ZD. Early Superbike Iron

Published Nov. 6 2014.

This article is about the Superbikes of the 1970s. The term “Superbike” was overused. Every manufacturer claimed at least one its models was a Superbike. I’m restriction my definition in this article to bikes that actually raced in an AMA Superbike National. Superbike race bikes, not Superbike street bikes.

One of the ideas behind the Superbike class was to provide a less-expensive route to road racing than the existing Class C or Formula 750. AMA Production racing started out with three classes, lightweight (250cc – 400cc), middleweight (401cc – 750cc) and heavyweight (751cc and up). The rules required the bikes to be very close to as-sold by the manufacturer, so the racing was indeed much less expensive.

That all changed in 1976. The AMA replaced the three production classes with a single class with a 1,000cc limit that was raised to 1,025cc in 1978. The bikes had to look like the ones on the showroom floor but many internal modifications were allowed. Let’s take a look at some of the early Superbikes from the years 1976-1979. Five different brands won AMA Superbike races during those years.

BMW R90S
According to Cycle magazine Butler and Smith, the BMW importer, spent $150,000 to field a professional team of racers and mechanics for the new class. Their bike won the championship in 1976 with Reg Pridmore. The B & S racing support was abruptly cancelled right after the 1977 Daytona race but the bikes continued under private sponsorship. They almost won the title again in 1978 when John Long was tied for the points lead at the end of the year, but lost the tie-breaker.

How stock was the racer? Not very. Udo Gietl and Todd Shuster took care of the engine and chassis, respectively, for both the B & S bikes and the effort with John Long. There is a lengthy article by Kevin Cameron about Long’s 1978 Beemer in the March 1979 issue of Cycle magazine. Much of my information is from that article.

The most obvious differences between the 1976 race bikes and the stock bike were dual-plug heads and monoshock rear suspension, Rule books were scanned – the rules required the stock frames but gussets and bracing could be added. The monoshock frame was a very creative form of added braces but nobody protested and the bikes were allow to run. The next year the AMA rules required the style of rear suspension be same as the stock bike, mono or dual. Other frame changes: the engine was moved forward 15mm, the steering head was heavily gusseted and the swing arm was reinforced.

The cylinders jutting out meant they ran cool in the airstream, but they caused ground clearance problems. To combat this the connecting rods were shortened 10mm and cylinders shortened to match. On the ’76 bikes the corners had to be taken with slightly positive throttle so the shaft drive would lift the bike on its suspension. Trail breaking into the turns was not an option. By 1978 Todd Shuster had devised an ingenious anti-dive system that transferred braking forces, via a Cummings diesel engine pushrod, upward to the steering head instead of into the fork lower. Applying the front brake actually caused the fork to extend instead of compressing it. In 1979 I raced one of the ex-B & S BMWs. They had a pretty strong engine and really, really good brakes, even though mine did not have the anti-dive feature.

The stock BMW inlet stubs forced the airflow do a sharp turn inside the cylinder head so Udo cut them off, welded up part of the inlet port and cut new ones that were much straighter. 40mm smooth-bore Dellorto carburetors were clamped to the ends of the new stubs. The inlet port was modified, expanded slightly in the conversion of the inlet stubs but the exhaust port was stock. Crane cams controlled the valves and the stock pistons were replaced by thin-wall Venolia pistons with special rings.

With the pistons going outward and inward at the same time, crankcase pressure varied greatly. Moving outward the pistons caused a vacuum and moving inward they caused positive pressure, in both cases resisting the movement of the pistons. Udo devised an effective crankcase breather with a tube going to an array of reed valves under the seat, neutralizing this power-robbing pressure variation.

There were a number of other changes not detailed here. At one point during the interview with Cameron, Udo Gietl paused and said, “It needs a lot of money, really.”

RegNCookAtRiversideCroppedCook Nielson (31 Ducati 750SS) tries an inside line on Reg Pridmore (163 BMW R90S) at the Riverside Superbike National in 1976. A Tod Rafferty Photo.

Ducati 750SS & 900SS
In 1976 the only bike that could match the BMWs in speed and handling was the Cycle magazine Ducati, affectionately called Old Blue. Cook Nielson rode it and Phil Schilling tuned it, but Cook was out-ridden by the more experienced BMW riders. The Ducati brand did better in 1977, winning two AMA Nationals, then one more each in 1978 and 1979. Cook won the Daytona Superbike race in 1977 on his 750SS-based Ducati while I won at Sears Point on Dale Newton’s 900SS-based Duck.

