Back home the propeller was used to turn the engine until it was at top-dead-centre on cylinder one. A TDC position is marked on the flywheel but will correspond to either cylinder one or cylinder two. As my engine has conventional tappets it was easy to check which by removing cylinder one's rocker cover and ensuring that both valves were closed. The crank was then rotated until 25 degrees before TDC which is the standard firing position for this engine. The magneto was also then positioned in the firing position for cylinder one using a special pin though a hole in the top of the magneto to locate a matching hole in the rotor arm drive gear. The magneto was then inserted into its position in the accessory housing at the back of the engine.
Then the flywheel was repositioned in the 25 degree before TDC position. When timing an impulse coupled magneto it is essential that the engine is moved past the point at which the impulse coupler trips and then rotated back to the 25 degree position. Using the magneto timing device I made a few days ago, the magneto was then turned until the points were just opening and the magneto clamped into position.
As a final check the plugs for the left magneto were removed (cylinder 1 & 3 top, cylinder 2 & 4 bottom) and the engine rotated with the propeller. A spark duly appeared at the correct plug and at the correct time allowing for the delay of the impulse coupling (this is a mechanical device that delays the spark when engine revs are low to allow for easier starting).
Then it was time to try and start the engine. First job was to secure the aircraft to ensure it couldn't run away. To do this it was chocked but also chained to the back of my car! My neighbour, Daryl, kept watch to ensure that no-one came close to the propeller. The elevator trim was moved to hold full up elevator to ensure the tail wouldn't lift.
I've fitted a conventional pump primer to the engine which feeds all 4 cylinders; 4 strokes were used. Then with the master on and then left impulse-coupled magneto on the starter button was pushed. A few coughs and splutters ensued but the engine didn't want to run. Then Daryl saw some liquid under the aircraft. This proved to be water and further inspection found that the airbox was full of it! Obviously the recent rain had somehow ended up in the airbox and the poor engine was trying to start on a fuel/air/water mixture. The airbox should have had a small hole in its lowest point - it has now! To solve the problem temporarily the airbox was disconnected and left hanging down below the carburettor. The spark plugs were removed and dried. The engine was turned over on the starter without the plugs in to ensure there was no water in the cylinders and then the plugs refitted.
Finally it was time to try again and this time the engine started perfectly. It ran for a few seconds on the prime before running out of fuel, presumably because the float chamber in the carburettor had been completely empty. However, after re-priming the engine started and with the right magneto also on began to run smoothly.
Then it was time to do some preliminary checks:
- the cylinder head temperature was registering off the scale but the exhaust gas temperature gauge was not moving - looks like the thermocouples are wired the wrong way round.
- the bus voltage looked good but the amp meter was showing a large discharge - I had a 50:50 chance of getting the current sensor round the correct way and had guessed wrong.
- The oil pressure was good but the oil temperature seemed pegged. Either the vernatherm hasn't opened or there is a fault in the temperature gauge or sender- another thing to check
- The fuel gauge had stopped working - presumably a bad connection somewhere
- The vacuum gauge was reading a bit low but the gyros were definitely spinning up
- No oil leaks
- Nothing coming loose
- High cylinder head temperature confirmed as a wiring error
- Good compressions on cylinders 1, 2, and 3 but not on 4
- Crankcase still cool so oil temperature not yet confirmed as an issue
