All the parts for the pump head on my Monotype Composition caster are now clean and mostly shiny. There are two cotter (split) pins which I did not bother cleaning since I plan on replacing them.

The lower crosshead 19H1, which I could not extract from its compartment, is still filthy. It looks like I might have to try to clean it in situ, as a test insertion of the Piston Operating Rod 19H would get stuck on grunge after going in about an inch. Furthermore, this part has oil passages in it which I should clear out as well. I can’t use the paint remover on this part because there would be no way to rinse it off properly, so I will have to use something that can just be wiped off.

I have already begun a bit of reassembly: The Pump Body Spring Rod 31H1 and its crosshead 31H2 have been reassembled and the nut 31H10 installed and tightened. This turned out to be a press fit loose enough that a rubber mallet could be used to drive the parts together. I made a quick try at re-installing this rod along with its spring and sleeve, but it has to run through a second hole in the lower crosshead 19H1, which also acts as the lower land for the spring, and I found that the pressure from the spring made it next to impossible to get the end of the rod inserted into the hold in the crosshead. Perhaps I could arrange something to keep the spring compressed during installation, or perhaps having the Piston Operating Rod 19H in position would stabilize the crosshead enough to enable insertion of the Pump Body Spring Rod.

(for a part code reference see the photo of the parts right after disassembly)

Once I have both crossheads (31H2 and a19H3) installed on their rods I will repaint the unmachined surfaces of these parts. Then I will do the reassembly in earnest of everything except the pump spring group 20H, for which I have to make modified parts to accommodate the pump latch mechanism, which was the goal that started this entire exercise.

The only parts of the Monotype pump head left to clean are the three long springs. To soak these in paint remover I made a trough from aluminum foil with the ends folded over several times. Some scraps of lumber support the sides.

The inner pump spring is in the foil trough covered with paint remover. The fresh paint remover is sort of milky but after soaking for a while some of the loosened grime floats to the surface forming brown spots.

After a few hours soaking, a water spray will remove the loosened grime, leaving a spring that, although not looking entire like new, is at least clean enough to handle without getting black hands.

The third branch of my Monotype pump refitting is the disassembly and cleaning of most of the parts of the pump head. I have started cleaning the parts and have some of the simpler pieces cleaned and ready to re-assemble.

All ready to start cleaning: A box of dirty parts, water-based paint stripper, steel wool, mineral spirits, and for tough spots, acetone, along with a variety of scrapers and brushes.

Most of the parts with simple shapes are cleaned, along with one of the odd-shaped castings.

This still leaves one more odd-shaped casting, a couple of other small parts, and three long springs to clean. I will try to find some sort of trough for soaking the springs in the paint remover, after which there will be plenty of messy brushing to do!

In order to repair two threaded holes in the Monotype caster pump latch, I thought I would have to make an extension for my drill bit because the holes to be drilled were so close to a side arm on the part. However, it turned out that I could place the required drill bit (#29 if I recall) in the collet chuck of the flex shaft handpiece of my Dremel. It is  a bit of a cheat since #29 is larger that the 1/8″ size the collet is made for but I managed to get the bit held properly anyway. It is also slow work because the Dremel motor easily gets bogged down. Essentially I have to turn it on to a speed that is far too high for a drill bit of that size, then apply enough drilling pressure by hand to slow the motor down to the right speed but not stall it completely. On the other hand the long handpiece makes it easy to visually keep the hole sufficiently square to the surface.

I will not be threading the holes to their original specifications, which is 5/32-36 with what I believe to be a 55° thread angle as I am willing to neither make nor purchase a custom-sized tap for the purpose. Instead I will be using a modern #8-36 tap, whose major diameter 0.164″ is slightly greater than 5/32 (0.156″) and whose thread angle is 60°. The original screws will screw into the new holes, but will have a weakened hold, so I may use #8-36 screws as well, with their heads modified to match the countersink depth.

Anyway, here are a couple of pictures of the drilling process: