ian_partridge_com

PROJECTOR HELP PAGES

Bell & Howell Worm Gear Help Page

Buy a new replacement worm gear available now, MAY 2017 Small Picture of Worm for Bell & Howell (£20.00 Includes printed Bell & Howell Worm Diagram and Service and Parts Manual. + £4.80 post to worldwide)

Bell & Howell part number 2304782

Bell & Howell Cracked Worm Gear on Model 655

Worm gears on Bell & Howell projectors are prone to hairline cracks that develop into fractures that eventually cause sudden breaking up while the projector is running. Shown above is a cracked animation worm gear from a Bell & Howell model 655.

Bell & Howell Worm Gear Intact

Here is an an example of original nylon 'animation' worm gear shown in a Bell & Howell model 2592. It remains uncracked and intact.

With the 'animation' model Bell & Howells, the worm gear consists of a thin outer nylon shell with a helical 'archimedean' worm gear that drives the sprockets and is prone to cracking. Replacement requires a major strip-down of the projector to replace the broken worm, usually with a solid, non-animation one.

Shown below left is an example of a new worm gear fitted to a Bell & Howell 652 QE projector.

Bell & Howell 562QE Replaced New Worm Gear

Below left measured diameter of an original animation worm removed from a Bell & Howell = 36.86 cm.

Old B&H Worm Gear Measured B&H New Worm Measured (Both measured when stone-cold)

Above right, new worm diameter 36.86mm. Below left, thread pitch of 2.5mm measured on old and new worm.

B&H Old Worm Thread 2.5mm B&H New Worm Thread 2.5mm

It is sensible to 'run-in' the worm gear mechanism on the bench to be sure that the worm gears are freely running before reassembling. In the Bell & Howell repair manual provided there are is a diagram plan to make a home-made motorised jig for setting up, adjusting, and running in the mechanism before fitting back in the projector.

There should be slight 'side shake' felt at all positions as you grasp the large plastic gear wheels that engage with the worm. You may need to apply a needle file to the large gear wheel teeth at the positions where there is binding, or no side shake is felt.

When the projector is running with the lamp on, the gears will expand due to heat, so it is necessary to allow sufficient clearance to avoid binding or uneven running.

 

New Bell & Howell projectors stored for many years in a government warehouse unused were all found to have cracked worm gears. This indicates that the problem was not incorrect lubricant or missuse. There is evidence that some Bell & Howell projector worm gears with diverse hairline fissures (that do not join together) can be run regularly without catastrophic failure. However it is only a matter of time before an original worm gear will inevitably fail. A Bell & Howell projector that has had a replacement solid worm fitted is to be preferred.

Return to Projector List Page

 

Home


About | Privacy/Terms Contact |  FAQ


www.ian-partridge.com ~ Web page content photography and design ~ Copyright 2011 ~2017 Ian Partridge.