Thunderchild (<back)
Thunderchild: Engine
Honda’s 750 and the Z900 were used more than any other engine by special frame builders in the 1970s/80s, and for two important reasons; power and availability. Getting a jump, Honda spat out many thousands of 750s as the aftermarket tuning parts grew, but three years or so after the Z1’s 1972 intro, preferences changed. With its solidly engineered wet sump crankcase design, the Kawasaki was better equipped to handle vast increases in output. Iconic as it is, the Z1’s stout, roller-bearing crank, geared primary, oversized clutch and increased displacement out shined rival Honda’s SOHC 750 in every way but one – crankcase width. Ground clearance was an issue on many Z-powered specials, but relocating the alternator to outboard was a popular racing modification for both engines. Not mentioned often enough, the Z1’s factory-issue 5-speed took everything racing threw at it.
Questioning why some builders consider the original 903cc Zed superior to the 1015cc tuning of 1977, I reached out to veteran Kawasaki tuner TJ Jackson. “Back in the day, racers preferred the Z1’s lighter crank and bigger carbs,” reports TJ, who successfully campaigned a Kawasaki drag bike during the same era. Seen as apples and oranges, TJ says the 900 and 1000 are different engines. “As a quick spooling hotrod the Z1 wins, but the 1000 is probably a better all arounder. Not as buzzy or peaky, with less vibration and benefiting from many useful updates. By design all of the old, 2v air-cooled Z-fours are durable, but plainly, these builders were more interested in sustaining horsepower than smooth touring manners.”
Some stolen lines from the spec-sheet says the engine is over-bored to 984cc using Omega 11:1 racing pistons with vented skirts. “Translation, holes drilled” says Jackson, who also pondered the extra “two-thou” clearance for heat expansion in the middle two cylinder walls. Still, as a period document this is a treat to read, and the engine’s vintage shopping list is impressive: Yoshi cams and valves went into the ported head, an electronically boosted contact breaker (need more info on that) and 31mm Keihin (Honda CR) carbs with accelerator pumps. To keep the oil flowing when pinned, leaned, or both, a baffled sump was configured and the factory clutch springs were replaced with Z1 valve springs. The five-gallon alloy fuel tank is baffled too. Per previous mention, Thunderchild’s Harris made Devil 4-into-1 exhaust went missing, but (as with the fairing) this replacement seems to improve it. I’ll need a listen to know for sure! All together, the package dyno-tuned to a reported 135-hp @ 9k rpm.
Slotted in Superbike’s four bike ‘cafe racer’ compo that included a very fast Seeley Honda, and an even faster Dunstall Suzuki, the Harris was dominate. “It took some acclimation to settle in, but in a very short time the Harris slipped on like a warm velvet glove,” wrote one tester. “Simply making speed easier, I soon realized this was a very special bike indeed.” Going on to establish itself as a global engineering force with deep ties to Suzuki, Yamaha, Ducati and others. I was tempted to re-post the build sheet, specification and history documents the owner so kindly shared, but that’s for him to do if he chooses. I’m sure Nick won’t mind if I share some of it though, like this section titled “Start Up Procedure”
1) “Fuel on
2) Prime each carburettor – DO NOT TOUCH THROTTLE
3) Turn Ignition ON
4) Press starter button
5) As engine catches SLOWLY pick up with throttle
Bonneville cams require an idle speed of not less than 2500 rpm
Note: Excessive oil smoke may show due to centre bores being 2 thou’ over allowing for additional piston expansion. Smoke will cease when engine hot.
Warning: Power band between 5,000 and 10,000 rpm”
Also included is a paragraph evaluating the Thunderchild’s engine builder, its condition (then) and reliability record. Written with some depth of subject, it is a glowing testimony of the Kawasaki four:
“The engine was prepared to its present level of tuning by Pat O’Neil, one of the racing world’s tuning specialists, prepping machines for Steve Parish and other famous international riders. Although regular maintenance checks have been carried out there has never been any need to repair or replace any component part due to mechanical failure or excessive wear. Upon retirement from racing at many top events, Goldsmith’s machine had completed over 4000 race miles with only the occasional piston ring replacement, and Thunderchild has covered no more than 500-miles since its race rebuild. With the present rating of 135 bhp, there is scope should you wish to lower the power and extend the life of the moving parts to that of a normal production machine. Having said this I don’t believe there has been an occasion when a Kawasaki engine has failed due to high power output.”
(Nick Burgoyne and his Harris Monoshock. ‘Thunderchild’ fits better. Designed to stand out and among the world’s most exotic when built)
Addressing the bodywork again, the long, swept fairing and its over/under headlight assembly were swapped for the taller and slightly more traditional F1 endurance style. Brilliantly sprayed then fogged in black and red, most agree it is an improvement but not everyone is dialed in on Thunderchild’s elaborate, loud first impression. “I’m told the first fairing didn’t perform very well,” says Nick, who admits Thunderchild is an acquired taste. “It’s definitely a love it or hate it motorcycle, there’s no middle ground.” Ongoing in the process of refurbishing Nick seems intent on keeping it a rider, and that’s exactly what a classic like this deserves.
Art and artistic vision being one of the few things that truly are subjective, Thunderchild exists to pinpoint a time when technology advanced from idea to action, and for that we remain grateful. All of these words, and not one sentence about its aerodynamics? Perhaps I should write more about it, later. Dripping with a sort of deep essence that only the English seem capable of, Thunderchild also represents an era when self expression allowed some humor and intrigue. I’m not alone in this, and it does seem some special builds have filtered into the collector ranks. This indeed qualifies, and gives a chance to again thank Nick for everything. Here’s being sure we’ll stay in touch, so please check this space for updates. Nothing more than a show stopping badass with a hot Kawasaki engine, Thunderchild illustrates what occurs when talent and passion are mixed without reservation. Nolan Woodbury
Harris/O’Neil Monoshock
Engine: 984cc
Omega 11:1 racing pistons. vented. (.002 extra on middle bores)
Yoshimura full race Bonneville cams
Yoshimura one-piece ‘big’ racing valves
DID continuous racing cam chain
DID continuous racing drive chain
Anti surge sump baffle – Duckhams 10w-40 with STP base
Carburation: 31mm Keihin/works Honda with accelerator pumps
Cylinder head has been ported from carb to HPP Devil exhaust
Ignition: Electric assisted contact breaker
Clutch: Springs replaced with standard internal valve springs
135-hp @ 9000 rpm
Gearing options:
15:32 (normal) 15:30/15:35 (optional). Dry weight: 440-lb
Chassis: Harris Performance Products Cantilever Monoshock T45 and Reynolds 531 tube. Every joint manganese bronze welded.
Forks: Ceriani 35mm using Castrol R30
Shock: De Carbon, fully adjustable
Wheels Dymag competition three spoke
Brakes Lockheed twin/single
Photos: Nick Burgoyne, Superbike magazine, Harris Performance