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Spark plugs
S U P P L I E D B Y
S P E E D E X
L U T O N
Original specifications usually came from the makers catalogues or from ones recommended from experience. Get in touch if you can fill in gaps or heads not listed here. Be aware that the wrong grade plug can be awkward to suss out. Too hot a grade will burn and eventually not fire, the insulator will be a grayey white colour. Too cold will foul and misfire, similar to an oily engine though with a dry black appearance rather than wet and oily. These can look very similar to a weak or rich mixture—so you start fiddling with the carb as well just to compound the problem!
Some useful websites that could help if you need it;
· All you need to know about plugs on this site
· Cross references between manufacturers (seems to be more for currently available ones though)
As a general guide the following table appeared in the February 1960 750 Motor Club Bulletin. It suggested that the plug grades were transferable across different heads, even to similar side valve Ford heads. If nothing else it gives something to start from. Modern equivalents will have a wider heat range so it shouldn’t be as much of a juggling act as it was then.
|
HEAD |
Original Spec plug |
Available alternatives |
|
A7 ‘37-’39 cast iron 14mm plugs |
KLG F50. Champion L10 |
Champion L86C or L90 NGK B7, B6HS or B7HS, oily engines try B5HS
If drilled for 18mm plugs try Champion B16 or B21 |
|
Early ALTA with inclined 18mm plugs |
Champion R1 or KLG 246 |
|
|
Later ALTA with vertical 14mm plugs |
|
|
|
SPEEDEX |
Champion N8, KLG FE70 or Wipac P40L for road use. KLG FE100, AC FL7, Lodge 3HLN or CLNP, Bosch W260T2, or Champion N3 for racing |
Champion N8, or N5C. NGK B7ES |
|
SUPALOY |
KLG F70, Wipac P4 or P6, AC F10, Lodge CN or HN, Champion L10 |
Champion L86C, NGK B6HS |
|
DANTE |
Wipac P40L |
As per SPEEDEX |
|
CAMBRIDGE-plain |
|
|
|
CAMBRIDGE—finned |
Lodge CNY |
Champion L92Y, NGK BP5HS |
|
|
Plug Grade |
Soft |
Soft—Hard |
Platignum pointed |
Medium hard |
Hard |
Very hard |
|
|
|
Road work |
Road, occasional race |
Racing some road |
Racing some road |
Racing only |
Racing |
|
|
Wipac |
P40L |
P60L |
- |
- |
- |
- |
|
14mm |
KLG |
FE50 |
FE70 |
PFE50 PFE70 |
FE80 |
FE100 |
FE220 |
|
3/4” |
AC |
FL9 |
45XL |
- |
- |
FL7 43XL |
- |
|
reach |
Lodge |
CLN CLNH |
HLN |
CLNP HLNP |
2HLN |
3HLN |
R47L |
|
|
Champion |
N8 |
N5 |
- |
- |
N3 |
- |
|
|
Wipac |
P4 |
P6 |
- |
- |
- |
- |
|
14mm |
KLG |
F50 |
F70 |
PF50 PF70 |
F80 |
F100 |
F220 |
|
1/2” |
AC |
F10 |
- |
- |
42 Com |
- |
- |
|
reach |
Lodge |
CN |
HN |
CNP HNP |
2HN |
3HN |
R47 |
|
|
Champion |
L10 |
L7 |
- |
- |
L5 |
- |