Yoshimura Suzuki: how to build an AMA winner
If we assume that the bike which Steve Mclaughlin scored the first win for the combined Yoshimura/suzuki tie-up was based on a pumped up GS750, here's how I think they did it.
The GS750 has a monstrous crank, it has huge main bearings and (critically) a straightcut set of gears on the crank and clutch basket. Why is this good? Several reasons: the fact that the side-thrust imparted by a helical gear-set is totally eliminated, there is minimal side-thrust on both crank and clutch basket, i.e. the torque of the engine is not trying to push the clutch (and the crank) sideways in the cases, this force is the main reason that the helical gears in all later roller crank engines are occasionally prone to cracking and ultimately, catastrophic creamed the opposition to win the inaugural Suzuka 8 Hours race, the bike wore the now well recognized ‘S' top fairing, probably a welcome addition in an eight-hour tussle with a 225 kilo, 135 horsepower bruiser.
In 1979 Cooley continued his winning ways, giving Suzuki its first AMA Superbike title and also being part of the squad that led Suzuki to a 1-2-3 result with Ron Pierce on the top step and Dave Emde in 3rd. In 1980 Wes took his second AMA crown after a huge post-race spat between Cooley and Eddie Lawson. Wes had passed Freddie Spencer by a nose to win failure, which isn't good. Also straight-cut gears are marginally more efficient (by a very small margin admittedly) but, if it's there, we'll take it.
By mixing up components from GS750, 850 and 1000 cranks it's entirely possible to create a 750 crank with 1000cc rods, the 1000 rods are tougher and have 18mm small-ends as opposed to the 16mm 750 ones. This facility allows pistons up to 73mm (debatably 73.5 but let's say 73 for now) to be fitted into the little motor. As the cylinder stud pattern is identical on both 750 and 1000 it is feasible to either install a 1000cc cylinder in its entirety or fit 1000 sleeves into a 750 casting. Likewise the 1000 head will fit the 750 stud pattern: the exhaust port angle is slightly different but otherwise with a bit of fettling the whole exercise is very feasible. I built two of these back in the day, one with a mainly stock 1000cc head and another very special one with a host of exceptional works Yoshimura bits.
The stock one was a treat, it revved very easily partially due to the lighter (than GS1000) 750 rotor, and it went on to give its new owner lots of fun. The other one went into a Bimota, sadly I never saw (or more importantly heard) it run. Where is it now? I dunno, any takers? As an addendum to this, whilst most of the components in the later XR69S cranks were standard Suzuki, Pops specified a much stronger XR69 specific forged rod and silver plated bearing cages for the works motors. the race but was then protested for a possible rule infringement regarding the rear shock configuration (possibly something that Steve Mclaughlin had instigated early on in the GS1000R'S career) on Wes's bike. A serious bout of handbags-at-dawn broke out and it was almost five months before an appeal court ruled in Wes and Yoshimura's favour: AMA title number two. In 1980 Wes teamed up with Croz to nail the Suzuka 8 Hours for the second time.
As the premier event in the eyes of the Japanese manufacturers, the relationship between Suzuki and Yoshimura was set in stone. Wes played a pivotal role in the process and in that respect I take my hat off to him, but I'd like to think that the other individual who has been almost struck out of the early Superbike results warrants a bit of credit too, Steve Mclaughlin, for what it's worth, you get five stars in my book.
Interestingly, in 1988 Steve Mclaughlin brought his ‘Superbike' idea to Europe and was instrumental in establishing the World Superbike Championship (or WSB as we often call it) based largely on the rules of the AMA Superbike. The first World Superbike Champion was Californian Fred Merkel, and the rest is history…