Distributor for Seagull 10cc Engine

[achtenhagen001]

Hello everyone,

I have a few questions regarding the seagull ignition setup and distributor setup. I have recently acquired an almost complete seagull engine, however the distributor cap was missing. The setup I have on my timing case end is as follows: there is a casing that contains the contact-breaker as well as the cam (which has two breaks on it), these two items are both mounted on the camshaft which is at half engine speed. The rotor then mounts directly onto the camshaft in front of the contact-breaker and the cam. I have been trying to find this particular setup with no success.

What I have been able to understand so far is that the engine is a 360 degree twin, meaning that both pistons are moving up and down at the same time, one would be at the compression stroke while the other one is at the exhaust stroke. Would that mean also that each spark plug would have to fire 180 degrees apart? If so will my ignition setup on the timing end work? I have not found an example yet where the contact-breaker and the high tension distributor are mounted on the same camshaft. Westbury does have such an example for the 4 cylinder engines. I am having a hard time understanding the timing here, since the distributor is at 1/2 engine speed. Any clarification as well as a wiring diagram would be highly appreciated. 

[Jo]

You need to make yourself a distributor cover with two HT pick ups. This is the one Graham Meek made for his Seagull:



And a picture of the distributor on Graham's engine once together:



Graham's is a very posh version of a Seagull, more agricultural looking versions are equally effective 

Your distributor/rotor is designed to have a cover (plastic or Delrin) with two brass pins to make contact with it as the engine rotates. I have attached the one fitted to my Wall engine.

I have attached the wiring diagram for the Seagull.

Jo

[achtenhagen001]

Hi Jo,

thank you very much for the fast reply. Looking at the wiring diagram, I see that the cam is at engine speed and not at the 1/2 engine speed. Sorry for asking about this, but does it matter at what speed the cam is driven at? I am fairly new to this and just want to make sure I fully understand. I do have some bar stock of delrin that I can make into the cap with the necessary contacts.

[Dave Otto]

Your breaker points are driven at half speed along with the rotor, that is why it needs two lobes because it needs to open the points once every revolution of the crankshaft. The only way the wiring diagram that Jo shared would be correct is if the breaker points were driven from the crank. Maybe some versions of this engine were this way but yours is not.

Dave

[achtenhagen001]

Thank you very much dave, that really clears it up, I had somewhat of a similar idea before and now it all comes together. Again really appreciate the help.

[Jo]

That is Westbury's original wiring diagram and I think it is a confusing: Top Right it says distributor 1/2 engine speed, in the middle it says the contact breaker goes at engine speed this is because of the two lobes on the cam.

Jo

[Charles Lamont]

If you use a wasted spark system, you don't need a distributor. Both plugs fire every crankshaft rotation. You can either use two coils or a purpose designed twin spark coil such as the Minimag Novus 2. I dispensed with the contact breaker on my Seagull and used a hall sensor instead, with two magnets on the rotor. Photo shows hall sensor and terminal block inside the "distributor cap".

[achtenhagen001]

So I’ve been looking at the plans again and reading up on the different systems and I think the original drawings by Westbury work if the cam is on the crankshaft. This would mean that every 360 degrees the contact breaker would open once and fire both plugs at the same time, this would be know as a wasted spark. This setup does not include a distributor. If the cam is mounted on the camshaft it would require two cam lobes since it is rotating at 1/2 engine speed. A cam with only one lob rotating at 1/2 engine speed would need 4 revolutions and that with a twin cylinder wouldn’t work. This would only work if the cam was mounted on the crankshaft and had one lobe. I think I got it right now although I could be wrong. I know that this engine ran before with this setup, however the seller does not remember what the distributor cap looked like.

Charles I have thought about using that type of ignition but I prefer to keep it with a distributor setup, I know that makes things unnecessarily difficult but that’s normally how I do things. I am actually at the time of writing this building anothe seagull from castings and used your treasure trove of knowledge as a starting point and cannot thank you enough for sharing that with us. Really appreciate it.

[Jo]

The distributor cam as drawn has two flats/lobes on it. Looking at your photograph - so does yours.

Jo

[Charles Lamont]

Thank you for those kind words, achtenhagen001, though I am not sure about 'knowledge'. I really must try to bring it more up to date.

The wiring diagram above is for the 1831/Wallaby engine. For the Seagull, Westbury recommends use of a twin-spark coil, which is presumably why he does not provide any drawings for a distributor. This is from the Seagull articles: