Running in

We had a minor issue with cylinder #4 on our recent annual service. It turned out to be nothing more that carbon build up that prevented the valves working properly, but for our sins, we were given new piston rings etc. which basically means that we must ‘run the cylinder in’ pretty much as thought it was a new engine.

What this means is running the engine for the next 50 hours or so:

- At high power settings for longer periods (75% with a bit of 65%)
- Keeping the CHT’s reasonably cool, below 224 degrees
- With the mixture pretty much fully rich
- Below 5000’ (or we won’t develop the necessary 75% power)
- Using straight 80 oil
- Keeping a careful record of oil consumption
- Being very careful to avoid rapid cooling
- Using gradual power reductions
- Without varying the power hugely over short periods

What this really means is we will be belting along at 2400 rpm and 165 – 170 kts – into the yellow band of airspeed, so smooth air operation only. It also means a fuel consumption of 37 litres an hour as compared to our more normal average of 29 litres an hour. It also means certainly NO circuits as the constant cycle of full power to idle and back again repeatedly over a short period of time is most definitely NOT what the engine needs! It also means careful planning and cruise descents into airfield circuits, which at these sort of speeds and only using slight reductions in power for cruise descents, means starting the descent some 40 nautical miles out – now I know how an airline pilot feels!

As for slowing the plane up from 170kts to the flap limiting speed of some 100 kts while trying not to shock cool the engine – well, it is interesting to say the least. To try to play my part, I am also asking for direct joins where possible, to cut the amount of time I have the engine running close to idle. It can all be done of course, but it is a far cry from my preferred method of flying the RV, which is at ‘economy cruise’ of probably 50% power (2000 rpm and leaned back to 21 litres and hour fuel burn) which gives a stately, but still respectable 125 kts – fine for me and great for touring.

Oh well. I will be doing my part to get the plane past it’s 50 hours, and therefore into normal engine operation before my planned touring in Denmark and Sweden in late-June.