Extended nose spark plugs

[Rummers]

Hi everyone I am a fairly new member so hello everyone!
Can I use extended nose spark plugs in my 67 A50?
I have looked before posting but couldn't find a definitive answer
Any guidance would be appreciated
Regards Dene

[DAVE BRADY]

Hi Dene,

Depends on what do you mean by 'extended nose'?
Plugs are usually short reach 1/2" or long reach 3/4" and there are longer ones that tend to be smaller diameter.  Your bike would use a long reach plug.
If you have a plug that is longer then there is the possibility of it fouling the valves or even the piston even if it is just the insulator and electrode.  There is also the possibility of the electrode becoming too hot and acting like a glow plug and messing up the timing.

Dave.

[Oily bloke]

I think you are referencing 'protruding nose' plugs.
NGK for example produce a B7ES (Std plug) and a BP7ES and a B7HS and a BP7HS where the plug anode and cathode are extended a few millimeters into the combustion chamber as apposed to the length of thread into the head.
I stand to be corrected but I think it unlikely, unless specified, that a protruded nose plug will be suitable. It would normally be prescribed where the combustion chamber shape and heat range would benefit it's use. a vintage bike for instance where the compression is low and the clearance is plenty, giving the spark further in can aid primary ignition. The nose of the plug would run hotter and will, obviously, extend into the chamber.
My S29 sloper has a P plug for that reason. An A50 may not have the clearance to run such a plug.

[Allan G]

An A50 with 9:1 pistons will take an extended electrode. The higher compression pistons have a much bigger dome.

[TTJOHN]

I have several new extended nose plugs but thought that they were mainly used for cars.

[EDDIE SIMPSON]

i tried extended nose spark plugs in my youth and they made my a10 sound like an unsilenced tractor but went really well. almost like a racer. classic race bikes probably use them but it was the noise that put me off. if your head has leaky guides i ve read they are less likely to oil up due to being away from any surface where the oil runs.

[Rummers]

An A50 with 9:1 pistons will take an extended electrode. The higher compression pistons have a much bigger dome.

thanks - mine actually has the low comp 7.5 pistons so this should be OK I would think