SUZUKI GSX-R750F
Jeff Ware on part one of a swift oil-cooled resto.
I’ve just completed a full ground-up restoration of a Slabside in just over three months – phew! I love these bikes and know them inside out, as they were popular back when I was an apprentice motorcycle mechanic, so I worked on them a fair bit. There is little argument against the general belief that the Suzuki GSX-R750F, the very first GSX-R750, was the first true four-stroke street superbike. It was faster, lighter and better looking than any four-stroke motorcycle available. It also out-performed most of the two-strokes and came in at a competitive price compared to its two-stroke sibling, the RG500. The brainchild of GSX-R Project Leader Etsuo Yokouchi, the GSX-R750 re-wrote the sportbike rulebook. Yokouchi-san was a firm believer in pushing technology to improve the breed in an era when many Japanese engineers were too conservative. So how did Yokouchi and the team make the GSX-R so good? What made it so special? To understand that we need to look at what was going on in Japan back then. Most big four-stroke superbikes at the time were simply beefed-up versions of the ‘Universal Japanese Motorcycle.’ They were heavy, poor handling but reliable and over-engineered. We were used to bikes like Suzuki’s own GS range, the Kawasaki Zeds, Honda CB900 and 1100s, Yamaha XS1.1, these were big heavy bikes, with small brakes and low-rent suspension, packaged up in flexible steel frames and finished off with narrow tyres. All of that was about to change… At Yokouchi’s direction, the GSX-R was developed through experience racing the GS and GSX750R, with Kiwi Graeme Crosby and Aussie brother of Warren Willing, Len Willing, (who I did my mechanical apprenticeship under at his shop Willing Motorcycles), riding the GSX750R in the Suzuka Eight-hour in 1984. While the GSX-R was being developed, Suzuki released the RG250WE two-stroke and GSX-R400 four-stroke. Both gave the public and the other big three Japanese manufacturers a preview of things to come from Suzuki. Yokouchi figured that if the GSX-R400 could be made 18% lighter than its competitors, then the scale could be applied to the GSX-R750. The horsepower limit at the time was already an agreed voluntary restriction of 100hp, so he knew that lightweight was the only way forward. Before the project began, he had his engineers strip a GS750 and paint any parts that had not failed out in production blue and any that had failed red. When the parts were gathered together almost all of them were blue. This told him something:
“We were too conservative. Nothing ever broke. Everything was over-engineered…” He set the target at 20% less weight than competitors’ 750s, which meant that both 100hp and 176kg were the goals. Chassis development began alongside engine development. Yokouchi also insisted on using the racetrack dimensions: “What works on the racetrack will work on the street. The motorcycle does not know where it is being ridden.” He started by using the 1983 Endurance World Championship-winning HB Suzuki GS1000R, ridden by Herve Moineau and Richard Hubin, as a base from which to build the GSX-R. Styling was in the hands of the amazing Tetsumi Ishii, who took as many angles from the GS1000R as possible. He did a brilliant job. Since the release of the GSX-R750 in 1985, sportsbikes have gone full circle – lightweight, then heavy, then back to lightweight again, but one thing is certain – motorcycling performance can be split into two clear eras – the eras before and after the GSX-R750F. More than 33 years on the GSX-R750F is still a stunning looking machine. In fact, I rate it as one of the best-looking motorcycles that has ever been released.
On the scales, it is 10kg lighter than the new GSX-R750! Don’t get me wrong – things have come a long, long way in 20 years and the old Slabbie wouldn’t even get close to catching the new 750 on the street or the track – but in terms of era, the 1985 bike must have blown the others into the weeds… I was 10 years old then but I still remember seeing them on the showroom floor of the Suzuki dealership up the street. I’d ride my BMX bike rain, hail or shine to gaze at the bike through the window and dream of owning one – which is why I have one now… The engineers definitely got that motor right – the fact that the new engine is the exact same bore and stroke of 70mm x 48.7mm proves that, despite a swing to a short-stroke 73mm x 44.7mm engine for 1988 and 1989, the factory reverted to the 70mm x 48.7mm engine in 1990 and it has remained that ever since, yet with modern cylinder-head technology, tuning, EFI, metallurgy and electronics, it is now a whopping 50% more powerful. Incredible. So let’s get onto the rebuild. I grabbed this bike for a real bargain off a mate who pressured me to buy it. He knew I’d do it justice and he had too many projects on the go. At the time I really didn’t have the funds or the spare hours to restore another bike, as I was flat out (I still am) trying to fit my RG500 resto into my schedule. However, after a few beers and him eventually showing up at my house with the bike in a van, the deal was done and the cash handed over… The bike was as rough, with a locked-up engine, the wrong carburettors fitted, fairings in bad condition, 17in wheels in place of the originals and crappy mixed fasteners, rust, dirt and general filth everywhere. It needed a full strip-down and rebuild. I decided to just attack it full-on and try and get it finished in a three-month period, otherwise I knew I would not finish it at all. I stripped the bodywork off and set that aside, then hung the bike from the roof of my shed and in one big day on what I call a ‘mechanic’s roll’, I completely stripped the bike back to a bare frame with just the engine in it and laid all the parts out ready for inspection. This gave me the opportunity to list the parts required and go through what I had left over from a previous 1985 750 resto that I had done in 2014. Before I did that, however, I needed to determine whether the engine required a full rebuild or not. Considering the low mileage (under 20,000 miles) and the originality of the bike (aside from the wheels and fairings), I was confident that
