Friday, July 31, 2009


I have chosen to call my present one-off Skorpion a Skorpion SP.

A few may have noticed in the last update that the Skorpion has new rearsets. As of this month, Gilles Tooling is officially offering rear sets specifically for the Skorpion. Together with Gilles, I put together a set using parts from their well known highest quality line. As with virtually all available models, this one also uses some parts common to many bikes. Each part can be individually reordered if needed. Both shift and brake levers are ball-bearing mounted, each with two bearings. The pegs shown are the new model which is slightly smaller and lighter than the old-style peg, which, however can also be had if desired. In fact all four sets mounted in the last two weeks had the old-style pegs.
The mounting plates are specially for the Skorpion and the model designation is AS31GT MZ01R. The pictures show my prototype set utilizing mounting plates for a Triumph with however did not fit exactly, I remachined them. The MZ01R set has plates machined to fit.
They come complete with all parts and bolts. Included but not shown here is the lever for the engine shaft, also CNC machined from aluminum and with two different possible lengths. As can be seen, the shift lever has three different ratio lengths. Thus, one can set the shift lever from virtually no travel to quite a lot. I have first gear up but of course the "normal" set up with the transmission shaft lever facing down is just as easily possible. The rear sets shown are titanium colored, but black or gold are also available.
Rearsets for the Skorpion Replica will be coming up soon.
These rear sets can be ordered from me or, of course, directly from Gilles.

I have now also fitted the the intended exhaust. As I mentioned in the last posting this has "Devil" performance headers with spring retainers. Mated to this is the LeoVince can for the TT 600 complete with its connecting tube. I made no changes to any of these parts! Together they fit almost perfectly. In the lower photo you can also see the old-style pegs which I had mounted to show. I personally prefer the new ones.

I have continued to prune and trim; after due deliberation I decided to remove the cross-tube above the cylinder head from the frame. Not for weight, I did this to finally be able to easily get at the engine. Now I can remove the cam cover or even the whole cylinderhead and cylinder from the installed engine without even removing the front down-tube, let alone drain the oil.


So easy to work on. And, I can tell no difference in handling without the tube, even with a tank top bag and heavy back pack, coming back from our yearly meeting.

I have in fact removed the head since cutting out the tube.
After the engine was run in, I removed it and took it entirely apart to check for undue signs. There was nothing alarming anywhere. At this point I did reinstall a balancer shaft, albeit a much lightened one and a solid drive gear for it as well.

The often mentioned problems with the woodruff key in the crankshaft are caused for the most part by the spring cushdrive in the drive gear. With the solid gear, the engine runs much smoother.

What else have a I changed?
Hardly worth mentioning, I exchanged the Brembo steel semi-floating rotor seen above for a full-floating cast iron rotor - Brembo of course. I think there is a big difference, at least with the Carbone Lorraine C55 pads I use.

Most Skorpion riders will have been bugged by the poor solution for retaining the gas tank. If "lucky," the bolts cannot be removed at all. While that is not the case with this particular tank, it was with both of my other Skorpions. I decided it was time to come up with something better.
This is a small snap lock from "Camloc." it has a safety catch. I made a piece from 1,5mm stainless sheetmetal to rivit the lock to and screwed this with spacers to the bolt holes of the tank. I cut open the two grommet retainers at the top so that the tank can be simply set in. the lock catches to the edge of the original bracket. (see also picture of rectifier farther down.)
No more bolts to undo or maybe loose; unlatch and pull the tank off - if you have a quick-release connector in the gas line like I do.

I also got very tired of unscrewing the seat - such a pain in the ...
"Camloc" again: I obtained their "Dus" fasteners and am using just one to hold down the seat. Sheet stainless again, i made the bracket for the bottom of the fastener ad rivited it to the seat frame. The fastener bolt with its retaining wahser were then marked out and drill through the seat and pressed in.
Just one half-turn of the latch and the seat can be lifted off.

To position the seat, I simply screwed all four M6 bolts - Poggipolini aluminum screws into the threaded sockets for good. Their tapered heads make fine positioning pins after their holes through the seat were reamed to fit with a tapered reamer. The front two screws can just be seen in the picture below as well as the latch for the tank.

