Kawasaki’s 750cc four cylin­der rac­ers were the choice of cham­pi­ons and pri­va­teers alike in the 1980s through to the 2000s: this replica is a lit­tle dif­fer­ent…

Classic Racer - - CLASSIC RACER ANTHONY GOBERT REPLICA - Words: Jeff Ware, Heath Grif­fin Pho­to­graphs: Heather Ware, JPM

Kawasaki’s in­line four-cylin­der 750cc pro­duc­tion rac­ers did well world­wide in the var­i­ous cham­pi­onships they were el­i­gi­ble in. In 1988, with the new global se­ries – the World Su­per­bike Cham­pi­onship – prov­ing to be the per­fect way for the ma­jor man­u­fac­tur­ers to show­case their new machin­ery, the long-inthe-tooth Kawasaki GPX750 needed re­plac­ing.

The first mod­els of the ZXR750 se­ries, the H1 and H2, had mo­tors based closely on the old GPX’S, but thechas­sis and styling were more in keep­ing with the com­pe­ti­tion of the time, most no­tably the racier ho­molo­ga­tion spe­cials such as Honda’s V4 RC30 and Yamaha’s OW-01. The Kwak would de­velop and evolve both on road and track, be­com­ing the ZX-7R from 1996 on.

On track the bike would be­come the only in­line four-cylin­der 750 to win the WSB ti­tle in 1993 with Scott Rus­sell aboard the Muzzyrun ma­chine but around the world the ‘green mea­nies’ would do well in all lev­els of rac­ing, be­ing plen­ti­ful, pow­er­ful and rel­a­tively cheap to run/tune – es­pe­cially in com­par­i­son to the likes of the Du­cati V-twin 888/916 fam­ily…

We are ‘down un­der’ and the An­tipodean con­nec­tion to the ZXR/ZX-7 se­ries is an im­por­tant one. Rob­bie Phillis cam­paigned the early ver­sions and the ini­tial ‘fac­tory’ ef­fort was run out of Aus­tralia. Rid­ers in­cluded race win­ner Aaron Slight from New Zealand. The Aussie con­nec­tion car­ried on even with the likes of Rob Muzzy and his Us-based team be­com­ing the fac­tory Kawasaki en­try in WSB from 1993. Slight was team-mate to Rus­sell in his ti­tle-win­ning year, but when the Kiwi went to ride Honda’s new V4 – the RC45– in came young­ster An­thony Go bert:aw­ild-rid­ing

Aussie who would ap­pear at the fi­nal round at Phillip Is­land as a re­place­ment for Terry Rymer.

Here’s where Heath Grif­fin – the cre­ator of this amaz­ing ma­chine – comes in. He’s al­ways had a soft spot for the 750cc WSB ma­chines (and 500cc two-stroke GP bikes too) but build­ing a four-stroke 750 replica of the rac­ers is eas­ier – and cheaper – to do… This bike was bought from a mate af­ter Heath and his wife An­gela re­turned from an ex­tended work­ing hol­i­day around Aus­tralia and then it was built to what you seenow.

Heath says: “I men­tioned to a mate Jon to keep an eye out for a ZXR750, to which he replied: ‘What about a ZXR750R?’ He then told me that another mate of ours, Mark Dean, had bought one while I was away and was now look­ing to off­load it. I was straight on the phone and a deal was struck. Af­ter pick­ing up my new pride and joy it be­came my daily trans­port to work and univer­sity. That’s right, a ZXR750R M1, lim­ited-edi­tion World Su­per­bike ho­molo­ga­tion model was my daily work hack! Sadly within a year the bike de­cided to throw the num­ber two con-rod out through the crank­case.”

Heath then started to look for a re­place­ment mo­tor on the cheap and found that the ZX-9R mo­tor was a pretty straight­for­ward swap – handy as it was cheaper than a 750 M mo­tor…

“So in goes the ZX-9R mo­tor, back on the road, job done. A few months of happy com­mut­ing go by, and off we go to Oran Park for a ca­sual friendly track ride day. By the end of the day I re­alised that the pe­riod 1993 brakes/sus­pen­sion left a lot to be de­sired and I didn’t want to trash the rare road-go­ing body­work and al­loy tank: time to strip that stuff off and build a track-day only ma­chine.”

