Leica M2 Overhaul
Disassembly Notes: Leica M2 / M3 / M4
Don't be afraid to disassemble your Leica M2 / M3 / M4, it's easy! You can clean and lubricate the camera without actually disassembling any of the tricky bits. This procedure walks through all the major components while releasing only a single spring. The camera remains functional through the whole process, and you can lubricate just about everything along the way. There is no cause for alarm!
Tools for Leica M
The primary specialized tool for this job is a circular clamping wrench, often called "Flexiclamp". I've made mine from aluminum sheet stock, as it's easy to cut, stiff enough to work well, and still soft enough not to leave tool marks on your Leica chrome. Each clamp has a circular cutout just sized for just one specific ring, and by sqeezing the clamp levers together, the cutout tightens evenly around the ring for a perfect tool mate.
You'll also need a good set of spanner wrenches, as well as precision screwdrivers such as Bondhus. And make sure they're sharp so they don't slip. Let's get started...
Top Plate
For the Leica M2 body, you'll need to use a circular clamping wrench to remove the flat-topped screw that points to the frame counter dial. For the Leica M3 / M4 / M6, you'll use a slightly larger wrench to remove the bezel ring around the frame counter window.
Re-assembly NotesThere is a specific order of rings around the M2 frame counter dial:
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For the Leica M2 body, remove the frame counter dial and make note of the cloth buffer ring that separates it from the chrome body top. This buffer pad may have detached from the chrome body, and you'll need to re-attach it during re-assembly.
For the Leica M2 / M3 / M4 / M6 / CL bodies, use a circular clamping wrench to remove the ring around the shutter trigger. This ring may be quite tight, as it's used to secure the rotating frame advance lever under friction.
On the Leica M2 / M3, remove the film rewind nob with a specialized tool having two prongs on a shaft. You can make one by grinding the two prongs into a steel flathead screwdriver. This is the only purpose this tool will have in life!
Second, the ring around the base of the rewind shaft removes with a clamping wrench (shown here).
On the Leica M4 / M6, the film rewing knob removes with a small set screw. Second, the ring around the base of the rewind shaft removes with a spanner wrench.
On the Leica M2 / M3 / M4 / M6, the flash sync sockets remove as follows: First, the outer ring, using a clamping wrench, then the inner bushing. Both remove in standard CCW threaded rotation. Note that I used a plastic wrench for the inner bushing, as you'll be clamping down on the threads, which are brass (relatively soft material).
The inner bushings must be removed, leaving flat openings, as shown here.
On the M2 / M3 / M4 / M6 bodies, you'll need to remove the flash shoe from the top of the camera.
Removing the Rewind Button
If you have a Leica M2 with button rewind release, here's the safest way to remove the button: Find a chunk of rubber or grippy Neoprene that you can cut to fit under the button. I use a sheet of rubber stock that's about 3mm thick. Wedge the cut material under the rim of the button, preventing the button from pressing down. The rubber material holds the button so it doesn't turn, and you can now press down and remove the button's screw.
Finally, take a deep breath if your Leica is "factory original"... Dig out the "L" seal and remove the screw from the top of the lens mount. 
You can now lift the top from the camera body.
Removing the Rangefinder
Begin by removing the plate with the film loading diagram, as shown here. Note the position of the blade that mates with the body unlocking cam ("auf / zu").
Inside the camera, on the floor of the lens chamber, you'll find the plug that covers the rangefinder adjustment hole. This hole is shown in this photo, exposing a straight path from the camera bottom to the rangefinder control arm.
The plug is mounted on a bayonet, and is removed by turning about 1/4 rotation. You can do this with a thin scribe or other sharp point, reaching in through the open bottom hole (shown here), engaging one of the two tool holes on the plug and turning against it.
Further, remove the two screws that are upside-down under the film rewind claw, as shown. These two screws hold the laregest part of the rangefinder assembly. 
Remove the components of the rangefinder control arm. The Leica M2 / M3 / M4 / M6 bodies all share this design. Make note of the components first, to save a lot of headaches later during re-alignment. Don't worry - it's easy with a photo like this to compare against.
The Leica rangefinder has two adjustments for distance, shown in this photo. First, the infinity point adjustment is done with the largest screw, at the shaft of the roller that rides against the lens. Turning this screw adjusts the offset of the full range of distances.
The second distance adjustment is the gain. You won't generally make the gain adjustment (except that it will be disturbed duing this disassembly procedure). The gain of the distance function is the relative difference between any two distance settings. The gain is controlled with the ring around the pivot shaft screw (far right in this photo). Turning this ring clockwise extends the roller arm out from the shaft, resulting in less visual movement of the rangefinder patch per lens movement. Turning this ring CCW retracts the roller arm in toward the shaft, resulting in more visual movement of the rangefinder patch. In the end, you adjust the rangefinder at two points: Infinity and 1 meter.
Re-assembly NotesThe arm has a tight fit on the pivot shaft. If you simply press the arm onto the shaft lightly, that may push the shaft up into the rangefinder and dislocate it from some of the internal mechanism. It won't cause damage, but you'll be puzzled as to why the action of the arm isn't registering inside the rangefinder. Ultimately, you will need to tighten the arm fully onto the pivot shaft, by installing the screw on the shaft. This pulls the arm fully onto the shaft, lowering the shaft and ensuring it's engaged within the rangefinder mechanism. |
Finally, remove the stop stud screw (bottom of the three in this photo). This is the final screw holding down the rangefinder, which can now be removed from the camera.
Low-Speed Escapement
This may be removed for cleaning and lubrication. It pivots on a single screw-down shaft, shown with tension spring here for reference.
To clean the escapement, soak it in a solvent such as lighter fluid (naptha) and work the gears to clean the bearings. If usin compressed air to blow out the solvent, be very careful not to damage the hairspring.
To lubricate the escapement, apply drops of lightweight oil on the bearings. Dip the escapement back into the cleaning solvent briefly, leaving a thin film of residual oil on the bearings.
Removing the Camera Core
On the Leica M2 / M3 / M4, use a spanner to remove the cover screw on the frame selector lever. Next, use a wider spanner wrench to remove the rest of the lever components. Pull out the shaft, as shown here.
Re-assembly NotesYou'll need to mount a lens on the body so the claw (inside the hole) moves down. If the claw is allowed to spring up against its end-of-travel, you probably won't be able to insert the tooth of the selector shaft. The claw actually consists of two parts, both under spring tension against each other, causing the claw to close down against the tooth and prevent re-assembly if not pushed down by a lens. |
Finally, you can pull the core up out of the camera shell. You may need to press the spring flange at the bottom of the lens mount to get it out of the way.
Note the position of this shim that goes inside the rewind chamber. To make re-assembly more convenient, you can stick this back in place (as shown) with two tiny patches of 3M 465 adhesive. 465 is a thin sheet of tenacious adhesive that's basically "double sticky tape without the tape".
