Friday, November 30, 2007


Bill's Skorpions....

1990 was the first showing of the award-winning Seymour Powell prototype with Rotax motor. Seeing it, I said this is the bike! I kept an eye on developments, meanwhile riding my 1974 Benelli/Motobi 2500SS. A late model with 5 speed trans. The engine - goes almost without saying with me - was heavily modified and had seen use in a Zanzani racing frame. In street-legal trim it still had 26hp and the bike weighed all of 105kg, ready to go.

Here in my home town of Lauffen, one of the oldest west German MZ dealers, Probst, has or rather had his shop. Had because, due to the turmoils caused by Kourus, they eventually got so fed up with MZ that they stopped dealing with them. 1994, they had the first two Skorpions in the Stuttart area, a yellow Sport and a blue Tour. I test drove both and bought the Tour straight away as the first Skorpion sold in the Stuttgart area. It was so early in production, that the modifications (cut off corner of exhaust can, longer vent hose, etc) were not yet done. I had the can modified at L&W in Lorch - they still existed in that form and they did it for nothing! Until September this year, I have been using it ever since, summer and winter.

Within the first year, I had exchanged the front springs for progressive Technoflex (now Wilbers) as my mechanic advised and the clipons for welded aluminum Harris racing clipons. Not two years, and I had to replace the strut because the spot-welded nose for the spring base tore out, emtpying the oil. Again the mechanic advised me against simply replacing the Bilstein, on the basis that a really good strut from Wilbers would be only 150DM more expensive. I ordered one with adjustable length to lift the tail. The fork had long since been stuck thru as far as possible. After replacing the tach twice, I replaced the entire unit with a DET 100 which I highly recommend.

Sooner or later, I replaced the muffler with a BSM Future, which, while prettier and lighter and louder, was also not long lived. The insides vibrated loose, the baffle slid forward, closing the pipe entrance to the can. I had wondered why the bike seemed to be getting quieter! No way to fix it, so I bought a BOS for a Kawa ZX750R; the three hole pattern is the same as the BSM, and this one is still going strong, even after several groundings. I no longer use it, however.

Somewhere around 35000km, the gear driving the counterbalancer sheared off the Woodruff key in the crank. EGU rebuilt the crank with the original conrod; the balancer went to the dustbin after due deliberation. I have not regretted throwing it out!
That was basically the condition the bike was in for the very first MZ Skorpion Forum meeting in 2002.

I had added a steering damper. Otherwise, the crappy Grimeca wheels and brakes were still in service. And the battle scares on the can from Hockenheim are clearly visible.











2003, I bought my green Sport from Heinz Weber, who basically built it.
It was built from scratch from a new Skorpion Sport and a new Yamaha SZR; the frame is the first prototype frame for the Replica from MZ development which was eventually rejected as being too light and flimsy. Actually, there was almost nothing from the new Sport used: swingarm, strut, gas tank and fairing, seatframe which was heavily modified, airbox, radiator, front frame brace, exhaust system tho the can was also highly modified by L&W. Motor, wheels, fork and brakes , wiring harness and instruments and headlight, all from the Yamaha. Rearsets homemade. This bike weighed 165kg ready to go.

After some encouraging outings on the track and more than one spill caused by the exhaust system grounding, I decided to use the green one only on the race track. That is when I started modifying engines, this one first, then the blue one, then the red one - more later. This one already had a Carillo conrod, a J&E 102mm 12:1 piston, a Megacycle 280/2 cam, and new one-off porkchop style crank. I rid it of its balancer, putting my balancer dummy and did some porting.


Next came the Bikeworx kit with Mikuni TM42. Then I had the idea of lightening the the flywheel/starter freewheel assembly. This was not used in this engine very long, however, because I threw out the starter and flywheel entirely, going to a magneto ignition. The lightened flywheel assembly, which I offer, went into the blue bike. The TM42 was replaced by a dual TM38-65 mounted on 2" long intakes and the magneto replaced by a constant-loss ignition system which made starting infinitely easier. The Megacycle 280/2 cam was replaced by a full-race cam with Kibblewhite valve springs, the ports reworked some more and a Barker 2-2 exhaust system mounted.

2003, I also bought a 1995 red Sport. Both it and the blue bike got SZR wheels and Brembo brakes, the red one a Mikuni TM34-65 carburator and a 8400rpm modified CDI like I was using generally. The red bike got the exhaust from the racer after I bought the Barker 2-2 racing system. It also got the rearsets from the racer for which I had made new billet CNC milled 7075 rearsets, both for it and the blue bike. The blue bike got the seat frame and seat from the racer since I had also bought a Barker aluminum subframe and a Pferrer seat. In the end, the blue bike also had the TM42 since the racer had gotten the TM38-65.

