Next up, the head shims had to be fitted. Six screws hold the head on [Note: One screw is between the valve rockers] so that came off in a jiffy.
The shims just sit between the head and the barrel. You actually need to fit them in the head first, it was just easier to get a photo of them sat on top of the barrel.
Getting the head back on was fairly easy but the push rods wouldn’t line up with the rockers for me so I ended up taking the rockers off (only one screw) and aligning everything carefully. None of this was difficult and took not many minutes at all.
Having shimmed up the head, the valve clearances were now huge, so they had to be brought back within tolerance (0.04mm-0.1mm). This is a simple matter of loosening the little lock nuts on the top of the rockers and then adjusting the screws down until the gaps are within tolerance. I checked the gap with a pair of feeler gauges (a 0.05mm and a 0.1mm). I managed to achieve a loose sliding fit on the thinner gauge and a tight fit on the thicker gauge. Again this only takes a short while.
The glow plug needs to be replaced with a spark plug. That was just the easiest job on this project.
The next job is the set the timing. The instruction pages that came with the CDI kit had an angle gauge printed on them so you just have to cut it out and stick it to some cardboard.
Just set the engine to Top Dead Centre and clamp the gauge up with the prop nut to read zero against some kind of fixed pointer.
The instructions said to set the timing between 28 and 30 degrees before TDC, so I set the angle to 29 degrees as my starting point. The prop driver and crankcase were marked at TDC and 29 degrees before TDC.
The sensor holder was then rotated so that it lined up with the magnet when the engine was at 29 degrees before TDC.
Finally here’s everything fitted together ready to run.
Down at the field the only trouble I had starting the thing was due to the fact that I mounted the tank way lower than the engine centre line. Once the fuel was drawn up she fired up fairly quickly.
After a short while I discovered that the back-pressure pipe to the tank needed a little clamp on it. The heat from the exhaust pipe made the Tygon tubing go very floppy and it fell off during running.
The engine ran at its best with the main needle ¾ of a turn out. The idle needle wasn’t altered from its glow setting.
The idle was good and throttle response was fine. At full throttle, she revved up to 8400 rpm on a 15×8 prop. I tried a degree of advance and retard on the timing but couldn’t improve on my first attempt at (or about) 28 degrees.
I have read that petrol conversions run hotter than glow motors because the methanol really cools the engine a lot. It certainly seemed hotter and I didn’t run it for that long so I shall have to ensure that there is extra cooling available when mounted in the plane.
The engine is destined for a Seagull Hawker Sea Fury I recently acquired.
One final note. The receiver, servos and associated leads must be kept as far away as possible from the ignition gear. It is advised that the throttle linkage is of the plastic snake variety to stop the RF noise finding its way in via a metal linkage. It’s not such a big issue with spread spectrum radio (e.g. Futaba FAAST or Spektrum DSMX) but 35MHz gear and lower spec. 2.4Ghz gear could suffer with interference from the ignition system unless care is taken. Apparently it was a particular problem with 72MHz radio but that doesn’t really affect UK fliers.
