Plugged spark plug holes

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RandyB

RandyB

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In my 273 I pulled the previous owners plugs out. They were the short plugs meant for a bb, and TWO different kinds. I bought correct plugs but come to find out they won’t go in all the way. With it running on short plugs it must of gummed up the threads. Is there a safe way to clean the threads without knocking all that crap down into the

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What I'd try. You can buy (or used to could) spark plug thread chasers. Specialty tool companies like Lisle sell them. I'd apply SMALL air pressure, through a regulator, or maybe even you shop vac plumbed (duct tape?) to the carb inlet. Crank the engine until the intake is open for the cylinder you are working on, AKA blowing air out the plug hole from the intake pressure. Then just chase the threads

I would be careful to disconnect anything from the intake vacuum that might be sensitive, including the carb, (if it has a diaphragm power valve), the cruise control if equipped, and power booster, and if this is a GM etc with a trans modulator, disconnect that. "Follow your vacuum ports"

On the good side, pressure from a shop vac, EG is unlikely to hurt any of the above
 
Back in the day plugs would strip out on my Volkswagen dune buggy. We would tap it and install an insert while still on the engine. Cranked it over with the plug out to blow out the debris. Worked fine. It was not a high value engine however.
 
Use a spark plug tap and coat it with heavy grease. What does fall inside will get blown out the exhaust and won't hurt a thing. If it is carbon build up.
 
Mike69cuda said:
Back in the day plugs would strip out on my Volkswagen dune buggy. We would tap it and install an insert while still on the engine. Cranked it over with the plug out to blow out the debris. Worked fine. It was not a high value engine however.
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What? The bottom threads of the OP's heads are carboned up because of the wrong plugs. Carefully, run a thread chaser down each plug hole. Or better yet, grind or saw a slot down the plug threads to make it a thread chaser. It won't fall in the hole like a chaser would. Blow the crud out of the chamber.

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toolmanmike said:
What? The bottom threads of the OP's heads are carboned up because of the wrong plugs. Carefully, run a thread chaser down each plug hole. Or better yet, grind or saw a slot down the plug threads to make it a thread chaser. It won't fall in the hole like a chaser would.
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That was my point, I got metal shavings from tapping new threads in the cylinder and blew them out harmlessly. Carbon should be much less of a risk.
 
Mike69cuda said:
That was my point, I got metal shavings from tapping new threads in the cylinder and blew them out harmlessly. Carbon should be much less of a risk.
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We are ok but after 28 years in the tool business I never recommended using a tap for cleaning threads. Taps are designed to cut threads and chasers clean and straighten.
 
Even thread chasers can leave small chips here and there. Don't just use a plug as suggested. It does not cut and may damage the threads because it can compact the material that has built up and "jam" the threads.
 
67Dart273 said:
Even thread chasers can leave small chips here and there. Don't just use a plug as suggested. It does not cut and may damage the threads because it can compact the material that has built up and "jam" the threads.
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Well it's either one or the other. I wouldn't use a tap only as a last resort. Plug thread chasers are designed for this particular use. The modified plug is a last resort before you pull the head and clean the threads with a thread chaser. :BangHead::BangHead:
 
toolmanmike said:
We are ok but after 28 years in the tool business I never recommended using a tap for cleaning threads. Taps are designed to cut threads and chasers clean and straighten.
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Yep agreed, I didn’t tell my story very well. I actually tapped a larger threaded hole in the aluminum head and installed a steel insert for the spark plug to screw back into. I think I was enough off topic to confuse things.....
 
last set of 920 heads I picked up one head had all the plugs only halfway in and it was ran that way long enough to have the same carbon buildup.

All were a bout 1/4 below the chamber side. Anti foul plugs are buried like that too, down in the case. Maybe fouling was an issue and mechanical skill sets weren't very high..lol
 
What about taking a few longer than needed spark plugs, remove the ceramic. Cut as mentioned earlier the side of the threads, Attach a vacuum to the hole. Be sure the exhast valve is open. Screw and unscrew the plug in and out till it is clean.
 
Dana67Dart said:
What about taking a few longer than needed spark plugs, remove the ceramic. Cut as mentioned earlier the side of the threads, Attach a vacuum to the hole. Be sure the exhast valve is open. Screw and unscrew the plug in and out till it is clean.
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Have you done this or am I the guinea pig?
 
Dana67Dart said:
What about taking a few longer than needed spark plugs, remove the ceramic. Cut as mentioned earlier the side of the threads, Attach a vacuum to the hole. Be sure the exhast valve is open. Screw and unscrew the plug in and out till it is clean.
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And what is the difference between what your suggesting and using a spark plug thread chase? Besides a lot more work?
 
The vacuum right at the point of chip creation. Your vacuuming through the hole in the spark plugs where the ceramic was
 
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