Heath set to work: “At first I was look­ing at build­ing an authentic An­thony Gobert replica, but the pukka Oh­lins forks and AP six-pot calipers from that era were too ex­pen­sive. In­stead I’d make the bike per­form on a bud­get.”

The front-end of the ma­chine would ef­fec­tively be from a Yamaha YZF-R6. “I pressed out the steer­ing stem and turned it down to fit the ZXR in­ner bear­ing race, made up a small spacer to ac­count for the slightly longer R6 steer­ing stem, and pressed it all back to­gether with some new ta­pered roller bear­ings.

“At this time I also fit­ted up the R6 master-cylin­der with some HEL braided lines and SBS race com­pound pads. A match­ing five-spoke R1 rear rim, brake caliper, and master-cylin­der were or­dered to match. Be­ing a fan of braced-up SBK swingarms (and not hav­ing the 4000 Eu­ros for a proper TKR one) I or­dered a 2005 model ZX-10R swingarm. These look a bit like a fac­tory swingarm from that very era.”

To get the look right – the ZXR-R frame be­ing light grey and the swingarm be­ing black – Heath set to work with paint strip­per and Scotch-brite pads to get a brushed al­loy look. He said: “Once the tape mea­sure came out it be­came ap­par­ent that this mix­ture of parts was go­ing to re­quire some work to fit! The R1 axle is a lot larger than that of the ZX-10R and no bear­ings were avail­able that would cope with the dif­fer­ence. To deal with this mis­match ei­ther a heap of spac­ers were go­ing to have to be made, or the axle slots and chain ad­justers in the ZX-10R swingarm needed to be ma­chined out to fit the R1 axle. It is about now that be­ing owner of a pre­ci­sion CNC ma­chin­ing com­pany - Rus­sell Symes & Com­pany – started to come in handy.”

Heath ini­tially de­cided to mod­ify the swinger: “I was so wrong, there­fore to the ma­chin­ing cen­tre it went. Now along with the prob­lem of fit­ting the R1 wheel, the 20042005 ZX-10R swingarm is sig­nif­i­cantly longer than that of the ZXR750R, so I also made up some blocks for the ad­justable swingarm pivot to move the pivot po­si­tion as far for­ward and up as pos­si­ble in or­der to keep the wheel­base to a min­i­mum. My sin­cere thanks to my friend Max at work who is a fel­low bike fan and stayed back late in his own time to help out with some of these ma­chin­ing jobs.”

Heath adds: “The fi­nal part of the chas­sis build was to find a de­cent rear shock. De­spite nu­mer­ous emails to Oh­lins, I was told that a suit­able unit couldn’t be sup­plied. Lucky for me a brand-new old stock WP race shock for a ZX-9R turned up on ebay. Cou­pled with a 2005 Kawasaki ZX636 link­age, and a small mod to in­crease the rear ride height, this shock was a per­fect fit.”

Body­work was next – and this had to look ‘right’. “I man­aged to source a full set of ex TKA (Team Kawasaki Aus­tralia) car­bon-fi­bre fair­ings, in­clud­ing a CF petrol tank, al­loy sub­frame, and an ex Troy Bayliss torque-arm,” ex­plains Heath. “Many hours were spent strip­ping and patch­ing the body­work to get a de­cent base for the new paint job. Next is­sue was find­ing the cor­rect tone of green for the job. De­spite days of search­ing, I couldn’t get any­one to sup­ply me the right colour. By the time I got to the fourth paint shop, I made the owner a deal that if he’d give me one chance to mix it my­self I’d leave him in peace and pay for the tin no mat­ter the re­sult. Lucky for me the re­sult was good and I left the shop a happy man!”

Heath bought him­self a spay gun and did the paint him­self – brave man: “It took a cou­ple of goes, but I’m pretty happy with the re­sult. It’s not show bike qual­ity, but cer­tainly good enough for a track bike. To fin­ish off the look I es­ti­mated the graphic sizes off old posters and pho­tos of An­thony Gobert and Scott Rus­sell and had the stick­ers laser cut. With these fit­ted, along with a ‘Gobert’ reaper on the tail­piece, and some Guy Martin stick­ers on the belly pan (don’t ask) the aes­thetic trans­for­ma­tion was com­plete.”

