I think it is FCD that provides a mark on their cam pins for indication of running position....it is my understanding the cam pin is supposed to be oriented the same direction when reinstalling after cleaning/maintenance....is this the correct procedure?  I thought for sure I read somewhere the opposite.

But the machinery engineer in me says keep the running position the same....

Which brings me to my next question...is there any issue with marking my cam pins with a very slight drill mark...assuming hardness of the cam pin will allow...

There are purpose made cam pins that are designed to fit only one way.  Standard cam pins fit either way and I have never read of any benefit of trying to keep them oriented one way.
That said if you wanna mark yours and run it only one direction go for it. My .02 is that it is your OCD kicking in and I really don’t know what benefit you will be able to see,

Yeah, FCD/SOTAR collaboration.

Cam pin usually wears more heavily on one side, putting the cam pin in one direction, then another randomly creates uneven wear on the cam pin, and it becomes sloppy and loose in the bolt.   When the cam pin is installed always facing the same direction,  it leaves one side less worn and more intact, this has the effect of better maintaining a tight fit of the cam pin in the bolt, and reduces wear cam pin itself as well as on the cam pin bore on the bolt.

The idea of consistently reinstalling the cam pin in the same orientation, isn't so much about saving the cam pin as it is reducing the resulting wear and stress introduced to the bolt.

Makes sense in theory, not something that I worry about personally. Inspection for "Cracks, damage,  excessive wear" per the TM. Keep spares on hand.


You can mark them easy enough, I'd apply some cold blue to replace removed finish.

I stopped OCDing over cam pins. At one time I replaced them when I observed wear. But it seems they wear in and then the wear slows. So I just put it them back in and let it eat. But on the other hand, they are cheap and probably could be considered consumable.

Need to clarify some....in the past I have not paid attention at all, cam pin out, cleaned, pin back in....been doing this way for years...not marking at all

Was digging around and found the discussion on the cam pin and keeping in one direction.  If the concensus is not to worry, will stay in that direction, as I have been doing.

Thanks,

Bronc

Smart guy (legit sme) says it’s best not to put it in the same way every time as rotating it spreads the wear.

I'm also in the "put it in and shoot it" camp.  Too many people try to make mountains out of molehills or try to find something to obsess over.  You can make the argument either way, let it wear only on one side (and maybe that uneven wear on that one side makes it fail sooner?), chance directions every time to spread the wear around and possibly make it last longer, or just installing the damned thing and get on with your life.  Your cam pin, your choice.

Reading Big-Bore's response made me think of this from MCV....."do you think the cam pin cares which way it is installed?"....sorry guys, just having fun today, and it is my question!!!

MCV

Best scene of the movie

Is the pin the same hardness as the carrier so that both parts will wear or will only the cam pin wear because it's softer?  This isn't something I've even once thought about since shooting my first rifle at Benning in the mid eighties and I certainly don't plan on starting now.  I'm merely curious about the hardness/wear relationship between the two parts.

4340 on the cam pin material,  8620 for carrier, unless my memory is borked.

You can use a center punch to just mark a dot, or use an etching tool to mark an arrow or something.

Thank you.  If your memory is accurate that would indicate carrier wear isn't relative to cam pin direction.  Cam pins are cheap enough to replace if wear becomes apparent.

I have never seen one that could be installed in both directions, one hole is enlarged and the other is not.

That’s to keep the bolt from being upside down.

OP is talking about spinning the cam pin 180 degrees.

I might start marking mine so I can pretend it is like a tire and rotate it for even wear.

Yep, or use a drill press.

https://www.youtube.com/watch?v=X-eRMvOYuiE

Center punch does not work.  I may make a jig and lightly mark with the drill press.  Project for early in the morning when I cannot sleep.

Marking a tiny indication mark on metal is about a half a second touch with a Dremel wheel.

I use a dremel with a small ball end bit then touch up with Perma Blue, takes 2 mins.
Attached File

There it is.

