I believe dieselspanner is correct, due to the heads on twins being "handed", both valve guide holes in the heads are threaded, but one thread is normally not used

My 1959 8/1 has aluminium piston, and a chromed bore. It is fitted to a SOM set, if that makes any difference, which I doubt.

Ian

Just tried my CS8/1 after making a simpler alternative to the Utterpower modification. All I have done is make a wire link so as to movethe spring away from the fixed end, such that the adjustment rod can be wound almost right into the crank. It cetainly seems to work better, and for no more cost than a few inches of galvanised wire. It probably doesn't look marvellous, but with my SOM set mounted the way it is it can hardly be seen, even if you know to look for it.

Seems to have been half an hour well spent

Ian

Tested the regulator from inside the ST3 yesterday. "mains" input provided by variac and isolating transformer, the triac connections were between the output of a 24V transformer and a 12R load. Monitored the resistor with a 'scope. The regulator contains a relay, whose NC contacts seem to be across the triac. With 24V on, but no mains, the resistors get the full 24V. Wind the "mains" up with the variac and the relay pulls in at 96V; the resistors still get all the 24V, but with a slight glitch at zero crossing. Keep winding the variac up and eventually it starts triggering the triac later, thus power delivered to resistors decreases. Conduction angle decreases from 180 degrees to about 100 to 110 degrees over a 3 volt change in the "mains" input, after which it goes to 0 degrees. There is an adjustment pot which adjusts the control point from 90V to 140V. The triac is a Sanken M1641.

I therefore conclude that the regulator is working fine, but due to its limited working conduction angle range the supply to it needs to be just a little more than required to give full output from the machine. Therefore my next task is to run the machine with the rotor supplied from the variac to find out what this voltage is, and what the current is at that point. I will then need a acquire a transformer, 240V input, and with an output of the voltage found.

I will also try adding capacitors after the rectifier, but I suspect that method will not work with the regulator, but might without it.

I am curious to know how well the regulator works on the spiky waveform from the harmonic winding. Obviously the fundamental problem with my machine is the output of the harmonic winding is too low.

I will certainly try the capacitors after the bridge. I can certainly see how that might improve the quality of the output waveform. Does smoothing the output of the bridge with capacitors affect the transient response, the voltage dip when switching a load on or the voltage peak when switching a load off, for example?

This unit is not like the diagram further up in several respects. It seems to have no connections for 60Hz (on its plate it only states 50Hz), the connections are therefore very different, and it came with the AVR as I described previously. It is still a dual voltage unit, however.

Presumably this manufacturer (I understand that there are several manufacturers of ST alternators, this one is "Saint") has tried to improve the design, but made it more market specific than the earlier versions. However, the improvements are not better. Where have I heard that before??

I have that diagram. The AVR on mine is connected in series at Z1 or Z2, and it monitors one of the main windings. I am going to try connected a variable resistor where the regulator is on mine, and I will report back, but it will be several days before I am likely to get time to do it. I do not believe mine has the option of 60Hz operation, but that doesn't matter for me.

You state that two are SOM units, but none of them have the big solenoid on the valve lifter, so how was the starting and stopping controlled on these SOM units?