mrcvs Posted July 23, 2018 Share Posted July 23, 2018 For an antique car? In this case, it's a 1917 Maxwell, but what's the principle behind it so that I can select a replacement spark plug for any vintage automobile, and not something I look up in a stock manual of specifications of replacement parts for recently manufactured automobiles? Right now, currently installed spark plugs are Champion. Link to comment Share on other sites More sharing options...
playswithbrass Posted July 23, 2018 Share Posted July 23, 2018 I like running old n.o.s. plugs form the era of the car.What I do is measure down the spark plug hole and measure what clearance I have in relation to the piston and valves in the open position and then get a plug that will put the electrode the deepest into the cylinder.I do not worry about heat ranges like in modern plugs because the compression ratio of older engines is not hot enough to cause worry.I don't even know when spark plug manufacturers started making different heat ranges for the same application.Also index the plug so the ground electrode is opposite or away from the combustion chamber--old drag race tip--but it works for more complete combustion. Hope this helps. Cheers Pete 1 Link to comment Share on other sites More sharing options...
TerryB Posted July 23, 2018 Share Posted July 23, 2018 From a 1927 auto parts supply catalog, Maxwell is AC type A 1 Link to comment Share on other sites More sharing options...
mrcvs Posted July 24, 2018 Author Share Posted July 24, 2018 Where does one obtain NOS spark plugs? Also, if not new old stock AC Type A? Link to comment Share on other sites More sharing options...
playswithbrass Posted July 24, 2018 Share Posted July 24, 2018 There are a couple of sparkplug vendors at Hershey by the stadium,and ebay buy them one at a time ,may take a couple of months. I have bought from Don McKinsey. Great guy 765-785-6284 has probably the most plugs of anybody around,tractor trailers full. Link to comment Share on other sites More sharing options...
Terry Bond Posted July 24, 2018 Share Posted July 24, 2018 Check your owners manual/parts catalog to see what the original brand plug might have been. If AC is what you need then you'll need to search Ebay or the recommended vendors for them. They should not be difficult to find. Link to comment Share on other sites More sharing options...
PONTIAC1953 Posted July 24, 2018 Share Posted July 24, 2018 most used spark plugs can be cleaned, check the gap, and reuse. Link to comment Share on other sites More sharing options...
Mark Shaw Posted July 24, 2018 Share Posted July 24, 2018 This is a handy guide to help identify spark plug equivalents: Spark Plug List 7/8" spark plugs cold down to hot New Champion Old Champion A--C Auto Lite Edison Bowers Globe Blue Crown Leonard W-10 0 Com 73 Com 40-T C78-C 6 73-Com 4-F W-14 1 Com 74 Com T-7 37-TS C78-N 7 74-Com 4 W-18 2 Com C 77L T-9 35-S 78-N 8 75-Com 3 W-20 3 Com or No 20 78 Com T-11 31-T 78-H 9 76-Com 2-A W-89D 44 18 3077 10 78L-Com 1-A W-85N 901 W-95D 45 The bottom three plugs are special extension models Recommended torque for a cast iron head is 37 lb-ft 35 lb-ft for aluminum 10 mm cold down to hot New Champion Old Champion A--C Auto Lite Edison Bowers Globe Blue Crown Leonard UY-6 Y-4A 104 P-4 3-S 10C F-10 T-4 10-F UY-6 Y-6 106 4 F-11 T-6 10-E UY-6 Y-8 108 P-6 2-S 10N F-11A T-8 10-D Recommended torque for cast iron head is 14 lb-ft 12 lb-ft for aluminum 14 mm cold down to hot New Champion Old Champion A--C Auto Lite Edison Bowers Globe Blue Crown Leonard J-57-R J-2 42 A3 58-T C14S 12A M-2-Com 14-G H-8 H-9 43L A5 57-TS 14C 13 M-4-Com 14-F CJ-8 J-8 45 A7 55-S 14N 14 M-7 14-E UJ-12 J-12 47 A11 52 14H 15 M-11 14-C Recommended torque is 30 lb-ft for cast iron heads 28 lb-ft for aluminum 18 mm cold down to hot New Champion Old Champion A--C Auto Lite Edison Bowers Globe Blue Crown Leonard D-6 4 Com 82S C18C R-82 6 D-9 5 Com 83-S B5 49-TS 18C 24 83 Com 6-F D-14 6 Com 84 B7 48-TS 25 84 Com 6-A D-16 7 85-S 45-S 18N 26 85 Com 5-HD D-16 8 Com 86 B9 43-TS 27 86 9 D-21 C-15 87 B11 43 18H 28 87-S 5 D-23 10 Com 88-L 388 44-HS 88 8 D-89D 49 18A 42-T The bottom plug is a special extension model Recommended torque for cast iron is 34 lb-ft 32 lb-ft for aluminum heads For 1/2" pipe plugs recommended torque in cast iron is 35 lb-ft All values are for clean lubricate threads. Over tightening a plug with a .025 gap the gap will increase to .031. Created from a 1947 heat range list and current Champion list. by Chris Klossner (email address deleted from original post) Link to comment Share on other sites More sharing options...
mrcvs Posted July 25, 2018 Author Share Posted July 25, 2018 Dumb question, but I don't know... Just noticed parts catalogue reprint states AC spark plugs. My mind was thinking AC Delco. Is this one and the same or two different spark plugs? Link to comment Share on other sites More sharing options...
TerryB Posted July 25, 2018 Share Posted July 25, 2018 AC spark plugs became AC Delco many years later. The pictures I posted are from an original 1927 catalog I have. The asterisk next to the auto brand indicates it was what the factory installed. As stated above, old AC plugs are out there, you just have to look hard for good useable ones. Link to comment Share on other sites More sharing options...
oily rag Posted July 25, 2018 Share Posted July 25, 2018 Maxwell may have used Champion plugs. The last one I worked on had (Montgomery) Wards #18 plugs in it. Link to comment Share on other sites More sharing options...
C Carl Posted July 26, 2018 Share Posted July 26, 2018 As you see, the replacement chart Mark has given us does not go far back enough to include AC "type A", as spec'd in Terry's data. In any case, even THOSE 1927 spec's may not apply to your 1917. Gasoline was different in 1927, from that of 1917, (and obviously RADICALLY different from todays fuel). And that is assuming everything else in your engine being equal over the intervening decade. Shaky assumption, at best. You will eventually find a perfectly acceptable modern substitution for your plugs. More important yet, is setting a significantly higher initial advance on your timing, and having your distributor re-curved for running on modern 87 gasoline, rather than the 40 octane of 1917. - Carl 1 Link to comment Share on other sites More sharing options...
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