Seagull Engine Construction Diary

Making a 10cc twin 4-stroke to the E T Westbury design


I have bought the Tim 6 kit, but have not done anything with it yet except peer at the little bits and scratch my head.

I have decided on twin-spark ignition and have bought a Minimag Novus 2 coil for the job. This system fires both plugs every revolution, giving a harmless 'wasted' spark, but avoiding the need for a distributor. It is only suitable for a 360° twin.

To trigger the ignition Hall-effect sensor, the two little button magnets need to be mounted in some kind of carrier. Rather than fix the carrier directly to the camshaft, I decided to make a ring, to be bolted to the camshaft gear, and to surround the camshaft gear retaining nut, thereby minimising the overall length of the assembly.


2013-06-22 - Making Plug Washers

Having put the plug holes in the Cylinder Heads, I found that the copper washers supplied with the plugs were too big to fit the 516″ diameter seatings. As a 'warm-up' job today I made some washers out of 516″ thick-walled copper pipe. Initially, parting them off left too much of a burr to deal with easily on such a small part, so I made a steel mandrel to fit inside the tube and parted some more with this in place. I found they needed a shave turning off the outside as well. After rubbing the faces and cleaning up the bores, I annealed them by putting them all between two small steel plates and heating the whole lot up to red.

2014-01-04 - Starting the Timing Ring

I sawed out a square piece aluminium alloy, large enough for the ring and a chucking piece, and turned the face and diameter of the ring. (1 hour)

2014-01-04 - Completing the Timing Ring

First, I bored the ring to fit on its shoulder on the timing gear (0.5315″), chamfered the edges and parted off. Next, I set it up in the 3-jaw chuck with soft jaws and card protection, and adjusted the Griptru chuck to ½ thou, faced it to length and again chamfered the edges.

In transferring the chuck and job to the dividing head on the boring table, I re-checked the truth, and as the DTI was reading nearly 2 thou out I decided to reset, but could not get better than ½ thou. In clocking the ring on the spindle centreline I found it was about 0.006″ low, but this will make no material difference to drilling the holes. The holes cannot go right through without drill into the chuck jaws, but they can be drilled part way and finished in the drilling machine. I carefully countersunk the four 2.3mm holes for the 8BA mounting screws almost to the edge of the ring, as it is important that the screws heads fit flush. I drilled the two pockets for the magnets 116″ through, to allow a pin to be put in from the back to eject the magnet if it ever becomes necessary. The pockets proper were cut 18″ diameter by 116″ deep with an end mill. There is also one 116″ hole for a dowel pin to ensure the correct timing. The holes were finished all the way through in the drill press.

The fit on the gear is a bit tight but it will be OK. The bought countersunk screws do not fit flush and will need doctoring so they do. I cleaned the job up, and fixed the first magnet (from the Howell kit) in place with Loctite bearing retainer (641). The extra magnet turned out to be only 1mm thick instead of 116″ so I made a brass washer to fit the pocket, 0.022″ thick and glued it in place, followed by the magnet. Idiotically, I had failed to check the diameter of the second magnet. It was a very sloppy fit. It must be 3mm diameter. I don't think I could be sure it would stay in place, so something will have to be done. (2¾ hours)

2014-03-01 - Reworking the Timing Ring

I emailed Kirk at Hemingway to explain there was a problem. He thanked me for making him aware of it, and sent a new 18″ by 116″ magnet. Using a little piece of 116″ silver steel as a drift, I knocked the undersize magnet out of its pocket. The spacer was more firmly fixed and would have to be machined away. Initially setting up on the hole, I could not make sense of the dial readings, but eventually concluded there was a residue of Loctite in the hole. Once I had cleaned it out it was much easier. Clocking up a 18″ hole is one of those jobs where it is worth fitting the smallest diameter ball probe on the DTI. Once set up, it was easy to machine away the spacer with a slot drill. Finally, I cleaned the parts with Loctite cleaner and glued the new magnet in place, having double-checked its orientation with a compass. (1½ hours)

2017-11-25 - Temporary Preview for HSEM forum


2020-05-24 – Electronic baby steps

This evening I connected the tacho output of the fan to an Arduino Uno microcontroller, which gave me a speed output of 3300, once I had debugged the program. This is the first time I have progressed beyond Starter Kit projects with the Arduino.

2020-06-07 – Fan Control

Here I am controlling the fan power with a relay, and its speed with a pulse width modulated signal from the Arduino. A potentiometer provides a variable input voltage to simulate a temperature sensor.

The PWM signal involves some messing about with the internal settings of the Arduino's processor chip because the fan wants its input at 25kHz, and that is much faster than the Arduino's default. The manual for the processor runs to about 650 pages, and I had take my socks off to fathom out enough of the 18 page section on setting up the one of the internal timers (not the clock, but based on it) for 'Fast PWM'. There is also plenty of help on the various Arduino forums. The 'registers' involved go back to defaults after a reset or if the Arduino is powered off, so there is no great risk.