Just a little progress update today - after discovering a good candidate yesterday for why the bike isn't running well (a faulty ignition coil), I turned back to the ongoing refurbishment of the spare engine.
Today's job was to get the starter motor off, partly to have a look inside the bit of engine that's behind it, but mainly to clean the area up thoroughly. There's decades worth of loose debris hiding there !
This photo is the start of the process; I've labelled a bunch of interesting parts.
Removing the starter motor was relatively easily, just a case of undoing the two long 10mm bolts at the end of the starter motor that hold it onto the crankcase, then pulling it out.
I was worried that the bolts might be seized, which is a common problem when steel bolts have been screwed into aluminium threads for long periods of time. Luckily, although they were very tight, they came out okay.
When I pulled the starter motor out, I made sure that after initial wiggles to get it moving, I pulled it directly backward. That way, the pinion cog on the end wasn't moved and it would hopefully slot straight back in again.
These next two photos show the awful crud I found that had accumulated under the starter motor. I used a torch to look inside the hole and could see that the starter motor gear on the secondary shaft was in very good condition. Then I blocked the hole with towel while I cleaned the debris up, just to make sure that nothing got accidentally pushed into it.
The photo below is the actual starter motor. The nut holding the electrical cable onto the terminal was badly seized, and removing it would likely have caused significant damage. So I decided to limit myself to giving it an exterior clean. The reality is that the motor is equipped with a kickstarter, and that's how I always start it anyway.
The starter motors on the early Z650's were pretty poor, and one of the very few weak points of the design, but then at that time, electric starting was still a relatively new technology. They're just about able to start the engine if it's warm, but struggle when the motor is cold, are so underpowered that you have to hold the clutch in while using them, and can drain the battery really quickly. In 30+ years, I've probably used the electric start no more than a dozen times.
This last photo is the side of the engine with the crud cleaned up, ready for the starter motor to be re-fitted. By that stage, the light was starting to fade for the day, so It's actually a bit shinier than it looks !
Refitting the starter motor was easy, because luckily the pinion hadn't moved so it located onto the internal gear without trouble. Before putting it in, I wiped a little clean engine oil onto the o-ring, to help it slide in and seal properly.
With this done, I am reasonably happy with the state of the engine's bottom end.
Next is the top end ! I'll start by cleaning the oxidation and debris from the barrels and cam cover, as well as maybe doing a bit more work on the oxidised surfaces elsewhere on the engine. I probably won't do any cleaning on the cylinder head itself, as I expect to have to replace it with one of the two others that (hopefully !) need less work.
