Wiseco profiles Ritchie Thornton’s Golden Era Superbike ZX7R

In Features, Thundersport GB

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 90s.

The Golden Era Superbike provides a platform for bikes produced from 1985-2000 to duke it out under the same rules and regulations as were maintained during that era. This meant that Ritchie needed to find either a smooth-revving 750cc four-cylinder or a torquey 1000cc twin-cylinder.

No stranger to two wheels, Ritchie raced motocross as a kid and eventually progressed to tarmac, racing a Suzuki GSX-R 600. 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.

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

Ritchie had already been riding a 1997 Kawasaki Ninja ZX-7R every day to work. To many, this bike seemed an old, heavy, obsolete sportbike. But legendary riders Scott Russell and Chris Walker both successfully campaigned Kawasaki Ninja ZX-7RR race bikes back in the day – bikes which are nearly identical to Ritchie’s own road-going machine.

The rules of Golden Era Superbike allow 750cc machines 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 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.

Aside from boring out the engine to fit the oversized Wiseco pistons, some special work needed to be performed on the longer-stroke crankshaft, which 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.

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.
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.

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. Overhauled dampers allowed Ritchie to chuck the boat-anchor ZX-7R wheels and install lightweight Dymag wheels.

Although the bike was ready for race duty, 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 engine had a lower-end failure, forcing the team to swap it for a standard ZX-7R motor which allowed Ritchie to get back out on the track to continue dialling in the chassis.

After the practice session, the 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. But things went from bad to worse as a connecting rod snapped and tore right through the crankcase and to this day, it’s still a mystery to Ritchie and his team as to what caused the catastrophic lower-end failure.

The failure was such a setback that it meant they had to run the stock-and-standard ZX-7R engine for the rest of the 2016 season as Ritchie looked ahead to 2017 and began a new build. He got in touch with Wiseco directly in need another piston kit, and they swiftly supplied him with a new kit for the new engine.

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.
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.

“They said they would be very happy to deal with us directly through their European distributor,” Ritchie explained. “It was just the boost we needed to help us build another engine in time for the next season. 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.

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 Wiseco pistons.

Luckily, Ritchie and his team were already in the process of building a spare engine that was fitted with Wiseco pistons. “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.”

The team managed to have the bike prepared in time for third round of 2017 at Snetterton, which has the longest straights on the calendar. If ever the engine was ever to be put to the test, it was going to be there. Ritchie ended up winning three of the four races at Snetterton, but ultimately crashed out while challenging for the lead in the final race.

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

Even after the crash, the engine continued to run faultlessly for a few more rounds. But another failure, caused by a blocked oil gallery, set the team back once again. This time it was a matter of stripping down the engine’s bottom end and building it back up, with the Wiseco pistons and rings in the engine still looking solid with no need to change them.

After the rebuild, the engine kept charging all the way to the final round of last season where Ritchie was able to win two crucial races to secure the Golden Era Superbike crown.

“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,” Ritchie admitted. “We did just that, thanks to our friends at Wiseco. We were so pleased that they answered our plea for help and to have them join our small team has meant so much.

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 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. And 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.

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 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. “They’ve hardly worn at all and look like they have only just gone in.”

Although 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.

*Images supplied by Wiseco

*Words: Peter Monshizadeh

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