the engine was not actually locked-up due to anything serious like a spun main bearing or seized cylinder. After popping the lid off and having a look at the cam-shafts, removing the spark plugs, clutch cover, left-hand crank cover and inspecting as much as I could, I removed the sump and had a sticky beak around. In the end I determined all was okay, so I removed the starter motor and lo and behold the magnets had cracked and jammed it. Happy days… I sourced a new starter motor, serviced the engine (valve-clearances, cam-chain tensioner and cam chain, new clutch plates and springs) and assembled the engine, then resprayed it with the perfect colour match – Mazda Flexible Bumper Bar Charcoal Grey, in a heat resistant flexible paint by Dupli-color (code TB102). It came up brilliantly – the results came from the preparation of high pressure washing, followed by spraying it with wax and grease remover, air-blowing, sanding scale off and repeating the process. Later, with the bike complete, I ran it carefully through heat cycles to cure the paint. Fantastic and cheap! With the knowledge that the engine was a good one, I moved to the frame. This is where hours and hours and days of cleaning the frame and swingarm with a wire wheel in a drill paid off, as after a final polish with Autosol, the chassis looked mint. I did the same with the shock linkages and triple-trees (yeah, okay, Poms call them ‘yokes’) and both ends went back on with brand new bearings and seals. The shock fitted was a custom re-valved 2008 Yamaha R6 unit and the forks got stripped, polished, new seals and progressive springs went in. The top fairing bracket was next. This is a complex unit and, of course, it was bent, along with the one that holds the top of the fairing, mounted to the front of the tank. Getting these straight was painstaking and took a weekend of trial and error, then they were painted black and set aside. I then went ahead and stripped and painted anything else on the chassis that is black, such as the top triple-clamp, handlebars, chain drawbolt plates, bar ends and so forth. Sourcing a set of original 18in wheels was the next job. I was fortunate enough to have a mate with a Slabside racer that had 18s and he wanted to convert to 17s, so we swapped. The wheels then got new bearings and even OEM spacers and seals, they were painted and got new Pirelli Sport Demon rubber. I also painted the rotor inner carriers and polished up the OEM disc bolts before fitting it all up. The axles needed a good clean and polish, I had some near-new sprockets, so that was lucky, and I bought a 530 X-ring chain and fitted that before moving onto the job I hate and had been avoiding – rebuilding calipers and master-cylinders that have crystallised up. I stripped the calipers first and cleaned them up with the wire wheel on the outside and hot soapy water afterwards. Once they were dry I prepped them and resprayed them with a heat-resistant rattle can caliper paint that is a very close match in the gold colour. As soon as the new seal kits arrived the calipers were reassembled with the bleed nipples cleaned out and new rubber caps for good measure. I also cleaned up the plastic pad covers and fitted new pin retaining R-clips. The actual pads were pretty good, so
went back in. Rebuilding the mastercylinders was straightforward using rebuild kits and while they were stripped (clutch and front brake) I resprayed them with sub-frame black enamel. I then did the same job at the rear and rebuilt the clutch slave cylinder before fitting Venhill lines and bleeding the systems up with fresh fluid. My next job was the side-stand, which needed to be stripped and painted and then fitted, along with the original safety cut-off switch. I also polished the gearlever parts and greased the rose joints, fitted new rubber (same on the brake pedal) and fitted that back to the motor. The rear-sets were polished and refitted as well. An afternoon of beer and rebuilding the pillion pegs, complete with spring and ball bearing retraction working was spent and then it was time to turn to the finer details like the wiring loom, OEM fasteners, lights and, of course, the exhaust system and carburettors. I chose to do the loom first. This was a massive job, I had to completely remove it, lay it out and painstakingly repair the entire thing with plenty of new connectors, soldering, heat-shrink, tape and plastic wrap. It was a day of work and another full day routing it as per the original, along with other lines and cables. Once the wiring was in, I stripped and repainted the battery box, fitted a new battery and tested the loom and dummy tested all the lights and the horn, which itself had been stripped and rebuilt, as it was OEM. With everything eventually working I turned my attention to the dash, which got new foam around the clocks (important) and some small dents and scratches taken out. I resprayed the mounting plate and frame and fitted new mounting/damping rubbers for each clock back. Before fitting the dash I assembled the headlight assembly after restoring all the parts nicely, then the dash went in place and a new speedo cable. Now came the toughest job really, rebuilding a very used set of OEM mechanical flat-slide carburettors I had purchased. These were very hard to find… Anyway, to cut a long story short, I managed to get hold of all the parts that I needed to rebuild these complex carbs and, after a weekend comprising of two ‘big days’, they were stripped, ultrasonically cleaned, rebuilt, assembled and in the bike. As a lot of you will know, the airbox side rubbers are bastards to fit! A new air filter went in and the new throttle cables were hooked up. Happy days… The next big undertaking was the exhaust system, which was a full strip and respray job. Once dry it was re-fitted with new nuts/gaskets. I then had a lovely rolling chassis to admire!