When my son started to ride, I reduced the red bike to the legal 35hp.
getting confused?

These are the MZs:


1) the 1994 blue Tour which I have now dismantled; it had over 80 000km:
SZR Wheels, Brembo brakes, one-off harness with Silenthektik box, Technoflex progressive springs, Sachs fully adjustable strut with White Power Spring (Replica), Gilles clipons, 101mm Wiseco piston, Megacycle 280/2 cam, no balancer, lightened flywheel assembly, SZR cluster, reversed shift pattern, TM 34/65 flatslides, light porting, Remus Cup exhaust system (5 mm larger headers and much better ungroundable routing), seatframe and one-off kevlar/glass seat from the green bike, 8400 CD, DET 100 Instrument. Dyno tested 59hp at the rear wheel, 150kg. 15/43 with DID 520 ERV chain. In this bike, ALL of the screws except the three long M6 bolts at the timing chain and the cylinderhead bolts have been replaced with either titanium or aluminum as necessary. That includes all the parts of the strut linkage; the dogbones are aluminum. The swingarm axle is also titanium.








2) The 1995 red Sport, which I then sold, or rather traded for the Yamaha SZR I still have: as above, Brembo SZR wheels and Brembo brakes, the handmade rearsets from the green bike, TM34/65 flatslides, 8400rpm CDI, Tommaselli forged clipons, lighter headlight from a TRX, Lighted seatframe and fairing frame, Mito mirrors, BSM Future exhaust, 15/43 rear sprocketwith DID 520ERV chain. DET 100 instrument. Aluminum screws were used here to a certain extent as well. Otherwise this bike was completely stock. It ran a verified 190kmh with the short ratio. I went from Milan to Turin at a nearly constant 180kmh. That's over 200km expressway at 8000rpm. Didn't break then - or later.








3) The Green bike was strictly for racing: 125kg race ready .
4 stroke, 5 Valve: 700ccm
weight of race-ready engine with carbs and all fasteners wired:: 40kg .
Special welded"Porkchop" crank. no counterbalancer, Carillo rod, JE 102mm 12:1 piston, Megacycle full-race cam, Slipstream rollerchain conversion, Kibblewhite springs and titanium retainers, titanium locknuts, ported head, Mikuni TM38/65, Barker 2 in 2 racing exhaust, Barker CNC sideplate, SilentHektik costant loss battery ignition, Yamaha works cluster. Of course, here, too, all screws, bolts and nuts are either titanium or aluminum just as above. triple tree is one-off CNC milled billet AL7075, SZR fork reworked by Wilbers, Wilbers fully adjustable strut, Barker aluminum set frame. Marvic magnesium wheels with Bridgestone slicks, ABM CNC billet front caliper and billet radial pump. Mecdine speed shifter. Just shy of 80hp at the rear wheel.


That was up till this year. I decided to stop racing due to my age and build the racer back to something approaching street-legal. It will have Brembo TZ250R 3MA wheels instead of the Marvics which cannot be registered in Germany - no mag wheels can. It will also have the Remus Cup exhaust shown above on the blue bike. Of course it will have the lightened flywheel assembly and a starter again and I will need to make a new harness for it. But inside, the engine will remain untouched. I hope to keep the aluminum subframe and Pferrer seat but the subframe needs considerable revamping and welding for street use. Of course the ABM brake will be retained. I hope I can keep the weight down to 135kgs and the hp still around 65, maybe even 70.

Lauffen in October, 2007
http://www.zabernet.de/bill/tuning.html

Saturday, November 17, 2007

riding position

After repeatedly reading a lot of BS on position and numbed hands and aching necks, allow me to make few observations on riding position.



But first a short account to start with: yesterday, I drove the 30th anniversary of a good friend's organbuilding shop with my blue Skorpion. Over 300km, coming back the next day, 300+km again plus 50-60km after removing the tank topbag. In general, my Toy is judged as having a radical racing setup and not at all good for riding any distance at all. The missing counterbalancer also contributes to this appraisal. OK, 300km ain't that far but Siegen, the town where I went, is just not further away.