Now, what to do with that stock ZX-9R mo­tor? Heath says: “I was orig­i­nally run­ning the 39mm Kei­hin flat-slides off the 750R mo­tor, how­ever these were in se­ri­ous need of a re­build, and there­fore gave me the per­fect ex­cuse to source some shiny new 41mm flat-slides from the same man­u­fac­turer. These also in­cluded medium length ve­loc­ity stacks, and came to me al­ready jet­ted to suit the 900 mo­tor, with a later dyno run prov­ing they were pretty close to spot-on straight out of the box.

“To house the flat-slides I orig­i­nally looked at us­ing a gen­uine WSBK fully en­closed air­box, how­ever some mea­sure­ments re­vealed that this wouldn’t fit over the taller 900cc en­gine, so a cus­tom fab­ri­ca­tion was re­quired. This was done by lin­ing the top of the mo­tor and in­side of the frame rails with plas­tic, then fill­ing this with an ex­pand­ing foam resin to cre­ate a mould. From the fin­ished mould I made my first at­tempt at work­ing with car­bon-fi­bre. The re­sult­ing vac­uum bagged wet lay-up car­bon-fi­bre air-box cer­tainly won’t win any beauty con­tests, how­ever it fits per­fectly, max­imises air-box vol­ume, and is su­per-light. It is pretty much com­pletely hid­den un­der the tank (which also acts as the air-box lid, like the fac­tory bikes), so the im­per­fect fin­ish is not re­ally crit­i­cal. I also moulded up the two air-in­take ducts.”

In­ter­nal en­gine mods have been kept min­i­mal. The head has had the ports ti­died up and matched to the in­take man­i­folds, the valve seats have been fully blended, and the cham­bers have been mod­i­fied as per the KRT man­ual, but how? Heath adds: “All this was done in my shed with the trusty Dremel. Com­plet­ing the head work was a light skim on the mill at work to up the com­pres­sion and in­stal­la­tion of the 750R dou­ble valve springs. A full re­build is planned for the fu­ture, which will in­clude a Zlock 950cc big-bore kit, a fully fresh­ened up head, some more com­pres­sion and maybe some ve­loc­ity port­ing. I will also be in­stalling the close ra­tio gear­box out of the 750R mo­tor.”

Other bits and pieces in­clude a Dy­natek ad­justable ig­ni­tion sys­tem: “The electrics are to­tal loss, with the al­ter­na­tor re­moved and a cus­tom car­bon-fi­bre bat­tery box po­si­tioned in its place,” says Heath. “A work­ing starter mo­tor is re­tained as I just don’t find it en­joy­able to push start mo­tor­cy­cles. A ZX-12R ra­dial clutch master-cylin­der helps re­duce arm pump with a much lighter pull than stock, and a dig­i­tal temp gauge rounds out the con­trol mods.” Matched to the mo­tor was a brand­new Akrapovic Race sys­tem for a ZX-9R, which – al­though not a Muzzy sys­tem like the orig­i­nal bike used – is more suited to the ZX-9R mo­tor. Heath says: “The cur­rent dyno fig­ure is 136.5bhp at the rear wheel, with­out ram-air, so with these mods 150-160hp should be read­ily achiev­able.”

So, Heath, what’s it like to ride? “Well, since com­ple­tion the bike has been to nu­mer­ous track days. The rear sus­pen­sion with the WP shock has been fan­tas­tic straight out of the box, with min­i­mal ad­just­ments re­sult­ing in ex­cel­lent grip and tyre life. The front-end is also very good, and the bike on the whole han­dles fan­tas­ti­cally. I love it! And it looks the part, too!”

Squint and it could al­most be the real thing...

41mm Kei­hin flat-slides sport medium-length ve­loc­ity stacks.

Much ma­chin­ing went into mak­ing this work! R6 forks ape Oh­lins orig­i­nals.

Paint was mixed by the owner him­self!

Mo­tor good for 130-140bhp.

Wood­craft rear-sets.

Brushed ally frame took el­bow grease!

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