Unsafe Thompson Center lock

[waarp8nt]

I purchased a T/C lock as parts that was disassembled with a minor part or two missing or broken. Since I was in no hurry, I waited to order the parts to fix it until I had a somewhat larger order, at least enough to justify shipping. The parts came in, a couple of missing screws and a new spring guide as the old guide was bent then broke. Upon assembling the lock, I found it wouldn't engage the full cock position properly. A little confused I removed a lock from a Renegade and installed the lock in question. Matters seemed somewhat worse as I could get it to the full cock position, but it wouldn't always stay and would fall easily if the stock or forearm was bumped, the trigger didn’t even need to be pulled. Needless to say, I removed the lock and disassembled it and another lock that was known to be good. I swapped the tumbler and sear from the known good lock to the lock plate in question. The lock acted the same way with the other parts installed. While removing the spring and spring guide I noticed something. The lock plate was bent, so I compared it to the other lock plate and then used a straight edge to verify the lock plate was bent. Sure enough, it was bent. I'm going to try to straighten the lock plate this weekend, I'm thinking it will fix the full cock issue. I have a nice vise and intend on making some oak shims to try to control the bend as not to over do it. Any thoughts on straighten the lock plate? Has anyone ever needed to straighten a lock plate? I wonder how it got bent in the first place?

 

[deerstalkert]

just straightened a siler, with my boot heel. but then i have been in a bad mood all day!.
is the fly present and working?
can you post a picture of the tumbler/bridle ?
the plate may have been installed in something other than a TC. and tightened too much with the bridle bottomed out in the inlet.
is there any extra holes for plate screws. fore and aft maybe?

 

[Phil Coffins]

I’ve seen a TC plate with a bend, that one was hige in the center but worked fine. Other plates that were bent I’ve straightened by putting in padded vise jaws with a pop sickle stick on the high spot and two at the points that would bring the bend where I wanted it. A gentle turn of the vise handle made a straight plate.

 

[Phil Coffins]

Does the sear spring plunger move freely? I’ve seen them with burrs that made them hang up so as to not return the sear as needed.

 

[waarp8nt]

is the fly present and working?

Yes

can you post a picture of the tumbler/bridle ?

I can take more pics tomorrow, but I don't think they are the isssue as they are not damaged.

the plate may have been installed in something other than a TC. and tightened too much with the bridle bottomed out in the inlet.

Not very forward thinking of me, but it never crossed my mind the mounting screw could have been used to cause the damage.

is there any extra holes for plate screws. fore and aft maybe?

No extra screw holes, only the factory mounted screw hole.

I’ve seen a TC plate with a bend, that one was hige in the center but worked fine. Other plates that were bent I’ve straightened by putting in padded vise jaws with a pop sickle stick on the high spot and two at the points that would bring the bend where I wanted it. A gentle turn of the vise handle made a straight plate.

I like that idea, something to keep from going too far in the straightening process.

Does the sear spring plunger move freely? I’ve seen them with burrs that made them hang up so as to not return the sear as needed.

Yes, the plunger functions as it should

 

[deerstalkert]

that bend must be throwing the sear/tumbler notch out of geometry. sure would like to see a full shot of the inside of the lock.
does it show any drag marks from the sear arm?

 

[waarp8nt]

that bend must be throwing the sear/tumbler notch out of geometry. sure would like to see a full shot of the inside of the lock.
does it show any drag marks from the sear arm?

That is what I am thinking, the bend is throwing everything out of proper alignment. There is some slight ware on the lock plate where the tumbler rides, however the sear arm area looks new. The lock is out in the shop, if it was in the house I would snap I quick picture for you.

Edit = ended up finding a pic on the phone from when I first disassembled the lock to clean it / soak it in white vinegar to remove the fake case hardening. No wear or signs of damage to the plate where the sear rides.

 

[necchi]

An odd circumstance, I've never had that trouble with a TC lock.
Sure does look like it's in need of straightening.
If this is a photo of the "broken piece" and rod guide from the lock,, that's not a TC spring guide,

View attachment 121161

 

[Dude]

I just got done straightening a TC lock plate. It's a pretty tough piece of steel. Phil's advice works and is what I did except thicker material than popsickle sticks, but it took a fair amount of force. The first several tries I didn't bend it far enough and it sprung back to where it was originally.

 

[Jim Evans]

Is your mainspring for a percussion lock? Because there is a difference between the flint spring.

 

[fillwa]

I have a similar problem with the original TC lock on my ‘70’s kit Hawken. I’ll check the lock flatness. I also notice play where the tumbler fits into the lock. I tried a new tumbler, thinking the tumbler was worn, but still have play where it fits into the lock. Does anyone know the correct size of the lock plate hole that the tumbler fits into?

