Mitch,
My concern was not that the threads wouldn't hold up, but that the aluminum threaded portion might break off the cover, as apparently has happened on several different brands of hub motors. The problem has been not a large enough radius between the threaded portion, and the side cover causing stress riser cracking.
My latest idea is to use two sprockets bolted to the disc brake mounting holes, on a 350 watt, front motor. It is almost a half pound lighter, mostly from the shorter axle.
I figure I will make a couple of spacers to separate the cogs from the motor and each other...enough to allow chain clearance.
http://www.velosolo.co.uk/shopdisc.html
http://www.tomicog.blogspot.com/
I will flip the motor so the cogs are on the right side. The inner cog will be a 16 tooth for the chain running to the rear wheel. The outer cog will be a 15 tooth for the chain to the front single chainring. This is to get my cadence down to a reasonable level. A 13 tooth would be my preference, but 15 is as small as the disc brake bolt circle will allow.
To compensate for the motor running backward, I will cross the chains (figure eight) running to the crank, and to the rear wheel. Since these are long runs on a recumbent, the side load where the chain crosses is small. A short section of teflon chaintube should allow the slack side chain to deflect around the tensioned chain. It will look essentially like the normal chain run on typical recumbent.
http://www.ransbikes.com/Enduro09/Enlarge09.html
Since I want to be pedaling, any time the bike is propelled, this should be about the simplest setup.
Cell_man, Paul, must be on holiday. He hasn't gotten back to me.
Warren