Lakeside have made the surprise move of replacing heat leader Adam Shields with veteran Swede Peter Karlsson, who joins on loan from Wolverhampton.
Former Scunthorpe rider Richie Worrall and ex-Plymouth Australian Justin Sedgman have also been brought in to share a reserve position.
They join marquee arrival Davey Watt and captain Lee Richardson.
Kim Nilsson, Robert Mear, Kauko Nieminen and Stuart Robson remain from last year's line-up.
Karlsson, 41, started his British career 20 years ago.
His long affiliation with Wolves has seen him build a strong connection with the Monmore support, which culminated in the team's 2009 Elite League title win.
The omission of Shields is unexpected, even though he missed the bulk of last season with a knee injury.
The prospect of having a fully-fit Shields and fellow Australian Watt in heat-leading positions had excited the Hammers faithful.
"Adam was in the team until a couple of days ago but we ran into some unexpected problems," co-promoter Jon Cook told BBC Essex.
"It was a difficult phone call to make to Adam but we've found another club for him and hopefully they'll be talking and making sure he's back in British speedway."
Youngster Sedgman will remain an asset of parent club Swindon Robins and will double up with Premier League outfit Redcar Bears. He averaged three points a meeting for the Robins last term.
Merseyside-born Worrall, 20, started out in motocross and switched to speedway in 2009. He spent last season on loan a Newcastle.