Dan Anderson: The Preferred Way to Make Repairs

March 8, 2018 09:54 AM
Dan Anderson

There are sometimes multiple ways to assemble parts when repairing farm equipment. The secret to optimizing repairs is to follow the “preferred” procedure.

Installing eccentric lock collars on bearings is a good example. When installing a bearing on a shaft that rotates, lock the bearing’s lock collar in the direction the shaft turns. If the shaft is stationary while the bearing and bearing housing rotate around it, the lock collar should be locked in the direction the housing rotates.

I tried to analyze the physics and logic behind which direction to lock an eccentric collar, gave myself a serious headache and finally consulted several engineers with bearing companies. Their unanimous answer: “Mirror the direction the shaft rotates” or “match the direction the bearing rotates if the shaft is stationary.”

They also mentioned when “setting” a lock collar on a bearing, more pounding is not always better. Hammering the set hole on a lock collar until it’s severely distorted risks creating so much torque between the lock collar and the bearing’s eccentric ring that it cracks the center race of the bearing. A properly set lock collar has only a minor distortion, perhaps a slightly raised edge, on the rim of the setting hole.

Retaining clips on roller chain master links are another reassembly issue that kinda/sorta matters. In a perfect world, the closed end of the retaining clip faces the direction the chain moves, and the split end faces away from the direction of movement. That way there’s less chance the clip will get knocked open and fall off if it rubs against a bracket or chain guide.

Master links that use cotter keys to retain their side plate present an interesting situation. If the cotter keys are installed with their heads toward chain movement, then the “tails” of the cotter keys, when crimped around the pins, are susceptible to snagging and breaking off so the cotter key can vibrate out of place. The alternative is to put the cotter key tails toward the direction of chain movement, with those tails bent around the pins, so any snagging keeps them crimped and in place.

Which way is preferred? I’ve noticed factory-assembled roller chains that use cotter keys to retain the master link often have one cotter key facing in the direction of chain movement and one facing away from chain movement. That way, if one cotter key becomes dislodged due to its orientation, the other one stays in place and holds the master link together until the operator notices and repairs the problem.

A single drop of thread locking compound, used in the right place on nuts and bolts, ensures fasteners don’t vibrate loose. But if you’re installing a bolt into a casting, or a nut onto a bolt, where should the drop of liquid be placed for optimum benefit?

Representatives with Loctite say a single drop of Loctite should be placed on the end of a clean, dry bolt before it is threaded into a casting. If the liquid is placed on the threads inside the casting, especially if excess liquid is applied to those female threads, it can be forced ahead of the bolt as the bolt is threaded-in, build up in the dead-end cavity and create a hydraulic lock that prevents the bolt from reaching full depth and proper torque.

When a nut is installed on a bolt, the drop of Loctite should go on the threads of the bolt where the nut will rest when it is fully torqued. Locking compound applied to the female threads of the nut, or to the initial threads of the bolt, gets dispersed across too many threads as the nut is threaded into place, decreasing its locking power.

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