Cook and Phil were always very open about their modifications – the usual “speed secrets” weren’t secrets atb all, all one had to do was ask. In fact they told the motorcycling world everything they had done to make the 750SS a winner in an article published in the June 1977 issue of Cycle magazine. The displacement was 883cc, up from the stock 748cc, using Venolia forged pistons with lightened Toyota wristpins and Yamaha XT500 rings. The Ducati gearbox was replaced in total with one from Marvin Webster. Jerry Branch ported the heads and re-worked the inlet manifolds. The stock 40mm inlet valves were replaced by 44mm ones from a Harley-Davidson and they installed 38mm BMW exhaust valves.

Their pal Pierre DesRoches added some bracing to the steering head area of the frame and removed all the stuff below the engine that mostly held the center stand. There was actually no indication that the frame needed the extra bracing but they put it in “just in case.” The stock wire-spoke wheels were replaced by lighter, stiffer Morris magnesium wheels fitted with Goodyear racing slicks, the muffler shells were converted to racing megaphones as per the rules, and the iron front disks were replaced with lighter Hunt plasma-sprayed aluminum rotors.

The 750SS came with a race kit that included an oil cooler and oil lines, hotter cams (called “Imola cams”), and high header pipes. Phil installed the cams, oil lines and oil cooler, adding a full-flow spin-on filter that was held in a custom bracket under the tank. The high header pipes had been in use for a while as the stock headers contacted the ground at even modest lean angles.

More work was done inside the motor besides the gearbox. For example, all the original bearings were replaced with high-grade German and American stock. It was an exceedingly thorough effort. Even though Cook and Phil were friends I was afraid to ask how much they spent on it.

Our bike took a little less work. We started with a newer 900SS which had a few improvements over the 750SS, mainly an oil filter and electronic ignition instead of points. The oil filter was partial flow – oil to the cams was filtered but oil to the crank was not. Dale modified the oil galleys to make it a full-flow system. Of course he installed the oil cooler and external oil lines that came in the race kit, and we used the high headers and megaphone exhaust.

We copied most of the chassis modifications that Cook and Phil did, making improvements where possible. For example the Morris mag wheels had little shock absorbing ability, just a plastic collar around the bolts that held the sprocket to the wheel. Dale engineered a way to adapt the Ducati’s standard cush hub to the wheel, giving the engine internals much more insulation from bumps and jolts from the rear wheel.

We left the motor mostly alone compared to the work Cook and Phil did. Our 1977 Sears Point winning bike used the stock pistons, giving an actual displacement of 864ccs. I think Dale installed the Webster gearbox but I can’t say for sure. We did use the Imola camshafts. The ports were just cleaned up a little, not the extreme porting that Jerry Branch did on Old Blue.

It was interesting to compare the results of the two different approaches. In 1978 I had the opportunity to ride a bike with the Nielson/Schilling motor. Dale’s Sears Point winning bike had considerably more torque and available acceleration but ran out of breath around 7,800 rpm. The motor from Old Blue gained speed more slowly but was able to rev up to 9,000 and had a much higher top speed. At Daytona the speed trap read 150 mph for Old Blue.

Our bike’s top speed was never measured but the stock 900SS claimed a top speed of 130 mph. With the Imola cams and free-flowing exhaust ours might have neared 140 mph. The dyno showed Old Blue had 90 rear wheel horse power at 8,300 rpm. We never put our bike on a dyno but I’m guessing we had about 70-75 rear-wheel hp somewhere around 7,500 rpm.

Kawasaki Z1 & KZ1000
The Kawasaki Z1 was the backbone of Superbike racing in those early years. It was the championship machine in 1977 and 1978 with Reg Pridmore. The Yoshimura team chose the Z1 for its initial platform and stuck with through 1977. During this period there were only a couple of riders each on Ducatis, BMWS and Moto Guzzis but there were a handful of Z1 racers including champ Reg Pridmore, Wes Cooley, Keith Code, Harry Klinzmann, Bill Addington, Steve McLaughlin, Dave Emde, and more. Freddie Spencer won two Superbike races in 1979 on a Kawasaki KZ1000.

The reason for this is probably because the Kawasaki Z1 motor, and that of its descendent the KZ1000, was the closest to the Superbike specs in those years. The Kawasaki was the only realistic option from the major Japanese manufacturers. Honda’s CB750 had a single overhead cam engine with 2 valves per cylinder and a true displacement of 736cc. There were oversize kits available to raise the capacity to 812cc but still it was SOHC, 2-valve per cylinder versus double overhead cams and four valve heads. Yamaha was the king of Class C/Formula 750 road racing and they weren’t really interested in the upstart Superbike class. Suzuki had the GT750, the water-cooled 3-cylinder two-stroke, but by 1976 the writing was on the wall for 2-stroke machines in the form of increasingly stringent emission controls. Besides, Suzuki was busy developing the GS750 4-cylinder four-stroke bike and didn’t seem interested in trying to turn the touring-oriented GT750 into a sport bike.

