VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Spark plug question

From the distributer question guy! Motor is a 52’ 235, fresh rebuild, everything seems good but still runs rough, as before. I put the same plugs back in so I thought I’d start there. In the Chev of 40’s catalog they list a 10mm and a 14 mm, how is this
Measured, the reach, from the shoulder to the outside of the rim, or is it the diameter the threads?
If reach, mine has the 10mm and according to the catalog it should be a 14mm?
Carb may be a problem as well, took it apart last summer and couldn’t tell much difference when it was the old motor.
Problem is intermittent missing under light load and at steady throttle.
Thanks again, great having this forum here to get advice,
Dan

10mm/14mm is the hole size. My '48 has the smaller 10mm while a '52 head used the 14mm hole size.

All 235 engines from 1949 and up has 14 MM spark plugs as did all 216s from 1949 and up.

Engine runs ruff-valves adjused too tight or intake manifold vacuum leak.

I’m confused, which don’t take much. My plug threads measure right at 10mm, according to the # on head it is a ”˜52 235 head, which according to the above posts should be 14mm.
What am I looking at wrong here?

14 MM is the diameter of the threaded part not the length.

The first number in a sparkplug designation indicates the thread size. 44's 45's, 46-5, etc. are 14 mm. Ford used 84,, 85, etc. indicating 18 mm. According to the earliest AC Sparkplug catalog I have dated 1956, all 1933-40 used 14 mm plugs; 1941-48 used M-8 which is a 10mm plug; 1949 up used 14 mm. heat ranges varied through the years.
Jeff

Oops, disregard last post, my plugs are 14mm! Think I’ll take another look at the timing?

1941s used AC 104s as well as M8s.



Under group 2.270 in my 1929-1950 Chevrolet parts book is shown, in part, the following 1941-48:

All...No. 104 (10 MM) Standard equip. on trucks. (alum oxide insul. sustained high speeds on pass. Part No. 1557801

All...No. M8 (10 MM) Standard equip. on 1946-48 pass. (alum. oxide insul. sustained low speed on trucks Part No. 559459

All others from 1929 -1950 listed:

1929-31 All...No. 87 (18 MM)
1932 All..No. 86 (18 MM)
1933-40 All No. 43 (14 MM)Heavy duty operation st med. or high speed.
1933-40 All No. 44 (14 MM) Ditto on speed and operatios
1933-40 All No. 45 (14 MM) Average operations
1933-40 All No. 46 (14 MM) Average operations
1949-50 All Pass. 46-5 (14 MM)
1949-50 All COMM and UtIL. 44-5 (14 MM)

This implies that 104s were used for 1941 and 1942 passenger whether low speed or high.

I assume that all the above were AC spark plugs.

Best,

Charlie

The 1941 pars book shows the AC 104 as being avaiable with either aluinum oxide insulator or porcelain insulator and the "hotter" 106 with porc. insulator.
After the new and improves M-8 came out in 1946 they were used for replacment in 1941 and 1942 engin
Engineering in 1941 indicates that the Porcelain plug was used in production.

The 104 and 106 had a short life and the M-8 was a little better. Packard and Buick also used those crapppy plugs back then.