Leica M4 Overhaul Notes

M4-1191556 was working fine, for a while, then got some issue with the first shutter curtain. The curtain pulled itself out from its shuttle bar. Everything else about this camera is in such great condition, so I decide to go ahead and try repairing this curtain myself...

1: Pull apart the camera and unroll the first curtain. In this case, the curtain hasn't torn, but is intact, and has only pulled itself free.

2: Using a thin knife, spread open the shuttle bar, beginning with the two end pieces that are folded over. Be careful to spread open just enough to reach the inner bottom edge, all along the whole width of the bar. You'll need to insert the fabric curtain all the way in.

 

3: Insert the fabric curtain, and re-clamp the shuttle bar together. It's difficult to maintain the zig-zag pattern of dented teeth. Make sure to leave the whole bar straight so that it mates with the second curtain's shuttle.

In this illustration, the first curtain has no tension so we're able to leave the ribbons loose and extended.

4: Re-tension the first curtain, at the tension control, bottom of camera. This will be the same for all Leica M2, M3, M4, M6.

Use a flat-bladed driver, just slightly wider than the slot shown here. The extra width of the driver will press down on the surrounding spring-loaded collar, releasing the spring so that you can adjust tension. This may require about 10 turns to reach proper tension.

5: Do final adjustments to first curtain tension, using the "TV method"... A TV CRT refreshes at 30 Hz, but is interleaved, making it effectively 60 Hz. As you increase shutter speed above 1/60th, you will find consecutively narrower light stripes of the CRT, visible through the working shutter. The critical adjustment to first curtain tension will be especially apparent at 1/1000th second, where the narrowest light stripe will be visible. If the stripe is not visible, or visible only for part of the exposure, then the first curtain tension is too loose. If the stripe is wider toward the later end, then the tension is too tight (first curtain travelling faster, away from the second curtain). Obviously, you want the light stripe at 1/1000th to be uniformly narrow over the whole exposure.