Jammed focus rack & pinion on 1954 Gurley Y level

[Mark Schneider]

Recently acquired this Gurley level, and the rack that moves the internal object focus lens is jammed (focus knob on scope won't turn either way. What to do? Since someone had already loosened the objective (front lens), I screwed it out and looked inside. Can't see anything that looks amiss. Everything looks clean. Tried loosening screw on focus knob, since I know that on some Gurley transit scopes this regulates focusing tension, but it has no effect on this scope. I have the Gurley (adjustment) Manual for a similar instrument and date to mine, but there's nothing about this problem. Any suggestions will be appreciated.
Mark

 

[John Garner]

There's a good chance that the lubricant between the pinion shaft and pinion shaft bushing has oxidized. I've never had a Gurley apart, so I don't know how the pinion shaft is held in place, nor do I know if the bushing is eccentric (which is one way to adjust pinion-to-rack clearance), but if your Gurley was mine I'd try mineral spirits where the shaft comes out of its bushing.

If there isn't any form of well to hold a few drops of mineral spirits at the shaft-to-bushing juncture, try to improvise one with a bit of putty or modeling clay.

Let it soak, giving the ficus knob a gentle torquing in both directions every so often.

I've never encountered a stuck focus slide, but I have seen some that were hard to operate. The same "few drops of solvent" approach worked to ease its operation, followed by disassembly, cleaning, and reassembly.


Hope this helps. I would love to hear more about your Gurley; wye level, dumpy level, or tilting level, telescope length, and bubble sensitivity.

 

[John Garner]

Oops. By the time I finished my essay, I had forgotten that you had identified your level as a wye level.

Beyond that, the usual survey instrument lubricants of that time were sperm whale oil or porpoise jaw oil. When those lubricants were taken off the market, they were largely replaced by clock oil and the lower-viscosity watch oil. However, the U S Federal specifications were largely revised to specify instrument lubrication with MIL-PRF-6085 aircraft instrument oil or an aircraft grease MIL-PRF-23827. (that last number is from memory, and may not be right. BUT, Aeroshell greases 7 and 33 meet the spec, as do Royco 27 and Mobilgrease 27.)

I've gotten my supply by taking a clean 2 ounce ointment jar and a clean 4 ounce medicine bottle to a local airport, along with a six-pack of Dr. Pepper, and asking nicely at one of the FBOs (Fixed Base Operators) that services private planes.