Champion 4K spark plug question

[redpackman]

I have a Champion 4K 7.9 hp engine from ’48-49. Runs pretty good. According to the spec sheets I’ve seen it was to take a Champion 7 plug. Well that plug is no longer made. When I inherited it from my father-in-law it had Champion 9 plugs in it which seem to work pretty well. From you old time plug experts, what’s the difference between these plugs?

[frankr]

By my old plug chart, 7 is replaced by D9 and 9 is replaced by D21 Or in other words the numbers in order of heat range (hottest first) are:

D23
D21 (old 9)
D16
D14
D10
D9 (old 7)
D6

[redpackman]

So, if I understand you right, the D9 is a direct replacement of the old Champion 7 plug?

[frankr]

Yes, but I didn’t go the next step and see if they still make them. The wire nut (or possible lack thereof) on the end might be a problem

[westwind]

You should be able to still find Champion D9, I think I found them at a Farm Equipment store.

[redpackman]

The D9 plugs I have, actually a D9F I believe, does have the wire nuts. so all is well there. Thanks.

[jcrigan]

The plugs now go by the numbers 509, or 516, etc when ordering. The people at our local auto parts store get confused if you ask for a D-9, or a D-16 plug now.

[wiscoboater]

The folks at my local auto parts store get confused no matter what plugs I ask for. I gave up with those "cross referencing" kids working the counter. I just order from club vendors now.

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