The Mainspring is slipping off the tumbler! How do I stop it?

I recently purchased a flintlock CVA mountain rifle.
Being a very average kit build I have redone the stock and (after removing the chrome) browned the metalwork including the lockplate which required disassembly.
The lock screws were all loose but are now tight.
But now I get about 3 shots and the mainspring slips off the side of the tumbler.

I did polish the mainspring but did not go over the nose. Well I dont think I did?
I did not touch the tumbler.

What have I done? How do I fix it?

Thanks in advance

The tumbler could be tilted letting the spring slide off to the side or you need a new spring. Also the hammer stop shoulder or lockplate might be might be off letting the hammer rotate too far. Then the spring slips off the nose of the tumbler. The spring pin could be working out of its hole and releasing the spring. Try it out of the wood and watch it.

CVA had an adjustment screw on the tumbler. If your model has that screw, try tightening the screw while the lock is out of the rifle.

ord sgt said:

CVA had an adjustment screw on the tumbler. If your model has that screw, try tightening the screw while the lock is out of the rifle.

Click to expand...

Yep. Screw thingy is first thing that came to my mind. If that is not it you may need a new mainspring.

LawrenceA said:

I recently purchased a flintlock CVA mountain rifle.
Being a very average kit build I have redone the stock and (after removing the chrome) browned the metalwork including the lockplate which required disassembly.
The lock screws were all loose but are now tight.
But now I get about 3 shots and the mainspring slips off the side of the tumbler.

I did polish the mainspring but did not go over the nose. Well I dont think I did?
I did not touch the tumbler.

What have I done? How do I fix it?

Thanks in advance

Click to expand...

That screw on the tumbler is there only to adjust the amount of engagement the sear has with the tumblers full cock notch. It has nothing to do with the mainspring slipping off of the front of the tumbler.

If I were to guess, it sounds like the mainspring might not be fully seated against the lock plate? Then there's also the possibility that you removed too much material from the area of the mainspring that engages the horn on the front of the tumbler. If that's the case, I don't know of a fix for the problem other than buying a new mainspring.

You mentioned the screws that hold the lock into the stock being loose "but now their tight". I should point out, if the screws are overtightened it can wedge the locks internal parts against the wood in the lock mortise. While this has nothing to do with a mainspring that slips off of the tumbler, it can keep the sear from fully engaging the notches in the tumbler. The lock retention screws should only be tightened a little firmer than "snug".

If you rule out the possible causes above, you may be able to relocate the mainspring. I’d need a picture of the internals and how the mainspring is attached to the plate. If the upper arm of the spring simply fits into a groove on the underside of the bolster then fill the existing lockplate hole for the stud on the mainspring by riveting a piece of mild steel in there. Then make a new hole just enough toward the tumbler. If not experienced I’d send it out or buy a new spring and hope for the best.

Zonie said:

You mentioned the screws that hold the lock into the stock being loose "but now their tight".

Click to expand...

HI I meant the screws that hold on the bridle. They were surprisingly loose.
The Mainspring definitely comes off the side of the horn not over the horn.
The short leg/upper arm and locating pin are still in there respective spots when I remove the lock.
I have "seated" the mainspring with a tack hammer as part of re assembly.
I did run a stone quickly over the inside of the lockplate to remove any burrs and also on the inside of the mainspring. You can see a whisker of light between the mainspring and the lockplate and there are no rub marks.
Chance of getting a new mainspring are nil unless you make it.
Maybe I need to check the angle on the long leg of the mainspring and do some judicious stoning if they are not square to try and minimise the tendency to drift across. I could also stone the back of the mainspring to bring it further in but that would only slow the sideways slip.

Thoughts please?

Piccies.
The wear marks on the nose of the Mainspring appear to be at the sideplate side. Also the width of the spring at the nose is wider than the tumbler horn and set at an angle with harder contact away from the sideplate such that as the mainspring is tilted to the point where the angle on the mainspring is parralell to the tumbler the spring is off the tumbler.
I think you have helped me find the issue.

Hi,
Is that picture of the lock at halfcock? If not, you put the flintcock back on in the wrong orientation.

dave

Yes it is halfcock

Deer Creek has some parts for some CVA rifles. Check out their website.

Just for future reference, Deer Creek still has replacement mainsprings.

Thanks Cherrybow.
I contacted Deer Creek but they won't send to Australia.
I stoned the front of the spring. It still shifts sideways but has not come off.
Well not yet anyway. Perhaps I should stone a little more.

I would pull the tumbler and lay the spring on the plate and see if it is warped or maybe the hole for the mainspring tab is wallowed out.This needs to be a fairly snug fit. If that is the case you could close the hole up a bit by peening around it with a center punch. If all else fails there is a ton of CVA parts on Ebay, I'm sure you could get someone to ship to you

tallpine said:

If that is the case you could close the hole up a bit by peening around it

Click to expand...

Thanks Tallpine
Yes the gap is huge, this photo is after the mainspring has slipped.
But when seated the gap is still maybe 10 to 20 thou. Is that too much?
Great advice on how to close up the hole.

I will keep my eye on Ebay.

I have found that I cannot purchase items listed under hunting categories. I tried to buy a rod retaining sprong for the same rifle. But the Seller warned me it wouldn't let me and he was right. Sporting Goods I can buy.

Well it looks like you are going to have to fix it then. Have you got it to throw the spring out of the rifle?

Well just working the lock you can see the spring sliding across. It was dropping off the tumbler after 3-4 goes.

I have stoned the angle out of the nose of the spring (well almost. Again do not want to take off more metal than necessary).
Since then I have again worked the lock about 20 times.
The spring has worked over about 1/8" but not kicked off the tumbler.

After reading your wisdom I think I will peen the tab hole for a tighter fit.
Depending on how that works I may stone the nose a little more with a slight angle to work the nose in.
I do not feel confident in altering the spring such that it sits closer into the lockplate.
I am afraid that I may change the geometry too much and make it unusable.

What I do not get is why this is a new problem. It did not appear until I took the lock apart and re assembled it. I probably removed a burr that was holding it all together.

Looking at the picture that shows the internal workings, the guide pin for the tumbler appears to have a gap above it as it passes through the bridle. That would indicate to me that the tumbler has slop in it causing hammer/tumbler to move from side to side. Leave the tumbler in place and remove the hammer and check to see if there is a gap around the hammer bolster. If there is a gap there and around the bridle guide you may end up fighting a losing cause with the tumbler and spring combination until the slop is removed through those two holes. When the hammer strikes the steel there is a force impacted on the hammer/tumbler which maybe causing wear on those two bearing surfaces.

Yes there are gaps.
How much gap is needed/allowable?

What I believe has happen, you have wear on both the tumblers pivot points, The hard part is to determine if its the lock plate hole for hammer/tumbler, tumbler pivot points and/or bridle. You want only a slight amount of friction between the bearing surfaces. To much slop and you'll have a cascading effect of wear down through all surfaces connected. This is what I believe has happened. If the lock plate bolster hole is worn I'd look for a new lock. If you like to tinker and challenge your self, start with making a new bushing for the lock bolster, buy a new tumbler and go from there. The less "wiggle" room you have in those bearing surfaces the better off you are. Please bear in mind that I'm basing my conclusion on what I've seen in your pictures and worn antiques. I've seen cva locks that were poorly made with soft steels. Good luck