The Goldern Era of Superbikes: Ritchie Thornton's Kawasaki Ninja ZX-7R

August 31, 2018 / by Peter Monshizadeh

Ritchie Thornton and his team race the Thundersport GB Goldern Era Superbike series aboard a race-modified 1997 Ninja ZX-7R. We take a deep dive into this bike build and how it pays tribute to the factory superbikes of its time.

This feature seen on UK Clubsport here.

Sometimes, the best ideas come from the most unlikely places. For Ritchie Thornton, the inspiration to build a motorcycle to compete in the Thundersport GB Golden Era Superbike racing class came after reading a magazine article on the very topic. Captivated by the idea of racing retro superbikes, Ritchie knew he had to put together a fire-breathing machine that would give tribute to the wild superbike racing scene of the nineties.

Ritchie turned his inspiration to reality. Ritchie's Ninja ZX-7Rs undoubtedly pay tribute to the Golden Era of Superbikes. Read on for all the details on these bikes.

The Golden Era Superbike (GES) racing class, which takes place on racing circuits in the United Kingdom, lets sportbikes from production years 1985 through 2000 duke it out under the same rules and regulations as were maintained during that era of motorcycle racing. This meant that Ritchie needed to find a sportbike that had an engine which met the following criteria: a smooth-revving 750cc four-cylinder or a torquey 1000cc twin-cylinder.

Now, it’s important to note that Ritchie is no beginner to motorcycle racing. He raced motocross as a kid and eventually progressed to tarmac, racing a Suzuki GSX-R 600. Excellent bike control and a healthy competitive drive were attributes Ritchie already had in spades. However, following a five-year hiatus from motorcycle racing, he knew that if he was going to start scrubbing tires again, he wanted to do it with something he already was familiar with.

Enter the Kawasaki Ninja ZX-7R.

After 5 years off from racing, Ritchie got back on the scene with the motorcycle he was commuting on: a Kawasaki Ninja ZX-7R.

As it turns out, Ritchie had already been riding a 1997 Kawasaki Ninja ZX-7R every day to work. To many, this bike might seem like an old, heavy, and obsolete sportbike. But remember, the Golden Era Superbike racing class pays homage to iconic bikes and riders of the time. We’re talking about racers such as Scott Russell and Chris Walker. Coincidence or not, both of these legendary riders successfully campaigned Kawasaki Ninja ZX-7RR race bikes back in the day – bikes which are nearly identical to Ritchie’s own road-going machine. With the Ninja ZX-7R having been so influential during superbike racing of the 1990s, Ritchie felt it only made sense to use his own ZX-7R as the foundation for his race bike build.

The rules of the GES racing class allow 750cc machines like the ZX-7R to be over-bored up to 860cc. Using 1.5mm oversized Wiseco pistons, as well as a longer stroke crankshaft from an earlier ZX-7R (the “J” model), Ritchie determined that he could increase his bike’s engine displacement to 824cc. But, as he and his team found out, punching the engine out for maximum performance would end up leading them on quite an interesting journey.

To make the bike competitive, Ritchie decided to go with 1.5mm overbore and a longer stroke for an ultimate displacement of 824cc. This build journey would prove to have its obstacles, however.

Aside from boring out the engine to fit the oversized Wiseco pistons, some special work needed to be performed on the longer stroke crankshaft Ritchie had sourced from an earlier-year ZX-7R. The crankshaft was sent out to be lightened and knife-edged to spin smoother and faster. The crankshaft was then installed in the engine case, where the standard connecting rods were retained. With the engine completely reassembled, it was finally time to test it out. Everything sounded and felt great - it ran perfectly for over 800 road-duty miles.

The crankshaft was lightened and knife-edged, and a set of fresh 1.5mm-over Wiseco pistons were installed.

With the engine build complete, Ritchie then turned to putting the chassis on a diet. The frame was lightened up by modifying the ZX-7R chassis to fit the forks and a swingarm from a 2006 Ninja ZX-10R. The bike’s suspension was then taken to the next level with a full race-spec Ohlins rear shock and fork internals. This modern suspension configuration allowed Ritchie to chuck the boat-anchor ZX-7R wheels and install lighter ZX-10R-specific Dymag wheels.

The ZX-7R received some updated components from a newer ZX-10R, including forks, swingarm, and Dymag wheels.

With Ritchie’s ZX-7R now thoroughly prepped for race duty, it was time to get it out to the track and run it through its paces. Unfortunately, it didn’t take long for the mechanical demons to throw Ritchie and his team their first curve ball.

During the bike’s very first race practice session, the built engine had a lower-end failure. With no time to diagnose what went wrong - let alone fix it - Ritchie and his team swapped the engine out for a standard ZX-7R motor. This allowed Ritchie to get back out on the track to continue dialing in the chassis.

After the practice session, Ritchie and his team set to figuring out what when wrong with the built engine. They hooked up the engine to a fuel and ignition source and started it up in the paddock garage. At this point, things went from bad to worse. A connecting rod snapped and tore right through the crankcase. The time and money spent on the built engine spilled out all over the garage floor in the form of bits of metal and oil. To this day, it’s still a mystery to Ritchie and his team as to what caused the catastrophic lower-end failure.

