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Dan Thomas

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Sep 17, 2008
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You mean to tell me Aluminum expands at twice the rate of steel irrespective of what alloy or composition or silicon content there is? And as for the Orenda 600, I don't see how you can compare an automotive engine that was converted for aviation use vs a purpose designed aircraft piston engine. The duty cycles are entirely different and one can't possibly expect the converted engine to have the same "life" as an aircraft piston engine.
There is such a thing as the Coefficient of Linear Thermal Expansion. How much a metal expands or contracts per degree of temperature change. Look at this list and see if you can find an aluminum alloy that has a coefficient similar to any of the steels other than stainless steels (some of which have little iron in them at all). Cast iron, cast steel, wrought carbon steels and mild steels are all around half of the expansion rates of aluminum alloys.
Metals - Temperature Expansion Coefficients

Aluminum pistons normally have steel "struts" cast into them, around the wrist pin hole areas, to limit expansion across that area. The piston is Cam-ground" to have larger cold clearances at the wrist pin areas, since the areas 90° to that get a lot hotter and expand more and close up that clearance. The hotter areas don't have the wrist pin and rod to conduct heat out of them.

The Orenda's operating life? You'll have to debate that with guys like Ross of SDS fame and some other that have run auto conversions really hard for a long time. I myself installed a Subaru 2.2 conversion in a Glastar and flew it. At full throttle sometimes. Tough little engine. The redrive was more trouble than the engine itself.
 
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