Whatever

no numbed hands
no aching wrists
no aching knees, altho my right knee was demolished beyond repair skiing decades ago
no stiff neck
and all this despite the would-be radically uncomfortable position and the vibrations.
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First, a simple test of you riding position:
Put the bike on its centerstand if available, a paddock stand or have someone hold it; seat yourself as if you were riding. Now let go of the bars, that is, open your hands but leave them on the grips, do not change anything else. Now attempt to stand up on the pegs. Can you do this? If so, your position is basically correct. If not - you will most probably fall forward - your pegs are too far back. Perhaps the bars are too far forward, as well. More probably, the bars are too wide which has a similar effect.

The point is this: you must be able to put your body weight on the balls of your feet. This is necessary both for a relaxed position and secure control. I repeat: the balls of your feet, NOT the INSTEPS, belong on the pegs, regardless of what you may have been told at drivers ed. Part of your weight should be on the pegs at all times, not on the seat. As with a bicycle, the seat is between your thighs, not just under your backside. More or less loose between your thighs - while driving of course.

Driving straight ahead, the weight should be distributed equally between both feet. This way you can immediately react to very bad road conditions, the bike can tip for and aft around the axis of the pegs/your feet without pounding on your back or wrists. In curves, the weight should be on the outside peg. It should be obvious that this is only possible when the pegs are far enough forward.  For a comparison, drive to you local friendly Yamaha dealer and test-sit (test drive even better) an R6. You'll be amazed how far forward you sit, how close to the bars, how far forward the pegs are and this on a so-called super sports bike.

Once you have sorted the position to pass the test above, you should be able to drive longer distances without aching wrists.
Mounting a superbike bars, so popular at the moment, is in reality a move in the wrong direction because the higher, wider bars move you weight too far back onto your backend . The very upright position also makes the front end very light and this tends to make it nervous, quite apart from steering geometry. Unweighting the seat to let the bike take care of itself is also much more strenuous unless you have thighs like a professional skier. In most cases, riders on such setups are taken for a ride; the bike controls them and not the other way around. Normally, the centrifugal forces of the wheels and to a lesser degree the crank if crosswise mounted stabilize the bike. Misbehavior is brought into the constellation rider/bike mostly by the rider himself. He must learn to let the bike have its way. It has not always been this way. Old weak or poorly designed frames definitely needed to be kept under control by clamping the knees on the tanksides, Long reaches, far back rearsets, all that is part and parcel of a bygone era. Modern bikes and, even more, modern tires worthy of the name not only do not need this, they react allergically to it.

Once again, the pegs must be positioned under the body and between steering head and seat so that a triangle is formed in which the rider center of gravity(CG) is exactly on the pegs, on the balls of your feet. If the pegs are too far back, the triangle tips forward, moving you weight away from your legs and onto your wrists. That is what the test I started with is all about.

It is a simple as that.

It is entirely possible that the stock settings cannot be made to fit. Very tall people should raise the tail without sticking the fork through, i.e.raise the entire bike, perhaps even put the clipons under the triple tree so that the fork can be pulled out even more. Raising the tail to match retains the original geometry while raising the entire bike. The higher CG requires less lean so pegs can be placed lower safely. Other brackets may be necessary to get the pegs low enough and far enough forward to suit.
When the best position is found, set the shift lever so that you can shift with your big toe without really moving your foot. The brake is similar, altho on modern bikes, the rear brake is only of limited usefulness and should never be able to lock up the rear wheel easily. That can be very dangerous indeed. Do not normally use the rear brake at speed, regardless of what you have been told. Racers use it only to quiet an unruly bike (shimmy or kickback which are not the same thing) by a quick tip on the pedal. And of course they also use it to steer the rear wheel, along with the twist grip. They do not use it as a rule for actual braking. Get out of the habit of using it for anything beyond coasting up to a traffic light. Or quieting shimmy while on the expressway with your overloaded vacation trip package.

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Knee down and hang off: it is a question of riding style and bike and above all seating position. You absolutely have to have your body weight on the pegs to ride hang-off with any control.
But it is also a question of tire width. A wider rear tire needs more hang-off than a narrow one. A low center of gravity also needs more hang-off. That is why the present 2005 RC-211 has a higher CG than the 2004. And also one reason why I raised my racer; 40mm for the bike itself with longer Wilber strut and shorter aluminum dogbones and another 40mm the seat alone. It is now quite tall. I still have to pull my knee back up in hard cornering to get it out of the way. Getting it on the ground is no problem at all.
Hang-off requires some practice and definitely requires some competent instruction to do correctly and it requires fitness. Race riding is hard work, contrary to popular belief. It does not require any particular bravery or abandon.
Do not do this in traffic on open roads.