The Z1, on the other hand, was a sporting motorcycle from the word go. With a strong, reliable 903cc motor (1015cc in the KZ1000) it didn’t take much to get it to make ample horsepower. The problem with the Z1 was getting that horsepower to the ground. The frame was loosely based on the Norton Featherbed frame, which worked great with a 500cc single-cylinder motor with 50-some horsepower, but wasn’t really adequate for a heavy, 4-cylinder with over 80 hp stock and 100 hp available with only a few modifications. Distortions under load caused the relationship between the steering head and swing arm pivot to change, producing creative handling. The swing arm pivot was sloppy and the arm itself twisted under load.

Let’s take a look at what tuner/builder Pierre DesRoches had to do to the KZ1000 chassis to produce the Kawasaki that was Superbike champion in 1979 and 1980. An article in the November 1978 Cycle magazine provides most of this information.

The swing arm tubing was widened by a quarter inch and fitted with an oversized pivot pin. The bosses in the frame were then precision reamed to provide a very tight fit. The top mount of the rear shocks were moved 4.75 inches forward from their stock position, a “lay-down” position providing 6 inches of rear wheel suspension. With the shock mounts moved forward DesRoches was able to cut away much of the rear sub-frame as well as the turn signal and passenger foot peg brackets, recovering some of the weight lost by making the swing arm heavier.

Lots of attention was paid to the frame strength around the steering head. Their frame was full of reinforcing tubes and gusseting plates. Then DesRoches got radical. The entire steering neck was cut off and replaced with a larger diameter neck fitted with Yamaha TZ750 tapered roller bearings. Relative to the stock neck position the new neck was moved lower to increase ground clearance, rearward to put more weight on the front wheel, over to the right for proper alignment of the front and rear wheels, and at a greater angle to improve steering.

With the frame thus improved the motor was used to stiffen it. The stock mounting bolts were rather loose and were replaced with oversized bolts that needed to be ream-fit to the frame, but the resulting tight fit locked the motor in place.

The motor is heavily modified as well, both for ground clearance and power. The change in Superbike rules between 1977 and 1978 allowed Pierre to completely remove the alternator and the rest of the charging system from the crankshaft’s left end and replace the stock cover with a flat plate, removing about four inches from the left side of the motor. The right side changes were more subtle. The points cam was shortened by removing the advance mechanism, allowing the points plate to move inward and the cover to be trimmed about an inch. Both these mods provided more cornering clearance.

The bottom end of the motor was otherwise basically stock with a close-ratio five speed transmission, available from Kawasaki. At the top end were 70mm Yoshimura pistons giving a true displacement of 1,015cc (1,025cc was by then the legal limit). C.R. Axtell handled the mods to the cylinder head, doing a porting job that increased flow by about 200 percent when fitted with a Yoshimura cam.

The resulting bike produced around 130 rear-wheel horsepower and went straight and cornered well. Mind you there were many other mods described in the article but I want to avoid tech overload.

freightrain600BIGReg Pridmore (Kawasaki KZ1000) leads Mike Baldwin (Moto Guzzi 850 LeMans), Myself (900SS Ducati), Erik Buell (900SS Ducati) and Ron Pierce (Suzuki GS750) in Loudon’s turn 6 in 1978. Photo from Reg Pridmore collection.

Suzuki GS750 & GS1000
Frustrated by their Kawasaki Z1’s poor handling, the Yoshimura team started working on the newer Suzuki GS750 in July of 1977. The frame was stiffened and reinforced with extra tubing, then fitted with lay-down rear shocks. At the front a special bottom triple clamp, milled out an aluminum block, changed the front wheel angle to make the steering more steady and predictable. Compared to the work DesRoches did on the Kawasaki Z1 frame, the Suzuki frame work was a piece of cake.

Inside the motor, Pops Yoshimura hand shaped 73mm Honda Civic racing pistons, giving the bike a true displacement of 944cc. Cams ground to Yoshimura’s own specifications were used to move valves with larger faces but smaller stems, held in place with special aluminum-bronze guides. Yoshimura reworked the head’s intake and exhaust ports for better flow and milled half a millimeter off the bottom to increase compression.

