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

Happy Birthday Jan

happy birthday and thank you!

Happy birthday Mr Jan and long live for you and your family.A lot of thanks for your contributions (and Frits...)in this forum.Zeze

Happy birthday to you, Jan!

Ian Harrison a écrit:

Hi Jan

Thanks for that info and the inserts are marked MW25, so indeed leaded as suspected. I am familiar with the AC designation as this was also used by BRC on their tandem twin engines that we raced for a few years.

Lozza, I checked the rotor and it is only marked with what I presume is a part number: 032000-2201 and seperately 10P.

The owner found a picture of a system off a 1998-2000 RSV, which looks identical (apart from it has the dash with it), so at least I can now assume that it is the standard issue Aprilia Kit of the time.

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I'll post up some more images on Monday, but for now I'm busy getting ready for a race meeting at Donington Park this weekend.

Best Regards

Ian

Hi Ian, the rotor number is the std ND number for the rotax 128/129/130/256/258 and the 4 bolt back plate is the later 258 style stator plate. Not sure if the cdi box is Aprilia as the connectors look the same as the Honda RS125/250 hopefully someone will be able to confirm. Yes you are missing the trigger cup which I just happen to have one sat on the bench here at work. The engine is more than likely the rotax258 which I have the parts manual for. The cylinders are the same as the 129 rotax. It is possible to identify the engine by the disc valve hub splines.
regards
Phil

Happy Birthday Jan

Thank you for sharing your knowledge on this forum. I know that we all appreciate it!

Thanks a lot for the birthday wishes!
It was the happiest birthday I ever had.

Happy belated Birthday, Jan!

And another late Happy Birthday, Jan, and all the best to you and yours.

Ian I suspect you will be able to trig that CDI with a standard yamaha trigger as widely used on both street and race 2 strokes from the '80s and 90s, it looks to be the same and the same goes for the valve servo pictured.

I however doubt it has a direct input for a knock sensor, but this is just a guess, it's more likely to have had an aamplifier/filter/converter in the form of a now missing small box that would transform the deto signal in a DC level(probably 5V)and that would be the fed to the CDI box to back off timing lead.
Like I said this is only my guess but is based on how things were generally done back then.

I believe the best option to be to get a fully programmable up to date Zeeltronic ECU (keep the rotor) or similar to get the last pony out of that engine with safe and reliable energy/timing, should be easier and cheaper than recommissioning the original system?

Hi Guys

Phil, thanks for further info. I have the 258 parts manual in PDF.
It would be great if you could take the trigger cup to Silverstone this weekend (assuming it's for sale!!)
The disc valve splined shafts are 15mm dia and look like Rotax 256/FPE, rather than the larger diameter Aprilia/BRC type.

Motoholic, yes it would be very easy to fit a a varietyny of variety of modern ignitions, but there is a desire to keep it largely as original. This will be a serious race bike, but also a collectors/display item as well.

Best Regards

Ian

quote from Howard Gillford (Our engines have typically a 2 mm clearance (give or take for casting flaws) between the crank webs and the case. We tried closing the clearance between the crank and the case to .5mm by machining an aluminum plug that was exactly 1 mm bigger than the crankshaft and injecting epoxy to fill the void. It was a lot of work and did reduce the volume of the cases substantially but resulted in less power. We then went the otherway and machined a crankshaft down adding an extra 2 mm clearance on another case which gave now 4 mm clearance. It resulted in a small gain in power. My dilema is that we do not know if the reduction in power was a result of added viscous drag or as a result of tighter volume and was the increasein power as a result of the fact that inlet flow was less impeded by the crank web or was the added volume the cause. My recommendation for crankcase volume is bigger is better than smaller (in moderation) anything that adds extra airflow always adds power. A good airflow turbine is a great tool)

Has anybody seen crankshaft work with lose clearance around the web area.

By '2 mm clearance' I assume you mean 1 mm either side between crank and case, and 1 mm between outer crank radius and inner case radius. Viscous drag increases strongly below 1 mm clearance; enlarging the clearance beyond 1 mm has only a limited effect on viscous drag. So if increasing the clearances beyond 1 mm improves power, I would assume that this improvement was caused by the increased crankcase volume. It could also have been caused by improved inlet flow, but I cannot comment on that without knowing your engine so I will leave this aside for now.

The most striking example of crankshaft clearance I saw in the old Rotax-124 kart engine that I worked on from 1978 onward. It was really a 250 cc motocross engine with a 125 cc crank in it. If I remember correctly the case diameter was about 12 mm larger than the crank diameter! But it was easily the fastest engine of that era, and the most susceptible to tuning modifications. It was also the grandfather of the Aprilia RSW125 Grand Prix engine.

Hello. Although I'm not posting many posts on this forum, I regularly check it for the tons of good information that are shared. Along with the information, it's a great source of inspiration, enough to push forward the ideas I wanted to realize.
So here is the fruit of the effort from a year or so;

Done for scooter engines, Bore 52, stroke 47mm, 98cc
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Exhaust port, with some bridge area to spare. The boosters exit at an awkward angle, but that was necessary in order to avoid the cylinder studs (not yet drilled in this picture)
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The transfers, the B port was divided in two, again in order to avoid the cylinder studs.
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The B port is divided also on the crankcase side.
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There is some(lots) of porosity, but such were the first castings I did. In the latest casts I nearly got rid of it.

The many compromises that were done surely hurt some performance, but still the performance is really satisfactory for a scooter engine.
Anyhow, thanks everybody for sharing, especially thanks to Mr. Thiel an Mr. Overmars.

This porosity is normal with that technique

SB07; I got rid of most of the porosity in the latest casts. Melt temperature seems to play a key role, since hydrogen solubility increases with temperature.

