Cracked engine case

[rizzz]

I'd go with the aluminium case for an aircraft engine for a multitude if reasons

Why exactly? Magnesium has lots going for it.

Let me start by saying All of the VWs I've owned have had mag cases except the buggy I built. So I don't have much of a problem with running them in my cars and actually have a lot of faith in them.

My reasons...
An aluminum case can be easily welded.
Aluminum is stronger and has less tendency to warp especially in low RPM under load. The fore/aft load the prop puts significant stress on the bearing saddles where stronger aluminum would be better in my opinion. The engine was designed to primarily handle the rotational forces which is good for spinning a trany but probably not so much for hauling around 1000lbs of plane and pilot under various G loads.
While Ferdinand designed one hell of an engine, it was running about 36hp, about 45% less displacement, and a smaller stroke than we're putting in these planes. Plus he designed it when aluminum was scarce during the war (same reason the Spruce Goose was made of wood).
All the Type4s (1700-2000cc) went to aluminum for a reason (bigger engines pushing heavier cars).
VW has stopped making mag cases. http://www.hotvws.com/news2.php?contentID=74
And finally...Have you ever seen a mag case burn? That's not something I want to even be in the back of my head while I fly through the air.

So, while a mag case is probably just fine, I have my reasons for preferring aluminum in an aircraft application.

All good points,

One more to add in favour of the aluminium cases is that aluminium cases do not work harden over time like the magnesium cases do.
All magnesium cases WILL eventually develop cracks because of this if kept in service long enough, it's just a property of the material.
Not sure what the average time is before the cracks develop, I remember reading a post on the Revmaster forum stating somewhere between 500 and 1000 hours.

That said, for me even this argument does not outweigh the fact that the aluminium cases are so much heavier.
I'm happy to replace the case after 500h in service if that's what's required.

[nwyooper]

Didn't see any cracks in my case but had may other problems/issues. The most serious of which was that the stud pattern for the cylinders was not concentric around the bore in the case. This resulted in severe oil leaks at cylinder bases because there was not an adequate sealing surface for shims that go under jugs.(Sent pics to Sonex) Had to take engine apart three times to repair. Spent 2 days scraping the inside of the case to get adequate clearance so connecting rods would not hit inside of case. Also had a bad crankshaft that had a blemish on number 3 rod bearing journal-bad enough to destroy a bearing on initial assembly.(Sonex notified). You really need to spend a lot of time cleaning the inside of the case to make sure all excess/loose casting is removed so it won't cause problems later. I think the assembly manual could be a little more specific about cleaning the case. I sent Sonex several pictures of the inside of my case to show the casting slag that needs to be removed.
Loren
Onex 33