Normal Hammer block contact? Model 36

Matt_X · Dec 29, 2023

Is it normal to observe some contact marks from the hammer on the back of hammer block?

This is a c.1975 Model 36
I opened it up after having failures to fire (light primer strikes) in double action.

Internals were dirty (see photo), but also looked like the hammer had just kissed the top edge of the hammer block.
Arrows on photo indicated location of marks on block and approximate matching location on hammer.

usedkid · Dec 29, 2023

Negative, no it's not normal...

armorer951 · Dec 29, 2023

If this persists after the thorough cleaning of the internals, you can crown the top edges of the "flag" at the top of the hammer block, and remove a small amount of material from the top of the flag. (note: The illustration is a K series hammer and hammer block, but the modification is the same)

The edge of the cutaway on the hammer, just beneath the hammer nose is not clearing the top of the hammer block as the hammer goes fully into battery.

If the hammer block cavity (hole) at the bottom that fits over the pin in the rebound slide is badly worn, you can always just replace the hammer block with a new OEM one.

Be sure not to cycle the action under pressure from the hammer spring while the sideplate is off. This can result in damage or breakage to the hammer stud, rebound stud or trigger stud.

[url=https://flic.kr/p/2ppmZs7]

Carter

Matt_X · Dec 29, 2023

Thank you. Yesterday there was at least one misfire every cylinder when fired double action. So range firing should be a pretty good check. Previous two sessions there were no misfires.

Everything but the extractor and ratchet was removed and cleaned with Kerosene, then mineral spirits. A very little bit of arkansaw stone on rough edges and burrs. Cleaned again and drop of Remoil on bearing and rubbing surfaces.

armorer951 · Dec 29, 2023

Not to get too far off the trail here, but just a reminder in terms of the many possible causes of misfires in DA..... "staging" the trigger in double action can cause what's called "hammer hits rebound". This "incomplete" rearward travel of the trigger in DA (staging) can result in the rebound seat on the hammer striking the hammer seat on the top of the rebound slide, causing the hammer to not go fully into battery, and cause misfires.

Just another thing to check for.....a little bit of "wink" (space) between those surfaces when the trigger is fully rearward and the hammer comes fully down.

Carter

chief38 · Dec 29, 2023

Just for S&G's, make sure the hammer is not rubbing up against the frame or side-plate.

Matt_X · Dec 29, 2023

Funny you mention that. There was evidence of rubbing on the side plate. I lightly went over the plate with a translucent stone and also broke the sharpness of the edge. The hammer I did not touch.

Observations as to whether that amount of contact could be a significant contributor are welcome.

chief38 · Dec 30, 2023

Matt_X said:
Funny you mention that. There was evidence of rubbing on the side plate. I lightly went over the plate with a translucent stone and also broke the sharpness of the edge. The hammer I did not touch.

Observations as to whether that amount of contact could be a significant contributor are welcome.

Once in a while a shim needs to be added. That rubbing looks to me like it is more than just the hammer block safety! I'd also check to make sure that the hammer is sitting all the way down on the stud. Dirt or debris could be raising it slightly and causing it to sit just a wee bit proud, causing rubbing.

steelslaver · Dec 30, 2023

If you really want to know if it is the hammer block(which I doubt) simply remove it and fire a few cylinders full.

I am with chief38 in believing your hammer is dragging. Those marks on the side plate and hammer show that.

Armorer951 gave some good thoughts and I will add that you should check for endshake.

Matt_X · Dec 30, 2023

The only change I can think of between the first two times at the range and the third is additional accumulation and movement of dirt and grit.

That doesn't mean that underlying factors (such as hammer block contact, hammer rub, or rebound contact) aren't at the root of the issue.

I can certainly try adding shim to the sideplate side if there is enough side play.

There's about .004" endshake based on the cylinder gap measurement pushing forward and back; .008 to .004"
headspace is .067"

Shim sources for J-frame shims? triggershims dot com or mcmaster-carr?

armorer951 · Dec 30, 2023

Triggershims.com.

Steelslaver has pointed out a great way of determining if the hammer block is the culprit or not.....just remove it for a test fire session.

chief38 · Dec 30, 2023

armorer951 said:
Triggershims.com.

Steelslaver has pointed out a great way of determining if the hammer block is the culprit or not.....just remove it for a test fire session.

Normally I would agree, but in this case the hammer and side-plate are so marked up (been going on for some time), you would need to coat them with Dykem machinists dye first. If no Dykem is on hand, then a good old magic marker would work. Then yes, that is a good suggestion. Removed with alcohol afterwards of course. Dykem comes off easily as it is made to.

Matt_X · Dec 30, 2023

That's a great idea. I have dykem and magic markers.

