What spark plug

[willowbedone]

Modern petrol and ethanol has an effect on what plug to use .I think it's a matter of try one and see

[spookefoote1956]

Has anyone tried those three point plugs by champion. Champion N9BYC

plug 3 point.jpg

[dave16mct]

not tried one but it may be a good one to try in my 18CS which has the slot type sparkplug hole. I'm using a Champion N9Y at the moment which I modified to a side firing type. Seems to work OK. Probably a bit soft for the CS but I'm still running it in
Dave

[Taid]

Showing my ignorance .. what's a 'slot type' hole?

[dave16mct]

Rather than putting the sparkplug right into the combustion chamber it fires through a slot. Makes it harder to start!
Dave.

[Taid]

Thanks D.

Never seen that before, but do recall, back in the 60s, reading about an engine which had a separate ignition chamber and the main combustion chamber. As I recall, the small ignition chamber had a rich mixture and the main chamber had a weak one .. can't recall the name but something like 'aerated' comes to mind .. is this slot system something similar?

[clive]

No the slot rather than full circle for the spark plug is because the inlet (and exhaust?) were increased in the CS models and a full circle would have impacted on the valve seats.

[spookefoote1956]

I've ordered one and will report back

[dave16mct]

No that sounds like the Puch 2 stroke split single. I think this slot type combustion chamber design may be because of the valve angles positioning them close together. If you look there doesn't seem enough room for a spark pug to fit. It's a central plug and the earlier angled type would've been to one side. It does start very easily on the rollers!
PS just read Clive's reply, yes the valves are very big!
Dave.

[Taid]

It seems it is now called 'pre-chamber' ignition .. a separate small chamber has the spark plug and when ignited flames pass through small holes into the main combustion chamber, rapidly igniting the fuel mix in there .. Maserati and Honda are playing with it and some F1 engines have it ..

Can't find any reference to what I may have been reading those years ago ..