During the yearly meeting my rectifier went bad - for the second time on this bike.

I did manage to limp home, running without the lights and charging the battery every nite.
I have replaced it with the "Charger" from Ignitech, seen at the right. Not a whole lot to see but it is very well made (just like the ignition box mentioned in the last posting) and comes plug and play if desired and specified at ordering. Since I do not have an OEM wiring harness, I got it standard. I simply cut a a piece of 4mm aluminum sheet, drilled it to fit the tabs of the seat frame and tied the rectifier to it with two binders.The rectifier has no mounting holes of its own but it is profusely ribbed. It works great and does not even get hand warm. I can supply both the "Charger" and the "Sparker TCIP4" ignitionbox which I normally supply preprogrammed for the XTZ engine, depending on the state of tuning.

Oh, in the last posting I said I 'd weigh the bike ASAP;
I did at the farmer coop: 152kg ready to ride and gased up.

Saturday, June 6, 2009


I mentioned the OVER works cluster I have.
In the past I have often recommended changing the XTZ shaft for that of the SZR in order to gain a longer 1st gear.
The two new engines mentioned in the last posting also have been changed. One of them has the SZR shaft and first gear, the other has an ex-MZ works racing cluster made by an east German machine shop for MZ. It differs slightly from the OVER.

Here are all four clusters:

You can see how rediculously short 1st gear is in the XTZ engine. Belgarda changed that for the SZR, leaving the rest alone. Both racing clusters are very different from stock, with extremely long 1st gears and close ratios. The OVER cluster is most extreme, being even longer in 1st and shorter in 5th. There are only about 800RPM between shifts which is perfect for racing but can be very trying in regular driving and downright exasperating in traffic. Speeds below 25MPH are only possible with a slipping clutch.
Having tested the ex-MZ cluster as well, I can say that it is only slightly better on the street. Both shift by themselves, fast and effortlessly, up and down without the clutch.
This of course has to do with the higher quality of the cluster itself, but more importantly with the small difference of speed between the two shafts. That is the reason why the SZR cluster also shifts better than the XTZ. The layshaft is driven by 1st gear, so the extremely low 1st of the XTZ makes the speed difference large. The slightly longer 1st of the SZR greatly improves the shiftability, and the extremely long 1st of the two racing clusters makes shifting nearly unconscious.

The OVER cluster is different in another way as well.

Here you can see both an SZR at the bottom and the OVER cluster at the top. You can see that the gears look different, and that 4th and 5th have coarser, stronger teeth and are considerably wider than the stock. The dogs are different as well.
The ex-MZ cluster does not use two different modules.

The OVER is no longer made and the ex-MZ was never offered as such. Reportedly, the machine shop which made them would make more if demand arose. Slipstream does offer an racing cluster. All of these, foremost the OVER, are or were very expensive. Slipstream also offers a shorter 5th gear.
More important though, for the "normal" Skorpion rider is the modification with the SZR shaft and 1st gear. This is a simple and worthwhile modification. For me a must-do.


I haven't written anything for a while; not a whole lot to tell really, at least not with regard to this blog.
I did build up two moderately tuned XTZ engines for Skorpions and also got around to a first stage of my pet idea, an air-cooled Skorpion. The original Seymour Powell design project had the 4-valve air-cooled Rotax engine which MZ was already using in their so-called Classic at the time.
I chose to stay with what I am familiar with, i.e. with Yamaha and assembled a bastard engine utilizing the XTZ crankcase of my racing engine with its one-off welded crankshaft with Carillo, the OVER racing cluster, and my own rollerchain timing gears (December 2007). On top of that I put a TT cylinder, bored out to 98mm with a Wiseco racing piston and a TT head with minor porting and a Megacycle 266/20 cam and RD's new Beehive springs.
These are very impressive to me. The pressure curve seems flatter, more constant and the dry engine turns over lighter by hand than with the more usual racing springs. The springs are 30% lighter even with steel retainers than the previous sets with Ti retainers according to RD.
Basically the engine looks like this now with a Grizzly manifold and Mikuni TM40/6:

Not needing a water pump, I turned an aluminum cover for that. The water pump drives off the crank at 1:1. I plan, when I find time(?), to make a timer with pickup for this position so that I can use any after market ignition and set the static advance as I see fit. That will also allow me to adapt a smaller lighter flywheel since the OEM pickup will no longer be necessary.

