Tuesday 5 April 2011

Mark 'Gyro' Geering and his pair of Suzuki GSX1100's

Your initial reaction to seeing these two GSX1100's must be one of envy, I know mine is. In fact, I'm envious of Gyro's complete collection of seventies and eighties Suzuki muscle bikes. The silver wheeled bike is in mint condition, restored to concourse level and looks to be completely original. The other bike, with gold wheels, is a bit of a wolf in sheeps clothing.  
The standard GSX1100 was carefully restored with considerable expertise. As I've mentioned in other articles (links at bottom of this page), Gyro is something of a legend when it comes to Suzuki muscle bikes, though he does restrict himself (mostly) to GS1000's and GSX1100's/Katanas. The exhaust system was hand made by Gyro and chromed and despite not having the stamping found on the originals, otherwise looks an exact copy.
Available from August 1979, the GSX1100 was a successful racebike taking 1st, 2nd and 4th in the 1981 Castrol 6 Hour endurance race which is about as tough a test of a production bike as could be imagined. The race is for standard production bikes, exactly as you would see on the sales floor. Typically manufacturers have new models ready around September and look for opportunities to build hype and expectation for the coming year. Since the 6 Hour was run in October, it was seen as a great oportunity to build brand and model recognition and boost sales.
Suzuki's record might have been better had not Honda fielded the inimitable CB1100R in 1980. While the GSX was a 'standard' production bike, the 1100R was anything but. Pure and simple this was a homlogated race bike specifically built to tackle endurance racing championships and it cost a fistful more than a GSX. Having said that, I'm a Honda fan so suck it up Suzuki riders, you only lost by 1 lap to Honda's 322.
The bike has a stanch look that screams burnout (to me anyway) everytime I see one. Riding an 80's musclebike is an experience, especially if you try to press on with your journey. Suspension  is OK if in good condition, brakes require a little bit of thought and the assistance of  a committed downshift to slow the beast on corner entry. It's not hard to break the back end loose and you can quickly approach a highside if you're a bit ambitious. When you get it right you look like a hero to your riding buddies, and no one need know the truth when you stop for coffee.

Looking at the golden wheeled bike, while it isn't standard, its modifications aren't discernible to the naked eye. Gyro successfully built himself a big-bang motor in a road going bike prior to Kawasaki's long-bang 2005 ZX-RR MotoGP bike, certainly before Rossi's big-bang YZR-M1 and well before Yamaha released the cross-plane YZF-R1 in 2009. You'd have to look back at 90's 500 GP 2-stroke history to find his inspiration. While the MotoGP boys do it to increase tyre grip when getting on the power while leant over, its done in road bikes to  produce a more torquey v-twin feel to the power delivery.
In a standard 4cyl motorcycle engine, the pistons move in pairs. The outer two, cylinders 1 & 4, are opposed (180º apart) from cylinders 2 & 3. Each time one pair of pistons is up, one of them fires. This way there's a power stroke every 180º of crank revolution. It's this even, regular output of power that makes a 4 cyl 4 stroke a smooth engine. So, how is this converted into a big-bang motor?
Well, that's simple really. You just fire both pistons of each pair at the same time. That would mean the first pair of pistons fires and then 180º later the second pair fires. You wait 540º and then it happens again. You get two pulses of power close together and then a nice long break for the rear tyre to attain maximum grip (considering lean angle etc) before the  next power pulse hits again.
Gyro told me he didn't really consider this to be a proper big bang engine (though by definition it is a long bang engine of the type Kawasaki used on Shinya Nakano's '05 ZX-RR) as most big bang engines have purpose built cranks and that was an expense Gyro couldn't justify. The job was easy enough he said "You just get a set of cams welded and regorund. Fit them and check piston clearance, and you're away." The man in Australia for this job is Ivan Tighe and fortunately he lives witihin driving distance of Gyro's northern New South Wales property.
What works in your favour is the ignition system. Most inline 4 cyl motorcycle engines waste a spark at the end of the exhaust stroke, since the crank is passing the ignition sensor at that time (again) and it doesn't affect anything to have the plug fire again. So changing the firing order in this way (long bang) let's you take advantage of this design characteristic and in theory, after you change the cams, the bike should fire straight up. There was some mucking around with the exhaust system, because you don't want the paired cylinders firing into the same collector at the same time, but that's not too difficult a task.

What possibly doesn't work in your favour however is the internal structure of the engine. Since two pistons are firing where before only one did, twice as much tourque is being applied through the crank and primary chain to the gearbox. And since that power is now bunched up, the effect would be more akin to a jerk on the drivetrain than a steady pull. It's a tough motor,  but the risk of damage was a nagging doubt in Gyro's mind. The motor never suffered a mechanical failure, but it wasn't hard to imagine that it could. It was this concern that eventually led Gyro to return the motor to stock. And that's how the bike is now. Less of the show bike, more of the go bike!



Previous articles on Gyro's bikes can be found here and here. Enjoy :-)

2 comments:

  1. so clean you could lick it. How do you control the hypertension when a spec of dust settles on it ?
    Nice to look at tho - Bangers

    ReplyDelete
  2. Hey Bangers - no time to worry bout dust, just hang on!

    ReplyDelete