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#453700 01/27/21 11:28 PM
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Does anyone have experience with using the newer style "cup" expansion plug to replace the original "dome" style freeze plug?

On the newer engines the opening is the same diameter all the way through the wall.
On the older engines (ie. 1936) the opening has a "lip" in it.

Thoughts?


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I would stay with the old dome type. Much more retention. Use a good sealer also.

devil Agrin



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I have never had any success using the deeper plug where a domed 1 came out of.
Tony


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I also have not been successful getting cupped plugs leak free. I also recommend a sealer like Permatex No. 2


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Built many engines. Use lock tight red. best.

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I have not been successful in finding "cupped" plugs at either of our two local car parts stores (O'Reilly's and NAPA).
So I "broke down" and went to eBay last night. Found them in less than 30 seconds. Reasonable price too.
Ordered them.

I'll try to take a close up photo of what I'm calling the "lip" around the hole. I think that this is the determining factor in whether the "domed" ones can be used or not.

And --- I've already decided to use JB Weld when I reinstall it. I'll add a photo here of the inside of the plug. You can see that the previous sealant was missing around some of the INTERIOR circumference. I think that JB will last longer.


Attached Images
Interior.jpg 2021-01-27 15.55.13 Plug Leak (2).jpg
Last edited by Bill Barker; 01/28/21 02:07 PM. Reason: Added photo of location of the leak

Bill Barker
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Looks like both of the plugs were leaking


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Looks like both of the plugs were rusted through the plug itself rather than leaking around their circumfrence(s). So why do you need any JB or permatex. Arn't those plugs of such maleable material that when correctly seated that they are water tight?

No, I'm not sniping or nitpicking. I really don't know. Educate me. Please. dance

Best.

Charlie computer

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It looks like the plug to the right side of the block has some surface rusting due to the coolant that leaked down the back of the block from the upper plug.

The plug on the right is at the rear of the camshaft galley and has oil behind it, not coolant. I do not see any indications of oil leakage.

I agree that in a clean new block a new plug should seal without any sealant.

I would use sealant on a replacement plug to compensate for any pitting of the machined bore or damage to it during plug removal.


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Yea, I just spent 4 hours out there cleaning up the parts. So now I'm ready to make my assessment.

If you look at the attached photo below, you can see that there are actually THREE plugs on the back side of the block.

The top one, which had no problems, is at the end of the crankshaft. Backed in oil, there's little chance that it needs to be replaced.

The middle one is actually an opening to the water jacket. Hence this is the one that will leak 99% of the time before the other two. It is called a "freeze plug" or a "cast plug" or an "expansion plug". The original purpose was to allow the casting sand to be removed from the inside of the block.

The bottom plug is against the camshaft and as Rusty said, does not have water behind it, so it should "never" be a problem.

Now having set the stage it appears that the middle (water-backed) plug began to leak and drained down both sides of the bell housing, including into the lower (camshaft) plug. As far as I can tell there is no problem with the lower plug.

As far as sealant --- my thought is that there is a minute possibility that the hot water running out of the middle plug may have (very slightly) eroded the opening in the block. So some sealant there would be cheap insurance. Also, if you think about it, I'm sure that in the factory, these plugs were PRESSED into the openings in a smooth and STRAIGHT manner. In my world, I'm going to use a hammer and a socket to insert it. So 1) I need to cover my a** with some sealant just incase the plug is just every-so-slightly at an angle. But equally important, I think that when you try to press something like this with close tolerances, it doesn't hurt to have a small amount of lubricant to assist it. And that's the second thing that the sealant does for me.

Be happy to hear any comments (and corrections) on my analysis above. I've not a mechanic, never have been. But I've been a backyard-mechanic all my life and I find that common sense and simple analysis can get you a long ways in this hobby.

Now.... where the heck are my keys???



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3 plugs.jpg

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I agree with you about applying sealant, Bill.


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As far as I know...

The 2 styles of plug can not, or should not, be used interchangeably.

The cup style is indeed pressed or driven into a bore or hole and relies more on the fact that it is made oversize in comparison to the bore to hold it there.

The dome or convex style is more of a true expansion plug and you will be able to push it in against the shoulder in the hole by hand, or maybe a light tap with a hammer. It won't seal or lock in until you flatten down the dome somewhat causing the outer edge to expand out in the hole and lock it in place. Use something flat like the back side of a socket so it is done evenly. Be careful not to drive the dome down too far using something much smaller than the diameter of the plug, as that will loosen it again.

I always use something like a gasket sealer on both types of plugs. In my view, not using a sealer is like putting on a tappet cover without a gasket. Metal on metal only seals well with lapped surfaces like in diesel injection equipment.

As always, I may be wrong. It's been a long time since I trained as a farm machinery mechanic. :-)

PS I'd do both of the upper plugs if I were you. A lot easier to do now than later!

Last edited by Stovblt; 01/29/21 12:34 AM.

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PPS So, long story short...

Definitely use the old dome or convex style of plug.
The shoulder in the hole is there to hold the plug while you drive it flatter to expand it.
And use sealer to take care of the inevitable imperfections in the hole and plug.


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Bill,

There is no such thing as common sense. Knowledge for us neanderthals is learned or intuition. Nothing is common to all minds. It's like instinct, birds and lower animals have it while we humans lack it. Try building a bird's nest.

On the instant thread, I still fail to see the need for some sealant material when it is only going to be left between the block and plug edge surfaces or pressed out - so why put it there - where it will/may deteriorate over time.

From what I can understand here is that a sealant - in the instant applications - is merely an unnecessary "piece of mind" crutch for those not sure of their work. Nothing more. bowdown tooth

Throwing sealant at any place it can be applied seems to be a fallback for shade-tree mechanics. Not you, of course but above you did say "backyard mechanic" whatever that means.

All I'm saying really is that I don't think the sealant is necessary or even wise where the casting plugs are found in the old Chevrolet blocks. It even may be adverse to what can be realized without it, i.e, an even better and more secure and lasting metal to metal seal. I would liken the mindset of the excessive use of sealant as like a 1941 owner painting every stinkin' groove red. Go figure.

Best,

Charlie computer

BTW: This thread has been informative and educational. I ani't the sharpest knife in the drawer and appreciate all sound advice I can get.

BTW2: The reason this post comes at such an early hour here at 5 a.m. EST is I had to get to pee and then after relief couldn't go back to sleep. Checking out the Chat usually cures that.

BTW3: Got up early yesterday morning to gain the usual relief and noticed that it was snowing. Mercy! Started to go out and write my name but chickened out. I'm moving farther south. dance Agrin


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In a perfect world metal to metal is fine but I have always used a sealer as insurance. As we are all well aware it is not a perfect world.


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I personally would replace all of them while they are accessible. JB Weld may be a problem down the road if you have to replace one. I have both types on my 216 and they fit differently.


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I agree with old216.
And I'd use Permatex Aviation or some other non hardening gasket maker to seal the deal.

Last edited by Stovblt; 01/29/21 09:50 PM.

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use Lock tite red, it's the best. Just a little around the edge!!!


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