Hey guys, I just bought a beat up old R75/5 for restoration and it's great to be in with a community; I've been working on old Honda's for several years now and forums like these have been a godsend.
So this 1970 R75/5 was complete and in decent condition...except the entire headlight assembly was mission. I've been able to ebay the bucket, lamp, chrome piece, and instruments, but I lack the internal wiring (not a problem) and the key ignition system (problem).
It's the "nail" key system. I'm pretty sure I can buy the board but it's ~$250; and looking at pictures of the thing, and considering it was made in 1970, I am figuring that fabricating one of these things from components shouldn't be too hard. My father used to build computers from scratch back in the day, soldering semiconductors and whatnot onto silicon boards.
Has anyone had experience doing this kind of thing? Is there anything, in my naivete, that I am overlooking?
Also, if I'm building this from spare parts, which piece is it that actually keeps the nail-key in? I'm assuming there's some sort of clamp-thing but I haven't run across it and I can't get a good look in any pictures.
Thanks! Looking forward to this classic bmw project!
I would think that one can't really build this, at least not to look like the original. There's a spring-ball detent system in there to grab the one portion of nail key and the other portion of the nail key pushes down to make/separate parts of the mechanism in order to run the bike. Plus the key moving left and right to give you parking lights, headlights, etc. Seems pretty complicated to build.
You might try and find a botched up board and then take it apart, understanding how it works, and then keeping the pieces you can't fabrication and go from there.
Vech at Bench Mark Works would be a source for this part...maybe he might have some trashed ones to play with.
Good luck! This seems like quite a challenge.
I don't think so...the part that accepts the key and holds it is somewhere in the #25 stackup. The best description I've seen of this board is on Duane's website:
#5 is the piece that holds the spike. What's not pictured is that there is a spring steel clip that surrounds a part of the body of #5 and captures a ball bearing. When the spike is inserted, it pushes the out against the clip, moving it out of the way until the groove on the spike aligns with the ball and it is pushed back into it, holding the spike in place.
If I understand it right, #9 is one of the screws that clamps a tinned wire end to a terminal on the board. The parts list probably shows that you need half a dozen of them or so.
Here's a quick description of how the ignition switch works:
The stack listed as #25, which includes #5, provides several of the mechanical functions necessary. The ferrule #6 fits into the hole in the headlight bucket that is covered by the chrome cover #17.
#5 holds the spike in place, but it also has a groove on its top surface that mates with a tab on the underside of the spike head; this can be used to twist #5 left or right to control the headlight and taillight. Because the bottom of #5 has flats that mate into the slot in #2, it can twist #2. The tab at the front part of #2 makes contact on the circuit board with a power lead and the rear part of #2 makes contact with different points to provide power for the headlight and/or taillight and speedometer lights.
The coil spring #4 and ferrule #3 hold #2 tightly against the top surface of the circuit board, when the whole stack is assembled and the board is locked to the inside of the headlight shell by the sheet metal tabs that protrude through the board and fold over.
The tip of the spike, when pressed down, fits into #1, which has a piece of plastic on the tip, insulating the spike electrically from the ignition switch. When the spike is pressed down, #1 is pushed through a hole in the circuit board and pushes a leaf spring on the underside of the board into contact with a brass bridge, just visible in the drawing, at the front of the board. The bridge contact is wired to the battery/alternator positive. The leaf provides energy to the ignition coil, to the starter relay coil and directly or indirectly, to the various auxiliary circuits.
Keep in mind that you'll need to be able to create a largish rivet head shaped contact point for the rear part of #2 to make contact when you twist it left or right. Other than that and the re-engineering needed to get the leaf spring and bridge contact to work, I don't see that you'd have a hard time creating the actual circuit board. Get a wiring diagram and look closely at how the board is diagrammed.