Small cracks have been discovered in 37 metal parts on wheel assemblies of Nozomi Shinkansen trains operating on the Tokaido Sanyo Line, West Japan Railway Co. (JR West) said Sunday.
The railway operator said the cracks were due to improper welding and that all the parts will be replaced by the end of the month. The cracks pose no danger to JR West's bullet train services, company officials said.
The cracks were discovered during inspections carried out on all of JR West's 500 Series Nozomi bullet trains.
They were found on the trains' trucks -- the wheel assemblies under train cars -- at welded connections.
Cracks were detected on joints attaching lids that prevent oil leaking into gear boxes and between electrical grounding devices and the trucks.
All of the cracks were about 0.02 mm wide.
The inspections were ordered after cracks were first discovered on the trains Thursday. Workers examined all 714 parts attached to the trucks of JR West's 500 Series bullet trains.
Several train and subway operators nationwide have also discovered similar cracks on train-car trucks in recent months, including the Yamagata Shinkansen.
The Tokaido Sanyo Line connects Tokyo Station with Hakata Station in Fukuoka Prefecture.