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

Jan what kind of 2-stroke oil did you find worked best and what ratio for the mixture? We have used several products including Amsoil, Lucas, Samurai at ratios from 20-1 to 100-1. There is a debate that more oil makes more power due to better sealing but I am skeptical. To me more oil means lower octane.
Also what fuel did you find made the best power with enough octane to prevent detonation? We have access to VP and Sunoco race fuels. Unfortunately there is not Elf distributor in Canada.

Howard, we tested various oils and fuels, there was not much difference.
I think they were all 'copied' from ELF.
1:20 was used, we tried more and less oil: no big difference!
Long ago, at Bultaco, I tested Bell Ray oil 1:50.
The result was 2 seized big-ends in 1 day!
Later we used MOTUL with very good results.
We were using pump fuel in those days.
In Spain there was pump fuel of 98 octane.

Did you try any other piston top designs?

Jan Thiel a écrit:

Long ago, at Bultaco, I tested Bell Ray oil 1:50.

Ah! Belray MC-1 was very good for big-end seizures! I also discovered Shell XP-1 was very efficient at wearing out cylinders...

XpTpSMTT a écrit:

Did you try any other piston top designs?

Yes, partially flat pistons were tried without succes.
Pistons with a radiused edge looked fantastic at the flowbench.
But gave no more power.

Mr Thiel,do you think variable crankcase volume would solve any issues?
eg.higher primary compression at part throtle.
Was some form of variable transfer port height tested or too complicated?
I noticed a allen bolt on the cylinder behind the rear port just above the rotary valve
what purpose does it serve?

XpTpSMTT a écrit:

Mr Thiel,do you think variable crankcase volume would solve any issues? eg.higher primary compression at part throtle.
Was some form of variable transfer port height tested or too complicated?
I noticed a allen bolt on the cylinder behind the rear port just above the rotary valve. what purpose does it serve?

Allow me to answer this, as Jan is probably fast asleep now because of the time difference.
A variable crankcase volume would give a higher primary compression ratio, not a higher compression pressure at part throttle, as there is hardly anything to compress in the crankcase if it has not been inhaled by exhaust pipe suction first.
Variable transfer port height was not tested. As I wrote the other day, I would love to employ it, but I see no simple way of implementing it.
The bolt above the C-port valve is just an air bleed bolt. It is unnecessary on the RSA125, but these cylinders were also fitted to the RSA250 and there the lower cylinder needed it.

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Thank you Frits and Jan for contributing so very very much! I have gone back and forth re-reading both part 1 (at least, the English parts!) and part 2 of this great thread. This has become a really great resource for many aspiring tuners! I appreciate you sharing your knowledge.

In reading around, I found this:

Citation :

Dears Colleague, Racers, and Constructors
We are pleased to invite you to a workshop dedicated to the institution of a new world
championship motorcycle racing series for pure prototypes concerning 50 - 125 - 250cc
engines; particular attention will be focused to ecology. This meeting will take place in Rome
on 2 April 2011 at 9:00 am at the Marriot Roma Airport Hotel, at walking distance from the
Fiumicino airport.
We will set out the project in detail and a part of the conference will be devoted to technical
suggestions from potential participants for the final draft of the technical regulation.
Speakers of the day will be:
Franco Barazzutti (creator and director)
Luigi Favaro (vice president UEM)
Jan Thiel (engine designer and constructor) exclusive interview recorded from Thailand
Joerg Moeller (engine designer) To be confirmed
Gabriele Gnani (motorcycles constructor)
Mike Austin (engine designer)
At the event attend Dolph Van der Woude (engine designer)

I know it's off topic, but curiosity has the best of me. Was Jan's interview in English by chance? Is it available anywhere? If not in English perhaps it can be sub titled?

On to a somewhat on-topic question - Did you find any certain difficulty with the manufacturing process of having a cylinder made that required touch-up porting when a cylinder arrived to you? Were there any certain tolerances that were difficult to keep out of the mold?

