The 500 Rotax motors in the Canam Sonics were a little underpowered, the 504's in the KTM's put out better power. The ATK's used the 605 motors. They can pump out around 70 horses with work, don't know how well they hold together then, probably get a bit fragile, but at what cost to win a race, right?. Stock they are very reliable, but have heard of some gearbox problems when thrashed. Can't remember what it is that lets go though. Had a mate that raced vintage road race and mentioned something about third gear letting go. Met a bloke with an ATK that had a box let go as well, he rode his hard. Parts are dear, but it looks like Lozza has a source. He probably knows more about them as well.
Years ago I picked up a KTM 504 with a shot motor. Bottom end seized, bore cracked, cases welded. I got a quote for $3,500 just for the main parts I needed, let alone machining and labour and whatever sundry bits I needed. The best solution I came up with would be to throw a Yamie 500 or 550 motor into the frame. And before anyone asks, no the dead motor is not for sale as I have other Rotax bikes.
As for the ATK in Nambour, I paid $2,600 for a rough ATK about ten years ago, I justified it to my better half that the sum of parts was worth more than the asking price. All she said was ""$2,600 is a lot of money for spare parts."
