I'm a bicycle mechanic - have been for a long time, and consider myself to be a pretty good one. I'm not a great car mechanic, but I'm getting better. I at least have a good sense of mechanical principle.

But there's one thing in particular I don't get: what's the aversion to treating most threads on automobiles with anything? I ask this in all seriousness, because I can't think of very many threads (any, really) on a bicycle that should go without grease or - ugh - blue Loctite. Torque specs on a bicycle are generally much lower, but there are a few exceptions where torque is very high and grease is still applied.

I guess this is an engineering question, maybe even a physics question. Why no thread treatment, grease in particular?

 

Most fastened joints on a car are engineered to be torqued dry, lubricating the threads will result in the joint being over torqued which may damage the threads or stretch the fastener beyond it's elastic limit, reducing the fasteners ability to clamp a joint.

Dave