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Discussion Starter #1
Does anyone have tips for getting these core plugs loose? Mine are leaking coolant under my valve covers. I pressurized the cooling system and four of the six plugs have drips See photo.

I’m worried about rounding out the hex. What hex socket should I use? The hex seems like a little larger than a 9/16 but smaller than 5/8. I measured it to .58 inches. I assume that it would be a bad idea to use an impact wrench on these?
Any thoughts are appreciated.
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9/16 is .5625. I don't think you're in any danger using 9/16. There has to be some tolerance for the tool to fit. A shade over .01 is good tolerance.
 
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I'd heat the engine up first, metal expands when hot, and then drain and hit them with the impact. They might be rusted out and the only real fix is to either go bigger on the plug with new threads or replace the head.
 

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Iron, you aren't supposed to take them out. In 40 years of engine work, I have never seen these leak. I wouldn't try to remove them. If you are convinced yours leak, how about heating up the head with a rosebud and then melting some solder in around the threads ? LSG
 

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Discussion Starter #7
Somebody must have removed them previously. I have never seen one leaking.
I think you are right on this one. It seems rare for these plugs to leak and I have four that are seeping. My machinist said he did not take them out when he did the valves. Must have been the prior engine owner who “rebuilt” it.
 

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Just reseal them. Permatex makes a high temp thread sealant. It's rated up to 400 degrees

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Discussion Starter #10
Bumping this for a follow-up report. Five of six of the core plugs turned easily with a breaker bar after a day’s soak in liquid wrench. One was trouble and I rounded out the Allen hex head. A multi-spline easy-out and a longer breaker bar did the trick though. Victory. Now let’s hope that new plugs and sealant takes care of the issue.
 

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Bumping this for a follow-up report. Five of six of the core plugs turned easily with a breaker bar after a day’s soak in liquid wrench. One was trouble and I rounded out the Allen hex head. A multi-spline easy-out and a longer breaker bar did the trick though. Victory. Now let’s hope that new plugs and sealant takes care of the issue.
Run a tap down them first. Not to deep just to make sure the threads are clean.
 

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Run a tap down them first. Not to deep just to make sure the threads are clean.
Absolutely! I don't want to do this again.
Nooooooooooooooo! Run a THREAD CHASER, not a tap. A thread chaser will force any deformed threads back into place and remove scale. A TAP will not repair the threads but will cut material away to make threads. What you can end up with is a thread that is "thin" on one side and will never hold the fastener tight. Only use TAPS when making NEW threads.
 

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Discussion Starter #15 (Edited)
Nooooooooooooooo! Run a THREAD CHASER, not a tap. A thread chaser will force any deformed threads back into place and remove scale. A TAP will not repair the threads but will cut material away to make threads. What you can end up with is a thread that is "thin" on one side and will never hold the fastener tight. Only use TAPS when making NEW threads.
I thought about this. I can’t seem to find a chase for pipe threads. Perhaps I can make my own chase out of a piece of 3/4 threaded pipe with a couple of flutes cut out of the side
 

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I thought about this. I can’t seem to find a chase for pipe threads. Perhaps I can make my own chase out of a piece of 3/4 threaded pipe with a couple of flutes cut out of the side
If it leaked, the threads weren't very good to start with. So chasing bad threads just makes them clean BAD THREADS. Think about that for a second.
 
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