Gary_Ash

Correct way to install cotter pins in castle nuts?

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It seems simple enough:  spin on a castle nut and torque it down, insert a cotter pin through the hole in the threaded shaft or bolt, bend the ends over.  But, there must be a right way to insert the pin and bend the ends.  I've been doing this for about 60 years but was never taught the correct procedure.  Here's what I now think is the right way:

 

Insert the pin in the hole until the head bottoms.  The head is positioned with the long dimension aligned with the shaft or bolt so it fits completely in the slot of the castle nut.  The longer end of the cotter pin is up so it's easy to grab.  With a finger or tool, bend the long end up and over the end of the bolt or shaft, tap it down tight.  Bend the short end down over the face of the nut, trimming as required to prevent snagging yourself later.

 

Yet, I see all kinds of demonstrations and photos - including from fastener suppliers - showing the cotter pin inserted with the head rotated 90 degrees and the two ends bent in opposite directions around the nut .  Besides being ugly, this doesn't seem right.  I also saw a video claiming that the short end should be left straight and not bent down around the nut - also seems wrong and leaves a pointy end to snag you.  I checked my current version of Machinery's Handbook and  a reputable book on machine design - they were both remarkably silent about installing cotter pins though they had all the dimensions for standard cotter pins and castle nuts.

 

Does anyone know a definitive reference on the subject?  I confess that as a kid, and short of a new cotter pin, I inserted a finishing nail and bent it over - more than once. 

cotter pin.jpg

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I have seen them installed the different ways you describe plus one other. Do it the 'right' way, then cut off the short end with side cutter pliers. Have seen them bent over so carelessly that the end was rubbing against the center cap. Have never seen one break or work loose no matter how it was installed.

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That is the way that I have always installed cotter keys. The "wrong" way never seemed right to me.

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The pre-war Rolls Royce method is to insert the cotter pin so the head is hard down in the nut groove,  grip the other end with pliers and twist it 90 degrees then bend the ends back around the sides of the nut. Finally the ends are cut to size, bent at 90 degrees inwards and pushed into the nut slot where the pin came through the bolt.

 

Why such a complicated method?   It is to stop the chauffeur cutting his hands when he is washing down the car and cleaning the exposed nuts on the suspension etc.

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The right way, the wrong way, and the Army way...

 

This is from an Army tech manual (TM 1-1500-204-23-6) on General Aircraft Maintenance.

 

TM-1-1500-204-23-6_87_0.jpg

Edited by joe_padavano (see edit history)
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Thanks, Joe, that looks right. The clevis pin example covers the cases where it’s not possible to bend the end of the cotter pin over the top of a castle nut. It’s also interesting to see the honeycomb example where the cotter pin ends are tucked into the nut to keep them from snagging things or people. I guess needle nose pliers are needed to bend the shapes. I’d better get a pair of heavy duty diagonal cutters for the steel cotter pins because I don’t want to dull my ones for cutting copper wire. 

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1 hour ago, Gary_Ash said:

Thanks, Joe, that looks right. The clevis pin example covers the cases where it’s not possible to bend the end of the cotter pin over the top of a castle nut. It’s also interesting to see the honeycomb example where the cotter pin ends are tucked into the nut to keep them from snagging things or people. I guess needle nose pliers are needed to bend the shapes. I’d better get a pair of heavy duty diagonal cutters for the steel cotter pins because I don’t want to dull my ones for cutting copper wire. 

As  you're likely aware, aluminum honeycomb usually has pretty thin face sheets. Tucking the ends of the cotter in like that preclude any chance of puncturing a face sheet, which and initiate a crack.

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On ‎8‎/‎31‎/‎2019 at 6:18 PM, joe_padavano said:

As  you're likely aware, aluminum honeycomb usually has pretty thin face sheets. Tucking the ends of the cotter in like that preclude any chance of puncturing a face sheet, which and initiate a crack.

 

I have seen that on old rear wheel drive vehicles where the front grease cap was cut because the cotter pin was not tucked in tight and wore on the cap.

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3 hours ago, Hupp36 said:

I only use stainless steal cotter pins  for  strength. The  run  of the  mill cotter pins  are  made of  soft  steel. The stainless steel pins  do  not  cost  much  more and have more shear strength.

 

You do realize that the shear load on a cotter pin is negligible, right? Stainless STEEL cotter pins resist rust, but shear strength? Not a concern. Yes, mild steel has a shear strength of about 40,000 PSI. while 304 stainless (the most common stainless for fasteners) is 75,000 PSI. Even at 40,000 PSI, it takes 1,100 lbs to shear a 0.190" diameter mild steel cotter pin. Three of those will lift my car.

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3 hours ago, Hupp36 said:

Well,  my  good  man , I  have  taken apart at  least 15  car  engines and  have  had some with  cotter  pins  broken and  laying in the  pan. I  do  realize if  the  guy  who  put  the  engine  back together properly, a plain cotter pin  may work  fine. My  analogy to  this  is. I  would  rather  have  4  sidewall plies on  my  car  tires  than 2

 

  For what it is worth, I am with Joe. I have never seen a cotter pin sheared. May yet do so. One never knows.

 

 

  Ben

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Ooops, I had better take the nail out of the Buick's right front axle nut.

Been in there for about 4 years now.

 

Mike in Colorado

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 Thanks for the concern Hupp. I am approaching 83 and have been working on cars and OTHER machinery since I was 12.  I have sheared them intentionally when unable to remove the bugger.

4 hours ago, FLYER15015 said:

Ooops, I had better take the nail out of the Buick's right front axle nut.

Been in there for about 4 years now.

 

Mike in Colorado

 

 Damn, Mike ,I was going to say that! 

 

  Ben

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The beautiful twists shown above assume that you can actually get a needle nose or dikes into position to bend them pretty. Sometimes just bending one leg to hole it in place is a challenge.   

