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Nord lock washers

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Tip of the Day,


We have at times washers called Nord lock washers in high vibration or critical areas on our planes. We have them on our props and brakes and can be other places too. They are a two piece washer and work extremely well unless you put the two halves together wrong. The washers have a fine serrated edge side and then a larger raised rib side. The serrated edges face outward and the large raised rib side face inward towards each other. When tightened to the proper torque these lock themselves in place. When you unscrew one you usually hear a click sound as it unlocks. If you put the halves together backwards or fail to torque them properly the screw could back out just like any un-secured screw. Below is a Matco brake disc where the screw backed out and caused some damage after it came out far enough to strike the caliper. You can, if it makes you fell better, put a drop of medium Blue Loctite on the screw, but is completely un-necessary if installed properly. This particular screw should have had 100 in/lbs of torque.

Sensenich feels so strongly about Nord washers they wouldn't even put a nut on the screw, but they know that wouldn't be politically correct so they do have lock nuts. The Nord lock washers on the Sensenich prop bolts is 225-240 in/lbs and they definitely click and snap when un-screwed.


You can also see the damage the backed out screw caused to the caliper and it even tweeked the hole on the disc. The picture of the screw shows the wrong direction of the mating surface of this washer.

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