Well done Paul, I wasn't sure you'd have room to pull the shaft all the way out to free the sprocket/cam so you could retime it. If you have to remove the engine from the base machine you add at least half an hour to the time the job takes.
The GCV engines are notorious for jumping their timing, and for breaking the plastic sprocket/cam. Neither is difficult to fix but I prefer reliable engines. (The GCVs also have no oil seal on the governor shaft, and it is not unusual for them to leak oil there).
I have read a couple of reports that it is common for the timing to jump once on GCVs, when the engine is relatively young, then not do it again until they get old and the belt is worn out. I can't imagine why your local mechanic would have had occasion to pull that shaft out, and if he didn't take it out, I doubt he'd have put it back in with incorrect cam timing. It seems more likely yours is just one of the ones that happened to jump. If it happened repeatedly you'd eventually have to replace the belt and/or sprockets, but as you've seen, it is not a big job to retime it. I've also read that there is a service fix consisting of a revised sprocket and belt, to reduce the likelihood of jumping:
http://www.hobbytalk.com/bbs1/archive/index.php/t-255329.htmlIf you have any pictures, please post them.
In response to your actual question, I suggest you should pay attention for a while to whether the engine loses power suddenly, after it has been shut down. Timing nearly always jumps during the engine's stopping or starting mode, when it passes through relatively low speeds of rotation.
I've had the experience of driving a car that had jumped its timing chain, and it was not difficult to tell that it had happened: it was way down on power, and very sluggish in its throttle response (highly evident when changing gears). It was a pity that my father was sitting in the back seat insisting that nothing was wrong, which resulted in us having to drive it from Perth to Kalgoorlie flat out at 35 mph, by which time it needed a new cylinder head and a new set of valves. However, I digress yet again. With items like lawnmowers, they are often used at much less than full power and the changes I've described might not be so obvious, especially if it just jumps one tooth rather than two. Nevertheless it is because it may only jump one tooth, that I think power loss and very sluggish running is more likely to be the main symptom if this happens again, rather than inability to run at less than maximum speed.
