Best Spark Plugs

[Terryb]

Hi All, I have a 1955 A7 SS, which I have been using N4C plugs. Now I know that the original hand book quotes champion L10, which aren't easy to get hold of. What do you guys use or could recommend?

[morris]

Seems to be a general consensus on either NGK B6HS or Champion L82C. Both widely available.
Both mine run happily on NGK

[RDfella]

Is this an alloy head? If so it needs a long reach plug - N4C would seem right. The ones morris recommends are short reach.

[morris]

Is this an alloy head? If so it needs a long reach plug - N4C would seem right. The ones morris recommends are short reach.

Right. A7SS. Forgot about that

[Rgs-Bill]

   Let me classify this statement,  this comment is for U S of A made N G K  plugs.  All of the major plug manufacturers have stopped putting the porcelin down inside on the insulator because the modern cars do not have a flooding problem, they are almost all fuel injected.  If you over tickle your BSA, getting too much gas in the manifold, and soaking the insulator, it is the same as flooding the carby.  What works best is (for my bike that is )  the BOSCH W8cc, and the Champion N-4's.  Just about every 3rd  U S made plug in  NGK is duff right out of the box, they just have no quality control any longer, they got the name and the corner on the market, then they cheapend the HE** out of them to get Richer.  Keep in mind that the U S Bosch at least, I have found that they cross over at least 1/2 of a heat range colder than the NGK crossover chart.  In other words the  B 7 ES would be the Bosch W8cc.  Now that is not for gospel, but the way they operate in my bike, your bike may have combustion different than mine so do not quote as the gospel, every bike will react differently

[RDfella]

Terryb, I forgot that your opening request for info stated that your plugs should be L10. L10 are short reach plugs. Generally speaking, short reach are used in cast iron heads, long reach in alloy heads. Don’t get them mixed up! If you put a long reach in a short-reach head, likely the piston will hit the plug. If not, you’ll get carbon on the plug threads that protrude into the combustion space and you’ll never get them out again. If you put short reach in a long reach engine it’ll work BUT, the cyl head threads not occupied by a plug will carbon up and you’ll not be able to fit a long reach plug later unless you clean the head threads first with a plug tap.