REPLACING a lock Mainspring

[TgeorgeZ]

Is there some secret to easily replacing a lock mainspring?

If I use a mainspring vise to compress the lock, try as I can. I can't get the peg in long arm of the spring into the hole of the lock, the tab on short end of the spring into the bolster, and the end of the long arm of the spring placed into position with respect to the tumbler.

Do you leave the hammer off the tumbler until the spring is inserted?

This is driving me out of my mind.

Any help would be appreciated.

[Acer Saccharum]

Tgeo, is this the same spring that came out of the lock?

If so, it should go back in. If not, you may have to do some fitting.

Tom

[SCLoyalist]

Are you sure you've got the right replacement main spring?

Any time I've removed and replaced a mainspring,  I've cocked the lock to compress the spring, put the mainspring vise on and snugged it down, then eased the hammer down as I tripped the lock.  

To replace, I put the (new) spring in the vise, tighten vise down just a couple of turns to compress the spring a very little bit.  With no spring in the lock, I trip the sear so the hammer goes all the way down, put the spring (still in the vise) into position (peg in long arm into lockplate hole, tab on short end into bolster, etc).  At that point the end of the long arm is just barely on the tumbler.  Bring the hammer to the half-cock position which should put the end of the long arm squarely on the tumbler and  make the spring vise rather loose on the mainspring.   Take the vise off.    Hammer/cock stays on the tumbler throughout the process.

That's how I've done it, never broke a spring yet, though I wouldn't be surprised to find there were slicker ways of doing it.

[Ben I. Voss]

Maybe there's something wrong with the fit of your mainspring vise that won't allow it to properly compress the spring??

[BJH]

Some of the locks out there can be Boogers. Grip the mainspring as far out on the widest part of the V as you can.  Then apply the squeeze.  When you remove a main spring you set the lock to half cock not full cock. Apply the vise and release the sear.  Applying the vise at full cock will some times result in broken main springs.  Jim Chambers set me srtaight on this. The tit that fits into the lock plate may need a bit of careful fitting. It must remain a mild press fit.  BJH

[Artificer]

When using the techniques others have already mentioned, I found most of the time when I had trouble getting a mainspring back into a lock - it was due to the top arm of the mainspring vice hitting the lock bolster or some other part. 

[TgeorgeZ]

Thanks to all for your advice and help.  Got it done with your help.