Electrical

Spark Plugs


Spark Plugs

Spark plugs come in many different shapes and sizes. The information here relates to spark plugs manufactured by NGK which are suitable for Vespas and Lambrettas. There are two basic types used on classic Italian scooters. The main difference between the two types is the reach of the threaded section into the combustion chamber. The use of a long thread type plug in a short thread head may allow the plug to touch the piston head at top dead center which can cause serious damage.

 


To the left is an example of a short reach plug - NGK plugs are classified with the following numbers and letters - Example B7HS

B: Indicates 14mm thread diameter in the cylinder head. This diameter is used on all Vespas & Lambrettas

1-9: Indicates temperature (1 Hottest - 9 coldest).

H: Indicates 12.7mm thread reach (approx 1/2")

S: Standard electrode

This type of plug is used on most older bikes before the Vespa Rally 180 and is NOT used on Lambrettas - but double check your plug type before fitting any plug.




To the left is an example of a long reach plug - NGK plugs are classified with the following numbers and letters - Example B8ES

B: Indicates 14mm thread diameter in the cylinder head. This diameter is used on all Vespas & Lambrettas

1-9: Indicates temperature (1 Hottest - 9 coldest).

E: Indicates 19mm thread reach (approx 3/4")

S: Standard electrode

This type of plug is used on most newer bikes after the Vespa Rally 180 and all Lambrettas - but double check your plug type before fitting any plug.

Full NGK plug codes

Below is a full list for anyone who might want to mess around with plugs for different applications. Click the mouse over a part of the example plug code to see the options and click again to close the window.

 











 
Thread size
A: 18mm
B: 14mm
C: 10mm
D: 12mm
J: 12mm
 
Construction
C: Hex size 5/8"
K: 5/8" projected tip (ISO)
M: Compact type
P: Projected insulator type
R: Resistor type
U: Surface or semi-surface discharge type
Z: Inductive resistor
Letters can be combined

 
Heat
1: Hot
through
9: Cold
 
Thread Reach
E: 19mm (3/4")
F: Tapered seat
H: 12.7mm(1/2")
L: 11.2mm (7/16")
 
If there is no number then standard is:
18mm thread size: 12mm
14mm thread size: 9.5mm (3/8)
 
Electrode Construction
A: Special design
B: Special design for Honda CVCC
C: Low angle ground electrode
G: Fine wire nickel alloy center electrode
GV: Gold-palladium center electrode Special construction of V-type Racing use
H: Partial thread
K: 2 ground electrodes (Toyota / BMW)
L: Half heat range
LM: Compact type for lawn mower
M: 2 ground electrodes for Mazda rotary engine
N: Special side electrode
P: Premium platinum
Q: 4 ground electrodes
R: Special ground electrode
S: Standard 2.6mmų center electrode
T: 3 ground electrode
U: Semi-surface discharge
V: Fine wire gold-palladium center electrode
VX: High performance platinum
W: Tungsten electrode
X: Booster gap
Y: V-grooved center electrode
Z: Thick 2.9mm center electrode

 
Gap
-8: 0.8mm (0.032")
-9: 0.9mm (0.036")
-10: 1.0mm (0.040")
-11: 1.1mm (0.044")
-13: 1.3mm (0.050")
-14: 1.4mm (0.055")
-15: 1.5mm (0.060")
-20: 2.1mm (0.080")