[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4)

Here's a picture of our coated dome piston.

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Jan, I find your comment really interesting. We have walked exactly the same road over the last 12 months and with similar conclusions and results.

Best Regards

Ian

nick gill a écrit:

Coating the crown with electroless nickel is common in racing turbocharged engines, to make the crown surface more resilient to the effects of detonation. I'm sure the wise ones have tried it on a 2T piston at some point?

Nickel is more detonation-resistant than bare aluminium, but that is not the only reason for using it. Some uncoated pistons also have a nice shine. Polishing the crown has a similar effect to nickel-coating it: it prevents the piston from heating up, not because the coating is a bad heat conductor but because the polished surface reflects the combustion heat.
The difference is that once the combustion is finished, there is no remaining surface heat that could affect the incoming fresh charge.

Ian Harrison a écrit:

In our SK250S 250 single superkart motor we run a forged piston with coated crown made for us by Mr. W. I can tell you that the coating lasts the life of the piston. Detonation is no different than running the same parameters with our cast piston option which has a non-coated dome, but the seizures associated with forged pistons in a 250 single race engine are gone!

Is that coating protecting the piston through low heat conduction or through reflexion, Ian?

Charles Kaneb a écrit:

After watching my friend's team struggle with inadequate ignition energy on a Honda RS80, I asked them to use a MSD 6AL ignition box and a Blaster coil capable of a 135 mJ spark. So far I haven't been able to convince them that it'll justify the roughly 5kg of the system + grounds. Do you think 135 mJ is enough that it's not the limiting factor, or should I pull a modern passenger car coil-on-plug system (some of which reach 1 J and can fire a .125" spark gap)

135 mJ sounds like a lot to me, Charles. But what really surprises me is your statement that some coil-on-plug ignitions reach 1 Joule. that would be ideal. Firing a .125" spark gap (3,175 mm in our world) however is an indication of the tension but not of the spark energy.

Hi Charles

As far as I'm concerned 135mJ is more than adequate for your application and perhaps  a bit "over the top".

I've tried just about every programmable ignition box/system on the market. We currently have about 85mJ with the system we use and the best results that we have ever achieved from a 250 single cylinder 2-stroke race engine.

Be interesting to know anyone else's thoughts and experience.

Best Regards

Ian

Hi Frits

I'm not sure I can honestly answer that, although my belief has been that it is a thermal barrier and I can't instantly put my hands on the information.

Don't want to give anyone the wrong info, so I'll ask Mr W and come back to you.

I guess either way, less heat is absorbed into the piston. Interested to read your thoughts above regarding that and it's possible effect on the incoming charge.

I did find this company/info: [Vous devez être inscrit et connecté pour voir ce lien]

Best Regards

Ian

"Reflection," that's interesting. The racer trick of "mirror"-polishing piston crowns has been used since the Thirties (even older than me!) if not earlier, but we imagined that what we were doing was not so much reflecting heat but simply reducing exposed crown area (on a microscopic level, but those peaks and valleys add up!). Same kind of benefit in going from the deflector pistons in an old cross-flow engine to a loop-scavenged engine piston: less surface area.

(Deflector pistons were a PITA to polish, with warm words shouted when the wheel ripped the piston out of your hands!!)

That the heat-barrier coating you tried, Mr. Thiel, moved the detonation from over the piston crown to over the ring and groove area is even more interesting. Why would that happen? Could it be that if you ceramic coat a piston crown, which should(?) slow heat absorption, you should maybe do this to a piston which you have machined with something less than the usual amount of taper and skirt clearance in order to end up with operating clearances that are the same as with normal, un-coated pistons? This kind of thing is why I wonder if it's a valid test of the coatings and whatever possibilities they might or might not offer, to merely add a coating while making no other modifications.

I wonder how the NASCAR engine-builders handle this, since, we hear, they are big customers of the coating services.

Speaking of coatings:
Does anyone have a source in Europe where Aluminium reedcages may be rubberized?

Frits Overmars a écrit:

Charles Kaneb a écrit:

After watching my friend's team struggle with inadequate ignition energy on a Honda RS80, I asked them to use a MSD 6AL ignition box and a Blaster coil capable of a 135 mJ spark. So far I haven't been able to convince them that it'll justify the roughly 5kg of the system + grounds. Do you think 135 mJ is enough that it's not the limiting factor, or should I pull a modern passenger car coil-on-plug system (some of which reach 1 J and can fire a .125" spark gap)

135 mJ sounds like a lot to me, Charles. But what really surprises me is your statement that some coil-on-plug ignitions reach 1 Joule. that would be ideal. Firing a .125" spark gap (3,175 mm in our world) however is an indication of the tension but not of the spark energy.

Frits, passenger car ignition tension (now up to 50 kV) and energy have been increasing especially since 1998. They have to pass tighter and tighter emissions standards and one good way to get complete combustion is to start with a larger flame kernel

Tim Ey a écrit:

Speaking of coatings:
Does anyone have a source in Europe where Aluminium reedcages may be rubberized?