 

[Jim]

I’m thinking the lock plate is an investment casting (as are a lot of the parts of a TC) so bending can be a mite tricky.

More than likely, the original casting is not BENT, but is WARPED.

 

[waarp8nt]

Straightening the lock went well. I decided to use the Arbor press with a wooden block to keep from scratching the lock face. The lock plate didn't need much support as one tab is naturally longer than the others, I did add a shim under that tab to allow it to bend a little further. However, I did not get to put it together last night, my wife worked over and that left me with other things more pressing to get done (pun intended). Picture below.

If this is a photo of the "broken piece" and rod guide from the lock,, that's not a TC spring guide,

I agree it is odd, having never seen a spring guide like that in a T/C before this lock. So, I ordered a new one from The Muzzleloading Emporium and the replacement part was just like the broken part? Along with straightening the lock plate last night I went on a mission to inspect several other T/C locks, both flint and percussion that is in my part drawers, not a single other lock has that style of spring guide. I have a couple locks to remove from stocks to inspect too, as it has me curious if T/C may have used such a guide rod on later builds?!?

 

[necchi]

a new one from The Muzzleloading Emporium and the replacement part was just like the broken part?
,,,,,,,,,,,,,, as it has me curious if T/C may have used such a guide rod on later builds?!?

Hmm, that is interesting, I too have messed with dozens of T/C locks in the past and never seen one like that.
I wonder if that design isn't an after-market "universal" type spring guide made to fit several locks(?)
Investarms/Lyman/TC,,
It could be your broken one was already a replacement. Most T/C's we have today have already passed through many hands before we touch'm.
Could be that bent plate caused stress to and broke the original, and was replaced,, without the correction you made,, the same bend stressed that replacement,(?)

 

[Jim Evans]

This is the spring and guide I have ,top is percussion ,bottom flint

 

[waarp8nt]

Hmm, that is interesting, I too have messed with dozens of T/C locks in the past and never seen one like that.
I wonder if that design isn't an after-market "universal" type spring guide made to fit several locks(?)
Investarms/Lyman/TC,,
It could be your broken one was already a replacement. Most T/C's we have today have already passed through many hands before we touch'm.
Could be that bent plate caused stress to and broke the original, and was replaced,, without the correction you made,, the same bend stressed that replacement,(?)

I agree. I believe on this particular lock the spring guide and upon further assembly / disassembly its possible the sear is a replacement too. Pics to follow.

This is the spring and guide I have ,top is percussion ,bottom flint

Thank you. I've not had the percussion and flint springs / guides setting side be side. The flint spring is certainly longer. I've been using another percussion lock as parts to figure this issue out. The springs are the same lenght, however the spring guide was contacting the lock screw bolster.

************************************************

After straightening the lock plate, the lock would go to full cock, but still wouldn't stay cocked if any pressure was put on the lock or it was bumped. I assembled and disassembled it a few times and found multiple contact points. The guide rod hitting the lock screw bolster, the edge of the tumbler was hitting the sear.

I removed some metal from the bolster and rounded the outer edge of the guide rod to match the factory rods. So they had clearance, see picture in the post above to see how much lock screw bolster.

Each step was better, however the lock still was having issues. So, I put just the tumbler and sear into the lock and it appeared to have contact at the edge of the tumbler and sear. I disassembled another lock enough to see how much clearance was normal. I ended up rounding the corner of the tumbler to allow it to clear the sear.

The lock now works perfectly. No issues cocking or staying cocked. I even dropped the lock several inches and it stayed cocked. I have no idea the history of the lock, but believe the spring guide rod and sear to be replacements. So, if your having issues with a T/C lock staying on full cock; watch for a bend plate, long spring or contact points on replacement parts.

 

[waarp8nt]

Clearance between tumbler and sear on a working factory lock.

 

[Phil Coffins]

I wonder if that last bit was the part that made it work. Bent plate may not of had any effect but that contact of the sear clearly did.
Good work anyhow!

 

[waarp8nt]

I wonder if that last bit was the part that made it work. Bent plate may not of had any effect but that contact of the sear clearly did.
Good work anyhow!

Wish I would have found the sear / tumbler contact issue first, it could have told a more accurate story of the problem. Although, I believe the spring guide failed prematurely due to contacting the mounting screw shoulder / bolster & the lock plate being bent aggravated the situation. Making a little clearance at that point, allows the hammer to pull back farther, without the guide rod taking a beating againstthe lock screw shoulder / bolster. Although, not knowing the history of the lock, someone make have broke the guide rod during assembly or disassembly.

Hopefully this thread helps someone figure out their lock issues. Thanks to all who contributed with suggestions and advice!

 

[deerstalkert]

condition of the working lock needs some tlc. a good soak in laquear thinner and a stiff bristle brush. gets much cruddier and it won't be working.