SonexBuilders.net

Hi, I would like to exchange info with people that use an Aluminum Engine case for the Sonex VW engine.
My engine, 470 Hrs TT runs very hot and get tide after heating up. I do get 3100 static rpm and 3400 rpm
wide open. I was told engines with alu cases act that way.

I don't think the case being aluminium would have much to do with heat. If you're running hot it's probably a tuning or a airflow issue.

Eisenflyer wrote:Hi, I would like to exchange info with people that use an Aluminum Engine case for the Sonex VW engine.
My engine, 470 Hrs TT runs very hot and get tide after heating up. I do get 3100 static rpm and 3400 rpm
wide open. I was told engines with alu cases act that way.

The AeroVee has never been supplied with an aluminum case.

I believe that he asked about aluminum vw cases on a VW powered Sonex, not specifically an Aerovee.

The aluminum cases do tend to run a little bit hotter but not by a lot. The aluminum is denser than magnesium and doesn't dissipate heat quite as easily. Is it CHT, EGT, or Oil temp that is running high?

If all other things are equal there shouldn't be enough of a difference in case material type to cause you to be running close to the limits. I would look into some of the other tips posted on here in the past (cowling inlet/outlet sizing, syncing timing with a timing light, smoothing the upper lip of the cowl opening, running a richer mixture, etc.)

Keith
#554

OK, I build the engine myself with an alu case because as everybody knows alu is stronger than magnesium. The differents I am talking about
is "engine cold, prop turns freely by hand, the engine hot, it feels like a lot of friction inside the engine. Now, I like to talk to people that
use an alu case, if you do not, please do not reply. Thank you.

You're the only Sonex driver on this forum I know of with an aluminium VW case.
You might want to pose your question in one of the Aero VW Yahoo groups:
https://groups.yahoo.com/neo/groups/VW_ ... s/messages
https://groups.yahoo.com/neo/groups/Air ... s/messages
https://groups.yahoo.com/neo/groups/Air ... s/messages

Sorry for responding, I do not have an aluminium case either...

Hi, thank you, this is a good lead.

Well I don't even have a VW engine, but my Jabiru does have aluminium cases, so does that qualify?

A couple of facts:
Aluminium has higher thermal conductivity than Magnesium so should spread the heat more evenly. (I read it on the internet, it must be true). Since the only way for the cases to get rid of heat is by radiation, which mostly depends on the colour of the cases (matte black good) and conduction, which is going to be mostly via the oil cooler, the difference in thermal conductivity is probably not going to matter.

Aluminium and magnesium have pretty similar coefficients of thermal expansion, but they both have much greater thermal expansion than the steel crankshaft, so the cases grow much more than the crank as the engine heats up. I'm not familiar with the arrangement of the thrust bearings in the VW, but it might be that your engine does not have sufficient clearance to allow for expansion of the cases relative to the crankshaft.

Peter
Sonex 894
303 hours

Sorry to interject, but your line noting you used an aluminum case "because as everybody knows alu is stronger than magnesium" isn't universally accurate. Here's what several metallurgy web sites say about the relative strength, weight and conductivity of Aluminum and Magnesium:

"Magnesium is 33% lighter than aluminum, 60% lighter than titanium, and 75% lighter than steel. Yet for many applications it's stronger per unit volume than all three of those structural metals. It is also an extremely versatile metal."

Also has excellent conductivity...guess that's why VW used magnesium crankcases on most of its engines...

Good luck seeking answers...

Thank you, I shal check that out at once, did not know that.