Almost no porosity:
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It's also a different shape of exhaust port I want to try, hopefully it will improve peak power while reducing the bottom power (it's really cruel to drive the scooter with CVT with too much bottom power).
What do You experts think? Could this kind of exhaust port do that? The single central exhaust port opens much more gradually due to the larger upper radius.

crankshaft a écrit:

quote from Howard Gillford (Our engines have typically a 2 mm clearance (give or take for casting flaws) between the crank webs and the case. We tried closing the clearance between the crank and the case to .5mm by machining an aluminum plug that was exactly 1 mm bigger than the crankshaft and injecting epoxy to fill the void. It was a lot of work and did reduce the volume of the cases substantially but resulted in less power. We then went the otherway and machined a crankshaft down adding an extra 2 mm clearance on another case which gave now 4 mm clearance. It resulted in a small gain in power. My dilema is that we do not know if the reduction in power was a result of added viscous drag or as a result of tighter volume and was the increasein power as a result of the fact that inlet flow was less impeded by the crank web or was the added volume the cause. My recommendation for crankcase volume is bigger is better than smaller (in moderation) anything that adds extra airflow always adds power. A good airflow turbine is a great tool)

Has anybody seen crankshaft work with lose clearance around the web area.

      A good Primary Ratio is 1,45:1

SPEEDSLUT a écrit:

A good Primary Ratio is 1,45:1

How did you arrive at this value, Speedslut?
The Aprilia RSA125 has a TDC crankcase volume of 675 cc. That gives a primary compression ratio of 675 / (675 - 125) = 1,23. Rather different from your value....

Hi Frits, can you tell us the best method to measure crankcase volume?
The only way I imagine is using a dome drilled piston and adding ..what?petrol? alcool?
Thanks

Filandro a écrit:

Hi Frits, can you tell us the best method to measure crankcase volume?
The only way I imagine is using a dome drilled piston and adding ..what?petrol? alcool?
Thanks

I use a piston with a hole in the dome. Before I install the cylinder, I coat the bore with grease in order to avoid leakage via the piston/bore clearance onto the exhaust port and, if present, the inlet port.
Then I put the piston in such a position that the transfer ports are about to close, leaving just a tiny split for the air to escape. I measure the distance from this piston position to TDC and calculate the corresponding volume. Then I pour thin oil through the hole in the piston until I see the oil appearing at the top of the transfer ports. Finally I add the poured volume to the calculated volume.
For a reed valve engine you'll need to position the engine so that air in the reed cavity can escape. For a rotary valve engine you'll need to watch the direction of crank rotation so that the disk is closed. You'll also need to grease the disk cover to avoid leakage there.

husaberger a écrit:

Frits Overmars a écrit:

SPEEDSLUT a écrit:

A good Primary Ratio is 1,45:1

How did you arrive at this value, Speedslut?
The Aprilia RSA125 has a TDC crankcase volume of 675 cc. That gives a primary compression ratio of 675 / (675 - 125) = 1,23. Rather different from your value....

Would that not relate only to a disk valve? I have often seen it mentioned the optimum Crankcase volume would be smaller on a Crankcase reed. but i have never seen a definitive figure. If you or Jan recalls what were the volumes on the Rumi and the Derbi reed valve. I realise that you may not have the figures available......but a a rough guide would be helpful

I remember Jan saying that the crankcase volume of the Derbi reed valve engine was even larger than that of the rotary engine. And after Jan had laid his hands on it, that reed valve engine was the strongest 125 cc reed valver ever.
You see, the volumes of the transfer ducts and the volumes between the crank wheels and inside the piston are largely equal, and the volume of the reed cavity is a lot larger than the volume of a rotary inlet duct.

Fascinating how things can change totally during the years.
In the 80-90's many tuners were obsessed by reducing at least possible the crankcase volume, now we found it's the opposite.
Frits, in a cylinder-reed engine, how could I position the engine?
Or is better using an old reed valve with a hole in the top, to let air escape?
Thanks a lot again!

Filandro a écrit:

Fascinating how things can change totally during the years.
In the 80-90's many tuners were obsessed by reducing at least possible the crankcase volume, now we found it's the opposite.

Tuners have been trying to reduce crankcase volume since the beginning of time. I went the opposite way in the late 70's; some people still think I'm crazy .

Citation :

Frits, in a cylinder-reed engine, how could I position the engine?
Or is better using an old reed valve with a hole in the top, to let air escape?

With a cylinder-reed engine bleeding the air can be difficult because the cylinder should be vertical in order to offer the air under the piston a way out. A second hole in an old reed may be a solution but you'll have to make sure that none of the measuring oil will escape.

Frits Overmars a écrit:

some people still think I'm crazy .

But Frits, you're sure that relates to crankcase volume?

GrahamB a écrit:

Frits Overmars a écrit:

some people still think I'm crazy .

But Frits, you're sure that relates to crankcase volume?

Not solely, Graham. I've said lots of things that seem hard to swallow. Here is an anthology:

'The part of the exhaust port area beneath the transfer port level is a waste of real estate'.

'A high secondary compression ratio improves power in a four-stroke;
in a two-stroke with an efficient exhaust system it is the other way around'.

'Two-stroke rpm is limited by blowdown and scavenging angle.areas, not by crankshaft reliability issues'.

'Comparisons of differently sized engines should be based on mean piston speed, not on rpm'.

'Piston clearance, coolant flow rate, radiator size and ambient temperature are practical limits to engine cooling,
but in theory there is no such thing as too much cooling'.

'Top speed is the most unimportant thing in racing. Keeping your minimum speed high is the most important'.

The above collection should be sufficient to earn me a reserved place in an asylum, don't you think, Graham? .