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MG MGB Technical - die size for threading the door lock

It's mentioned in the archives that some have cut threads on the door lock.

Though no one has indicated what size die they used to cut the threads.

Anyone know the size?
Steven Rechter

Steven. A little more information, please. What are you talking about here? Do you mean the striker mechanism that bolts onto the B post or do you mean the latch mechanism that is mounted on the door? A die is used to cut a thread on a rod, screw, or bolt. A tap is used to cut internal threads that the rod, screw, or bolt will fit into. Exactly what are you asking?

Les
Les Bengtson

Les,

Cutting threads on the metal housing that holds the door lock tumbler.

(Like in the attached photo.)


Steven Rechter

Steven. Looking at the photo you have a ring/nut that is removed from the lock, the lock slipped into the door, then the nut replaced (on the inside of the door) and tightened to hold the mechanism in place. I do not see how it would be possible for it to work any other way. If the door were threaded for the locking mechanism to be turned into it you would have to have some form of captive nut system inside the door. None that I have seen have had such a system. So, two questions:

First, what is the real problem you are having?

Second, what makes you think that you have to tap the hole or rethread the barrel of the lock?

If necessary, you can determine the thread by measuring the outside diameter of the threaded portion of the lock, then looking for the closest fractional size--i.e. a measurement of .310" would be a 5/16" (.312") diameter. The thread pitch (TPI) would be determined by either using a thread pitch gauge or using a set of dial calipers to measure out 1/4 inch on the threaded portion and counting the number of threads present. Multiply that by four to get the number of threads per inch--e.g. you count seven threads in your 1/4 inch sample and multiply by four to get 28 threads per inch.

Please, let us know what you are doing and what problem you are finding. It may well be a case of an incorrect part or of a poorly made part.

Les
Les Bengtson

Les,

The photo actually shows an improved version of an MGB lock. I believe MGOC sells them.

The improvement is the lock is held more securely than the OEM spring fingers.

I am reassembling my GT and did not trust putting the 46 year old spring fingers back into service.

Steven Rechter

Steven. Still wondering what you are talking/posting about. By "spring fingers", I am assuming you are posting about the form of lock washer that has a number of arms moving out from the central, inner, surface. If you do not trust the "46 year old spring fingers) a small dab of blue LocTite (I am currently exploring the gel version with good results) should take care of the matter. I, still, do not know why you would need a die, used for external threading, nor a tap, used for internal threading. All of the door locks I have seen slipped into the sheet metal of the door and were secured by a nut on the inside. If you do not trust the original lock washer, and your supplier did not send you a new lock washer, try some Loctite.

But, as a matter of practice, I do not leave anything of great value visible inside my MGs. Too easy to cut the top of the roadsters or break the window of the GT and get inside. Only takes a razor blade (top) or an "automatic center punch" to do either. Are you installing some form of quite loud car alarm as a part of this process? I would rather allow someone to open the doors, find only the registration and proof of insurance card, than to have to replace a window or top. Both of which are rather expensive compared to a call to the local DVM and insurance company to report the stolen items.

Les
Les Bengtson

Steven,
If you are contemplating threading the lock barrel. The diameter of the latter determines the size, and the thickness of metal determines the thread form. i.e.,the finer the thread the shallower the thread. But the barrel is only zinc alloy and therefor quite weak Personally I have made copies of the clamp plates sold by many MG traders and they work really well and don't run the risk of "screwing up" (pardon the pun) the lock barrel.
Allan Reeling

Steven,

I understand exactly what you want to do - measure the barrel and find a suitable nut that has a major thread diameter close to that size - then get a die for that thread and cut the thread onto the barrel.

Les - I am surprised that you have never come across the horrid spring steel collar with legs that holds ( or fails to hold) the door locks in place!

Allan, I don't trust the "C" clamps unless you use a drop of loctite on the screws - they vibrate loose pretty easily otherwise.


If it is a roadster I never bother locking it anyway - I'd rather they opened the door than stick a knife through the hood ....
Chris at Octarine Services

Chris. When I first started driving Brit cars they did not have locks on the doors. Like you, I have never locked my roadsters because the cost of a new top is more than anything I would leave inside. Similar though with the GT--the cost of a new window, easily and quickly broken with an automatic center punch, is more than the value of anything inside. Fortunately, I am fairly hard of hearing and, as such, an expensive stereo system is not needed. Besides, the sound of the engine and exhaust is all the music I need when driving.

Les
Les Bengtson

Chris, My design has lock nuts, but always use thread lock as well, as you would have to do if you thread the barrel.
Allan Reeling

I have been threading the barrels for over 30 years. The nut is 26 tpi about 3/4 dia & I think they are from the MGB clutch hose (I have 4 left - bought them in bulk back then & memory has faded at 74) I dismantle the lock, press it onto a mandrel & cut the thread in a lathe. Good to see someone has had the same ides.
Garth
J G Bagnall

JG,

Do you have any threaded barrels w/nuts left?

If so $? including shipping to U.S.
Steven Rechter

Hi Steven, sorry only have 4 nuts left and no barrels as I usually thread what comes off the car I am working on. Now retired so don't see many now.
Garth
J G Bagnall

This thread was discussed between 04/08/2013 and 09/08/2013

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