The iconic Flying Scotsman steam engine will be back on the rails by 2010 if a further £250,000 is raised to complete its restoration.
The engine is currently undergoing a major overhaul at the National Railway Museum (NRM) in York.
The museum bought the locomotive for £2m in 2004 and has since stripped it down for renovation and repair work.
Now rising costs have forced the museum to launch an SOS "Steam Our Scotsman" appeal to bring the engine to life.
The class A3 Pacific locomotive was built in 1923 for the London and North Eastern Railway (LNER) at Doncaster.
It was employed on long-distance express trains on the LNER and its successors, British Railways Eastern and North-Eastern Regions, notably the 10am London to Edinburgh Flying Scotsman service after which the locomotive was named.
In its career it travelled 2,000,000 miles (3,200,000 km) and was withdrawn from service in 1963.
It was sold for preservation but in 2004, after having several owners, its future became uncertain and the NRM purchased it.
A spokeswoman for the NRM said: "The cost of the Flying Scotsman overhaul has risen as a result of the increased price of metal and a number of unforeseen problems with the locomotive.
"These problems included the frames being misaligned and a large longitudinal crack in the right-hand cylinder.
"Firebox repairs have also presented challenges, involving extensive work with new copper to make it similar to the old in order to reduce the risk of problems at a later date.
"All of these problems and challenges take money and time to ensure Scotsman is restored to the highest standards of safety, efficiency and engineering quality.
"The NRM is still dedicated to ensuring Scotsman is restored and back in steam in 2010."
When the engine is running once again, it will be competing for attention with Tornado, the first new main line steam engine to be built in Britain for nearly 50 years, which will take fare-paying passengers for the first time later this month.
Enthusiasts in Darlington raised £3m to build Tornado - a class A1 Pacific locomotive.
It is due to make its first mainline run between York and Newcastle on 31 January, with others planned later.