1927 DB fast four

[1927DB124]

what is the proper spark plug

[Minibago]

The correct spark plug C76-S is no longer made and each brands discontinued line’s replacement (which has happened many times over the years) is not quite the same, not easily available and rather expensive.

 

As Roger Hartley says,

“There are now more opinions on suitable spark plugs  than there are brands”.

 

I like and use the W-89D which I buy in bulk from the UK to share on tours with members having trouble, with some success.

[1927DB124]

to my surprise the champion listing in Canada has no listing for C26 but C4 is still available at Car QUEST

[Mark Gregush]

C4 would be the Model A Ford plug, which is why they may still list it. So you know, there are other plugs such as Motorcraft, that might be lower cost and would have the same fit. The C4 had a little extra reach between the thread and end. You can also buy adapters to use 14mm plugs. That would allow you to try different heat ranges. 

[Minibago]

Having the same fit, thread size and reach is important as is the heat range.

An issue I found in Australia is that the easily obtained plugs are one or two levels colder, e.g. the AC plug equivalent is the 3077, the AC plug commonly available is the 3076.

In my experience some cars are okay with whatever is a available but folk who have mentioned “hard to start”  “rough running” over a cup of tea have seen a dramatic change when a set of W89D’s are offered for a “try before you buy”.