Drilling and tapping in solid brass.

[#1]

@shutter 

Looking at the photo it looks like the pivot screw has a separate small locking screw entering from the top of the block. Doesn’t this stop any wobble?

Are you sure that this is your problem? Is it not the point on the old screw or the indent in the arm being worn that’s the issue?

[#2]

@Baldrick1 All points you have mentioned, do come into the equation,.... and yes, the lock screw, does stop some movement.. however, I have held the pivot screw during operation, and can feel the "wobble" even with the lock screw done up tight. 

As for the pointy bit... yes.. that was well worn on the original, and also the pivot hole... I have replaced the rocker arm and re-centred the pivot point holes, used replacement 6mm pointy pivot screws ( new ) which "kinda" lets that area out of the problem... Drilling out to 8mm and replacing the pointy screws with those shown, should eliminate the "wobble" ... hopefully..

Shame that it needs so much replacement.. but it was a key I used in the Navy, and has some sentimental value to me.

[#3]

@shutter 

Another thought, if the pointed screw is ok and it's only wobble that you're worried about, have you tried wrapping the thread with PTFE tape as used in plumbing?

[#4]

@Baldrick1 Yes... I have tried that... it seems to work for a short while, but anything over 5 minutes, and it seems to come back again... hence the choice of drilling out and re-threading... 

The thing is,,   A morse key needs some really fine adjustments to get it to work properly, any part of it that becomes worn slightly, can affect it`s performance... e.g my preferred gap setting is 6thou... if I use 5thou it does not work well for me.. using 7thou and it sounds like a machine gun firing away.

[#5]

@shutter 

I get where you're coming from, it's all dots and dashes to some though !

Dan.

[#6]

Have you considered using a helicoip kit?

Other venders are available.

https://www.screwfix.com/c/screws-nails-fixings/thread-repair/cat12120002?brand=helicoil&ds_kid=4370... 

[#7]

@Mustrum 

How does that help? The hole still needs drilling out then tapping.

[#8]

@Baldrick1  the inserts are stainless steel so will provide a stronger fixing than brass.

If he is lucky and there is thread left, he may get away without having to drill and tap the hole.

[#9]

@Mustrum  Have you ever tried doing that? That’s not withstanding that due to the age it’s probably a BA thread form?

Helicoils are great in aluminium but not required for this application.

[#10]

Helicoils are great when you just have to go into your works stores and pick up all the bits. I expect if you have to pay for the coils, the tap, and the insert tool it would work out quite expensive. And with that cross lock screw it just wouldn't work.

[#11]

---

@Baldrick1 wrote:

@Mustrum  Have you ever tried doing that? That’s not withstanding that due to the age it’s probably a BA thread form?

Helicoils are great in aluminium but not required for this application.

---

Totally agree OK for repairing a stripped thread on a spark plug on an alloy head but not this 

[#12]

@Mustrum  Nice idea !... but I think it will be too expensive to progress.!. My current solution will cost me less than £3 !

[#13 · Accepted solution]

Just thought I would update, to those who are interested.

 I drilled ou the original thread with a 6mm and then a 6.5 mm drill bit... I had bought a new tap and die set.. which had the 8mm with a starter taper on the bit... but I decided to just give it a bit more, by a slight indent with a 7 mm drill.

Started off the tap in the Main Drill stand, so that it would start off correctly, and once it had started to bite, I removed it from the drill stand and use the Manual tap driver head... this worked very well, and very pleased with the thread cut .

Manual tap and die set....    https://www.ebay.co.uk/itm/224754008088

I also re-centered the pivot holes on both sides, using masking tape around the rocker arm and then locating it in the yoke in the correct position... then tightened up the pointy screws to make a location mark for re-drilling.

After putting it all back together again, resetting it up... It works very well, and I`m pleased with the result.

well worth the effort, !

Thanks to all those who helped... Much appreciated, as usual .  

[#14]

---

@shutter wrote:

@Mustrum  Nice idea !... but I think it will be too expensive to progress.!. My current solution will cost me less than £3 !

---

---

@shutter wrote:

Manual tap and die set....    https://www.ebay.co.uk/itm/224754008088

---

 https://www.ebay.co.uk/itm/224754008088   - Price £4.61