The piston, cast, turned and fitted by Mr Munro is for the streamlined Indian motorcycle which set a record of 183.586mph (295.453kmh) on the Bonneville salt flats in the United States in August 1967, since made into a popular film.
John Munro, of Weston, and sisters June, Margaret and Gwen decided their father would have wanted to help the people of Christchurch and decided to auction the piston on TradeMe.
Mr Munro said the family expected it would fetch a few hundred dollars but yesterday, bidding was over $4000 after only about 48 hours, with the auction running until Wednesday.
There had already been 14,600 hits on the piston auction page by yesterday, with 623 people putting it on their "watch list".
The piston up for auction was originally one of hundreds of items which sat on shelves in Burt Munro's shed as "offerings to the God of Speed".
When the shed was cleared, Mr Munro's family kept many of the parts, with the rest going on display at Hayes Hardware in Invercargill.