Hi Tim, I wouldnt bother with rubber coating. I made a 4 bank reed cage in alluminium several years ago
for a CR250 superkart and its been the most reliable reed block I have known for reed life and produces
good sealing against one made with coating on rubber.
Phil

hello

has someone ever tried to hard anodize a piston? it would not prevent the detonations, but they dont make so much damage on the harder surface. or is this total wrong?



If i remember right Jan or Frits has somewhere said that the optimal bore to stroke ratio is slightly oversquare. is there a exact ratio?
in the RSA there is 54x54,5. so there is circa 1% over stroked. is this the right ratio for a racing 2 Stroke engine?

thanks Manuel

Hard anodizing was practised by us already in 1981 on a Suzuki 24Hrs endurance racer with very positive results. The proces we made use of was with bedded in ptfe partciles, Teflon if you wish so.
After a full 24 race including extensive practice the diameter loss on the piston skirts was vey little, somewhere in the less than 10 mu range. Measuring of the pistons before and after racing was done at the Philps machine shop in Eindhoven. The hard anodizing with Teflon took place at Surface Treatment in Maasbracht, Netherlands.
Another Philips shop carried out flame spraying of F1 pistons for Renault's F1 turbo engines. Renault shipped pre machined pistons to Eindhoven where the oversized top ring grooves were filled with a flame spraying compound. Renault then got the pistons finally machined. The purpose of this operation was to locate the top compression ring higher in the pistons top land. I do not know however what the results were.
For a racing twostroke an approach like this could now be tried with laser welding. The right man for this job is obvious Thomas Müller in Neukirchen-Vluyn / Germany.

Manuel Rainer a écrit:

If i remember right Jan or Frits has somewhere said that the optimal bore to stroke ratio is slightly oversquare

Not me.

Quote from Jan:
The port timings remained practically the same during 15 years!
What we did was trying different angles and radiuses, mainly on
the transfer ducts. I think we tried 40 different types of transfer ducts that did not change the time/area
Hi Jan,
Can you tell me please by how much HP did you gained from the development on the Transfer ports over the 15 years as quoted above?
Best regards
Allan.

I started with 46,5 in 1995 and ended with 54 HP in 2007.
About half of this was due to the transfer ducts development.

He Frits,
do you have the 2007 RSA Angles in your superduper Visual Scavenge Port Direction Program?

Polinizei a écrit:

He Frits, do you have the 2007 RSA Angles in your superduper Visual Scavenge Port Direction Program?

That's not superduper and it's not a program either; it's just a concept to help two-stroke tuners on their way.
But yes, the RSA angles are not completely different .

Thanks Jan for the information.
Could you please give some advice for the tuners who are modifying a Japanese two stroke motor cycle motor for more power in general terms regarding Transfer Port development – maybe the mistakes to avoid and the areas that make the most gains. As you know, the Japanese Transfer design appears to use the “kickers” (shape angle change) at the entrance into the cylinders on the “B” Transfers and the passages do not follow the RSA concepts of design. In this photo of the Honda CR250 cylinder transfer pattern , they even have an extra-large volume in the “A” Transfer passage just before the cylinder entrance. I am not really sure what they were trying to achieve with this idea.
Thank you and best regards
Allan.


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gtg001 the sharp kickers are a bad idea. this was discussed not long ago but i cant recall the exact page. epoxy can help eliminate the sharp kicker and make a better shaped duct

some of the newer engines like ktm have improved from what they were years ago. now days they use larger sweeping radiuses into the bore, rather than prehistoric kickers.

Here's some mind-bending pattern work.

Incredible talent & skill.

Study & learn !

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Absolutely! of the artist's work. They have the "know how" the Grandads and magic fingers.
Have you noticed the "small table" on the last picture!

Please explain.

Tim Ey a écrit:

Speaking of coatings:
Does anyone have a source in Europe where Aluminium reedcages may be rubberized?

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This is a company based in the Isle of Man that specialises in Rubber mouldings for the motorcycle industry.
They produced the carb rubbers pictured below for us, as a replacement for the RS125 angled inlet rubber once it was discontinued.

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Finished article, with the rough prototype on the right:
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I has discussions with them regarding rubber coating of reed blocks and metal parts in general. This is within their capability, but I have no idea what sort of minimum quantities they would require.

Best Regards

Ian

@ ambike

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Only the calculator is a bit anachronistic

French humor

fpayart a écrit:

" about 1 ton"

Do you think it's an aluminium table Francis ? (dutch humor).
My guesstimate: 2220 kg (without counting the 6 legs ).

Oh, OK ! It's a beauty. I was looking for a SMALL table with another part.

Maybe with a motor part YOU were making.

The table appears cement or concrete ?? Like a pre-fab wall or floor for a building / structure ??

The calculator & heighth-mic are needed.

That IS some beautiful work. The man is a da Vinci.

You guys are pretty good yourselves !!!!

Ambike, No it's cast iron,
Exact Frits, my estimate was half undervalued.
More than 2 tons of course that depends on the exact dimensions.