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Need original spark plug # for a 1920 Buick 6cyl.


just me
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Charley I Have a 1920 k-45 touring, It is in storage right now so I cant see what plugs are in it. I do have the brand and numbers written down some where, I Will have to look and see if I can find it. The car is all original let me know if need any other info. Bill

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I have a 1920 Model K-46 with less than 5,000 actual, documented miles on it since new. The correct plugs for a Buick through the 1924 model year is AC 78L. I have quite a few NOS, AC 78L plugs. I am asking $25.00 apiece for them.

Let me know if you should be interested in them.

Terry Wiegand

South Hutchinson, Kansas

Phone - (620) 665-7672

terrywiegand@prodigy.net

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New / modern plugs are longer than the originals, stick out of the engine further and will short out to the spark plug cover unless you put boots over them or run without the sheet metal cover.

Been Touring for 16 years now and can say the Autolites run the hottest and best. Set your gap at 0.035 inch. There was a study done some years ago and published. You will make more power but a slightly worse idle.

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Brian is right about the new plugs being longer and having a case of hitting the pushrod cover. The AC 78L (the 'L' standing for long reach) plugs have a shorter insulator and thus will not cause problems like a new plug will. I can honestly say that I have never had any problems with my cars at engine idle speeds.

Terry Wiegand

terrywiegand@prodigy.net

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  • 2 years later...
Guest markmelbair

Hello, I'm looking for spark plugs too. I read that it's possible to give there some new (longer). Do you have any more info or photos of it?

Thank you

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I agree with Jim and Brian that if you don't have to have the OEM plugs use the Autolite 3076. They are the correct length so they stay clear of the plug cover, they work great, and they are available at most parts stores over the counter. I bought mine at Advance Auto for about $2.25 each. Also want to second what Brian said about the plug gap: the best running gap is .035. Dave Chambers in his extensive 1971 Antique Automobile article on Buicks said to gap the plugs at .040. Dave said it will affect the idle but not very noticeably imho.

Dave

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Funny that this article should jump back up just now. Cleaned my Autolite 3076's just this past weekend after running all summer including a big tour week ~600 miles and then another 600 running around home on rides including Greenfield Village Old Car Festival 62 miles each way from Fenton to Dearborn a couple of weeks ago. I bet these plugs are at least 10 years old and have 15,000 miles on them, that's nothing for a plug's life. I tend to clean them twice a year. At 0.035 gap it idles like a rock.

I had a chance to buy a set of used Titans several years ago. They are stubby little short plugs. For the what the guy wanted and then to be hidden under the side cover, I 'passed'.

I gave up years ago on the AC78L's they fouled everytime and I never get that with the AutoLite 3076's. One man's opinion.

Golden Oldies car show this Sunday at the Sloan in Flint (same location at the 2003 and 2008 BCA National Meets) Great show. Cars must be 50 years old and must be stock. No fees, no judging, no BS, well, actually, lots of BS. Ha. Come over on Sunday and kick some tires and help spread the BS!

Edited by Brian_Heil
typo (see edit history)
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Did some digging. Apparently the 775 refers to porcelain type. The size is 7/8". The Radd is from 1920, and its claim to fame was a special plate at the bottom of the plug with several small holes in a star shape that was supposed to enhance the spark to the ground electrode. Mine has this as well. I guess it fit all autos of the day.

Cheers, Dave

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Guest markmelbair
I agree with Jim and Brian that if you don't have to have the OEM plugs use the Autolite 3076. They are the correct length so they stay clear of the plug cover, they work great, and they are available at most parts stores over the counter. I bought mine at Advance Auto for about $2.25 each. Also want to second what Brian said about the plug gap: the best running gap is .035. Dave Chambers in his extensive 1971 Antique Automobile article on Buicks said to gap the plugs at .040. Dave said it will affect the idle but not very noticeably imho.

Dave

So you think that I can replace spark plugs on photo with Autolite 3076?

post-103158-143142745267_thumb.jpg

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Measure your plug from the underside of the hex to the bottom of the electrode and then measure a 3076 what is called the 'reach'

What you have looks longer. If you need this long reach to get the electrode out into the combustion chamber then a 3076 may be too short. I have no idea what to use in that case.

Take a look on your engine and see how deep your threads are in the block/head to determine how much a 3076 may or may not stick out into the combustion chamber.

You don't want to be too short and firing within the threads of the head (not sticking out), and you don't want to be too long and hit the piston either when it comes up. Now with that said, these old engines are very low compression so the chance of hitting the piston is pretty low. But I'm certain you get my point. Also don't worry about heat range. These engines are so low compression by today's standards and run so rich too, you need as hot a plug as you can find which is the 3076.

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