Installed in the bike, we now have this:

The oil cooler is from XJ600, the leads are new as is the direct feed to the camshaft. the exhaust manifold is from Devil for a TT. Suprisingly, it fits the Skorpion frame almost exactly.

For the time being, however, I have adapted the Skorpion's original Lenhart und Wagner exhaust system to fit the TT head.
There will be a SR Racing can eventually matched up to the headers shown above.

As with my Yamaha, I use an Ignitech Sparker TCIP4 programmable iginition box. Both of the aforementioned XTZ engines also use this box.
The bike started right up and all the new oilsupply lines are tight; everything is dry. Now to test ride and above all to break in the new barrel, piston and cam.

During the winter I will dismantle this engine again and install a new crank. This is what my pet idea is really about. The new crank will have 10mm LESS stroke, have a 5mm longer conrod and be lighter. Barrel and piston will remain as they are now, reducing the capacity to 560cc from the 630 I now have. A much lighten balancer shaft will also be installed, together with a solid drive gear for it. Both of the new engines mentioned above have these solid gears, one of them a lighter balancer and that one in particular is "smooth as silk." The lighter generator will also contribute (I hope) to making an engine with a much higher usable rev-range and ( I hope again) not much less performance, if at all.

The Czech ignition box has proven to be a real improvement. The advance curve of the DENSO box is too extreme of anything bu the stock engine and even the stock engine benefits from less advance above 1000RPM. In the stock Yamaha SZR, I have the box set up to a maximum advance of 28º at 6000RPM instead of the 37º of the OEM box. The limiter ist set to 9000 and I regularly rev the stock engine in 1st, 2nd and 3rd over 8000. Instead of wasting money on having the OEM box modified as most do ( and I did as well when I didn't know better!) it is definitely better to buy the Ignitech Sparker. The price is another argument for the Sparker and the support from the company couldn't be better.

Like my earlier blue Skorpion, this bike also has the Brembo TZR wheels that the Skorpion prototypes had: 3"/17" front and 3,5"/17" rear. I am testing the Haidenau Cup racing tire in 110/70 and 130/70. The first few miles were very encouraging: light-footed as a bicycle.

I will update about the aircooled Skorpion as time goes on. Next week I will definitely get it on the scales.

Sunday, April 19, 2009

more on ridig position, this time in German

Hang off, ein "Predigt"

Die geneigte Achse des Fahrzeuges in einer Kurve, die immer gleich ist bei gleichen
Bedingungen, ist nicht unbedingt mit der Linie durch die senkrechte Mitteachse des Fahrzeugs identisch. Im Gegenteil; sie ist es nur, wenn das Fahrzeug senkrecht steht. Sonst ist sie die Verbindung der Mitte der Kontaktflaeche und des Schwerpunktes des Fahrzeugs. bei gleichem Schwerpunkt aber breiteren Reifen dreht sich diese Linie entgegen der "Schraeglage," was zur Folge hat, dass die physikalische Schraeglage gleich bleibt, also diese Linie durch Kontaktflaeche und Schwerpunkt mit Fahrer, aber die Schraege des Fahrzeuges selbst groesser wird. Eben diese Erscheinung begegnet man durch das Hang off, was ja den Schwerpunkt des Fahrzeugs MIT Fahrer nach innen verschiebt, also die Schraege des eigentlichen Fahrzeugs mit der des Gesamtsytems Fahrzeug+Fahrer annaehrt.

Krasses Gegenbeispiel, ein Fahrrad: hier hat man einen sehr hohen Schwerpunkt und einen sehr schmahlen Reifen, dessen Kontaktflaeche kaum aus der Ruheachse wandert. In diesem Falle ist die gefahrene Schraege praktisch identisch mit der Theorie.

