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A secret to the speed of the "world's fastest Indian" is being auctioned for the Christchurch earthquake appeal.

And a doodle by Prime Minister John Key is set to swell the coffers further.

A piston belonging to legendary motorcycle racer Burt Munro is for sale on Trade Me, with bids already topping $4000.

Munro's son John was delighted with the response.

"I thought we might get $100 for it but it looks like it will get more."

The piston comes from a collection of parts called the "offerings to the God of Speed" and was built for the engine that set the under-1000cc world record.

Munro became famous aged 68 when he set the world record, which still stands, in Bonneville, Utah, America, in 1967.

He worked for 18 years from his Invercargill home to modify the 1920 Indian motorcycle, increasing its maximum speed from 80km/h to more than 300km/h.

"The parts that he made certainly improved the performance of the engine and the piston contributed to that," said John Munro.

The story of his father's success formed the 2005 film The World's Fastest Indian, starring Anthony Hopkins.

John Munro and his sisters June, Margaret and Gwen decided to donate proceeds of the auction to the Red Cross in their father's memory.

The auction closes at 5.30pm on Wednesday.

Meanwhile a doodle of a firetruck done by Key in just three minutes is expected to raise big money for firefighters who lost their homes in the quake. The A4-sized drawing has been framed with six donated photos that capture the incredible efforts of firefighters during the disaster.

The item was posted on Trade Me on Friday with a reserve price of $500.

But United Fire Brigade Association chief executive George Verry hoped for a high overall fundraising total.

"Our expectations are close to $400,000 ... the Fire Service is contributing a significant amount," Verry said.

The funds will go towards new homes, food, supplies and wages for firefighters who have lost their day jobs.

The auction will run for a week.

Trade Me spokesman Paul Ford said the proceeds of thousands of site listings were destined for the quake appeal.

Trade Me has a free-to-list earthquake support site.