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The Castrol 6 Hour was a race for standard production motorcycles that was first run on Sunday, October 18, 1970, at the Amaroo Park circuit near Sydney, Australia. The Race continued at Amaroo until 1983, when the venue was changed to Oran Park until the final 6 hour, in 1987. All races featured a Le Mans start.

The race was organised by the Willoughby District Motorcycle Club that felt that an endurance event would be a way of proving the reliability of the motorcycles of the day, and also offer an outlet for riders that were increasingly racing on the public roads. The race immediately attracted the interest of the public and manufacturers alike, and grew to be regarded as the greatest race in Australia and was highly regarded for the impact success would have on sales of motorcycles and parts. Manufacturers were known to rush examples of new products to Australia knowing that a good showing would guarantee sales success. 

It was often suspected that some motorcycles and tyres were a bit better than average and the Willoughby club worked hard to ensure that the race remained pure to its concept of a race for standard production motorcycles that the average person could buy the day after the race.

Originally the race was called the Castrol 1000 in recognition of the prize money on offer from Castrol. $1000 was a considerable sum in 1970, in fact the eventual winning bike in the first race, a Triumph Bonneville 650, could be purchased for around $1,150.00 at the time.

At first the race was for 3 classes, Unlimited, 500cc and 250cc.  It continued in that format until 1975, when the 250cc class was dropped for "rider safety". In 1978 the 500cc class was dropped and a 750cc class introduced. 1978 also saw the minimum capacity raised to 500cc, where it remained until 1984 when it was reduced to 345cc, thus allowing the entry of the Yamaha RZ350.  For 1983 The maximum capacity was limited to 1000cc, probably to comply with the ACCA regulations and in 1987 a 250cc class was reintroduced.