Spark plug dilemma..

[en7jos]

So here's a dilemma for you with regards to which type I spark plug I should fit in my 1951 G3Ls 350cc single. I know this is a question that has been asked countless times already on this forum, but there is a twist this time so please bear with me! The twist is that none of the plugs that people elsewhere use are available here in India.

The manual says to use a KLG KE80 - a 14mm 3/4" thread length plus with a gap set to .015-.018. But no chance of getting one locally.

There are NGK agents so I thought no problem, I can just pick up a B7ES (seems to be most peoples equivalent plug of choice?). But they only have a very limited range of plugs here. The closest I can get is a BPR7HS which is wrong on count of the "R" for resistor (magneto ignition) and the "H" for short (1/2") reach thread. So NGK is out.

Similarly I can't track down anything vaguely equivalent in Champion such as a N3, N4 or similar.

The only big range of plugs stocked locally is the local version of Bosch which is called "Mico". This is what all the Bullets around here run. There seems to be two different numbering systems used. The ones sold for Bullets (and by default for any other old 350cc singles) are labelled "W-175-Z1" and "W-145-Z1". After much searching on the web I found an old Bosch catalog in German which said these were the equivalent of a NGK BP6HS or BP5HS respectively (or Bosch W7BC or W8BC in the other Bosch notation).

As you will have no doubt noticed, these are short reach (1/2" thread) plugs. This is what was fitted to my bike when I bought it and what all the local mechanics, owners and shops say are the ones to for my Matchless. On inspection last week I found the lower 1/4" of the plug hole thread was fully carboned up - not surprising hey! And so this is where my search for a more appropriate (i.e. 3/4" thread) plug started.

I have managed to find only one plug type which (in terms of physical size at least) seems vaguely suitable. This is a Bosch (Mico) "W8DC". From the Bosch catalog, the "W" is the thread size (14x1.25 - correct!) and the "C" is the thread length (3/4" - correct!). The "8" is the heat range, so three ranges higher than the equivalent NGK (NGK B7ES = Bosch W5C). The "D" means the centre electrode is projected 3mm rather than the standard 1mm, I'm guessing the equivalent of a NGK "P" projector plug?

So, in simpler (to me at least) NGK terms, I have the equivalent of something like a BP4ES I think. And that's the closest I can get!

I checked clearance with the piston and the projected central electrode is no problem. Obviously this is quite a hot plug relatively, so I'm prepared for fouling as it won't get up to temp to self-clean, especially as I'm going easy on the engine whilst running in a new piston and mostly only plodding around on short runs.

The engine was running reasonably happily on the short Bosch (Bullet) plugs so that at least goes to show that these engines will probably run on anything that fills the hole and sparks! But I've found starting is easier,tickover smoother at lower revs and theres less misfires with the longer plug.

Your thoughts and comments please? Any other owners out here in India found something better?

Cheers in advance, James Edited by - en7jos on 22 Feb 2011 08:12:06 AMEdited by - en7jos on 22 Feb 2011 08:14:39 AM

[GOLDSTAR]

can you not import a box of 10 plugs of whatever make you want direct off an internet site? kind regards

[en7jos]

Hi Goldstar. In theory, yes I could. In practice, the Indian postal service is not the best and I've only successfully managed to receive about 2 items of post from the UK in the last 18 months of being here!

I ordered some 6v and LED bulbs before Christmas which were posted across, but still no sign of them. I'll obviously go on a shopping spree when I go home next, but until then I need some temporary supplies.

India - the land where everything (and yet at the same time nothing) is possible! You've got to love it

[paul knapp]

quote: Obviously this is quite a hot plug relatively, so I'm prepared for fouling as it won't get up to temp to self-clean, especially as I'm going easy on the engine whilst running in a new piston and mostly only plodding around on short runs.

Other way around James!
The hotter plug will run hotter just plonking around, so is less likely to foul.

[en7jos]

Thanks Paul - useful correction. Too much time spent staring at various spark plug charts must have fried my brains!

So, if this is the case, it seems the plugs I have might be more suitable than I had initially thought for my plonking around the local lanes. I'll keep an eye on the plug over the next few weeks and see if there is anything notable going on in there...