Aus­trian reader Wolf­gang with his spe­cial brew bike!

Pop the Ket­tle on and we will tell you about one Aus­trian’s amaz­ing cross be­tween a Suzuki GT750 and a Bi­mota HB1.

Classic Motorcycle Mechanics - - CONTENTS - WORDS AND PHO­TOS: WOLF­GANG HROMADA

It’s fair to say that Bi­mota’s HB1 has al­ways been one of Wolf­gang Hromada’s all-time favourite mo­tor­bikes. Re­cently the 58-year-old sales di­rec­tor from Vi­enna made his dream come true – he built his own in­ter­pre­ta­tion of the HB1 in a Bi­mota-like chas­sis and Suzuki’s sem­i­nal GT750 Ket­tle en­gine. Wolf­gang ad­mits: “Since I was a teenager, I was al­ways swim­ming (or should I say rid­ing) against the main­stream in re­gards to mo­tor ve­hi­cles. While my friends in the 1970s all had two-stroke mopeds like KTM, PUCH, Zün­dapp etc. and some­times reached the-then magic 60mph mark, I had to have a four-stroke Honda SS50Z; hope­lessly slower on flat ter­rain, but lead­ing the pack when it went up­hill. When we grew older and got our mo­tor­bike li­cences, my friends ex­changed their mopeds for four-stroke bikes like the Kawasaki Z650, Honda CB500 and the like; I had to do the op­po­site of course and got my­self a 1976 Ket­tle, Suzuki’s wa­ter-cooled, three-cylin­der two-stroke bike. It was not nec­es­sar­ily my plan, it just hap­pened when this bike was of­fered to me in 1981 at a fair price. To­day, 37 years later, I still have this bike. I fully re­stored it in 1999, and still ride it oc­ca­sion­ally.” Over the years, Wolf­gang bought other bikes depend­ing on his fi­nan­cial sit­u­a­tion (sound fa­mil­iar?) but he rarely sold any on, so he was able to keep most of them. He says: “As a re­sult, I have a col­lec­tion of 20 mo­tor­cy­cles cur­rently, each ei­ther in very good orig­i­nal con­di­tion, fully re­stored or cus­tomised to my tastes. The range is from 50cc to 1100cc, from 1971 to 2003: half of them be­ing clas­sic two-stroke bikes from the 1980s.

“One of these cus­tomised bikes is my Bi­mota Suzuki GT750B. For me Bi­mota’s HB1 has al­ways been one of the most beau­ti­ful and de­sir­able mo­tor­cy­cles. For ob­vi­ous rea­son (only 10 have been built), it was al­ways un­af­ford­able. At least, my be­spoke GT750 al­ready had a typ­i­cal Bi­mota-style seat unit with the duck-tail 30 years ago. “My dream of own­ing one of Bi­mota’s clas­sic mod­els goes back much longer than the 10 years that I had a GT750 spare en­gine, ported to TR750 specs, lay­ing in the cor­ner of my work­shop/garage. I pur­chased it from a chap in the UK, and I had plans to build a cafe racer one day. I had al­ready pur­chased an ex­tra com­plete GT750 donor bike mi­nus en­gine as ba­sis for my build soon af­ter. “Over the years, I hunted for suit­able com­po­nents to im­prove on the Suzuki’s out­dated tech­nol­ogy to some­thing more ex­clu­sive and bet­ter per­form­ing. So ebay and sim­i­lar sites were pe­rused at night and I pur­chased a 38mm fork front-end, 18in wheels and brake discs off a Kawasaki Z1000J plus some other ac­ces­sories for the planned cafe racer project. “Then, one day, it must have been in 2014, I was sit­ting with friends over some re­fresh­ments at my favourite place, Sch­wammerl­wirt in Vi­enna (this would trans­late to some­thing like ’The Mush­rooms’). One of my friends told me about a Ser­bian guy who builds beau­ti­ful car­bon body parts mainly for clas­sic Laverda mod­els, but he ob­vi­ously had also built a tank and seat unit in ex­actly the same HB1 style re­cently for a project bike in the US. I am not sure if it was the beer which ac­cel­er­ated my de­ci­sion to build an HB1 replica with my Ket­tle en­gine in­stead of a typ­i­cal cafe racer, but I im­me­di­ately had an ex­act pic­ture of the fin­ished bike in my head. My brain at that mo­ment was al­ready in a state where it could hardly for­mu­late com­plete sen­tences, only able to see pic­tures, but this im­me­di­ate de­ci­sion I would never re­gret, it just hit me like light­ning! “My new plan was to build a HB1 replica, as close as pos­si­ble to the orig­i­nal, us­ing com­po­nents from that era and pos­si­bly avoid­ing mod­ern tech­nol­ogy. A bike that could have looked the same in the early 1970s. “I started to ship my spare GT750 frame, front-end, an af­ter­mar­ket swingarm, wheels, an HB1 tank cover as a tem­plate and an empty en­gine to a Ger­ard (aka Jer­ryt) in The Nether­lands, who builds beau­ti­ful cus­tom chas­sis and body­parts in steel and

