Spark Plug cross reference

[pint4]

I just pulled a plug from my 33 Buick and printed on the side is "AC86". I am guessing these plugs are no longer available-maybe I am wrong. Is there a cross reference for this plug or modern replacement?

Thanks.

Bob

[mlander]

The plugs you have are made by General Motors AC-Delco division the ?8? indicates an 18mm thread size and the 6 in an indication of the heat range. Your car probably had H-9 or J-12 according to my 1932 Buick CD by Detroit Iron. AC changed the designation in the 1930s to the now used 8 for 18 mm, 4 for 14mm and 7 for 7-8? threads. To the best of my knowledge AC does not make ½? NPT nor can I find an NGK plug in the series that has an 18mm by 1/2" reach sparkplugs. You should not have any problem finding plugs for your Buick the only thing you have to watch is it the proper Heat Range.

If you wish to know more about the old spark plugs you can go

http://www.antiquetractors.com/Research/Spark_Plug_List.htm

I believe tha the plug new designation is C86 or maybe a C86S which would have an extended core nose.

One must remember always that such things as sparkplugs are still used in tractors, earthmoving equipment etc that are no longer used in automobiles.

18mm by

½? reach

CHAMPION

D6

D9

D14

D16

D18

D21

D23

D15Y POWER TIP

D18Y POWER TIP

DELCO AC

C81

C82

C83

C85

C86

C87

C88

C85S POWER TIP

C86S POWER TIP

AUTOLITE

373

386 RESISTOR

388 RESISTOR

3116 POWER TIP

Yours, M. L. Anderson

[mlander]

From an old GM AC 1945 sparkplug chart and the Buick section only.

1945 issue Passenger cars --1924-1942

First 8 denotes the 18mm series, second number denotes the heat range

and since there is no letter after the second number it has a 1/2" reach.

1929-30...................AC-88

1931 thru 1937..........AC-86

1938-39-40-41-42.... AC-46

Also at this time there was

a big fiasco on the 10mm plug!

According to the Buick book by

Automobile Quarterly, page 226

thru 227 which explains the

problem and its cure by Buick.

This was to drill out the 10mm

sparkplug holes and retap them to

14mm and use the 14mm plugs

numbered AC-46.!

According to my 2005 NGK catalog the AB-6 sparkplug has a reach of only

3/8" whereas the proper reach for an AC 86 is 1/2" or a 1/8" difference a

decimal equivalent of .125". The AB-6 is for a Champion "J" series sparkplug!

M.L. Anderson

[Guest]

A number of years ago I started using NGK AB-6 plugs in place of the the champions that were a replacement for the AC 86 that my Pontiac was supposed to have. I found them twice as good as the AC or Autolite or Champion. I used to have to regap and clean my plugs about every 8,000 miles and replace them at 10,000 miles. The NGKs go 24,000 miles, about two years driving for my daily driver and have never given me any trouble. I am now on my fifth set.