Remington Model 8 Bolt Timing

[johnm1]

In my previous thread about this rifles jamb (now corrected), HiBC astutely noted that the bolt locking lugs were not returning to the correct 12/6 o'clock positions when the bolt is withdrawn from the locked position. This has not posed a function problem, yet. I note that the bolt can be turned to bring the lugs to the correct position while holding the bolt open by hand. It can't easily be reached it when locked back.

Now, I would 'assume' that this indicates that either one or both cam pins are worn/mismatched or the helical channel the cam pins travel in is worn. The real question here is if my assumption is a good place to start my investigation or if I should be looking at other things I am not thinking about.

I have 2 cam pins due to arrive today. If for no other reason to compare to the ones I have. Lord knows if the ones arriving today are 109 years old and completely worn out or not. But they were cheap and I had other parts for another rifle coming anyway.

Although the locking lugs are not exactly at 12/6 o'clock, the lugs pass the end of the barrel without contact. There is no sign of battering of the lugs one would see if the lugs contacted the end of the barrel barrel. Is it possible that this timing was close enough to leave the factory the way it is?

The rifle is 91 years old and although in very nice mechanical shape there were tell tale signs of people working on it that didn't know what they were doing. There were several small pieces missing (now replaced). But the cam pins could have been from another rifle. There just isn't a way to know for sure.

Is there any source that could tell us what the nominal dimensions are for the cam pins? Also how to determine if the helical channels are worn?

I am still trying to re-activate my account at the Great Model 8 forum. But until someone there replies to my e mail I am locked out.

[johnm1]

As an add to the above post, another thing I think needs to be considered is the travel the bolt head in/out of the carrier. I hope I'm using the correct terms. As I understand it, the bolt moves in and out of the carrier and it is that motion that the cam pins act on the helical grooves in the body of the bolt that rotates the bolt head into and out of the locked position. It seems to me if the bolt was not being 'pulled' out enough on its trip from locked to unlocked position the bolt head might not rotate all the way to the 12/6 o'clock position. I'm not sure what mechanism does the pulling though. I have an idea but inspection should answer the question.

Just another thing to consider while noodling this out.

[johnm1]

I disassembled the rifle/bolt this weekend just so I could understand the relationship of the pieces better. I also received 2 cam pins from Numrich. It appears that the bolt is pulled forward inside the carrier while the carrier is locked back and the barrel travels forward. This forward movement of the bolt allows the cam pins in the carrier to act on the helical grooves in the bolt body to rotate the bolt head. The bolt head appears to "pull out" enough though I don't have a measurement to confirm that. So this is an observation not a measured conclusion.

We inspected the helical grooves/slots in the bolt head and don't see any signs of battering or a place that appears to have wear. I was surprised that the grooves/slots did not follow a consistant curve. The amount of curve increased as the groove/slot came to an end. I can only assume this was to apply additional camming force at either end of travel within the slot. The additional curve was intentionally put there either during manufacture or during a repair at some point during its life. I assume that this curve is how the bolt was originally timed during manufacture but I don't have another bolt to compare to. All I can conclude from inspecting the helical grooves in the bolt head is that there are no signs of battering or wear in what is there.

I measured the two cam pins in the rifle and one had a smaller diameter then the other by about 0.004. Both had a generous amount of room within the helical grooves in the bolt body. I couldn't figure a way to measure that gap accurately so I don't have a measurement. The replacements I received also had two different diameters. One measured the same as the larger of the two existing pins and one was about 0.001 larger. The larger of the two would not slide all the way in to the hole in the carrier. There may have been some 'mushrooming" involved on that pin.

What I did was install a single replacement pin that matched the diameter of the larger of the two original pins. Now both pins are the same diameter. The bolt head now comes closer to returning to the 12/6 o'clock position, though not quite exactly 12/6 o'clock.

I think, and this is the subject of this post, that by partially correcting the issue with a single larger cam pin, I have at least identified the issue and at least one way to correct it. Opinions on if that is correct are welcome.

I can take additional photographs if necessary. I do have to take it down again to do that though. Remember that there was no malfunction originally and now the locking lugs come closer to to the 12/6 o'clock position when in the withdrawn position. To my knowledge there has never been an issue with the 3/9 o'clock position during lock up. Though I admit that there was no way to measure that. Or is there?

This whole post is really taxing my technical writing skills. I hope I haven't confused things. Keep in mind I understand exactly what I wrote. But it's easier to understand it while I'm looking at it and I readily admit it my be difficult or even impossible to understand by someone reading this. Thanks for bearing with me.

[johnm1]

Well, maybe not. I set up to take pictures to show the bolt head closer to 12/6 o'clock. But after closer inspection there really isn't a difference. In reality the amount out of time varies. Sometimes it is closer to 12/6 o'clock and sometimes it looks like picture #1 in my first post. So I suspect I had little impact on the condition.

The only saving grace is that it is not so far out of time that there is a collision of the bolt head and the rear of the barrel. And it does not appear that there is enough movement to allow it to collide. At this point I need to figure how close to correct the bolt is in the locked position. That will take some more noodling.