Replacing mim parts

I previously replaced the hammer with an Apex Evolution IV DAO hammer and got lucky with it being a drop in replacement...so I decided to also replace the trigger (Power Custom), cylinder stop (TK Custom), rebound slide (NOS part from Ebay, and bolt (NOS part from Ebay)...and I've run out of luck/the new parts require some fitting.

The Power Custom trigger hook is longer and not as beveled as the original mim trigger which is causing it to bind on the cylinder stop bevel (it's unable to return without pushing down on the ball). It's also causing the ball to drop lower than the original.

Original/Mim:



New Hammer and Cylinder Stop:



If I take it slow and continually check the fit/function/shape against the original/mim trigger, is slightly shortening and beveling the trigger hook top something that I could do or is this best left to a more experienced person?

Also, the new bolt isn't flush and protrudes through the recoil shield hole... can I file bolt tip until it's flush?



I've been studying Jerry's Shop Manual but figured that I'd tap into the knowledge here as well so thanks in advance.

Here are a couple of pics comparing the mim and Power Custom trigger hooks:

First - I think the MIM parts are better, each to his own. You want the bolt a little long, put the thumb release on and see if it comes out that fare. If it does you can trim a little, bet it wont need it. The hammer is OK if you are going to make a comp gun out of it. A 3.5 lbs trigger on double action you don't want a spur on the hammer. You can polish the MIM parts and they will be nice bright finish. Yes you can trim the trigger, but it is only case harden. Two or three thousands down the metal will be soft.

I appreciate your response but I'm surprised to hear that you think the mim parts are better. If you don't mind me asking, what do you believe is better about them?

Originally, I was thinking about leaving the mim parts in until I saw that the mim stirrup was cracked...





I also enjoy personalizing / "enhancing" my guns (almost as much as shooting them) so I'm having fun with it.

Reference your question concerning the interference from the "unfit" stop bevel, it would be better to fit the stop to the trigger hook than it would to modify the trigger hook itself....just based on the cost of the parts involved. They leave these fitted surfaces a bit oversized to accommodate tolerances. Stops are cheap, compared to the trigger you have there.

If the action works properly aside from the problem with the cylinder stop bevel being too long, you can move the point on the bevel away from the trigger hook by carefully filing the bevel back a bit at a time, and then checking your progress. The angle of the bevel should remain the same as you move the point back. Hopefully, modification of the hook on the trigger will not be necessary, other than light stoning and polishing of the contact surfaces. After correct function is achieved, a stroke or two with a very fine ceramic stone is all that is necessary in terms of polishing the contact points.

Be careful to observe the hand and ratchet timing as you modify the cylinder stop, as the ball of the stop needs to be pulled down out of the way at the right time, consequently, if you go too far with the point of the bevel, the stop ball will no longer come down and stay down long enough for rotation of the cylinder to begin....or may come back up too soon.

Ideally, the ball should come down to the extent that the top of the ball of the stop is flush with the stop window....and not be released until the cylinder is approx half the distance to the next approaching stop slot in the cylinder. The stop bevel fitting controls both of these movements. You may still have to modify the hook slightly if it is catching on the ledge of the cylinder stop just above the point (hook contact area) as you pull the trigger back. Usually, just carefully breaking the sharp corner on the bottom front of the hook is enough to help this hard hesitation or "click".

You may also have to remove material from the surface on the stop that is contacted by the trigger hook, the flat area inside the cavity, just above the point of the bevel......so that it can properly accomodate the trigger hook itself. This is timing sensitive also, because removal of material here delays the start of the downward movement of the stop.

To me, it's much easier to fit this contact point between the stop bevel and the trigger hook with only the "lower" parts in the action.....the trigger w/hand, rebound slide, reb spring and the cylinder stop. (hammer and hammer spring removed) As you go, you can add in the cylinder assembly to make sure the hand and the stop are still working properly together. The movement of the stop is a "four direction sequence.....down, up, forward, back.....as it travels over the trigger hook as the trigger is pulled back and returns forward to reset.

Always remember not to cycle the completely assembled action (with mainspring tension applied) in the frame with the sideplate off. This puts added stress on the hammer stud and trigger stud, and the hammer sometimes "walks" out away from the frame on the stud, and can strike the frame as it decends into the frame cutout.

Reference your question concerning the bolt...... yes, you may have to remove material from the end of the bolt to make sure it's flush with the breechface when it is pushed fully forward.

armorer951 said:

Reference your question concerning the interference from the "unfit" stop bevel, it would be better to fit the stop to the trigger hook than it would to modify the trigger hook itself....just based on the cost of the parts involved. Stops are cheap, compared to the trigger you have there.

If the action works properly aside from the problem with the cylinder stop bevel being too long, you can move the point on the bevel away from the trigger hook by carefully filing the bevel back a bit at a time, and then checking your progress.

