Spark plug resistance and 2 open circuit?

[TVR Beaver]

Has anyone ever measured or know what the plug resistance should be?.. .reason I ask is that I pulled mine out last night and checked the electrode to nipple resistance…. Some of the nipples were loose before I did this so tightened them up first…
The readings I got were as follows

1 x 0.4 Ohm
4 x around 20 Ohm
1 x 50 Ohm
2 x Open circuit

I was initially concerned about the two open circuit ones but them thought it was on the HT side and like the dizzy cap / plug gap etc… the current will just jump across?..
Anyone else found this at all or measured resistances?
(I’m running NGK B7ECS plugs BTW with about 4000 miles on them)

[blitzracing]

Those are non resistive plugs, so they should be near 0 ohms between connector and electrode. The HT may well punch its way through an open circuit, but its not correct.

http://www.1stautobulbs.com/webimages/plug_cross_s...

Are you sre your test meter is really making a good contact to the metal, not any oxides on the tip?

Edited by blitzracing on Wednesday 8th September 12:26

[TVR Beaver]

Yes,, made sure I dug the point in... If you look at the top it's a ali cover that goes over the electrode that runs thru the plug.. thats where it must go open circuit?.. may be a bit of build up that stops the meter seeing it?.. I'm sure when 50K volts goes thru it (or what ever the voltage is) it won't be a problem.. but did think it was strange??

[blitzracing]

The conductors about 2mm diameter, so how it goes O/C I dont know.

[TVR Beaver]

I agree?... but they probably build up ali oxide over time (which is a good insulator) and then don't work with a meter... as I say, I'm sure 5000 volts will get thru as they are a good colour (except 1!) and obviously fireing okay... Think for £3.50 I'll replace them anyway...
There must be 2 joints, one at the top and one at the bottom as the electrode tip is some other material?... Try some old plugd your end see if they are the same... got to say it's something I've never tested before...
.
You know the problem is having too much equipment to do these tests... compression testers etc... if we didn't we be blisfully un-aware of any of these issues!!!

[Simon says]

5000 volts you sure?

[TVR Beaver]

Simon says said:

5000 volts you sure?

No.. but I still wouldn't stick my finger in!!

[chris52]

TVR Beaver said:

Simon says said:

5000 volts you sure?

No.. but I still wouldn't stick my finger in!!

Volts at a spark plug can be anything from about 30,000v up to as much as 100,000v


Chris

[Simon says]

TVR Beaver said:

Simon says said:

5000 volts you sure?

No.. but I still wouldn't stick my finger in!!

He He bright spark

[TVR Beaver]

Many years ago… I witnessed my friend messing with his BSA and the throttle getting stuck wide open… So he immediately pulled of the plug lead… Unfortunately for him…. It then earthed thru him for what seemed like 5 minutes until the engine eventualy stopped… he couldn’t let go of it!!..Then the bike and my friend literally fell to the ground!!... He was not a happy bunny for a few hours!!

Edited by TVR Beaver on Thursday 9th September 08:11