Bingo

Will do that

@77Bronc here’s the dremel bit I use.
EDIT- Straight down with tip and it won’t walk.
Attached File

@FONTY

I have a bit like this in my collection.  Thanks for the picture

Bronc

Well took the advice here

Made a jig out of solid maple.  Drilled a 5/16” hole to hold the cam pin


Used the ball end mill in the drill press

Disregard the messy bench.  We are in a complete house remodel and I have crap crammed everywhere

Cam pin post milling.  Next time will get a little further from the edge


Put some cold blue on it and back in the rifle.  

Start to finish 7 minutes.

Looks good. Did you mark it on the side of the cam pin? I mark it so the it faces forward when installed in the bc.

Attached File

I marked it on the short side which would be up or down when installed....so all I need to note will be facing gas key or not.....

I am on the OCD side, so when I am cleaning the rifles, I am taking notes in my binder, what I cleaned, observed, spring conditions....etc....yeah, I am obsessed....39 years as a machinery engineering advisor for ExxonMobil, we took notes on everything

Gotcha, yeah i’d have to say people marking cam pin orientation have a touch of OCD including myself

I've seen pics on line of broken cam pins but I have never replaced any ever.  Like any other part it can fail at some point.  Replace when applicable.  I always travel with a complete spare BCG in my tool bag when traveling around theater.  Just gave out my firing pin in it after we shipped all parts out of Astan week before we left.  

CD

The cam angles for locking and unlocking are equal, the bolt carrier is a cylinder and the cam pin is a cylinder. This means the contact areas as the pin moves forward are exactly the same as the contact areas as the pin moves backwards only rotated 180 degrees. That means the wear areas are exactly the same.

The increase "slop" is caused by and increase in clearance between the parts, so if you want to reduce your shock loading, you want to reduce the amount of wear. The pin is softer than the carrier so most all the wear in on the pin.

The loading during the unlocking camming is much greater that the loading during locking camming, therefore the "front" of the pin will wear faster than the "back". If you keep one side towards the front all the time, the front wear will accumulate faster than the back. If you switch pin orientation regularly, or randomly, the wear will be distributed equally on the front and the back of the pin, so on average the amount of wear on any one face will be less.

Also, the cam pin does not bottom out in the cam track during locking, the carrier stops on contact with the barrel extension well before the pin reaches the back end of the cam slot, so this side doesn't wear at all. The highest load on the cam pin is at the end of unlocking when the pin bottoms out at the front of the cam slot. Again, randomly switching the orientation of the cam pin will reduce the wear on any one side.

If you want to reduce the loads on the hole in the bolt, the way to achieve that is find a way to reduce the amount of wear on the face of the cam pin that faces forward. Flipping it 180 degrees every now and again is a better way to do that than leaving one face always facing forward....

Personally, I think liberal use of a good lubricant in the cam slot is a most cost effective way of achieving the desired end.





I have to congratulate the guys that first thought of selling marked "positional" cam pins, not only did you manage to get some people to pay for something completely useless, you have convince many others that this "uni-directional" cam pin is a good idea.  At best it is worthless, at worst, it halves the life of the cam pin.

I swear, I bet some of you guys change the air in your tires at the same time you rotate them.

Prozac is your friend, or should be.

I just can't wrap my head around the urge to focus wear in one area instead of spreading it around evenly, if it even makes a difference one way or the other.  Maybe the cam pin was designed to be installed either direction for a reason.

This cam pin has been in the AR I bought in '81 , never thought about which way it was installed .

For a number of years I used a $9 chromed cam pin in my National Match M16.  Nice and hard (though not polished and smooth) it just got shiny where it rubbed in its slot in the carrier.

I turned it in for a barrel change and it came back with a GI cam pin.  No big deal.  I think you can get nitrided or boron-nitrided ones now.

I don't think it makes a difference.  I LSA spooge the snot out of those slots before shooting.

