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

I don't see what holds the 'keys' in place? The cut-outs are for the transfer ports correct? Also am I correct in thinking these 'keys' are located in the same bore holes as the hold down bolts for the cylinder to the case? Thank you.

jfn2 a écrit:

I don't see what holds the 'keys' in place?

Each key is bolted to the head. It is also secured against rotating. The head itself is bolted to the cylinder with four other bolts.

Citation :

The cut-outs are for the transfer ports correct?

Yes, for the transfers and for the auxiliary exhaust ducts.

Citation :

Also am I correct in thinking these 'keys' are located in the same bore holes as the hold down bolts for the cylinder to the case?

Correct.

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Thank you Frits, I understand.
I'm assuming the grooves' circled in red below are for seals. Any thoughts to residue build-up or corrosion around the 'keys' hindering removal during maintainance periods?
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jfn2 a écrit:

Any thoughts to residue build-up or corrosion around the 'keys' hindering removal?

Loosening the four bolts that hold the keys to the head will allow to lift the head a couple of millimeters. Then you can slide strips between cylinder and head, and tighten the bolts again, which will pull the keys out of the cylinder.

Again, thank you Frits. Are there any specifics on the twin cyl engine with the green heads?

jfn2 a écrit:

Are there any specifics on the twin cyl engine with the green heads?

You'll need to ask designer-constructor Michael Burgard. He is a forum member here.

Thats what I know

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I have a question about ignitions, do you have any numbers on how much sparkenergy the ignition on the RSA makes? Is this comparable to modern production engines like shifter karts or Mx engines?

Is the spark duration significally different from those production engines, and does it use multiple sparks?

Senne s a écrit:

do you have any numbers on how much sparkenergy the ignition on the RSA makes? Is this comparable to modern production engines like shifter karts or Mx engines? Is the spark duration significally different from those production engines, and does it use multiple sparks?

No, no, maybe, no.
I have no data at hand about the number of milliJoules the RSA-ignition delivered, but it was certainly more than what modern shifterkarts have, because those are all compelled by regulations to use a rather weak ignition system. The difference may be in the tension, the current, the duration or a combination thereof.
Any real-terms spark is in fact a multiple spark but if you mean a series of time-separated sparks, the answer should be no.

Hello All.

I have a question here I am sure has not been posted in the 4 parts already.

I have an 'off the shelf' bare steel expansion chamber that is 20-25mm longer than my ideal for my given exhaust duration and application. The path of the pipe is rather snake like and I'd prefer not to modify it unless I had to.
Would it be possible to alter the resonant length usefully by having the pipe coated with a 'ceramic' paint coating. The applicator claims a "50% reduction in component skin temperature" with his particular product. I was thinking to coat from the beginning until half way along the parallel section.
I gathered that due to the use of titanium for the RSA exhaust that there would be no detrimental issues from elevated gas temperature, so long as I took this into account when reading EGT temps.
Many thanks in advance for your kind consideration.

I would certainly try this Nick!

Hi All
I read some years ago the piston could be paint with the ceramic paint Nick talked about to keep it from warm , does somebody tried it ?
many thanks

Motors31 a écrit:

the piston could be paint with the ceramic paint Nick talked about to keep it from warm , does somebody tried it ?

Oh yes. And everybody who tried it, regretted it. With a normal, uncoated piston the heat can move from the piston surface to the surrounding material.
With a coating, all heat remains at the surface, so the surface temperature is much higher: instant detonation.

Thanks a lot Frits, if compared to Ignitech, is there a lot of hp to be gained from that extra energy?

Senne s a écrit:

Thanks a lot Frits, if compared to Ignitech, is there a lot of hp to be gained from that extra energy?

That question is not so simple to answer, Senne. Ignitech produces several different versions ; you can run some versions at up to 16 Volt which almost doubles their output energy; you can combine the pickup-inputs and feed both coil-outputs into a single coil, etc.
And then there is the engine itself. If it is a low-compression, low-turbulence engine, the ignition will make not make much difference. You will have to find out for yourself if a powerful ignition is worth while in your case.
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IGNITECH doesn't pull a sausage from a plate as typical used car merchants in The Netherlands use to say about certain cars that perform not too well. However IGNITECH is programmable and very cheap indeed but what can one expect from cheap stuff ? The ratio quality vs price isn't that bad after all !
When talking fe about ignition systemsI am rather disappointed on the level of knowledge and vision regarding the subjects ignition and injection on this forum. Therefore it would be very wise to do ones homework properly before grabbing the digital pencil...