Be careful to observe the hand and ratchet timing as you do this, as the ball of the stop needs to be pulled down out of the way at the right time, consequently, if you go too far with the point of the bevel, the stop ball will no longer come down and stay down long enough for rotation of the cylinder to begin....or may come back up too soon.

Ideally, the ball should come down to the point that the top of the ball of the stop is flush with the stop window....and not be released until the cylinder is approx half the distance to the next approaching stop slot in the cylinder. The stop bevel fitting controls both of these movements. You may still have to modify the hook slightly if it is catching on the ledge of the cylinder stop just above the point (hook contact area) as you pull the trigger back. Usually, just carefully breaking the sharp corner on the bottom front of the hook may help this.

You may also have to remove material from the surface on the stop that is contacted by the trigger hook, the flat area inside the cavity, just above the point of the bevel......so that it can accomodate the hook itself. This is timing sensitive also, because removal of material here delays the start of the downward movement of the stop.

To me, it's much easier to fit this contact point between the stop bevel and the trigger hook with only the "lower" parts in the action.....the trigger w/hand, rebound slide, reb spring and the cylinder stiop. (hammer and hammer spring removed) As you go, you can add in the cylinder assembly to make sure the hand and the stop are still working properly together.

Always remember not to cycle the completely assembled action (with mainspring tension applied) in the frame with the sideplate off. This puts added stress on the hammer stud and trigger stud, and the hammer sometimes "walks" out away from the frame on the stud, and can strike the frame as it decends into the frame cutout.

Click to expand...

Thank you for the detailed response!

Here's a picture of where the trigger is binding on the stop:

armorer951 said:

Always remember not to cycle the completely assembled action (with mainspring tension applied) in the frame with the sideplate off. This puts added stress on the hammer stud and trigger stud, and the hammer sometimes "walks" out away from the frame on the stud, and can strike the frame as it decends into the frame cutout.

Click to expand...

Thank you, Sir, for stating this advice about cycling the assembled action with tension on the mainspring and the sideplate removed. It is a very important bit of information for all of us to have, sometimes just because we wish to see the action in motion the first time we are brave enough to remove the sideplate! I am particularly speaking off the added stress on the hammer stud here.

You stated all of this very well, but I believe it bears repeating much more often than we (I) see it in print. We all start out as newbies in this business, but in my view, knowing this bit of information is really important for all of us to remember, newbie's or old timers! I really appreciate your comments and advice about how to do these kinds of things. Even I can understand what you are describing, and that's meant to be a high compliment to you!!

And here's a picture of the cylinder stop position just before it's released by the trigger... well below flush:



I'd prefer to fit just the cylinder stop but I'm thinking that the trigger hook does need to be slightly shortened / beveled since it's binding on the return?

Have you tried the original MIM stop in the assembly with the new trigger? If the old MIM stop functions properly with the new trigger, it would tell you how much material needed to be removed from the point of the bevel on the new stop. The point on the MIM stop looks quite a bit shorter from here.

armorer951 said:

Have you tried the original MIM stop in the assembly with the new trigger? If the old stop functions properly, it would tell you how much material needed to be removed from the point of the bevel. The point on the MIM stop looks quite a bit shorter from here.

Click to expand...

No, but I did try the opposite (mim trigger with the new stop) and it functioned fine.

Just swapped the cylinder stops... tried the mim stop with the new trigger... it pulls the ball a bit past flush but doesn't bind and functions fine... here are a few comparison pics:









Based on that, I'm thinking that you're right and I can modify the stop and not the trigger.

Fitting an oversize stop may also include modification of the width of the ball of the stop so that it fits the stop slots in the cylinder properly. The ball on the new stop looks wider than the MIM part......does the replacement fit the cylinder slots ok?

For safety's sake, you might also consider checking your finished work with a range rod, to verify proper barrel cylinder alignment......another variable when fitting a new cylinder stop, especially an oversized one. (You can borrow mine if you don't have one)

The TK Custom stop is not described as oversized but I noticed that the ball is larger as well.

I checked it in each of stop slots and while the fit is definitely tighter it slides into each without resistance/with a very slight bit of slide to side movement.

I was planning to check the alignment so thank you, I'd greatly appreciate borrowing the rod.

Special thanks to armorer951 !

Thanks to armorer951, I was able to complete the fitting/install of the new power custom trigger, TK custom cylinder stop, and stainless bolt along with a new polished stainless rebound slide, and SDM thumb latch. I also added Triggershims.com shims to the hammer and trigger.

As part of my post install testing, I noticed that the timing was a bit slow on a few chambers (when intentionally pulling the trigger very slowly) so he also walked me through fitting/installing an oversized S&W hand as well.

Now the action is very smooth and the timing/lockup are excellent.