Nimmt ein Blatt Papier und zeichne eine Waagerechte und eine Senkrechte darauf. Nun male einen Kreis mit 15mm auf die Waagerechte, mittig um die Senkrechte; ein 150er Reifen. Nun, einen 80mm Kreisbogen mit Mitte im Schnittpunkt (A) der beiden Geraden. Der Schwerpunkt bei angenommene 80cm ueberm Boden. Nur eine Annahme; hier geht es nur um das Prinzip. Nun mit dem Geodreieck oder frei-Schnauze eine Linie (A-B) mit 30º aus dem Schnittpunkt A: eine theoretische Schraeglage. Nun noch eine Gerade (C-D) mit 30º von der Mitte der Kontaktflaeche - kann man an Hand der 15mm Kreises abschaetzen, oder wer es genau will nimmt 1/6tel des Umfanges (15*3.14/6) neben dem Schnittpunkt A. diese Linie C-D liegt aber neben dem ersten Schwerpunkt B, wenngleich auf dem Bogen der den Schwerpunkt darstellt. Diese Linie C-D naehert aber der phsykalischen Schraege an. Wenn man nun aus dem urspruenglichen Schnittpunkt A durch
den Schnittpunkt D des Bogens mit dieser zweiten Schraege C-D eine dritte Schraege A-D zeichnet, kann man leicht sehen, dass diese Linie - die eigentliche Fahrzeugachse - schraeger ist als 30º. Das ganze kann man leicht mit einem 12mm Kreis = 120er Reifen und einem 18mm Kreis = 180er Reifen wiederholen um die Aenderung der Linie A-D Kontaktflaeche/Schwerpunkt zu beobachten.
Hangt nun der Fahrer off und legt sein Gewicht nach innen, wandert der Schwerpunkt des Gesamtsystems auch nach innen Richtung der Linie C-D. Um diesen Versatz veringert sich die Schraege des Fahrzeugs. Aber die theoretische Schraege von angenommenen 30º fuer das Gesamtsystem bleibt konstant.
Bitte, ist sehr vereinfacht.

Eine Anmerkung in Zusammenhang mit hang off; Viele sprechen von "...sitzen..." und da liegt das eigentliche Problem: bei korrektem hang off sitzt man nicht, man hat das meiste Gewicht auf den Rasten. Drum muessen die Rasten weit genug vorn sein und der Sitz nicht zu schmahl oder zu weich; der Sitz dient am meisten dazu, den Bock zwischen den Schenkeln zu begrenzen, aber man belastet nicht wirklich den Arsch, man laesst dem Moped soviel Freiheit wie moeglich.

Noergler sprechen vom Turnen, Rumturnen, gar abschaetzig in manchen Lagern von
Rumhampeln, aber es trifft's recht gut. Der Stil ist nichts fuer Touren, er ist auch sehr anstrengend und braucht Kondition. Aber traeger ist er nicht als klassischer Knieschluss, und das vermaladeite Runterdruecken, bzw. Gegenimpluslenken ist, schon aus physikalischen Gruenden, potentiell viel traeger. Gefaehrlicher ist er allemal.
In diesem Zusammenhang; ein anderer hat angemerkt, dass dass es zu lange braeuchte, aus der "abgehangenen" Haltung wieder zurueck zu kommen, also von einer zur anderen Seite oder wieder in die Mitte und deshalb fuer den Alltag und in Notsituationen nicht angebracht sei. Oder so aehnlich.
Lassen wir den alltaeglichen Nutzen.
Wenn aber man zulange braucht, macht er entschieden was falsch dabei. Ich tippe darauf, dass er sein Gewicht nicht auf den Rasten, insbesondere auf dem kurven aeusseren Rasten hat, also dass er mehr oder weniger immer noch sitzt, wahrscheinlich auch den Koerper in einem Kreisbogen, von oben gesehen, um die Lenkachse dreht, anstatt gerade seitlich hin und her zu rutschen. Die Hauptursache hierfuer sind die Rasten selbst, die fast immer zu weit hinten sind. Die alte "sportliche" Sitzposition mit lang ausgestreckten Aerm' und Rasten weit hinten taugt nur fuer den klassichen Knieschluss. Sitz mal auf eine aktuelle Superbike (e.g. R6 oder Gixxer); Du wirst erstaunt ob die kommode, fast tourenmaessiger Position, Rasten ziemlich weit vorn aber auch recht hoch, alles nahe am Lenker. Die Position muss so sein, dass man ueberm eigenen Schwerpunkt sitzt, ohne das Gewicht des Oberkoepers auf den Lenker abstuetzen zumuessen.
Beide Fahrstile, Knieschluss und Hangoff, lassen sich nicht kombinieren. Immerhin, der absolut unknackbare Nordschleifenrekord haelt der Daehne - mit 18" Trennscheiben diagonaler Bauart. und mehr oder weniger mit Knieschluss.

