Many engines use splash or gravity lubrication to the cam lobes, it is conventional. Whether or not the cam lobes are pressure lubricated, rotating the engine by hand is unlikely to deliver oil to the cam/follower area, and likely to wipe off whatever is already there.
There is an STCd replacement camshaft available which has an oil gallery within it. I don’t know the details but somehow it gets oil fed into the end of it.
For some reason it isn’t a commonly implemented mod. I guess because people who fly frequently don’t need it, and people who fly rarely aren’t so bothered to spend money on their plane… Lyco have chosen to partially sidestep the issue by introducing roller tappets which do a lot less damage to the camshaft to start with.
Jan_Olieslagers wrote:
I reckon the low rpm figures must help to make a certain degree of maltreatment bearable. Compared to the 912, that is.
912 is based on a comparatively modern automotive engine, right? Those are more demanding in terms of lubrication in general. Primitive designs are sometimes also robust.
Martin wrote:
912 is based on a comparatively modern automotive engine, right?
No, that’s wrong. Limbachs and Sauers are based on an automotive engine, though not a comparatively modern one 
europaxs wrote:
No, that’s wrong. Limbachs and Sauers are based on an automotive engine, though not a comparatively modern one
Thank you. I’ll try to remember that. 
I seem to remember that the Rotax 912 started life as a snow-mobile engine.
Rotax certainly started with snowmobile engines, but I never knew they offered any four-stroke for that market. To this day they have (separate!) ranges of two-strokes for snowmobiles and for aviation use, plus some offer for some other markets like karting. The aviation models being generally less powerful for the same displacement, if I remember correctly.
I am curious though about the 912’s history: was it a clean-sheet design? It does look like it.
The Rotax 912 was a mid-1980s clean sheet design that combines features of other aircraft engines (4 cylinder 4 stroke boxer configuration), earlier Rotax engines (e.g. built up crankshaft) and even some motorcycle components (carbs from BMW and Ducati Energia electrical components). It was fairly unique as an aircraft engine in running at ~5000 rpm, with water cooled heads and gearing added to make that possible.
Rotax is a Canadian owned Austrian company that’s made snowmobile engines for Ski-Doo, motorcycle engines for Can-Am, BMW and Aprilia, go-kart racing engines and other stuff as well as aircraft engines. Ski-Doo and Can-Am are associated brands and building engines for them was the reason Rotax exists today as a company. Starting in the 1960s they built engines under contract for Bombardier/Ski-Doo, and were then purchased by Bombardier. Building dedicated aircraft engines grew out of people using snowmobile engines in ultralights in the 1970s, but the 912 has little in common with them except for the method of crankshaft construction.
Other companies had parallel initiatives to build clean sheet light aircraft engine designs in the same 1980s period during which ultralights ‘grew up’, but were not as successful as Rotax. One that comes to mind was the KFM 112 from Italy, also developed by a successful kart engine company, that sort of evolved into the Australian Jabiru engine when the Italians dropped it. A man I know, the former long term owner of my plane, was involved with the KFM engine
How long should you ground run an engine as an “interim” measure
I normally fly my PA28 at least once a week even if it’s going in the circuit or a quick local flight for at least 40 minutes to protect the cam and other areas from corrosion.
I’m told you have to get the engine up to temperature so any water vapour/ moisture in the engine can boil off. I understand short ground runs could possibly be detrimental or at least do no good.
My “owner assisted” annual normally takes 3-5 days with myself and an engineer working on it. I normally fly away at the end of the Annual but a few times I’ve booked the plane in for planned maintenance such as corrosion work, 8.33 radios and next year a bare metal respray which will take weeks.
When the plane sits there for more than 2 weeks without being run I start getting very, very twitchy.
What do people think about a 30 minute ground run as an interim measure in these circumstances? I have an EDM engine monitor so whoever runs the engine can be instructed to keep CHT’s to below 400 degrees F. I would imagine that the oil would heat up enough to boil off the vapour and at least the cam would be covered with a layer of oil. I can check the tack time or EDM download to ensure it was run long enough.
Good idea or Bad idea? Any feedback most welcome!
The water/moisture comes from running the engine, not from letting it sit. Water is a by-product of combustion and enters the crankcase through the cylinders. If the oil is hot, most of the moisture evaporates. However, not all as the oil usually doesn’t get hotter than 100°C and even then boiling it off requires a lot of time.
I think you’re overthinking this. There’s no problem letting an aircraft sit for a few weeks. 90% of piston aircrafts do that and at least over here, the average age of an engine should be higher than its time TBO…
