Sparkplug Trivia

[Bruce Frey]

For the DM175T1S, the part that I was speculating about was the "1S" suffix.

I put the question to Bosch and they were unable to tell me exactly what "1S" means. It seems that at that time:

"....a single number or letter has no meaning of its own, only together they describe an assembly (as the Special number S1, S2, etc., because neither the S or the number behind it have a meaning of itself)."

They sent a data sheet for DM175/1 which also has some information for other DM175 series plugs. Variables include the length of the insulator, different end caps, different electrode gaps, etc. There does not appear to be any consistency to the suffixes, which seems to confirm the above statement.

Interestingly, they all seem to have the cone shaped tip on the center electrode and the angled ground electrode.

My DM175T1S plugs have a thin porcelain insulator and a "demontable" piece that requires a special wrench. The DM175/1 data sheet shows a thick insulator and a SW22 hexagonal "demontable" piece.

Peter, can you shed any more light on this?

Best regards,

Bruce

[Darryl.Richman]

Speaking of trivia, where does one find a spark plug wrench for the M18 style (18mm internal threads, 24mm external hex) spark plugs? Alas, my R52 didn't come with one.

[Bruce Frey]

I believe Huggett, Dreher and Vech have M175T1 plugs. Other heat ranges are hard to find.

If you need M225T1, I have a few spares as a part of an eBay purchase.

Best regards,

Bruce

[Darryl.Richman]

If Bosch M7AC is good enough -- it is good enough for me -- then you can have one for about €6 at any Bosch dealer in Germany. Dreher definitely also has them for the same price, and also the M8AC plugs.

Maybe I should have a box of them sent and gray market them...?

Regarding the socket, I went down to Sears and bought a 1" deep socket.

[Peter D. Nettesheim]

Gentlemen,

The "S" in Bosch plug DM 175 T1S stands for..................................

Silver.

The electrode is made of Silver. It should cleaned very carefully. If done with a wire brush, its soft composition will cause it to scratch and change its firing and ability to stay clean. I agree with the other details of Mr. Freys response as to what each of the other letters stand for.

Peter D. Nettesheim

[VBMWMO]

Now I'm going to have to find a real bitch of a question to ask. Let see, humm.......how about the meaning of the "S" on the end of the original DM 175 T1S spark plugs for the R17....... How about what the "D" means on the same part?......
Peter D. Nettesheim

This is somewhat speculative, but I think the following:

The "D" means "Demontable" or "zerlegbar", meaning that with the correct tool the sparkplug can be disassembled.

The "M" indicates an M18x1.5 thread on the ground.

We know 175 is the heat range...lower being hotter, i.e., 175 is hotter than 225.

The "T" means a porcelain insulator.

The "1" indicates the reach or length of the threaded ground portion.

The "S" is the odd electrode configuration with the tip of the center electrode being conical and the ground electrode being angled normal to the angle of the center electrode tip.

I looked around at Veterama and the normal M175T1 is easy to find. I did not see any DMxxxT1S, however.

Best regards,

Bruce
(whose 1935 twin carb R12 came fitted with DM175T1S sparkplugs.....maybe a small start for a new project)