[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 5)

Hi Frits,

i've got a question about the power valve of the RSW.

My engine got originally pneumatic activated power valve (RAVE)
Due to the disadvantages of the pneumatic i build my own, electronic activation. (2-step)
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The servo is Honda NX5.

Here you wrote about the guillotine shaped exhaust valve of the RSW.
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Can you tell me about the opening rpm in the Aprilia RSW?
Best regards,
Bernd

Döllinger a écrit:

Here you wrote about the guillotine shaped exhaust valve of the RSW.
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Can you tell me about the opening rpm in the Aprilia RSW?

It started opening at 10.000 rpm and was fully open at 12.000 rpm.

Hi Frits,

thanks for your information. When you see my slides; you think that is comparable to the RSW system?
I never saw an Aprilia slide in real life.
Best regards,
Bernd

Döllinger a écrit:

Hi Frits, thanks for your information. When you see my slides; you think that is comparable to the RSW system? I never saw an Aprilia slide in real life.

Here you go Bernd: the twin-blade Aprilia power valve.
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Rendering by GighenZz Marco

Hi Frits,

the slides don´t look that much different.
Of course the Aprilia activation is much smaller, but not applicable on my cylinders.
Thank you very much for the efforts!

The gear housings were welded yesterday.
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Best regards,
Bernd

Nice work !

Good evening everyone !

I have 2 questions for Frits: from your explanation based on the "Pisa tower" concept, it appears that we need to give some axial angle to the transfer channels, and that the A need to have way more than the B.
I have an old 125 TZR that I use some times on the racetracks.
To my surprise, the transfer channels of the stock cylinder show exactly the reverse: the A have a small angle and the B are angled much more upwards. Do you think it is really catastrophic or may I do something to improve the situation and still use this cylinder?
I also have a Suzuki 125 TSR, and it has a flat top piston, which I understand is not ideal (unfortunately there's no possibility to get a domed one). The transfer ducts have no upwards angle. I understand that I may need to change this to get some angle. What do you think would be a correct upwards angle to both avoid slowing down the transfer streams too much and keep some fresh gas close to the top of the flat top piston?

Carlo, correcting the axial scavenging angles on that TZR 125 cylinder would certainly improve it, but I don't know if there is sufficient material in the right places to carry out that improvement.
The flat-top piston in your Suzuki will not make much difference for the optimal axial scavenging angles. All I could say about these angles, I have already said in the 'Tower of Pisa'-story; I would only repeat myself here. But how hard can it be to find a domed piston with the correct bore and pin diameters for that engine?

Thanks for your replies, Frits !
The point is that I will certainly not have enough material to completely correct the TZR cylinder.
I certainly can give more angle to the A ports, but probably not correct the B ones in sufficient proportion. Do you think having both A and B with about the same angle will make things worse or improve?

About the Suzuki, I checked all the pistons catalogs I could find, at the moment I did not find something satisfactory (bore is 56mm, with a 54 it would certainly have been much easier), I have trouble to find one with an acceptable crown height but will go on.

carlovitch1 a écrit:

Thanks for your replies, Frits !
The point is that I will certainly not have enough material to completely correct the TZR cylinder.
I certainly can give more angle to the A ports, but probably not correct the B ones in sufficient proportion. Do you think having both A and B with about the same angle will make things worse or improve?

About the Suzuki, I checked all the pistons catalogs I could find, at the moment I did not find something satisfactory (bore is 56mm, with a 54 it would certainly have been much easier), I have trouble to find one with an acceptable crown height but will go on.

You don't make it easy for me Carlo. "the A have a small angle and the B are angled much more upwards" is not exactly numerical information, so you ask me to gamble with a cylinder that I do not know. But I suppose you could give the A-transfers a 15° axial angle and make the axial angle for the B-transfers as low as material will permit.

You wil find more options for your Suzuki piston if you remove the compression height from your wish list. You can correct this dimension with cylinder base gaskets, or by removing base material from the cylinder, although I would not do this as a first step.

Sorry for my imprecision, Frits.
The TZR cylinder A transfer port channel is almost flat, I would say somewhat 5° upwards, as the B is 20° upwards. In the meantime, I could measure deeper and there's enough material to make the A at 15° and the B lowered to 10-15°. Would this work better?

About the piston, I also found in the Mitaka catalog that the Kawasaki KR1S 250 model may fit on the Suzuki with a small plate under the cylinder and of course some head machining. My concern is more about ringpeg position: all the pistons I see which may work with some adaptation have a way wider one (like 14mm for my original 10mm for the KR1S). I know some guys who have managed to re-locate the ringpeg, but I feel it quite risky with my actual skills and equipment. I still need to think about it to decide whether I try or not.

KR1S piston has holes in it's skirt to lube the exhaust bridges, they will also have to match or you'd need to fill them.

Thanks for info JanBros. This worries me less because it is also the case on the 125 TSR piston.

quelqu'un reconnait ces échapement ?

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ils avaient un étiquette "KR1" mais le support au midi de l'échapement est faut  et la spipe-sortie est trop bas pour un KR1

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on peut pas le monter sur un KR1 (ça manque pas grand chose) mais aussi le support est complètement faux



ils sont "after market" et tres légère