 

On suspensions (front ball joints and tire rod ends), I like to leave the head sticking out a bit to make it easier to grasp later with the diagonal cutting pliers. 

The ball joints seem to get badly crudded up with grease that then attracts dirt, and somehow they also become rusted in the hole. Sometimes I have been lucky enough to clip the head and work out one leg which allows a little room for the other leg to jiggle out. But completely stuck they can become. Once I clipped and trimmed and tugged and still had to unscrew the nut over the remains of a pin that was still partially in place. Hours spent on a 3 minute job. Very happy that it was mild steel. . . . .

 

Also on front wheels if there is a static collector under the hub cover (1950s & 60s) the folded over leg needs to be cut short to insure that it doesnt grab and destroy the collector which runs against the end of the spindle. I have found very few original static collectors because of poorly place pins. 

Edited by m-mman (see edit history)

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My engine rebuilder, who mainly works on Porsche road and race engines, states that no cotter pin is needed on ANY connecting rod nut if nut is torqued correctly.

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8 hours ago, Ben Bruce aka First Born said:

I have sheared them intentionally when unable to remove the bugger.

 

^^^This! Usually on suspension parts that I'm replacing anyway. And I'll add that forming the open end up over the stud as opposed to around the sides of the nut makes it MUCH easier to hammer a socket over the nut and offending cotter. 😁

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I agree with Joe`s (and the US army`s) view on cotter pins, except that we call them split pins. A cotter pin, in the UK, is a round pin with a flat on one side and a nut on the end, as used to secure kingpins (or are those steering swivel pins???) :)

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Per our "friend" Mr. Google, the split cotter pin was invented by Mr. Ira J. Young in 1912 in St Louis.

Not Harry Cotter.  Wasn't he a kid magician  ?

 

Boy, we're really off track now................

 

Mike in Colorado

Edited by FLYER15015 (see edit history)
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I use needle nose pliers to remove cotter pins from suspension and other parts. Open pliers, put one point through the head of the cotter pin. and use hammer (small 8 oz ball peen with a short handle) to apply force to the side of the pliers to remove the cotter pin. I gave up on those awl looking tools to remove cotter pins.

 

I also drive sockets on when the pin refuses to move. 👍

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3 hours ago, Frank DuVal said:

I use needle nose pliers to remove cotter pins from suspension and other parts. Open pliers, put one point through the head of the cotter pin. and use hammer (small 8 oz ball peen with a short handle) to apply force to the side of the pliers to remove the cotter pin. I gave up on those awl looking tools to remove cotter pins.

 

I also drive sockets on when the pin refuses to move. 👍

 

I actually have a cotter pin puller tool. It's often good at splitting the OTHER end of a split pin. 😉

 

3R553_AS01?$zmmain$

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I use a large pair of diagonal cutter pliers.  Catch the head of the cotter pin with the blades of the pliers with the end of the pliers against the nut and use the pliers as a lever to pull the pin.  Usually I do not even have to un bend the pin.

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16 hours ago, Tinindian said:

I use a large pair of diagonal cutter pliers.  Catch the head of the cotter pin with the blades of the pliers with the end of the pliers against the nut and use the pliers as a lever to pull the pin.  Usually I do not even have to un bend the pin.

 That is the same way I learned to easily "jack" stubborn cotter pins put of sail boat rigging, when I worked in boat yards over 45 years ago.   Sailboat rigging pliers have a wire cutter built into the plier jaws and it makes quick work of pulling out the most stubborn cotter pins.

 

By pinching with the pliers and levering against the surface, as Tinindian said, then move the pliers down close to the nut and pinch the pin again, by repeating that you can "jack" out any size or length cotter pin because it exerts enough force to easily pull cotter pins that are stuck with rust and dirt.  And as Tin pointed out, that leverage is strong enough pulling force that often they can be jacked out even if the pin still has the tails spread.

 

I have one of the cotter pin puller hook handles, but the tails of the pin have to be very close together to get it to work because there's no leverage force like the pliers can do.  And for that pliers are needed to straighten the tails well enough.  With the diagonal cutter pliers one tool does it all.   

 

Paul

Edited by PFitz (see edit history)
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2 hours ago, PFitz said:

 That is the same way I learned to easily "jack" stubborn cotter pins put of sail boat rigging, when I worked in boat yards over 45 years ago.   Sailboat rigging pliers have a wire cutter built into the plier jaws and it makes quick work of pulling out the most stubborn cotter pins.

 

By pinching with the pliers and levering against the surface, as Tinindian said, then move the pliers down close to the nut and pinch the pin again, by repeating that you can "jack" out any size or length cotter pin because it exerts enough force to easily pull cotter pins that are stuck with rust and dirt.  And as Tin pointed out, that leverage is strong enough pulling force that often they can be jacked out even if the pin still has the tails spread.

 

I have one of the cotter pin puller hook handles, but the tails of the pin have to be very close together to get it to work because there's no leverage force like the pliers can do.  And for that pliers are needed to straighten the tails well enough.  With the diagonal cutter pliers one tool does it all.   

 

Paul

 

I use diagonal cutters. I use channel-lock style pliers and lever the pin out. I use the extractor tool I showed. I straighten the ends and tap them out. Invariably there will be one stubborn cotter that refuses to come out and all of the above just breaks the end. At that point, a hammered-on socket and (if there's room) an impact wrench solves the problem every time.

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I find a 24" flex head Snap-On ratchet makes short work of removing castle nuts when the cotter pin does not want to come out!😁

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Before installing a split pin run a drill through the hole and smear a little grease in the hole. Installation of every nut  bolt and even wood screws should be smeared . I find using a smear of grease on wood screws take less pressure to sink the head in.  

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