprillia showing that, Im just building up a tough 50cc scooter for a race we have. Im looking at all different ways to try and get the last little bit out of it.

I would be interested to know if you ever played with ceramic bearings as well. I think they are sold as the 2nd coming but not really sure if they are worth the money

Thanks heaps.
Oh and nice family by the way. I to have an asian wife, Japanese. Life is so much easier with a asian lady

wax a écrit:

Do you have a picture of the cases on the aprillia showing that, Im just building up a tough 50cc scooter for a race we have. Im looking at all different ways to try and get the last little bit out of it.

Do you mean this?
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But like Jan said, that is not the place to look for big improvements.

Yes like that,
Thanks im not going to do much more than just a clean up in there. But just good to see what was done.
Thanks Jan and frits its awesome to be able to talk to two guys who have been there done that.

wax a écrit:

Im a kiwi living in australia...

Then you might feel right at home here:
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Just have a look, have some sleepless nights .

Far to cold to live there, even going on there web site made me feel cold

"The amount of material between the auxiliary exhaust ports and the A-transfers in the Aprilia cylinders is minimal too, as you can see in the picture below. Only the rear part of the aux. port bottoms is raised; too close a proximity would enhance short-circuiting via the piston pin bores. Apart from this, the aux. ports have solely been designed for optimum blowdown time.area." [/quote]

Thank you for your FritS I appreciate being able to ask you and Jan these questions.
As the RSA did use a piston pin with end caps; were there any experiments to find the limit of extending the sub ports further to increase power. I was wondering how one requirement such as blowdown time/area can be balanced against disturbing or mixing the returning exhaust /escaped charged with the main centre column of new charge. I thought that the higher rear part of the sub ports might have been to this end?

"Covering the crankshaft is unnecessary when the crankshaft rotates with the flow. When it rotates against the flow, covering is somewhat helpful but it will not cancel the negative effect and it also is disadvantageous to the lubrication of main and big end bearings." [/quote]

Does the rear transfer port benefit from the crankshaft rotation when the crankshaft rotation is as in the RSA. The Japanese use a smaller area rear transfer but the RSA is much larger; do you know why this is?

I hope you do mind my many questions but it is so good to have knowledge gentlemen like yourselves and others that I must take the opportunity while it is available.

The pressure waves and flow within a 2 stroke exhaust pipe travel in both directions and respond to the chances in the angle/ area of the pipe as they go. What is a diverging cone while the waves are leaving the exhaust port becomes a converging cone on the return journey; how do you arrive at the best balance between suction frequency / amplitude and pressure frequency / amplitude.

Many thanks in advance.

I would love to answer all your questions now, GtG001, but there is a life outside the WorldWideWeb and my presence is required there.....

Here is a jetski engine I built for my race ski, Im not trying to go off topic but i thought you would like the induction system

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Frits Overmars a écrit:

I would love to answer all your questions now, GtG001, but there is a life outside the WorldWideWeb and my presence is required there.....

Hi Jan and Frits,
To gain the high compression (18:1) that you were running with leaded fuel on the RSW/A, I imagine that you had to have about 7.3cc in the head volume. As the bowl would have been about 42mm (?) the spark plug must have been closer to the top of the piston than it is with unleaded; did this create any problems with localized hot spots on the piston? Can you elaborate on the relationship with head volume and the spark plug depth into the chamber, and the problems that need to be avoided?

Thanks for your answer in advance.

Oh, by the way, Skippy has been to the gym ...

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We only used unleaded fuel in the RSW after 1997.
In the RSA leaded fuel was never used.
Compression ratio was 1:16 without any problems.

Jan Thiel a écrit:

We only used unleaded fuel in the RSW after 1997.
In the RSA it was never used.
Compression ratio was 1:16 without any problems.

Thanks Jan,
Frits has told us that you ran some test with different radius’s between the squish band and the chamber but that you found that the best results were with virtually no radius.
Can you tell us more about this please?

There is not much to tell: we tried different radiusses and the best result by far was without any radius!

