Spark plugs

[morrisminor]

I've bought some champion d21 for my 34 Rp , does the extra length matter
The Old ones are ngk a b 6

[John Cornforth]

Hi

The information I have suggests that original Champion No 7 plugs had a 1/2 inch reach. The D21 is also listed as 1/2 inch reach

I don't have a LC head to hand, but the thread in the head shouldn't be too different to this.

[John Mason]

morrisminor, I tried to count the number of threads on each plug from your photograph but my eyesight is not what it once was. The Champion only look a tad larger. If they are the same thread screw them in then with the IGNITION SWITCHED OFF turn the engine over on the handle to see if they catch the piston crowns. If there is any signs of catching stop there and remove them, if the engine turn freely switch on and see how it runs.

John Mason

[Reckless Rat]

It's not likely to make any difference. On the low compression head there's a big clearance between the spark plug and the top of the piston at TDC so no worries. On this head of mine the 18mm plugs don't go all the way to the bottom of the thread anyway:

[morrisminor]

Thanks Reckless