An August test run at Ontario showed the Suzuki to be nearly as fast as their Z-1 but with much better handling. It also showed that the extra power overwhelmed the clutch, causing it to slip. The test was interrupted when the automatic cam chain tensioner failed and the chain snapped. The team replaced the tensioner with a manually adjustable one and installed a racing cam chain. The clutch basket was modified to hold 10 plates instead of 8.

The bike was ready for the AMA National Superbike race at Laguna Seca in September and rider Steve McLaughlin went out and won; a new bike wining on its first try was noteworthy. Yoshimura dropped their Kawasaki after the 1977 race season and became completely Suzuki oriented.

Moto Guzzi 850 LeMans
I’m not as familiar with the Moto Guzzi as the other bikes and as far as I know there aren’t any articles describing its modifications. Tuned by Reno Leoni and ridden by Mike Baldwin they had the only non-BMW win in 1976 when Mike won at Loudon. Rumor has it that Leoni did some special reshaping of the combustion chamber to increase compression and improve combustion, but I can’t confirm that. Maybe Reno will see this and make a comment.

In 1977 at Charlotte Motor Speedway Baldwin and Kurt Liebman finished one-two on the Leoni-tuned Guzzis. The Charlotte track was like a slightly smaller Daytona but it was a lot bumpier and the Guzzi’s balance of decent speed and good handling easily out-distanced the more powerful but ill-handling Z1s.

The Moto Guzzi LeMans was a fine sporting street bike, but a little fragile when pushed hard enough to win Superbike races. The team was plagued with mechanical failures. At the 1978 AMA National in Pocono Leoni had switched brands and both Baldwin and Liebman were riding Ducatis.

Also Rans
Honda CB750: East coast rider John Fuchs raced with a modified Honda CB750 and got a string of top-ten places, his best being a 3rd place at the rain interrupted race at Pocono in 1978. Honda wasn’t particularly interested in the Superbike class at first and they had no wins in the 1970s. In 1980 Honda got serious and turned the new CB750F Super Sport model into a winner, but that’s another story.

Yamaha RD400: Superbike rules required the race bikes be based on production models with 351cc or larger motors, and a few riders took to the track with their RDs. They didn’t have much impact as the best finish in the 1970s was a 9th place at the 1977 Riverside Superbike race.

Laverda Jota 1000: One might think this would be a good starting point for a Superbike racer. It was fast but a bit heavy for track work, and there was absolutely no support system for the brand in the U.S. A few Laverda 1000s appeared in the early years, with the best showing a 5th place in the 1977 Charlotte Superbike race.

British Brands: The BSA/Triumph and Norton companies were on the ropes in the mid to late 1970s and riders had absolutely no racing support, but a few loyal-to-the-end men raced them. At Sears Point in 1977 the 9th and 10th places were a Triumph and a Norton, respectively. The Triumph was a twin and the Norton was probably the 850 Commando.

AMA Superbikes in the 1970s proved to be a dynamic class, bringing in an excellent mix of brands, which is what supporters of the new class hoped. Winning bikes included BMW, Kawasaki, Ducati, Moto Guzzi, and Suzuki. Top ten spots were earned by Honda, Yamaha, Laverda, Triumph and Norton. As for being inexpensive, well, not so much.

Who was missing? The only major brand not listed here is Harley Davidson. At the time it seemed Harley was concentrating on the dirt flat track side of racing — miles, half-miles, and TT events. Harley did get involved a few years later with Lucifer’s Hammer in the Battle of the Twins class, but that too is another story.

9 thoughts on “ZD. Early Superbike Iron

  1. paul, your always taking me to good memeries as i raced against you in afm back then on a triumph tripple 750,900 from tt motors and later on a 900 ducati thanks paul williams

  2. Great stuff Paul! Since you raced both the BMW and the Ducati perhaps you could provide a riders perspective as to their idiosyncrasies in handling, braking, engine characteristics, etc.

  3. Paul interesting take on early Superbike…as to DesRoches mod’s to the Z1 chassis it was obvious he never had one in a chassis stress jig…the swinging arm and the steering head had NO flex the problems lay in the sloopy swinging arm bolt, weak engine tabs and two flexing down tubes…as to Yosh and Suzuki it was for $$$$ money they changed and the GS750 in a pre-production form was tested several times at Willow with factory technicians to assure its handling…was tje pm;

  4. Hello. Great Blog you have here. I have been searching online for a story that was published I think in Cycle World maybe 1969? I don’t remember the title. It was a fictional story about a guy racing a flat-track Triumph. I know its a long shot but maybe you or one of your readers may be able to shed some light on this and make my old bones happy. regards, Kevin.

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