7/27/2019 Cotter Pins

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30 Recreational Flyer July - August 2009

Technical

Cotter Pins – Part NumberMS24665 - are used to secure bolts,screws, nuts, and pins. Some cotterpins are made of low-carbon steel(Formerly AN380), while othersconsist of stainless steel (FormerlyAN381), and thus are more resis-tant to corrosion or where heat-resisting qualities are desired, suchas forward of rewall. Use stainless

steel cotter pins in locations wherenonmagnetic material is required.Regardless of shape or material, useall cotter pins for the same generalpurpose - safetying.

Most Cotter Pins have uneven-prongs; the length measurement isto the end of the shorter prong.

Cotter pin installation is shownin Figure 1. Castellated nuts areused with bolts that have beendrilled for cotter pins. The cotterpin should t neatly into the hole,with very little side play.

Fig. 1(Alternate method) (Preferred method)

The following general rulesapply to cotter pin safetying.

Do not bend the prong over the bolt end beyond the bolt diameter.(Cut it off if necessary as this endmay interfere with other structure –Reference Fig. 5. This will also saveexcessive lacerations and scaring

on your hands!)Do not bend the prong down

against the surface of the washer.

(Again, cut it off if necessary. Refer-ence Fig. 3)Do not extend the prongs out-

ward from the sides of the nutif you use the optional wraparoundmethod.

Bend all prongs over a reason-able radius. Sharp angled bendsinvite breakage.

Tap the prongs lightly with amallet to bend them.

Install cotter pins in rotat-

ing parts such as propellers, rotorheads, and the like, with head indirection of rotation.

Install cotter pins in stationary bolts with heads up or facing for-ward whenever possible. Wheninstalling a cotter pin in a station-ary bolt in a moving control (suchas elevator control push rod end toelevator, carburetor mixture con-trol rod end to carburetor mixturearm, etc.) the head of the cotter pin

should be up or facing forwardthroughout the range of that con-trol as much as possible.

Fig. 2 (Correct Cotter Pin Installation)

Fig 3

When safetying a clevis pin,install the cotter pin with the axis

of the eye parallel to the shank ofthe clevis pin or rod end. Bend theprongs around the shank of the

clevis pin or rod end, as shown ingure 4.Fig. 4

The cotter pin installationshown in Figure 5 is a photo is ofan aileron trim tab pushrod attach

 bolt. This is incorrect, as the bentprongs were not cut to the properlength and due to this had causedholes to be worn through the lead-

ing edge of the trim tab.

Fig. 5

Related References:FAA Advisory Circular – AC 43.13-1B(Section 6)Standard Aircraft Handbook – SixthEdition.

Cotter Pins

 Michael Adams