Frits Overmars a écrit:

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Jan or Frits,

I am interested to know details about how to dress the port edges. What are the most important things to know to avoid ring clipping? Do the vertical edges have a different (sharper) form than the timing edges? Do you make it more like a round or more like a chamfer?

What about before plating? Is any special care taken to round the aluminum edges to avoid concentrating the electrical flux that would build too much coating on the edge?

Finally, what is the best honing texture to use? Do you do a simple peak hone at a fine roughness like 0.1µm Ra, or is it rougher like 0.4 µm, or is it a plateau-valley texture?

This message is for Jan regarding the location and the shape of the inlet port on the RSA.
I see you designed the RSA with the inlet port located vertically centered on the cylinder.
Did this give any gains versus the port located on the side?
The valve shaft is also located inline with the horizontal center of the port.
Does the plate close the top or the bottom of the port?
ie does it spin clockwise or counterclockwise when looking at the outsifde of the plate.
Would it make any difference if it spun in either direction?
I think the RSW motor has the shaft located below the port closing it from left to right or vice versa. It would make sense to me that the plate would be best to rotate counterclockwise closing at the top and opening at the bottom.
What are your thoughts on this?
Thanks

Somes made a copy of the rsw for a scooter, Would love to know what frits and jan think of this

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Frits Overmars a écrit:

wax a écrit:

Do you have a picture of the cases on the aprillia showing that, Im just building up a tough 50cc scooter for a race we have. Im looking at all different ways to try and get the last little bit out of it.

Do you mean this?
[Vous devez être inscrit et connecté pour voir cette image]
But like Jan said, that is not the place to look for big improvements.

Looking at this picture, I am wondering if the inlet port blends into the transfers, or if it just goes straight in?

The inlet port did not blend into the transfers.
It is one of the things I would have liked to try!
It may have been done after I left.

wax a écrit:

Somes made a copy of the rsw for a scooter, Would love to know what frits and jan think of this

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

Nice engine, but I do'nt like the cylinder too much.
Why 3 C-ports?

Howard Gifford a écrit:

This message is for Jan regarding the location and the shape of the inlet port on the RSA.
I see you designed the RSA with the inlet port located vertically centered on the cylinder.
Did this give any gains versus the port located on the side?
The valve shaft is also located inline with the horizontal center of the port.
Does the plate close the top or the bottom of the port?
ie does it spin clockwise or counterclockwise when looking at the outsifde of the plate.
Would it make any difference if it spun in either direction?
I think the RSW motor has the shaft located below the port closing it from left to right or vice versa. It would make sense to me that the plate would be best to rotate counterclockwise closing at the top and opening at the bottom.
What are your thoughts on this?
Thanks

A horizontally shaped inlet port would have meant a MUCH bigger inlet valve diameter!
The inlet valve spins counterclockwise, so it is opening at the underside.
Just like the carburetor!

Brian Callahan a écrit:

Frits Overmars a écrit:

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Jan or Frits,

I am interested to know details about how to dress the port edges. What are the most important things to know to avoid ring clipping? Do the vertical edges have a different (sharper) form than the timing edges? Do you make it more like a round or more like a chamfer?

What about before plating? Is any special care taken to round the aluminum edges to avoid concentrating the electrical flux that would build too much coating on the edge?

Finally, what is the best honing texture to use? Do you do a simple peak hone at a fine roughness like 0.1µm Ra, or is it rougher like 0.4 µm, or is it a plateau-valley texture?

The ports had very small chamfers.
The exhaust port had a radius at the top, but this was more for the flow and not to avoid ring clipping.
We never had problems with the piston rings, the central exhaust port was not so wide.
Plateau honing was used.

Jan Thiel a écrit:

wax a écrit:

Somes made a copy of the rsw for a scooter, Would love to know what frits and jan think of this

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

Nice engine, but I do'nt like the cylinder too much.
Why 3 C-ports?

I see alot of cylinders like that, I thought it was to bring up transfer flow. Would you rather just one c port and wider b ports ??

Yes, a wider B-port flows much more than a wider C-port.
Because of its inclination!