al­loy. I in­cluded sketches with di­men­sions of how I wanted the frame to be mod­i­fied to mimic the HB1 chas­sis. Jerry looked at it, placed the tank cover on the frame and re­alised that the most typ­i­cal de­sign el­e­ment of the Bi­mota, the con­tour of the tank with its con­tin­u­a­tion in the frame down to the swingarm pivot point, was not eas­ily achiev­able by just mod­i­fy­ing a stock frame. So he pro­posed to build me a com­pletely new frame and swingarm, in ex­act Bi­mota HB1 style, to ac­cept my GT750 en­gine and the Z1000J forks that I still wanted to use. To my sur­prise, the price he was ask­ing was more than fair, so it took me only a few sec­onds to hap­pily agree to that plan. “Dur­ing the fol­low­ing weeks, I reg­u­larly re­ceived pic­tures show­ing the ac­tual state of my build, so that I could ad­dress any po­ten­tial changes if needed be­fore Jerry con­tin­ued with the next steps. I saw how more and more tubes were bent, cut, milled and welded around my en­gine, keep­ing more or less the Ket­tle’s orig­i­nal ge­om­e­try ex­cept a steeper steer­ing head and dif­fer­ent swingarm pivot po­si­tion. Us­ing the tank cover as a tem­plate, the frame ex­actly matched the tank, which is quite the op­po­site of what other peo­ple would nor­mally do – usu­ally the frame comes first, and then the tank is made to match it. “The swingarm in­cor­po­rates an ec­cen­tric chain ad­juster and the swingarm pivot has moved a bit for­ward, closer to the sprocket to re­duce the im­pact of chain ten­sion on the rear sus­pen­sion. The orig­i­nal HB1 frame used the en­gine as a stressed mem­ber and had no lower sub­frame. I did not want to put that much stress on the old GT750 en­gine since I did not know if it was de­signed for this, so I had sep­a­rate de­tach­able lower frame cra­dles pro­duced, which were pow­der-coated in black later, so that they op­ti­cally al­most dis­ap­pear on the fin­ished bike with the red frame. “Af­ter eight weeks, I re­ceived the com­pleted frame and swingarm back home in Vi­enna. Dur­ing the fol­low­ing months – my job only al­lows me few hours here and there to spend in my work­shop – I com­pletely dis­as­sem­bled the en­gine to check ev­ery­thing, re­place all seals and gas­kets and had the crank in­spected and new crank seals in­stalled. I just did not want to rely on an en­gine that was sit­ting on the garage floor for over 10 years and which I had

not built up my­self. I re­placed the orig­i­nal head gas­ket with a cop­per gas­ket and ex­actly matched the com­bus­tion cham­bers in the head with the cylin­der bore with my Dremel. All en­gine parts had been vapour blasted, and then ei­ther painted or pol­ished. “Fit­ting the af­ter­mar­ket Mikuni VM34 carbs was a chal­lenge too. The float bowl of the right-hand carb was rest­ing on the clutch hump of the up­per en­gine case, so I had to find slightly an­gled carb boots to clear. Most of the re­quired smaller parts like col­lars, ec­cen­tric swingarm ad­juster, rear brake caliper adapters etc. I fab­ri­cated in my own lit­tle work­shop, while more com­plex parts like the up­per triple clamp or the front caliper adap­tors I out­sourced. The wir­ing was com­pletely built from scratch, and most elec­tric parts like bat­tery, rec­ti­fier/reg­u­la­tor, starter re­lay, ig­ni­tion switch are lo­cated in the tri­an­gu­lar space above the swingarm pivot to keep wires short and re­duce elec­tri­cal losses. With the bat­tery, I didn’t use pe­riod-cor­rect com­po­nents: I ac­tu­ally put a mod­ern Lifepo4 bat­tery pack into the empty shell of a clas­sic lead-acid bat­tery, to save weight and keep the bat­tery small (the orig­i­nal GT750 bat­tery is a very bulky and a heavy 14Ah type since it has to sup­ply the elec­tric starter). Wher­ever pos­si­ble, I tried to use orig­i­nal Bi­mota parts, but I only suc­ceeded with a pair of clip-ons and the rear-sets. “For the ex­haust sys­tem, I knew from the very be­gin­ning that it had to be a three-into-three sys­tem, in black. I de­cided on a set of Jemco ex­haust pipes from Texas. When I first started the en­gine with these pipes on, it sounded as if there were no pipes on at all! These pipes have pretty small in­te­grated si­lencers, and they sound as if there was no muf­fler at all, cre­at­ing a very loud crack­ling sound: im­pos­si­ble to ride in civilised ar­eas in Aus­tria, I would get ar­rested im­me­di­ately! On the other hand, they look the real deal and are a per­fect fit to the bike. So I put them away on stor­age for some club events or track days where the noise level would be ac­cepted, and or­dered a se­cond set from Jemco, but this time with­out any si­lencers. I de­signed my own ver­sion of the si­lencers by use of sim­u­la­tion soft­ware. They are 20mm larger in di­am­e­ter and 50mm longer than the orig­i­nal Jemco muf­flers but brought the ex­haust noise down to al­most stock level. “I al­ways hate the oil leak­ages at the header flanges of ev­ery af­ter­mar­ket rac­ing ex­haust sys­tem I used till now; I did not want to ac­cept this on my Bi­mota/ket­tle, so I had adapters ma­chined that were welded onto the header pipes of the Jem­cos and now ac­cept the orig­i­nal GT750 ex­haust clamps which bolt to the cylin­der, they are 100% tight now. I also welded bungs for EGT (ex­haust gas tem­per­a­ture) sen­sors on the head­ers, and I use these sen­sors when di­alling in the carbs on the dyno. Once all work on the pipes was com­pleted, I had them Cer­akoted in semi-gloss black. “Brakes? Well, clas­sic Ap-lock­heed brake calipers se­cure more than ad­e­quate stop­ping power; they bite into cross-drilled and skimmed brake discs off a Kawasaki Z1000J. The front brake pump is also a clas­sic Ap-lock­heed: the rear is from the same Kwak model. The clas­sic Z-se­ries mod­els also con­trib­uted with the con­trol switches left and right; the tach is