Nochwas: ein dritter Punkt im Sinne des Fahrzeuggewichtes sind die Knie nicht, stabilisieren aber sehr wohl die Schraeglage, besonders bei schlechtem Belag. Und sie geben Information ueber die momentanen Schraege, die z.B. bei nach aussen abfallenden Kurven optisch taeuschen kann. Sie sind aber nicht die Notbremse oder die Anzeige dafuer, das es reicht. In sehr schnelle Kurven oder solchen die eine grosse Schraglage zulassen (z.B. 180º wie Sachskurve oder Lausitzring Infeld) wird das Knie wiedereingeklappt, weil es dafuer keinen Platz mehr hat; die Notfunktion uebernehmen die Schuhspitzen. Auch ein Grund warum die meisten mit erstem Gang oben fahren. Und beim rausbeschleunigen richten man das Moped nach und nach auf zwischen den Schenkeln, OHNE die Hang off Haltung zu aendern oder gar zu verlassen, um dem Gripverlust beim Beschleunigen zu begegnen, aber auch um das Vorderrad mehr zu belasten. Beim Knieschluss kann man so was schlicht nicht machen. Da ist das System Fahrzeug/Fahrer zu traege. Auch beim Reinbremsen ist es aehnlich: das mehr oder weniger senkrecht stehende Vorderrad rutscht bei weitem nicht so leicht unten weg = lowsider.

Es wird behautet, dass man relativ gleichmäßigen Haftungsverlust mit dem Knie abfangen kann. Nur bedingt; eher handelt man sich einen lowsider damit ein. Driften benoetigt, ja bedingt weniger schraege. Dagegen kann man einen potentiellen highsider - wohl gemerkt nicht immer - eben dadurch begegnen, das man das Moped einfach machen laesst.
Highsider auf der Rennstrecke kommen meist beim Rausbeschleunigen aus der Ecke wenn das Hinterrad voruebergehnd Grip verliert infolge der einsetzend Leistung und zum dem Zeitpunkt als mehr Koepergewicht auf dem Sitz liegt und das Moped eben nicht zwischen den Schenkeln austoben kann.

Durch die Kreiselkraefte ist das Moped zunaechst inherent stabil. Die Unruhen werden von aussen primaer durch den Fahrer eingebracht , und dann die auesseren Bedingungen wie Belag, aber auch bei Strassenfahrzeugen durch technische Unzulaenglichkeiten wie ungeeigneten Reifen, schlechte Lenkkopflager, falsche oder falsch eingestellte Federelemente u.ä.m.
Natuerlich kommen Highsider auch, besonders auf der Strasse, beim krassen Belagwechsel wie vom griffen Asphalt zu Bitumen und dann Asphalt wieder und da ist man meist machtlos.

Nochmal zur Schraeglage selbst: je hoeher der Schwerpunkt aber auch je schmaeler die Reifen, desto weniger die Schraeglage fuer die gleichen Bedingungen. Also z.B. mit einer srx. Beides: schmahl und hoch. Oder einer Koenigswelle 900SS: vorn 100/110-18, hinten 100/120-18... die Ur-Superbike.
Was den Reifen angeht, bei zunehmender Breite wandert die Kontaktflaeche aus der senkrechten Achse , je mehr Schraeglage, desto mehr und dies bedingt eben mehr und mehr hang off.
Schon deshalb sollte man die SZR oder Skorpion mit 140er Reifen hinten fahren..