A BEAUTIFUL DAY - THEN IT ALL WENT A BIT WRONG!!

BEFORE THE DRAMA -
DQV IN THE EARLY MORNING SUN

Superb weather in the Waikato for the past few days with glorious sunshine - quite a change from the windy, wet Spring. Having looked at the weather forecast at the beginning of the week I had booked the Arrow, DQV for a few hours and drove to the club in the early morning sun looking forward to a cross-country over to Whakatane and back.
By the time I had filed a flight plan, pushed DQV out of its hangar and preflighted, the early morning mist had gone, the few low clouds were burning off and it looked good to go. I taxied over to the pumps to fill up the tanks, got my departure clearance and went off to run up and do the pre take-off checks. There were no problems with the run-up and after a short wait for the circuit traffic I was cleared to line up behind a twin-star taking off on 18L.
All proceeded smoothly to start with, line up, line up checks, full throttle, nice and straight, rotate at 65 knots, out of runway - gear up, 80 knots and accelerating, flaps up, fuel pump off, landing light off - all good so far. Then it was set power and propeller pitch for climb and things rapidly turned to custard. As soon as I coarsened the pitch the whole front of the aircraft started to shake (quite violently, it seemed to me). Hey, this is not right, I thought, time to abort the flight and get back "home" PDQ!!
As I turned crosswind I keyed the mike and announced I had a vibration problem to the tower and requested a circuit to land. I levelled out at about 700' agl turning downwind, eyeing the paddocks nearby just in case (there was almost no wind so any landing direction would do, I reckoned, if the engine actually stopped). Fuel pump on, back to cruise power and I then attempted to set the power and pitch for cruise (24" manifold pressure and 2400rpm) hoping the shakes would get better but, if anything, it felt worse. Gear down, rest of downwind checks complete and I was cleared to approach.
The tower very kindly asked me (twice, in fact) if I required assistance but by now I was abeam the downwind threshold and within range for a glide approach so I replied in the negative, just asking confirmation I was number one. I was, as other traffic had been held or cleared off the runway which was good, and as soon as the throttle was closed back to about 15" of manifold pressure the vibes stopped and I did a pretty fair approach and smooth landing. PHEW!! A happy end to my first ever real in-flight emergency.
I taxied back to the club where senior instructor, Ash, was waiting for me. After I shut down he hopped up on the wing to ask what the problem was (the tower had told the club I was coming back because of a problem). After hearing my story and checking over the prop, Ash got into the right hand seat and we taxied around a bit throttling up and back and moving the prop. All seemed well on the ground and I was left wondering if it was something I had done. Still, Ash reckoned it was a good call to return and I left to go home.
As it turned out, it wasn't me. The owner of DQV took it out later and the same thing happened. It turned out not to be a prop problem as I thought, but a fouled spark plug which, for some reason, did not show itself on the ground run-up checks! So, even if all checks on the ground are good, things can still go wrong, sooner rather than later, too!! One for the learning curve and a good outcome.