BigToe wrote:
Quote:hedge wrote:
Lock washers can be the problem sometimes because they break and fall out, i'd rather use loctite and or nylock nuts
Look on your truck, you won't find a lock washer
/Quote.
And keep looking under your truck...you won't find a Nylock nut either!
Elevated underbody temperatures (like exhaust heat from turn up pipes over the axle, mufflers, catalytic converters, and diesel exhaust aftertreatment systems) can partially melt the elastomer in the nylock nut, whereupon it looses all of it's "locking" feature. The OEM's strongly caution approved vehicle upfitters about this.
The best nuts to use are prevailing torque flange nuts. The locking feature of the nut is inherent in the manufactured eccentricity in the thread bore. The friction loss potential is reduced by the elimination of a washer, ANY washer, and the friction/bearing surface is broadened by the integrated flange that is integral to the nut. This is the type of nut you will see under the truck. Any brand of truck... from Toyota to Peterbilt, and all the Ford/Chevy/Rams in between.
The reason why "double nutting" is not seen is because the second nut removes the preload off of the first nut. Friction is most important nearest the parts being clamped, which partially involves the mating surface of the parts themselves, as well as the first two threada after that surface to nut transition along the bolt axis. The second nut in a double nut situation can unload the torque value of the primary nut. Not something seen done by OEM's on vehicles either.
Actually, Nylocks are used in under hood applications in at least a few spots. All the GM intercooler hose clamps use Nylocks. Nylon melts somewhere in the 400+F region. Also, there are fiber (non Nylon) locking nuts that reportedly have a higher melt point). Nylocks are pretty pricey and in a production environment where thousands of units are being produced, this cost would most likely be deemed unacceptable for the risk/benefit ratio gained.
Flange bolt heads and flange nuts, at least when I was an engineer in aerospace/military, high production environments, was used primarily as a cost/labor savings. Good practice is to not let a hex head nut dig into the material being clamped. A flat washer helps avoids generating the metal particulates and also effectively distributes the clamping force. However, it takes additional time, stockroom space and materials management/procurement to deal with separate flat washers, so flange nuts and bolts solve this issue and save time and money.
From my perspective/experience, if a fastener is torqued properly it isn't going to back out in all but the most dynamic (thermal and mechanical) of environments. In my current business (spacecraft applications), we stake the head/side of the fastener with structural adhesive to ensure it doesn't move. I haven't measured the spring force of a 1/2" or 5/8" Grade 8 lock nut but they are pretty hefty and do their job well and I think they add a significant amount of insurance to a properly torqued fastener. Again, in a production environment, adding an additional piece to the fastener, or adding expensive Nylocks is not desirable for cost purposes and one shouldn't deem their absence or low usage in our vehicles as an indication of their reliability.
My two cents.
Phil