the orig­i­nal GT750 in­stru­ment, I re­placed the dial face with my own de­sign, with a Bi­mota logo and in­te­grated a neu­tral con­trol light. The only vis­i­ble de­vi­a­tion of the pe­riod-cor­rect ap­proach is the small dig­i­tal KOSO OLED in­stru­ment, in­te­grated into the up­per triple clamp. It pro­vides in­for­ma­tion about speed, dis­tance, coolant temp, bat­tery volt­age, rpm, fuel level, oil tank level, am­bi­ent temp etc. and the con­trol lights for in­di­ca­tors, high beam, fuel re­serve and oil tank level. “Ap­par­ently Suzuki’s GT750 runs on a sep­a­rate oil pump for en­gine lu­bri­ca­tion depend­ing on throt­tle po­si­tion. The re­quired ex­ter­nal oil tank was in­te­grated into my fuel tank by an in­ter­nal di­vider in the rear sec­tion of the tank, with a filler neck un­der the seat. Speak­ing about the seat up­hol­stery, I was not able to find any­one in Aus­tria who could pro­duce it to my re­quire­ments, luck­ily the guy from Ser­bia who pro­duced the body­work was able to con­nect me with an up­hol­sterer in Hun­gary who did a per­fect job for very rea­son­able money! “Fi­nally, the paint job: I am def­i­nitely not an easy per­son to please when it comes to qual­ity of paint­ing. My eyes are very sen­si­tive to any­thing that isn’t per­fect, even a mis­place­ment of a de­cal by one mill­me­tre, I just catch it im­me­di­ately. So it took me many years un­til I found a paintshop who I can fully trust. Franz Fir­linger is a one-man show in a beau­ti­ful ru­ral area close to the bor­ders of the Czech Re­pub­lic. Franz un­der­stands the spe­cial re­quire­ments for cus­tom bikes or fully re­stored bikes com­pared to the rel­a­tively sim­ple task of paint­ing a car. He is a biker him­self and as he’s painted 10 of my bikes I know he’s a per­fec­tion­ist. So, Franz is re­spon­si­ble for the look of my Bi­mota: he painted the wheels, the frame and swingarm, the en­gine cases and the body­work. Cheers Franz! “The frus­trat­ing thing is that I will never be able to do a real ex­tended road test with my bike be­cause of the one-off frame: there is no way I can get the bike street le­gal in Aus­tria. It would be treated like a new bike which was never reg­is­tered be­fore, and it would need to meet ac­tual emis­sion and noise lim­its – you can imag­ine how im­pos­si­ble this would be once you see, smell and hear this Wa­ter Buf­falo! My rides will be lim­ited to pa­rades on club events, maybe track days and on pri­vate roads. It does not mat­ter too much, I en­joy it so much even if I only sit in front of it and watch it, with a pint of lager in my hands (here in Aus­tria we would say “ein kruegel bier”). “I made my dream of an HB1 come true at a frac­tion of the price of the orig­i­nal bike. And don’t for­get: com­pared to my unique replica bike with its large dis­place­ment two-stroke en­gine, an orig­i­nal Bi­mota HB1 is al­most main­stream... and that’s not my thing!”

“I am def­i­nitely not an easy per­son to please when it comes to qual­ity of paint­ing. My eyes are very sen­si­tive to any­thing that isn’t per­fect, even a mis­place­ment of a de­cal by one mil­lime­tre, I just catch it im­me­di­ately. It had to be per­fect...”

ABOVE: Wolf­gang and his amaz­ing ma­chine.

Orig­i­nal frame in­for­ma­tion (be­low) led to copy-cat ver­sion which would hold the three-cylin­der Suzuki two-stroke mo­tor.

At­ten­tion to de­tail was ev­ery­thing for Wolf­gang. This would look like a ‘proper’ Bi­mota ma­chine...

BE­LOW: Ket­tle en­gine lends it­self well to the ‘Bi­mota’ look...

ABOVE: Red frame and seat: pukka Bi­mota!

The DNA of Wolf­gang’s ma­chine comes from this beauty.

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