Diesel Solenoid Overhaul
By Bill Adams
I just spent last evening resurrecting a 2A diesel starter solenoid. Most of the time, the soft copper bolts have stripped, and the connection points become weak (or worthless,as in this case) Additionally, the bakelite was cracked and pieces of it were missing. Here's how I did it: First of all, I warn you there's a LOT of file work involved here. If you are uncomfortable with such a tool, or don't have the patience to sculpt new parts from off-the-shelf stock, then quit reading now. Anyway, you'll need a soldering iron...a cheapie will do,solder and flux, a set of BRASS toilet tank bolts...get ones with large heads, preferably 3" x 5/16ths, Two brass 5/16 washers, some flat brass or copper stock for making new contact plates (hobby shops have it), JB Weld epoxy, new brass 5/16thsx18 nuts (4), and a bastard file. Step 1: Demolition. Remove the small nuts on the studs atop the bakelite. Remove the large brass nuts on the big studs. Warm up the soldering iron and de solder the connections on the contact plates. Don't fret, you can't mix up the connections later...it only goes back together one way. Pull off the bakelite. Step 2: Assess the damage. My bakelite was broken and a big chunk was missing, the copper studs were stripped, and the little contacts on the top were broken off or badly corroded (one was steel with galvy coating for soldering...cheesy). There is no way to order parts for this unit,but it is fortunately quite a simple device, and easy to fab up parts from common stuff. Step 3: Gather materials: The big studs are originally copper with a bizarre head designed to make contact inside with a spring-loaded copper washer. I figured brass is a little harder and should hold up as well as copper or better. In any case it's easy to find brass bolts at the hardware store in the form of toilet tank bolts. Sheet stock for the contacts on top of the bakelite was easy, as I had some laying around. It can also be found at hobbyists. Don't need much, like 2 square inches. The bakelite was repaired with JB Weld epoxy. Step 4: repair bakelite. I made a form out of a margarine bucket and clamped it to the outside of the bakelite with a hose clamp. Then I buttered JB weld on the inside of the form and let it set. I had to do two passes as the JB tended to ooze, and not hold shape. eventually I built it up enough so that I could pull the form off and trim and sand it back to original shape. Check also for cracks and burnt bakelite around the stud holes, and fill them if they look bad. Step 5: make new studs. This is the most labor-intensive part of the process, but also the most rewarding. The bolts I used have a fairly large rounded head which had to be flattened. File, file, file. Flatten the head off. Took about ten minutes per, but eventually got there. At this point, I simply held one of the old bolt heads against the new and scribed the shape onto it. Then, I merely filed the sides until I got to the scribe lines and checked the fit. Not perfect, but serviceable. I also padded the back of the bolt head with a brass washer to bring it up to the same thickness as the old bolts Step 6: make new contact plates. The sheet goods can be cut with a set of metal shears. If the old ones are not destroyed, use them as patterns for the new. One is kinda 'comma' shaped and fits under the one stud, so it needs a 5/16ths hole in it, and the other is riveted (3/16ths rivet hole needed) to the top of the bakelite and gets a spade clip attached. I don't need to describe how to make the new ones other than to say that they should be like the old ones. Step 7:reassembly. With all these spiffy new parts you just made, there's a hurry to get them back together. Spend a minute and clean up the greasy bore of the solenoid body, paint it, re grease it. Place the spring plunger in the body,and install the studs and brass nuts on the bakelite (don't forget the contact plate under the stud!) Rivet the new spade connector contact plate. Drill holes (one's bigger than the other) up from inside through the contact plates and give each one a scrub with some sandpaper so that the new solder will stick.Warm up the soldering iron again. Place the bakelite on the small studs being careful to get the wires up into the holes for the contact plates. With the wires sticking through, flux and solder the wires to the contact plates. Reinstall the small nuts on the small studs. Wrap the joint between the bakelite and the body with a couple turns of vinyl electrician's tape. Step 8: Testing. Attach a 12v negative wire to the stud with the comma shaped contact plate. Holding the plunger in the bore with the spring under it, touch the positive 12v wire to the spade connector contact plate. The plunger should jump into the bore with a solid "Cluck". The first time I did that I just about jumped a mile. Install the newly refurbished solenoid on the starter and breathe a sigh of relief that you saved yourself a hundred bucks and a two-week wait.
Bill Adams Design Director, On-Air Graphics Softimage 3|D, Quantel Hal