I can feel play in the hammer, so a shim may be a good idea anyway.

chief38 · Dec 31, 2023

Matt X,

Don't know exactly what the grease or grit is on your original photo, but it should not be reapplied after solving the issue here. Only a [U]light[/U] lubrication on the pivot and sliding points - that's it! Excess oil and or grease does little to help and lots to hurt because it attracts unburned powder. lint, debris, etc.

I can also tell you that the rearward most mark on the back of the hammer can not be from the hammer block safety because it can not touch it - too far rearward. Must be from side-plate.

Matt_X · Jan 7, 2024

Who knows what lubes were on the mechanism when I bought it.

Triggershims was a good source. I like that they mark the thickness on the shim.

A few trials for rubbing and binding resulted in two .002 shims on the right side of the hammer. Also a .002 cylinder bearing shim.

While it was apart, here is a little better photo of peening I saw on the hammer block.
I think its good. It will be at least another week before I can get to the range.

Matt_X · Feb 3, 2024

I got to the range and not solved.

As I failed to think out the 'what if' I didn't examine carefully the primers and document at the time. Likewise forgot to bring a screwdriver so I could trial without the hammer block.

However as far as the spent brass goes, there was one that clearly had a light strike. (photo shows a mix of single action and double action fired brass)

There is a little roughness in the hammer block channel, but I would think that a) movement is dictated by the pin on the rebound slide, and b) round slide in double action is in the same position single action.

Next post will be looking at the 'wink' between the rebound slide and the hammer's rebound.

Matt_X · Feb 3, 2024

There does seem to be a little space between the hammer and the rebound, although less so when releasing double action.

I'll let the photos do the talking here.

First one is with the trigger held at the point where the hammer releases.

Second is with the trigger all the way back.

Third is contact on with the trigger returning and the rebound slide moving forward.

This problem only showed up after its third trip to the range.
Only after the failures to fire did I open the sideplate. So whatever changed is probably subtle

armorer951 · Feb 3, 2024

When there is abnormal contact between the rebound slide and the rebound seat on the hammer when the hammer drops in double action, you can usually "hear" the difference in the sound of the hammer impact when it goes into battery.

When the parts are fit correctly, the hammer makes a very clear and loud "click" when it completes it's forward rotation and strikes the frame cutout. When the hammer seat on the rebound slide is a bit too far forward, the sound of the hammer impact is not sharp and distinct.....more like a dull thud.

In this scenario, misfires or "light" primer strikes can often be due to an incomplete follow through on the trigger by the shooter either because of improper trigger technique, or perhaps because of an attempt at "staging" the trigger rearward, instead of pulling it though completely.

If you determine the front of the hammer seat on the rebound is literally "in the way" at the completion of a clean and complete DA trigger pull, you can remove material from the front face of the seat to accommodate the hammer and make a bit more room here. The shape of the seat should remain the same. Another alternative would be to substitute a different rebound slide with a slightly shorter dimension at the front of the hammer seat interface.

Under no circumstances should material be removed from the top of the hammer seat on the rebound slide, as this is a critical part of the primary safety in the revolver.

Carter

Matt_X · Feb 4, 2024

@armorer951 Thank you. All the dry firing had been with dummy cartridges or spent brass. Trying the action both SA and DA the hammer is hitting the frame first. I can't say that was the situation before, but it clears up where that stands now. Now being after I touched up the angle on the front hammer seat so it is even all the way across.

Also, after better shaping the bevels at the hammer block top (again to be even and square all the way across) I coated the them with red Dykem. The red is all still there, so I think that's OK now.

Firing pin protrusion is around .044 or .045" (comparing with feeler gages). Khunhausen writes that he has measured .039 to .045" so I think thats OK. (He also suggests .055 to .062 max should be good, but I infer that is if one is replacing the nose)

Head space is about .063"

Finally, put Dykem on the back of the spent brass with the lightests primer indents ran them through in double action. All look to have decent strike marks now.

I think the next step is to go back the range.

Matt_X · Feb 11, 2024

This afternoon was the least successful range session since I bought this revolver. There were 2 out of five light strikes in single action, and consistant light strikes in double action.

I find this interesting in one respect, whatever is failing is getting worse. Not many mechanical things get worse that quickly.

To recap range sessions and work on gun:
1. 25 shots SA, 35 shots DA. Worked perfect.
Changed from Target stocks to Magna Stocks with grip filler
2. 30 SA, 30 DA. Worked fine
No changes. Just regular cleaning of chambers and bore.
3. 20 SA, 30 DA. Some failures to fire double action
Remove sideplate, clean, and try to identify causes.
Started this thread 29 Dec 2023

4. 10 SA, 10 DA. About 6 out of 10 Failure to fire double action. Second strike in single action generally fired.
Further work discussed above.
5. 5 SA with two out 5 light strikes, 5 Double Action all light strikes. (see photo)

Normal Hammer block contact? Model 36

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