doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Main Spring Installation

I acquired a sxs that is built on an english box lock pattern. It came with a broken main spring. I have driven the pins out (with a brass punch)and got replacement springs from Brownells.
The replacement springs are the proper shape. However, they seem to be 2 or 3 times as strong as the remaining original spring. I am having difficulty compressing the spring and getting the firing pin / hammer into position while I insert the pin. (links to pictures included at the end)

Is there a trick to doing this?

Any help is appreciated.

http://s127.photobucket.com/albums/p159/baldferd/Mashiro/

you need to regulate the spring. Replacement springs are oversize and need to be fit. With a caliper measure both ends of both leaves and match the existing taper of the original spring. Replacement springs not being regulated properly is the cause of many gun problems. Springs have a gentle taper and no thin or thick spots on the leaves in order to work properly. Good luck,
Steve

Be sure not to overheat the spring or it will be ruined. Ideally, the taper should be reduced on a water-flooded grinding wheel where there is no possibility of overheating. Failing that, good SHARP files are the answer. Then polish the area to remove any tool marks which become potential fracture lines.

By over-sized, do you mean that the "V" of the spring is more than the original spring? Or do you mean that they are overlength?
The original spring had no taper on the width of the spring, it was the same width for the entire length. I'm not sure it was original to the gun, it has some pretty rough filing work.

The "V" width on the replacement spring that I recieved is larger than the original, but I assumed it would compress. The original spring was flat on the bottom leg while the replacement spring has an arc of about 1/8 - 3/16" over the length of the spring.
I know how to reshape and retemper the spring, I just didn't want to have to reshape the spring unless it was necessary.

The bottom leg of the spring was over-length and I trimmed it to length and removed the burrs.

Is the best plan to make the bottom (non-engaging) leg flat like the original and reduce the "V" width to the same as the original? (I have the tools and the skill to do it, just want to make sure its necessary)

Thanks for the help

Most of the 'hairpin' style springs have tapered thickness legs. The width of the springs are typically not tapered.

To get the same spring rate as the original, you'll need to match the thickness, any taper, width, and free shape of the spring.

You should be able to straighten that arced leg without annealing. But it may be easier to anneal it and reheat treat.

I am no expert but I think you need what I call a spring compressor. I have made three fo them out of wood and a long one out of some 1/4 inch plate. You have to compress the spring with the hammer in place while you put the holding pin in. I use a vise with led jaw inserts and get by.
You are in Arlington. I am in Mesquite. Call me at 972-681-4240
Regards, Gordon

Thanks everyone. I decided to anneal and reform to get the bottom leg flat. I will also thin the spring down to reduce the spring force.
I decided it wasn't worth risking the hammer with an overpowered spring.

Gordon, I was wondering if most people were able to compress the springs by hand or if they used some form of a spring compressor. I was going to use 1/4 aluminum plate slightly smaller than the floor plate and use the screw holes in the receiver body to compress the springs. I may give you a call if I have any problems.

Thanks

I'm using something like this to help during installation:


http://www.trackofthewolf.com/(S(gx4xu04...amp;styleID=314

I annealed the springs and used the barrel sander on my dremel tool to take down the spring thickness.
I took down the overall thickness of the spring by about 25%.

I used the polishing wheel on the dremel and some buffing / polishing compound (silver color, I don't remember the grit). It took about 15 minutes to polish both springs. It probably would have taken 5 on my old polishing wheel, but my wheel got mislaid in my last move.

I retempered the springs and they are cooling now. I will let you know how the installation goes.

Thanks for everyone's help.

A trick that usually works on box locks is to;

1. remove the cocking levers
2. position the mainsprings forward in the slot
3 install the hammers
4. using a modified screwdriver slide the mainspring back while compressing it until it snaps into the notch on the hammer

works for me, your results may vary.

Jim A.