Yamaha may delay its return to the World Superbike Championship with its YZF-RR1 after testing in Japan revealed reliability problems with the engine using standard components.

Sources inside the factory say they are struggling to make a reliable, fast engine using stock parts as the 2015 WSBK rules outlaw the use of aftermarket parts made from expensive materials such as titanium to construct fast-moving parts like conrods.

It is believed the factory have two specs of engine in 220bhp and 240bhp forms but are unable to demonstrate a sufficient level of reliability and the bike may well not be ready for competition until at least this time next year.

When asked about Yamaha’s return to the championship, series director Gregoria Lavilla said he simply didn’t know what the factory’s plans were.