After experiencing a bottom-end problem at the track, the engine underwent further inspection back at the shop. A connecting snapped, putting Ritchie and his team back to square 1 with his race engine build.

This engine failure was a huge setback for Ritchie and his team - so much so that it meant they had to run the stock-and-standard ZX-7R engine for the rest of the 2016 season. Looking ahead to the 2017 season, Ritchie began his efforts in building a new race engine.

Ritchie contacted Wiseco directly in the USA – he needed another piston kit, and he needed it quick. Wiseco responded warmly to Ritchie’s email for help and supplied him with a new kit for the new engine.  “They said they would be very happy to deal with us directly through their European distributor. It was just the boost we needed to help us build another engine in time for the next season,” Ritchie explains, “The people at Wiseco have been so supportive and have been an absolute pleasure to work with.”

Once all the new Wiseco parts arrived, the team started from scratch building up the new engine. This time Carrillo connecting rods were used instead of stock ones. With the engine fully assembled, it was fitted up to a road bike to be broken-in. The engine ran sweet and made excellent power from the very beginning. Ritchie and his team felt it was a powerplant they could count on for the 2017 season.

Find Wiseco pistons for your machine here.

The ZX-7R build began again with all new components, including another new set of Wiseco forged pistons.

With the new engine, Ritchie won all four races of the very first round of the 2017 season. Unfortunately, bad luck struck again at the next round when a valve in the cylinder head snapped. This in turn ruined the cylinder head and a cylinder bore, as well as damaged one of the pistons.

Luckily, Ritchie and his team were already in the process of building a spare engine that was fitted with Wiseco pistons. “So, we took the cylinder block intended for that [spare] engine. It was bored out already, so we set about rebuilding the engine again for the next round,” says Ritchie. This sort of situation shows why it’s always a good idea to have a backup engine, even if you hope to never use it.

Luckily, a valve breaking only warranted a single piston replacement.

The team had to quickly break-in the newly-rebuilt engine so that it would be ready for the next race. They managed to have the bike prepared in time for the Snetterton round of the 2017 GES season. The Snetterton circuit has the longest straightaways of all tracks in the UK. If ever the engine was ever to be put to the test, it was going to be here. Ritchie ended up winning three of the four races at Snetterton, but ultimately crashed out while challenging for the lead in the final race.

After the broken valve damage was addressed, the engine was put to the test at Snetterton, and it powered Ritchie to victory in three out of four races.

Even following the crash, the engine continued to run faultlessly for a few more championship rounds. But then, another big-end failure (caused by a blocked oil gallery) set Ritchie and his team back once again. This time around it was a matter of stripping down the engine’s bottom end and building it back up. The Wiseco pistons and rings in the engine still looked great and there was no need to change them, so the team elected to leave them be.

The team had another bottom-end hiccup, but the top-end was still in great shape and was able to be reused.

After the rebuild, the engine kept charging all the way to the final round of the 2017 GES racing series where Ritchie was able to win two crucial races to secure the championship title.

“We said at the beginning of the season that with the combination of a competitive engine and a talented rider we could win the championship. We did just that, thanks to our friends at Wiseco. We were so pleased that they answered our plea for help. To have them join our small team has meant so much,” Ritchie says.

See how forging pistons makes the difference here.

For the 2018 season, the team will be running two bikes to defend the title – both of which have race-winning engines fitted with Wiseco pistons. The team’s main bike is now about as close as you can get to a proper superbike from the pre-2000s era. It has flat-slide carbs, a Nova Racing transmission, and a Kawasaki factory cylinder head from an Eckl Engineering ZX7-RR race bike that competed during the nineties. Inside the cylinder head are adjustable race cams from a Japanese Superbike Series racing bike, along with stiffer factory valve springs and one-piece racing valves.

The race bike now sits almost as the factory superbikes of its time did, with factory-level carbs, transmission, and cylinder head.

Ritchie reports that both engines tested very well at the beginning of the 2018 season and the bikes have run perfectly ever since. He’s been able to take the main race engine up to 14,000 RPM, and so far he’s won 10 out of 14 races with it. The team took the main bike’s engine apart for routine maintenance recently and were pleasantly surprised by how good the pistons and the rings looked. As Ritchie explains, “They’ve hardly worn at all and look like they have only just gone in!”

Ritchie has won 10 out of 14 races so far this season, spinning the race engine up to 14,000 RPM!

The Golden Era Superbike championship has eight rounds, and when you think about what each of those rounds entails – six to seven practice sessions, a qualifying session and four races over two days – it serves as a testament to how robust Wiseco piston kits truly are. Ritchie and his team demand the very most from their bikes and engines. Even though Ritchie’s idea to race retro superbikes may have seemingly come by chance, he and his team’s choice for quality engine parts have come through experience.

Topics: ENGINE BUILDS, featured, Powersports, BIKE FEATURES

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Written by Peter Monshizadeh