Spark Plug Confusion! Need some help figuring this out.

[johnwbechtel]

Good Morning. I have a 1941 Studebaker Commander - 11A B3. Seems to have original motor but who knows after 75 years. Where the engine number is supposed to be it was really rusted and even after steel brushing I can't even come close to seeing the engine number.
MY PROBLEM: I recently ordered some spark plugs off of RockAuto.com. Autolite 306. Seemed like a good deal so I ordered a dozen. Unfortunately they were 14mm size and not 18mm that I need. Trying to do some internet research to figure out if the plug is right and I have a non-original engine OR the plug is wrong and the engine is right.
What is the right plug? How about some cross reference alternatives?
I'll probably just end up ordering them from Studebaker International.
Any advice and wisdom is appreciated.
John in NJ

(I put this on AACA Studebaker forum also)

[Bud]

According to my latest Champion spark plug catalogue, all 1941 engines should use a Champion J8 or Autolite 295 plug which is 14mm. Engines from 1940 back to 1933 use a Champion D16 or Autolite 376 plug which is an 18mm plug. It sounds like the engine in your car or possibly just the cylinder head was replaced sometime in the past with parts from an earlier car. Bud

[johnwbechtel]

Bud - thanks so much. I am going to assume that a 18mm size 1940 (and before) Commander Six spark plug is close enough in heat range to a 14mm 1941 Commander Six spark plug that it will be an OK exchange. (that is assuming that it is the original engine and just had the head switched out). If it is actually an older engine then I'm in like Flint. Thanks again.

Any one know for sure that Bud's theory could be correct. That is that I could have a 1941 engine and a pre-1941 head on the engine. Does it bolt up the same?

[Bud]

John, I'm just guessing about which engine is in your car. The Champion J8 and the D16 are approximately the same heat range so you shouldn't have any problems there. I don't know if an earlier head will fit on a 1941 block, but a way to tell is check head gasket part numbers. If they are the same, then an earlier head will fit on a later block. If you have access to an S. I. catalogue, you should find the information you need. Bud

[Dwain G.]

The Champion Spark Plug catalog is wrong. They are showing the same plug for 'all sixes'. The Studebaker Parts book confirms that most '41 Commanders used 18mm spark plugs, and Studebaker Shop Manual shows the original plug for a Commander was Champion #8. Not J8, just '8'. Discontinued of course, but replaced by Champion # RD16 (stock #541). The AC number is C86.
The casting number and date code on the top of the cylinder head will help identify it for sure.

[Bud]

The Champion catalogue having the wrong information isn't the first time I've seen product catalogues with the wrong parts information. It happens more frequently with older and specialty cars. Bud

[studerex]

Good Morning. I have a 1941 Studebaker Commander - 11A B3. Seems to have original motor but who knows after 75 years. Where the engine number is supposed to be it was really rusted and even after steel brushing I can't even come close to seeing the engine number.
MY PROBLEM: I recently ordered some spark plugs off of RockAuto.com. Autolite 306. Seemed like a good deal so I ordered a dozen. Unfortunately they were 14mm size and not 18mm that I need. Trying to do some internet research to figure out if the plug is right and I have a non-original engine OR the plug is wrong and the engine is right.
What is the right plug? How about some cross reference alternatives?
I'll probably just end up ordering them from Studebaker International.
Any advice and wisdom is appreciated.
John in NJ

(I put this on AACA Studebaker forum also)

The block and head is date coded. look for the raised casting letter and numbers. Early 41 is T and late 41 is U. Then month and day.

[TrickyRick]

It doesn't help that the spark plug companies keep changing the numbering system.....

[BobPalma]

John: I bought out a supply of NOS spark plugs a year ago. I just checked and among them are eleven (11) new Champion D16 plugs like this:



Also among the purchase was a sealed six-pack of new Champion UD16 plugs. All are the larger size you need; all packages are wrinkled a bit but still sealed, per the photo above.

You are welcome to have any six plugs for $20 including shipping. If you want the six UD16s and six of the D16s, $35 for all twelve, including shipping.

I don't "do" PayPal, so you could send a check to my address, which is in The Co-Operator section of any Turning Wheels for the last 30 years or so; we haven't moved. BP