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Bolex EBM Shutter Sync Repair

Marko Steinberg

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Hello all!

A few weeks ago, I put my first test roll through my new Bolex EBM camera. Unfortunately, it turned out the shutter and claw system were completely out of sync. 

I took it upon myself to do the repair as I couldn't not afford to send it for a general overhaul and fix abroad. I've spent many weeks going through the repair manual and reading plenty of helpful posts on this forum, to understand how the system operates before I even try to disassemble it. I got the right tools and after some time, I think I've managed to perfect it. Here are links to some slow mo footage of film passing through the system:


https://www.youtube.com/shorts/1zNsxUi_lp0 (the first second when the film is passing through the gate, you can see the film move as the shutter is open, but that's only as the film is not yet engaged with the sprockets and claws, once it engages, it seems to properly stabilise).



I was wondering does this now seem to be properly in sync?

Obviously I'll have to have another test roll shot and developed before any conclusions but I was wondering what's your opinion just by looking at the footage above.

Many Thanks! 

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There are a few things to be set correctly.

  • The shutter should be halted with its leading edge one to two millimeters above the aperture in the TIME function when side release is held to front;
  • The shutter should cover the aperture entirely before the claw begins to exert pressure on a hole edge;
  • The shutter should not free the aperture before the claw has cleared a perforation hole after a pulldown. Variable shutters set fully open.

I investigate the functions from behind against a window, pressure plate removed, with a crank either on the 8-1 shaft or on the 1-1 shaft with the younger models. MOT switch on 0, side release all the way rearward. The halt position must be checked frontally.

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That seems to be OK, but I would check it by slowly hand-cranking so you can really see if there's any movement. If the timing is only a little out the film will move just as the shutter is opening or closing, so I tend to mark the film with a squiggle that extends to the edges so you can see it even if the shutter is covering most of the gate.

EBMs are pretty simple mechanically, there's no stop pawl or single frame or variable shutter to worry about, you just need to get the pulldown synched to the shutter. Some timelapse/animation motors need the 1:1 drive to be correctly synched to the shutter to work properly, in terms of where the pin and the red dot is.

If you removed the front, you will need to remake the light seal. Did you de-solder the wiring and remove the mechanism? If so then the light seal needs to extend around the inside. If you undid the sprockets or shifted the claw gear you will need to re-time the auto-threading. 

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Simon, thank you for the insight on the positioning the claws with the shutter in detail, very helpful and will keep it in mind when 


And Dom, thanks you as well. I will do the squiggle test and double check by hand-cranking for even the slightest of movement, fingers crossed! I did not remove the front of the camera at all, as I've realised it would probably be messy putting everything back together, especially the light seal.

I did however shift the claw gear around, so I will have to re-time the auto-threading. If you have any insight on that and are willing to share, that would be greatly appreciated. The repair manual also has some good insight into this, so will study it carefully. I'm assuming if the auto-threading was way off, it would be noticeable by observing the film loop? 

Thank you both for the valuable insight! 

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When you load the film with the loop formers closed, and it runs through the gate, it should be picked up by the claw just as a perf reaches it, and then the same with the lower sprocket. So you need to slowly hand crank the film through and first set the rotational position of the upper sprocket so that the claw picks up a perf just as it begins to move forward, and then set the rotational position of the lower sprocket so that a tooth cleanly picks up a perf when the film reaches it. If these are misaligned, either the film will jam or when you open the loop formers the loop will shift up and be off centre.  It can be tricky to set correctly. There are two screws holding each sprocket in position, and when you secure them again you should also try to keep the sprocket height the same as you found it, with slight clearance above the guides. I have a tool to help set the height. Normally I would say this is a job for a tech, but see how you go.

The alternative is to manually load and form the loop, or always check that the loop stays centred and never hits a loop former, and adjust it by hand if necessary.

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