Tada to all of you

So, this would be the perfect moment to let us participate on your knowledge, don't you think, Bob?

Hello Bob

Is 400 Volt oke to the bobine

Frits Overmars a écrit:

Motors31 a écrit:

the piston could be paint with the ceramic paint Nick talked about to keep it from warm , does somebody tried it ?

Oh yes. And everybody who tried it, regretted it. With a normal, uncoated piston the heat can move from the piston surface to the surrounding material.
With a coating, all heat remains at the surface, so the surface temperature is much higher: instant detonation.

But is this result telling us that the coating is a bad idea, or that, as with nearly all other engine alterations, you can't simply add this change in isolation without changing some other things to make it work? Presumably the piston is dissipating heat through the rings and skirt and the F/A beneath it at some given rate, and that if you add a barrier to heat input, the piston should run cooler, which would seem a desirable thing since as it is you are having to take such measures as very carefully aiming your transfers to cool the piston.

Someone had the wonderful idea that we 2-stroke lovers should adopt as our universal symbol a used piston with big skid-marks across the ring-groove and skirt!! If a ceramic coating can reduce this common occurance, might it not pay us to see if we can make some adjustments to reduce the detonation problem with the coating? Maybe a little less compression? More attention to coolant flow? Better yet, more attention to the internal shaping of the cooling surface on the back side of the head, by casting or machining (in a multi-piece head) fins to greatly increase the surface exposure to the coolant? Maybe then we could even gain a little power from the coating, which was the original idea. Hard for me to guess on this, since maybe this would be merely trading one heat-flow path for another, with no net gain in thermal efficiency of the engine.

I keep reading complaints of how hard it is to water-cool a modern racing 2-stroke motorcycle engine, reading about flow-rates and coolant volume and big radiators and super-pumps. Well, to exaggerate, suppose you fabricated a water-jacket and put it over an air-cooled head, with its enormous surface area? Do you see what I'm getting at? You would at least transfer your cooling problem from the engine to the radiator (glad I'm a boat-guy when I read about these things!).

As usual, I ask these things in all innocence and ignorance, not to contradict but to learn the errors in my thinking.

my nitwit thoughts on this :

seattle smitty a écrit:

if you add a barrier to heat input, the piston should run cooler, which would seem a desirable thing since as it is you are having to take such measures as very carefully aiming your transfers to cool the piston.

heat is inserted to the piston through it's top surface as part of the combustion chamber, so it won't help coating the skirts to prevent the piston from heating.
if such a coating excists, it must be a damned tuff coating not to be burned away from all the combustion cycles.
as the incoming charge through the transfers that travels over the piston top is very important to cool the piston, wouldn't it be silly to put a coating on top of it that will stop the "cold" transfer from the charge to the piston ?
and coating on the skirts limits the possibilities of loosing heat, I don't think anyone wants that.

Years ago we ceramic coated the piston crown of a low compression oversquare aircooled cylinder (sorry Frits I know...). The engine detonated so badly it would auto ignite even at idle, which meant we couldn't turn it off without stalling it. A colossal failure.
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?

Hi Guys

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!. Perhaps a small amount of extra power as a bonus!

The negative is that the grey coating makes the piston hard to read.

I'll post up some pictures tomorrow.

Best Regards

Ian

Thanks Ian.
The BSL500 V3 MotoGP bike also ran ceramic coated pistons reliably, way back in year 2000.
Unfortunately Dorna revoked the teams 'Development' status and gave that to Ducati and so the project was ended.

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)

nick gill a écrit:

Years ago we ceramic coated the piston crown of a low compression oversquare aircooled cylinder (sorry Frits I know...). The engine detonated so badly it would auto ignite even at idle, which meant we couldn't turn it off without stalling it. A colossal failure.
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?

I tried it in 1987, but it gave me no advantage.
There was no more detonation on top of the piston.
But heavy detonation above the piston ring, and even in the ring groove!
At the time I thought detonation was a limiting factor for getting more HP.
That was a big error!
By improving the transfer ports and ducts all detonation disappeared!
At least at full throttle!
Part-throttle remained a problem however.....
100% throttle opening saves your engine!
Keeping the throttle wide open, and using the rear brake could be a solution.