Spark Plug Gap
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Senior User
Joined: Jun 2008
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From: Greenwood, SC
Spark Plug Gap
I recently lost the engine in my 74 f100. i replaced it with a shortblock 302 from an 80 thunderbird retaining all the other stuff from the 74. My question is about gapping the spark plugs. Do i gap the plugs to the 74 specs or the 80 specs? I checked the plugs and they are at .045. Not quite sure how that happened since they are supposed to be .035. Any input would be appreciated.
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
Set it to the '80 specs. Spark plug gap is a function of firing voltage. Your '74 probably had points and the '80 probably has Duraspark, so it's even more important to use the '80 specs. It has nothing to do with what engine used to be in the truck, assuming you kept the ignition system from the T-bird.
Elder User
Joined: Nov 2004
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From: Ashland, KY
I did the samething in my 79. It has a 91 302 block and heads but everything eles is 79. I use all the 79 specs. and it works great. So I would go with the 74 specs. since you just changed the block.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
You need to find out if he has points first. If you set a Duraspark ignition system to the gap of a points system, you'll burn out the plugs. I'm under the impression he took the entire 302. I don't think a 302 and 400 distributor are interchangable (could be wrong though).
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From: Greenwood, SC
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I gapped the plugs at .035 and at idle it seemed to run the same. I have a ticking coming from the front drivers side. The motor that blew had the same ticking in the same spot. since i used the same head with the same spark plugs i figure it has something to do with the head on that side. Could the carb needing adjustment cause this or anything else i can check fairly easy? The motor runs good and smooth but it just has an annoying tick to it.
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Senior User
Joined: Jun 2008
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From: Greenwood, SC
the valves are non adjustable. i havn't tried new plugs and wires even though i should have. money is alittle tight right now. its not an exhaust leak, new gaskets and no air coming from anywhere. thanks for the ideas. it could use plugs and wires so i guess should try that and see.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Spark plugs should be clean and free of oil and soot. The porcelain should be a light tan color after you've got some miles on it. I'm assuming you are hearing the engine noise at idle when you're standing next to the motor? If so, that sound is coming from the lifters. One is either collapsed, or you have low oil pressure. Check your oil pressure with a mechanical gauge. It's not related to the carburetor at all.
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1980 - 1986 Bullnose F100, F150 & Larger F-Series Trucks
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