SQ4 - updating the ignition system

 The Square Four is on the bench at the moment for some maintenance and an electronic ignition conversion. 

I'm fitting an Accuspark system to see what advantages I can really gain. I'm led to believe that the bike will start more easily and will be smoother - I'm hoping that it may be slightly less rattly particularly in the coupling gears and I've also been told that running in town is better as the Hall effect sensor is less sensitive to the low voltage the dynamo provides at low speeds.

This is what you get in the kit - a new distributor base with the Hall effect sensor and 3 magnetic sleeves to go over the distributor cam. I understand that they are all the same magnetically but you use the one that fits best.

Here's the old setup - it works perfectly and is original. Starting is very easy so it will be interesting to see what I gain, if anything. I don't have to change anything permanently here: I can retrofit this system easily if I want to - I won't be cutting or removing any wires

There's two things to check in the battery box - one that it really is negative earth and two that I have removed the fuse to isolate the battery.

This is a useful view of the current cam and auto advance setup - you'll notice the odd springs. I don't think they're supposed to be like that but it's curious that I have a single spare spring in my box of ignition parts. Anyway, the second thing is that those rivets are raised compared to the body of the distributor and will foul the base plate of the new electronic ignition sensor so there is some work to do to provide clearance.

I've measured the diameter of the circle described by the rivets and marked it out on the base plate using a pair of odd-leg callipers, ready to cut a hole.

The base plate is actually quite thick - probably 2 mm or so. Since I can't find my Abrafile I have chain drilled inside the circle and will have to file it out. The housing is made from sheet steel set into thermosetting plastic and we don't want to crack it using some over-brutal method.

So that's it filed out quite neatly but we don't want to be too self-congratulatory at the moment do we! The problem is not obvious but actually it is not only the rivets in that ignition cam that are proud of the distributor body mounting face - that diamond shaped piece is also verging on being too high as well. I toyed with the idea of reducing the height of the whole cam assembly for a while but the real solution is to open the hole out again.

And as if by magic here it is, opened out to 40 mm. The difficulty that arises now is that the two M3 mounting holes for the sensor are very close to the edge of the hole and in one case the hole is no longer complete so I'll have to think of some other method.

The sensor was originally mounted on a little brass plate so what I've done is used that brass plate and the existing holes in the steel base plate to position a much larger brass plate that bridges the 40 mm hole in the base plate. I made the brass plate much too large but roughly the right shape and drilled for the two M3 holes for the sensor, fixing the brass plate into place on the base plate through the sensor holes. I then drilled two more holes outside of the large central 40 mm hole and fixed the new brass plate with two additional M3 screws. That way I could guarantee that the sensor would remain in its original position.

And here it is fitting nicely. The three rotating magnets are quite different shapes internally, and only one fits this cam - and it fits firmly.

And again we have the rotor arm in place and the distributor base plate screwed down.

I've temporarily wired it up for the moment - the red wire goes to the positive feed on the coil and the black wire goes to the contact breaker side of the coil. It will need some PVC tubing over the wires and some better quality eyelets, and I'm waiting for some thermal paste to use with the sensor and the brass plate but it will do for the purposes of testing. 

Hopefully I will get an opportunity in the next day or two to start the engine.

Post script: I started the engine on the 13th May, loosening off the distributor and retarding the timing to get it going; the Hall Effect sensor made an odd buzzing or fizzing sound which made me switch off in a hurry to check the wiring. The wiring was fine; the sensor wasn't tight enough on the baseplate which seemed to improve matters. It's still doing it and it sounds thermal. With the engine warm I advanced the timing to more or less where it had been before and went for a test ride. It's certainly smoother.

A few weeks later, and it's all working fine. The battery seems to be remaining at full charge most of the time now, so it appears that the ignition system is drawing less current than it used to.

Winter Work on the SQ4

It's time to think about winter jobs on the SQ4. The W/NG is the go-to bike and with no chrome makes an ideal machine for the winter, so if I can resist the temptation to tinker with it I can get on with the SQ4 and still have a bike to ride. The SQ4 jobs are:

1. Fix the speedo and get the blurred dial replaced
2. Get a new slow-running screw for the Solex
3. Remove the indicators - I have decided to do this, because they look awful and because the indicators are regular tungsten bulbs and the load causes the LED headlamp to flash with the indicators. This is a bit disconcerting at night...
4. Upgrade the headlight again
5. Replace the front wheel bearings with sealed bearings
6. Replace the front inner tube which leaks slowly
7. Look at the brakes again as they bed in
8. Make a new tool roll
9. Fit a couple of transfers
10. Change the oil tank for the one with a good filler neck thread
11. Make a lower chain guard

I'll make a separate post for the chain guard. It's here.

But first, checking the bike over reveals that the horn doesn't work. A quick nose about with the multimeter reveals no supply at the horn, so we look at the 15A horn fuse. This is blown, and was probably too low for the horn so we will change it for a 20A. This works fine and consistently, so we will leave this for now. We'll also pull the indicator circuit fuse...

I've stripped out the headlight, in preparation for sending the speedo away, uprating the headlamp and removing the indicators.The speedo has gone to Russell at Chronometric Instrument Services for a clean, new springs and a new face:

And here it is, back again just over a week later:

Soundly packed with lots of bubble wrap

New face, all numbers in correct positions

Guarantee sticker on the back

New screws and nuts

Now we can put the headlamp shell back in place with new bolts:

This is the new headlight bulb and it's driver:

It's from CDRC, like some other bulbs I have bought and is their 5th Generation LED headlamp bulb shown here. Not cheap, especially as to fit it I needed an H4 reflector which I bought from Paul Goff as usual. It's the 7" Lucas reflector with a pilot bulb. The bulb is very nicely made - aluminium, powder coated black with nice elastomeric seals and good quality connectors. I've chosen a 6V bulb, so that I can keep the ignition & generating systems running at 6V.

The bulb fits into an adapter ring, which is provided with the bulb. This allows you to twist the bulb through 360 degrees, offering left, right or central dip:

Whilst the bulb looks quite long it appears to fit into the SSU700 shell quite nicely. The cable goes off to the driver box which I will mount in the bottom of the shell.

All done and back together:

One job that wasn't on the list was to fix the offside fork leg which sticks down over large bumps. I pulled it apart to find that it was actually sticking with maybe a third of its total stroke left unused, so now that I have eased some very tight new bushes I am looking for better behaviour from the front suspension! I checked the other leg while I had most of it apart, which moved freely.

Battery Carrier

This is about the carrier I am using to mount my gel batteries. Here are the batteries:

Now these will happily fit in the box, indeed they were chosen to do so. But because they are so short they will be a pig to get out, and I want to hide a fuse box and maybe some other wizardry in there. So, I have come up with this:

It's a simple carrier made from 18 swg cold rolled sheet; the batteries enter from one side and it is lifted out of the battery box by the two handles on top. The top deck is to carry the fuse box. I plan for the cables to exit through a slot in the upper inboard edge of the battery box:

So, now I have identified where the cables are going, I can cut a slot in the box. A coping saw and a half round file does the job nicely:



So next, final wiring and painting. I have used closed cell neoprene foam to cushion the batteries; painted with U-POL etch primer and black gloss, and wired in accordance with the diagram on the wiring page.

All that remains is to put the lid back on and look at sealing the lid.