Hi Alan, unless you have a pre-arranged clearance permit from Australia, don't do it. You'll have your bike impounded. I've done it before on a vintage bike into Oz and it was no problem but as a Brit and Ozzie resident it was relatively easy, if you are a non-resident, you will need a carnet I think and will need to re-export within 6 months. Thailand will only give you as a tourist 29 days, but this is pretty easy as they do not require a carnet, but you must move the bike out of the country in 29 days.
Hope this helps.....