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General Tech Rusted Cylinder Head Freeze Plug--WOW

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KVH

KVH

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Yikes, what happened to my cylinder head? I had it cleaned two years ago, new valves and guides, checked and given report of good health. Since then, it sat in my Arizona garage in a sealed plastic bag for two years. It's possible there was a four-month period where the bag wasn't sealed very well. Anyway, I just torqued the head to the block and was all ready to congratulate myself when I noticed an odd spot on that core plug you see in the pic. I poked at it, and it's like cardboard. I could probably just knock it with a few taps.

But, of course, the issue is what to do. I see Moss sells this plug, but is this a sign of severe internal rust? Is this readily fixable and commonplace? I can't imagine this is a home project given the forces within an operating cylinder head, but I am fortunate enough to have a friend with a full machine shop at his house and he's quite a bit more than just handy.

Have any of you had experience with this sort of issue before. Definitely a first for me.

Head Plug Rusted 1.jpg
Any advice appreciated.

Thanks all.
 
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It's been empty and on my garage floor in a sealed bag. I haven't driven this particular car in five years. I've been rebuilding it.
 
I would guess that it was never swapped out. And the cleaning process added to the plug being “eaten” away.
even a new plug is a few mm of metal and that doesn’t rust through just being sat.
the head itself will be ok.
but I would swap out all the plugs on the engine especially if it’s also been cleaned- not a difficult job done on the bench.
There should only be 4lb pressure in the water ways some run 7lb rad caps that control this. You don’t want to stress the rad with excess pressure.

Is the combustion and head gasket area rusty as that will need cleaning off.
then oil it and wrap it in paper not a plastic bag.

I still say thats an old plug.
 
Pry it out, along with any others in the head (and the block if they've not been changed). Doing it with the engine out of the car is MUCH easier than finding out later and having to change them in situ! Especially at the rear of the engine.
 
Totally rusted out. Must have been original. I yanked it out and it was a mess. I cleaned up the head and actually took it back off the block. I guess that means a new head gasket even though I just torqued it on, new, 10 hours ago?

Can you shed light on the process for replacing that plug. Some kind of sealant, special process for centering and setting? With my record I better buy a few plugs and plan on some trial and error.

FYI, my shop replaced the other plugs when I dropped the block off for cam bearings a while back.

Thx
 
Just thoroughly clean the hole especially the seating face.
knock in the new dished core plug gently until it seats on the inner edge then wack it in the middle with a blunt drift and heavy hammer this spreads the edges of the core plug sealing the hole. Shouldn’t need any sealant.

has the top aluminium screw in plug been changed as part of the head work as these can be eaten away from the inside. And if the head people missed this rear core plug did they even bother with the top ali one ?

ps
If the head gasket is copper re use it.
 
Was it mentioned to use Brass core plugs, not steel? Tom Lang has them. PJ
 
Just to be clear--you shouldn't have the remove the head to fix this. Brass plugs are a good option, but steel should be OK. Just be sure to replace coolant regularly, as the rust inhibitors wear out after a few years.

The plugs are easy to replace; just follow Hamish's instructions.
 
Thanks guys. I didn’t want to remove the head, but since the engine was in a stand, and several good sized pieces of rust from the plug had fallen into the cooling jacket area, I felt I ought to. I cleaned it all up, but I guess I should now replace my new gasket. It’s composite, never saw a second of use.
 
I am sure it is a result of the head being tanked in a slightly acidic solution and not having been rinsed completely. I had a radiator do that once. I had them replace the core, but did not need the radiator for about a year. When I went to install it, it was like putting water in a screen...at least a dozen leaks. In that case it was the acid flux was never rinsed out properly and acted on the core for a year in storage.

There was no need to remove the head to fix a simple freeze plug. I would not recommend re-using the head gasket after it was torqued. It imprints to all the microscopic variances in the head, block, and sleeves...and can never be installed in the precise same way a second time.
 
Funny...I wrote the above very early this morning. I guess I never hit "post". I came back 12 hours later and the post was still waiting to be posted. This new forum holds on to things!
 
Thanks for the help, guys. I'll put a new head gasket on and pop a plug as best I can. I've learned this isn't as uncommon as I first thought.
 
As Bob said, replace them all! If one plug goes bad, there are others waiting to go. And, Brass plugs are pretty much a permanent fix. Use a rotary brush to clean the plug seats and just a tad of sealant to fill in the pores before installing the plugs. I use Permatex Gold. 10 years and zero leaks on mine! PJ
 
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When mine failed in a similar fashion to yours I caught it in the act...

Freeze Plug.JPG


Looked like this on the reverse side (big hole is where I drilled to pry it out):

Freeze Plug Reverse.JPG


I replaced using a steel plug and JBWeld for a sealant.
 
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