Oiling a bolt before insertion?

[beefsalad]

So I've finally started putting the 9 back together and just before installing the flywheel I figured I would look in the service manual for torque values and to find out if I needed to use thread lock. To my surprise they say to oil the threads of the bolt, and the mating surface for the flywheel. Can anyone explain why oil is used on the threads instead of a thread locker? If this were a self-tapping bolt I could see oil being used to ease the cutting process, but this doesn't appear to be such a bolt to me.

[robtharalson]

It seems counterintiutive, doesn't it? An oiled bolt is going to come loose, right? Actually, exactly the reverse is true. In order to attain the specified torque on most hardware the threads must be free to rotate: a dry bolt will develop adhesions to the threads as the final torque value is approached and will suddenly freeze up, seemingly giving the required torque at which point you will stop tightening it. In actuality the clamping force will be insufficient and it is considerably more likely to break the adhesions and back out. Most critical fasteners in an engine specify some sort of lubricant to insure proper torque is acheived. Standard motor oil is usually called for and all that is required.
Have fun putting it back together and getting it back on the road!

Rob

[Sniper]

The mechanic at work told me the little secret of oiling bolts. I've been doing it for years now. It's a habit of mine that no nut or bolt goes on dry. It gets either Loctite or grease. Loctite is especially good for motorcycle applications because often we're dealing with small, aluminum threads, and overtightening is definatly the wrong thing to do.