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#4 Mk 1 bolt cocking piece thread

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captainjohn View Drop Down
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    Posted: December 19 2018 at 10:10pm
New member, so thank you for the forum and my being able to ask a question about one of my Enfields.   In my search, I didn't find a match from previous inquires, so here goes;   I'm in the process of cleaning/fixing two #4 Mk1 full rifles. On one, I removed the bolt, removed the firing pin using the "T" handled tool, (which took a bit of coaxing), cleaned everything up and was ready to put the pin/spring together by screwing the firing pin back into the cocking piece. However, it wouldn't tread back in. Looking into the cocking piece, there appears to be one thread that's "bunged up," the first thread on the female component. In my limited knowledge of this rifle, it seems reasonable that if I were to tap (or "clean up") the threads in the cocking piece, I might be able to reassemble the bolt and remove the tiny thread imperfection.   Presuming this will work, I'm not sure of the tread size tap for the cocking piece. Threads on the firing pin look good, so I think it's just the female threads that are an issue. Has this ever happened, and is a re-tap to clean up this one spot a reasonable fix? AND most important, what is the tap size for these threads? I'm sure it's a metric size... Appreciate the help. I can send photos if that might help.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote maxwell smart Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2018 at 12:44am
Not metric. 

1/4" BSF (26 tpi)

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zed Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2018 at 4:31am
I take it you are trying to refit the original firing pin to it's original cocking piece?
I ask because if you are fitting replacement part's; I believe  the thread on the firing pin of the earlier No1 type rifle is different to that of the No4. Parts look the similar; but if you've got an No 4 cocking piece and a No1 pin you may have a problem
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2018 at 6:37am
Correct, the No1 series was a unique Enfield pitch & form, the later no4's were BA (British Association) pitch & form


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Post Options Post Options   Thanks (0) Thanks(0)   Quote hoadie Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2018 at 7:10am
Loose wimmen tightened here
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2018 at 8:15am
Sorry, is this better?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Canuck Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2018 at 8:32am
That is correct information. The #1 vs #4 pitch thread on striker/cocking pieces are different.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote captainjohn Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2018 at 9:48am
Thank you all for taking a moment to help! I purchased the rifle at an antique store a few years ago, so I'm not sure if something happened to the bolt parts prior to my ownership. However, from my perspective, all parts appear to be original. I'm not currently trying to reinstall a replacement for either the striker or cocking piece. (It doesn't look as if this rifle has been disassembled for decades). With that, and also looking at the link provided by Shamu, (which is a fantastic link... thank you Shamu!), should I presume that the response by Maxwell Smart, that being 1/4" BSF (26 tap) is right? If I read correctly, it looks like the link... "Royal Small Arms Factory Enfield" article verifies that a #4 Mk 1 "striker" is the 1/4" BSF (26 tap). So, here's my plan... since the striker threads are undamaged, I pick up, then gently screw on the corresponding die down the striker to verify a correct size. Then, (if and when confirmed correct), use the 1/4" BSF tap to clean up the cocking piece threads. Not being a machinist, does my reasoning make sense?   

I've never shot either of my two Enfields and may never do so. But I must say they are two of the most beautiful rifles in my collection! Thank you all once again.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote maxwell smart Quote  Post ReplyReply Direct Link To This Post Posted: December 20 2018 at 11:24pm
The No 4 rifle has screws mostly of various BA (British Association) sizes, but also a couple in BS (British Standard) size. BSW is the coarser Whitworth thread form, and BSF is the fine pitch thread.

A tap of size 1/4" BSF (26 threads per inch) - "tpi" rather than "tap" - would be the right one.
UNLESS, as Zed has pointed out, the striker/cocking piece assembly is from a No 1 rifle. Things get very difficult if that is the case.

