SonexBuilders.net

Has anyone come across a cracked engine case like this one before?




The engine has done 60 hours and has basically leaked oil since new. I at first thought it was a cam plug or rear main seal continually leaking but after attending to both realized it was something else and finally spotted it. It's not a big leak but after a few reasonable flights it will make a mess of the lower cowl.

-Brett

btw - this picture is just an example of the where the crack is. This is not my actual engine.

Normally the cracks happen on the other side, behind #4 cylinder, hence the supercases have that side welded.
Your crack must have been there from the start, the case was dropped somewhere along the line perhaps?

Magnesium cases can be welded (you’ll need to find a specialist), but if it was there to begin with you deserve a new one I’d say.
You’ll have to rebuild the engine in any case.

What Rizz said. They normally crack on the other side. I wouldn't bother trying to weld a mag case and I'd go with the aluminium case for an aircraft engine for a multitude if reasons. If' it is aluminum, you certainly could get that welded too. But if it's been leaking since new I'd suspect you just got a bad case or something happened to it during install and/or shipping.

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

Why exactly? Magnesium has lots going for it.

An aluminum case weighs 12 pounds more than a magnesium one. That is why all major aero VW conversions use magnesium, which is as Dr. Porsche designed it.

Jake

SonexN76ET wrote:An aluminum case weighs 12 pounds more than a magnesium one. That is why all major aero VW conversions use magnesium, which is as Dr. Porsche designed it.

Jake

Correct, that is the main issue with the aluminium cases and it is a good reason not to go with one on a Sonex, however, on a different airframe this might not be as much of a concern.

If I was building an airplane where the extra 12lbs were not so much of a problem, I’d buy one of these:
http://www.cbperformance.com/SearchResults.asp?Cat=200

These cases are made with all the mods that have to be/can be done to an original magnesium already in place, you can buy the bore/stroke as required straight out of the factory with the desired deck height set (no spacers required). Drilled/tapped for full flow, HVX mods done, … you name it.

SvingenB wrote:

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.

Good points Glenn!

vwglenn wrote:
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.

Like this: https://youtu.be/nhY0xzKcPoE

Magnesium is used pretty extensively in helicopter gearboxes. That is a pretty important part so the material is not all bad as long as it is designed appropriately for the loads.

The youtube vid was impressive but I would also recognize that it is not that easy to get a big case going like that, and in the video they threw water on the fire to make the explosion. Water for mag fires is a no-no unless you are just in it for the fun.

For me, I would rather save the 12 lbs. Weight is the enemy!