Hi guys,
Thanks for your replies!

Unfortunately I have no further info other than the image - there are a couple of these wackers going cheap on Ebay (U.K.) and I was thinking that a 25cc petrol/gas motor would be ideal for my winter project. If they're cheap enough then it's worth the risk as I can get basic metal fabrication & turning done by a friend but I don't want to have to actually mess with the engine itself (I started reading the Toro thread until my head hurt then I gave up ).