Your plan to test the striker thread for size with a 1/4" BSF die first is a most sensible one.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote captainjohn Quote  Post ReplyReply Direct Link To This Post Posted: December 21 2018 at 12:09am
Thank you once again, Maxwell Smart.   Capt. John
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Zed Quote  Post ReplyReply Direct Link To This Post Posted: December 21 2018 at 4:29am
Another point to note. Sometimes the firing pin thread can be a little loose in the cocking piece; which will cause an irregular trigger let off. To cure this; the screw thread would be tinned with solder very lightly to take up the slack. It does tend to make the thread feel tight refitting the parts.
I have used this method to correct a loose thread; it does work very well.

As Maxwell has already stated though; probably best to check and clean the threads with the correct tap's and die's first.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote englishman_ca Quote  Post ReplyReply Direct Link To This Post Posted: December 21 2018 at 9:38am
One must make certain that you have a matched set. ie cocking piece and striker are both No.1 rifle or both No.4 rifle. They are interchangeable between guns as a pair. However a No.1 rifle striker will not work with a No.4 rifle cocking piece, et vice versa, due to the different thread forms.

I have to find threads that are pretty mangled or bruised before I will recut with a tap or die. Running a tap through the cocking piece and a die down the striker will open up tolerances and the fit of the thread, which for a nut and bolt is fine, but not in this instance. There are different classes of thread fit, this one is engineered to be snug. 

I would be tempted to run the striker back and forth in the cocking piece with lots of oil. Sometimes the threads will chase themselves and 'work in'. 

As Zed notes, the cocking piece needs to be tight on the threads in the cocking piece. There must be no relative movement between the two, otherwise it will be difficult if not impossible to set up a consistent trigger pull off.
An armourer would use used soft solder to tighten things up, Bubba uses a hammer to put a flat on the striker thread.

What seems to be the issue that you are having with screwing the two together?

OK, I'm dumb, Duhh.
I just re-read your original post and understand that the threads in the cocking piece need help?

Will the threaded portion of the striker screw into the cocking piece from the opposite direction? If it does, it might be enough to chase the internal thread enough to get the striker to start. Seems that since you screwed the striker out, it should screw back in.

If the striker doesn't do it, perhaps a 1/4 BSF bolt with an axial hacksaw cut would work as a thread chaser? whatever it needs, it don't need much.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote captainjohn Quote  Post ReplyReply Direct Link To This Post Posted: December 21 2018 at 10:20am
What great information!   These final two replies are of extreme value! SO, yesterday I took the cocking piece and striker to my local gunsmith, who happened to have an extra striker and cocking piece in a drawer for a #4 Mk 1! SO I grabbed that from him to use as a replacement, exactly for the reason stated by Englishman-ca... Knowing that if I run a tap through the cocking piece and a die down the striker, I'll lose some of the strength of the entire unit. I've kept the old "bad thread" pieces, but now have a fix with another "pair" (cocking piece and striker) that are matched with each other, and will fit the bolt. But even more insightful are the comments about "taking up slack!" When reassembled, the "new" striker threads in a few threads further than the old, therefore the striker only slightly extends beyond the end of the bolt. It's far less than the 0.040-0.050. (If I understand that correctly). I find that if I back out the striker to get a greater firing pin extension, then the cocking piece is loose and wobbly. Last night I was studying that, (even thought about it as I was trying to get to sleep), wanting to figure how to take up the slack... If I understand what's being said by englishman-ca (and correct me if I'm wrong), if I inhibit the last thread or two in the striker, it'll allow me to tighten the striker into the cocking piece, eliminating the slack, and therefore give me a greater extension with the firing pin... My gun smith is 15 minutes away (isn't that great!) and I plan to run this by him. This board is fantastic! The knowledge base is outstanding. I'll have to post some pictures of these two beauties as soon as I get further along with their "clean-up." I'm ashamed to share what I had to pay for my first Enfield... what's the saying... "I got it for a song!" and that adds to my love for this piece of history. I always wonder, what these specific rifles part was during WW II if any! To answer the last question, "why the two original pieces won't screw together" It's because there is one thread (probably the first thread in the series) in the cocking piece, when viewing down the opening, that sticks out ever so slightly, which prevents me from even starting the threads. It's possible I could force them through, but that's why I was wanting to simply "clean them up" first.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote englishman_ca Quote  Post ReplyReply Direct Link To This Post Posted: December 21 2018 at 11:41am
The bolt is actually quite easy to take apart and reassemble. But what appears to be a simple design is a tuned system. A very clever design with built in safety mechanisms, that bolt is doing more than one thing when it opens and closes. However, adjusting one component can have negative effect elsewhere. So there is a set procedure to go through to set things up. 