Best Regards from the United States,

~Josh

Hello Josh,

The interview was in Italian, and is not available anymore, sorry.

At Aprilia we made our own molds so if there were any problems they were immediately corrected.
After some little problems in the beginning we never had any problem any more
The cylinders were cast to very close tolerances.
We went to a very good foundry which also cast the 12cylinder Lamborghini cylinderheads.
Some month's ago it was destroyed by an earthquake!

We always sent our cylinders to Germany for 'Hipping', with excellent results!
We never had any scrap.

Jan,
At what point is made "hipping"?
Before or after the heat treatment?

Francis, the hipping is made before heat treatment.

Jan,
Sorry, my question is incomplete the "Hipping" is probably done after a roughing machining close to the finished dimension ?
Thanks again

No Francis, they were done before any machining

So the steps are:

1. Casting
2. HIP Treatment
3. T6 heat treatment
4. Machining
5. Nicasil plating

Right?

Francis, peux tu expliciter en français la terminologie de "hipping" , please

Yes Mic, that is right!

Plus exactement HIP en anglais: Heat Isostatic Pressing, en francais: CIC Compression Isostatique à Chaud. C'est une opération qui consiste à faire pénétrer à haute température, sous haute pression dans une pièce de fonderie, un alliage à base de zinc destiné à combler toutes les porosités de manière à densifier l'alliage d'origine.

More precisely: HIP Heat Isostatic Pressing. This is an operation which is to penetrate at high temperature under high pressure into a casting, an alloy of zinc intended to fill all the pores so as to densify the original alloy.

Thank you guys, we will die less stupid!

Most fascinating topic ever !
It allows me for the first time (and probably many others on Pit-Lane were in the same situation) to get a little hint of the huge amount of work and skills that is behind the manufacturing of an engine.

@Francis -> I don't think zinc is part of the HIP process.

Only argon gas together with extreme pressure and high temperature. This combination closes any small holes and pores in the casting.

That's right, Mic.

[Vous devez être inscrit et connecté pour voir ce lien] (sorry, it's in English).

Frits thank you for your reply,
but i dont get what you need an air bleed bolt on the bottom cylinder.
the "+8"?

Because the bottom cylinder is upside down, there would be a pocket of air trapped in the highest point of the water jacket, if there wasn't a way to bleed it off.

So the 125 & 250 cylinders were identical? Did the 250 make exactly twice the power of the RSW125, or did they never run the same cylinder with the same intake arrangements?

Because the water outlet in the cylinderhead sits lower than the inlet at the bottom of the lower cylinder an the RSA250. On the top cylinder the bleed screw isn't needed because here the outlet is at the highest point.

N.B. The +8 means that the cylinder is 8 micron above nominal size ( Ø54,000 ) so the cylinder on the picture has a Ø54,008 mm. bore.

@GrahamB -> Yes the RSA250 used the same cylinders as the RSA125. But the 250 had side mounted rotary valves like the RSW250 and RSW125.

The RSA250 didn't produced twice the power of the RSA125 due to a couple of setbacks.

1. unsymetrical flow into the crankcase because of the side mounted rotary valve.

2. The old RSW250 used the top crankshaft to run the inputshaft of the gearbox. The RSA250 had a higher mounted output shaft in the gearbox which required the lower crankshaft to drive the inputshaft. This then required the need for reversed crankshaft rotation which lead to a powerloss. This loss was then compensated by exchanging the RSW250 cylinder ( type APE ) with RSA125 cylinder ( type APF )

The higher mounted output shaft allow the frame designers to make some handeling improvements. Lower mounted engine I guess.

I think a RSW250 with APF cylinder ( not possible due to different mounting hole pattern ) would have performed very similar to the RSA125 x2. Or of course a RSA250 with the right crankshaft rotation.

Jan please correct me if I'm mistanken.

If you're good at Italian RSA250