A little SP101 help

[oso grande]

Well guys, I've just installed a new main spring in my Ruger sp101 9mm, now the hammer won't cock.Pull hammer to the rear let it go and wham! Hammer goes forward. Can't shoot it in single action. Maybe some of you sp101 guys can tell me how to fix it.
I'm looking forward to to your insight.
Thanks.

[NaClAddict]

You sure it’s not DAO?

[sealocan]

Hopefully someone can help but you might have to take some photos of what you've done.

If it was mine, I'd go to YouTube and watch video about installing the mainspring correctly.

[ar15barrels]

Well guys, I've just installed a new main spring in my Ruger sp101 9mm, now the hammer won't cock.
Pull hammer to the rear let it go and wham! Hammer goes forward.
Can't shoot it in single action.
Maybe some of you sp101 guys can tell me how to fix it.
I'm looking forward to to your insight.
Thanks.

First thing to try is to reinstall the old spring and see if the problem goes away.

If it does, you need to compare your two springs at their fully compressed lengths.
It could be that the new spring has a slightly longer compressed length and the spring is going to full coil bind before the single action sear can catch.
If that's the case, the new spring is too long and needs to be shortened or replaced with a spring that's the proper length.

If it's not a spring length problem, you need to look closer at the gun and see if you lost something related to the single action sear while you had it apart.

[IVC]

Different spring weight should NEVER change how the gun works. It might cause light primer strikes, but not cause the loss of the ability to cock the hammer.

If you have a functional difference after installing the new spring, it's either not compatible (what ar15barrels says above) because it's not dimensionally compliant, or you missed a part somewhere (unlikely, but possible).

[JTROKS]

All you did was replaced the hammer spring, right? You didn’t completely disassemble to replace trigger return spring or removed the trigger assembly and hammer??

Did you make sure the hammer strut & seat is properly oriented?

[MyOdessa]

I would check if you correctly assembled the SP101. The mainspring strut and saddle can be installed in reverse, I don't know if this would cause your issue.