$8-$10 component. Widely available, keep spares.


Attached File

I've never heard of this before.  Interesting to know, but with that being said, I don't intend to change my ways now.  I just install and shoot.

This is FCD's demographic.  

When I started rotating my tires front to back and not criss-crossed I stopped changing the air....as with front to back, the tires stay rotating in the same direction....when they are criss-crossed, the tires will be turning the opposite direction than they were and the air will be moving in the opposite direction which can create a seperation at the molecular level...can casue an issue....Has save me some money over the years...

In all of my time with their group, I've never seen it but cool story bro

Covered above, my mistake.

That make no sense.

The fact that there is a high force on one side means there is going to be high wear on that side.  Swapping directions periodically evens the wear out on both sides.

As to the actual amount of force, that has been both measured and calculated and is about 2000 pounds.   This not enough to set up an fatigue issues by swapping directions every few thousand rounds.

Actually, there are reasons for the various tire rotation methods, mainly due to the fact that tire wear is unevenly distributed under normal driving, generally speaking the left front tire wears faster that any other tire, and the left rear, the least.

Rotation patterns recommended by the Tire and Rim Association, Inc.

For tires that are of uniform size and non-directional:

1.     Rearward cross - For vehicles that are 4-wheel, all-wheel, or rear-wheel drive, the rearward cross pattern is recommended. Rear tires are moved to the forward axle and kept on the same side of the vehicle while the front tires are moved to opposite sides of the rear axle.

2.     X-Pattern - Recommended for front-wheel drive vehicles such as light-weight trucks and sedans, all tires are moved diagonally, meaning tires are switched from one axle to the opposite as well as being repositioned from one side to the other.

3.     Forward cross - This is the most common pattern for front-wheel drive vehicles. The front axle tires are moved directly back while the rear tires are moved up diagonally to the opposite side of the front axle.

For tires that are of uniform size and non-directional with a full-size spare tire:

In order to insure that all of the tires on your vehicle have even tread wear, you’ll want to be sure to rotate your full-size spare tire along with the other four. This is especially vital for all-wheel or 4-wheel drive vehicles where even small differences can put undue strain on your car’s drive train.

1.     Rearward cross (Rear-wheel or 4-wheel drive vehicles) - Both rear axle tires move directly forward to the front axle while the spare tire moves to the right side of the rear axle. The right front tire moves diagonally back to the left side of the rear axle while the left front tire becomes your new spare tire.

2.     Forward cross (front-wheel drive vehicles) - Rear tires are moved diagonally to opposite sides on the front axle while the right front tire becomes the new spare tire. The spare tire is positioned on the right side of the rear axle while the left tire on the front axle is moved directly back into the left rear position.

For high performance and directional tires:

1.     Side-to-side (for differently-sized performance tires on the front and rear axles) - All tires are switched with their same-sized partner and remain on the same axle. The two rear tires switch to the opposite side with one another while the two front tires do the same.

2.     Front-to-back (for directional tires) - All tires are moved from one axle to the other but remain on the same side of the vehicle. For example, the front left tire is moved to the left side of the rear axle while the rear left tire is repositioned on the left side of the front axle.

How many rounds?

Bruh......
the air gets stale, duh.

All this over a $8 part

I  honestly don't know , I've shot it every year except this year .

Good information on this thread!  It also reminded me that I need to get some spare cam pins.  

Where's the best place online to get good quality mil-spec cam pins?

G&R Tactical

Do you guys rotate the lifters in your engine too?

How about re-indexing your u-joints every other oil change?

Granted, this is an easy thing to do, but it's a non-issue. I'd guarantee that pin was designed to be assembled in either direction to make reassembly easier, not so you can rotate it for wear.

I have a tire rotation problem,
If I am not careful when pushing down on the gas peddle,
the rear tires rotate faster than the fronts, and that lets out the magic smoke

Anyone know where I can get replacement smoke,
or is that just bad air, and I need to change out the old air ?