Came across this while surfing.
They design aircraft engines and gearboxes. The site has a very extensive list of technical articles on mechanical basics, engine theory, gearbox and bearing design and propeller design. I'm not so interested in the aircraft specific bits but the engine, gear design and general mechanical sections I've read so far are excellent. Well written, technically correct as far as I can see, no dumb typos and spelling errors which always put me straight off. The explanation of gear tooth pressure angle is the first one I've actually ever understood fully. It's always been a bit of a mystery to me prior to this.
There's a very nice bit on piston velocity and acceleration which demonstrates why maximum negative piston acceleration doesn't occur at BDC contrary to what most engineers would first think but actually manifests as a W shaped curve except with infinitely long conrods. We had a very detailed debate on this in rec.crafts.metalworking several years ago.
Anyway, worth a read to most in here I'd suggest.