I recently purchased on eBay a new engine said to be a Hobao Hyper 28. It had been removed from a Hobao car. I was expecting it to be .28 cu in (4.6cc) but when I measured it, it had bore 17.5mm stroke 16.8mm, which equals 4.0 cc or .25 cu in. It was clearly a Hyper 21 that had been re-sleeved. Hobao wont answer my emails about this. Can anyone shed some light on this apparent deception? The dealer has agreed to replace the engine.