Not going to poke the monster about fitting a bolt, changing out bolt heads and setting head space. Original bolt in the rifle. We good to go.

The amount of striker protrusion though the face of the bolt should be 40 thou. But in all practical use, if the striker sticks out a bit, the gun should go bang. If not, fit another striker.

This protrusion is set by the length of the striker in front of the collar and the length of the bolt head. The back of the bolt head is the stop for the striker. The striker collar hits and stops at the back of the bolt head. 
Theoretically, if one were to shave the back of the bolt head, the protrusion would increase. But in practice, the striker should just be considered worn out and it should be replaced. So the spares you grabbed might not be perfect. maybe that is why they were not inside a gun. If there is wobble on the threads, that can be fixed with the soft solder technique.

Try to use the original cocking piece if you can. It is nicely worn in with the sear. Try the new cocking piece though, it might be fine too. The test is in the feel of the trigger.

Sometimes a thread can be made to start by slightly tapering the first couple of threads on the striker with a fine file or stone. Often the last thread on the striker will get burred over a bit if the striker sticks out the back of the cocking piece at all.

If you think that it is the very first thread in the cocking piece that is the problem, get it into a drill press and run a drill bit in there to clean out that first boogered thread.

Adjustment of the striker into the cocking piece in and out only sets the cocking piece at rest position, which is important. The cocking piece should have a slight clearance between it and the back of the bolt. As mentioned, the striker stop is the collar and the back of the bolt head, not the cocking piece smacking the back of the bolt body. Screw the striker out to lift it away. 
If the cocking piece is subject to impact, there can be future problems. The cocking piece is a casting, it is actually quite brittle. There is a cam running in a cam track happening in there, if adjusted wrong they could be taking a hammering. Not good. Impact on the cocking piece can also eventually loosen it on the striker thread.  

One test to check for correct adjustment is when screwing the bolt head into the front of the bolt body, within the last turn of the bolt head to tight, one should feel the back of the bolt head touch on the striker collar as it lifts the cocking piece ever so slightly away from the back of the bolt body.

You mention that you will not likely be firing the rifle. But you are just a temporary custodian of the rifle who is looking after it for a while. It was here before you were born and hopefully will be here after you gone. If it is worth fixing, while in your care, it is worth the best that you can do. Sometimes the best repair is the simplest. Fit new parts.

Happy to help. I encourage you to give it a go.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote captainjohn Quote  Post ReplyReply Direct Link To This Post Posted: December 21 2018 at 12:37pm
My plan is to ensure these are fire ready. I'm heading to the gunsmith shortly to have him look over everything on both rifles before I fire off a round, expecting to get a "mule kick." At least that was the description one person gave me when describing the recoil on the 303 British round in the Enfield.

An interesting note: Now that I have removed and disassembled/reassembled both bolts, I'm noticing a difference between the removal technique between both rifles, even though both say "#4 Mk 1" One bolt is removed by lining up the extractor with the rifle "slot," turning it up and then removing the bolt. The other requires pushing down on a release at the close end of the action in order to turn the extractor up and remove the bolt. The first one is stamped from the factory "#4 Mk1 * Long Branch 1944" but no serial number there, it's down by the trigger.   On the other, someone filed/ground the original serial number down, but then used an inscriber to engrave "#4 Mk 1" plus putting the "hand scribed" serial number in the same location.   Interesting to me and adds to the mystery of these rifles.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: December 21 2018 at 12:58pm
I had a series of pierced primer events (only with MilSurp) for just this reason.
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