The spark plugs on my 1951 Series I 2.0-litre oil up: would hotter plugs or opening the plug gap cure it? I have KLG plugs fitted. The bottom of the plug recesses are oily, although I screw the plugs in tight. The Land Rover is only ever used for very short runs.
S Skase, Lincoln
Short runs don’t allow the engine to reach operating temperature and can cause plugs to oil up, although there are other reasons for oily plugs, one of which is bore wear. A garage could do a compression check if you’re worried – 120psi is healthy for a good engine. If pressure is down on one cylinder, expect that cylinder’s plug to foul up sooner.
Another way to check for bore wear is to clean the plugs, then do at least an hour’s hard driving and recheck them. If cool running is your problem, the plugs will still be clean. To raise the temperature, consider blocking off part of the radiator or removing two of the four fan blades – but that risks overheating in warm weather.
I looked in Series I literature for plug specifications. Mostly, plug make and type isn’t specified, but where mentioned is either Lodge CLN or HNLR. Plug gap specs show ridiculous variation, from 0.45mm to 0.80mm. These variations don’t even seem to match up with different versions of the engine.
Rover-published information looks suspect to me, so I checked with Tim Green at Green Spark Plug Co, a leading supplier of oldtype spark plugs. Tim is sure your KLG plug will be the B6ES version:
‘A lot of people recommend them but they’re too cold for a Series I – that’s probably why the plugs are oiling up.’
The second letter of that fourdigit code refers to the plug’s heat range (note: different makes of plug have different codes). Tim recommends a KLG B5ES, which he says is right for a Series I in normal operation. Try this first. If you still need a hotter plug, try a B4ES – but that could be too hot if you go for a long thrash, maybe causing pre-ignition.
Adjusting the plug gap away from specifications won’t cure oiliness. Tim suggests the gap should be about 0.60mm (also, 0.60-0.65mm is the value most often quoted in Rover literature).
Oil in the recesses is likely due to over-tightening. The washer under a plug deforms when the plug is tightened and is supposedly a one-time-use item.
Most people re-use them, though that’s not good practice. I didn’t find a definite figure for torquing the plugs (if anyone has it, please let me know) but the standard technique for 14mm plugs is: with clean plug and cylinder-head threads and a trace of lubrication, screw in until finger-tight, then tighten a further half turn. Just nip the plug washer firmly – don’t over-do it.
Plug washers (10 for 99p) and the plugs mentioned (£6.68 for a set of four) are all available from Green Spark Plug Co (gsparkplug.com, 01477 532317).
This workshop advice appeared in the January 2016 issue of LRO. Back issues are available to download on digital devices here.