Watch Scrapheap Challenge online: Episode 4 Amphibious Motorcycles

Amphi Bike In the first intentionally wet challenge this year, the teams have to build motorbikes that can swim. The Amphibious Bikes have to complete a three-stage test involving driving on land and water before finally competing in a head-to-head amphibious slalom race. Rockin' Rabble Geoff Bunting, Trevor Cartwright and Philip Lodge are a team of Yorkshire Teddy Boys who intend to bring a touch of retro culture to the 'heap. They are Fifties fanatics and are ready for some rockin' and a rollin'. They've agreed to switch off their jukebox and stop living in the past to concentrate on stepping to Scrapheap success. The Rockin' Rabble's technical consultant is Mike Ryan, who came second in Bike magazine's Amphibious Motorbike Challenge and has built an amphibious Lamborghini that looks like the real thing until it hits the water. He's a real geezer, somebody who can make something out of nothing. He's going to fix floats to the left and right of an off-road Enduro motorbike, then add a propeller at the rear, which is driven by a chain from the rear wheel of the motorbike. The front wheel will sit in a specially made bow section to help it enter the water quickly. Double Deckers Jason Blossom, Jon Green and Owen Hunt are boys who work on the buses. They are based in a bus workshop in High Wycombe. They fix and maintain Carousel buses to rent out to companies around London. There is only one route for this team and there will be no scheduled stop until they have got to the end of the competition. The Double Deckers' technical consultant is Gordon Halley, a potato farmer from Scotland. He's won Bike magazine's Amphibious Motorbike Challenge twice and is an old competitor of Mike Ryan, the Rockin' Rabble's consultant. He's going to build one of the weirdest machines the 'heap has ever seen – an off-road trial bike stuck in a rowing boat. The drive will come from a paddle wheel made out of metal garden chairs and will be driven by a chain off the back wheel. In order to stabilise the whole thing, he's going to have two outriggers, which the driver can put on the ground by pressing pedals to the left and to the right of the motorbike. These outriggers also double up as rudders when he's in the water. Weird or what? The expert This week's expert is Richard Fincher. He was the Editor of Bike magazine when he came up with the idea to challenge his readers to build a swimming motorbike. He's been around bikes for donkey's years and has done plenty of TV presenting.

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