What size block core plugs and how to seal them?

[cjshaker]

What size core plugs do you engine builders use, and how do you seal them when you install them? I'm talking about the block water jacket plugs. I'm assuming I can find them in McMaster Carr or something similar and need to get them ordered. I know this was discussed in Mr. Foxwells engine build thread, but apparently he didn't want to be helpful to anyone and had all his threads deleted.

[blykins]

Doug, are you referring to the drive-in freeze plugs?

[cjshaker]

Yes, the ones that go into the side of the block.

[Barry_R]

We use 1-49/64 brass plugs with TA-31 silicone (you can use any of your favorite sealers - they all work - I know some guys even use epoxy)

[C6AE]

I use the 49/64 brass plugs and loctite...

[cjshaker]

Thanks for the replies. In case anyone is interested, the Dorman part # is 565-036. My local Napa couldn't get them, so I ordered them through Summit, in a package of 10. I always have a couple tubes of TA-31 around since that's what I use on most gaskets.

[CaptCobrajet]

I don't use any type of silicone there.  It just lubricates it good for exit!  Clean well and green Loctite. (sleeve retainer)

[cammerfe]

I know where to borrow a proper-size tap, so I thread them, use brass plugs and put them in with epoxy. (Extra support by doing so.)

KS

[blykins]

I use silicone.  I've been using Dow Corning 732 for a few years now for pretty much everything.  Little bit around the outside edge, drive her in, and I'm done.  I can't recall ever having a freeze plug come out, but I've had a few blocks where the holes were a hair oversized for some reason and I've had to use metric plugs. 

[GJCAT427]

I`ve used good ole Permatex aviation sealer (the brown stuff) for years. Never had one pop out yet. I got my core plug from Pioneer and got the ones for FEs by correct size.

[Joe-JDC]

X-2 on the Permatex sealer.  Joe-JDC

[cammerfe]

By all means, use the brass plugs. I had a steel one rust through once on a 460, behind the engine mount. Bitch to fix it!

KS

[C6AE]

Put a magnet to those " brass" plugs.
More than once I have been sent brass plated plugs...

[66FAIRLANE]

Put a magnet to those " brass" plugs.
More than once I have been sent brass plated plugs...

Thats good advice right there!

[427Fastback]

Personally I would never use silicone on them for the stated reasons.I would use permatex or gasket cinch on them.That being said I have never had one come out regardless of what was used when they were installed.

[Barry_R]

Consider how hard it is to remove a siliconed on intake with the bolts out.  You need to slice through the end seals and pry.  Now imagine a press fit core plug with silicone dried in place after assembly.  Good luck pushing that thing out without considerable force.  You have 10-20 psi in the cooling system.  A proper size plug ain't going nowhere...

[My427stang]

I use the proper size and whatever RTV I have around, and usually the random tube of stuff I don't want to use somewhere else. 

To be hones, I have never seen any significant remnants of RTV on an old plug, I consider it more of a sealing lubricant than a sealing glue

[cjshaker]

Blair isn't one to speak, just to hear his own voice. I'm sure he has his reasons for stating what he did.
According to the Dorman website, the plugs are solid brass (at least that's how I take it). I don't want steel. The biggest reason for pulling the engine was a leaking plug behind the engine mount.

[shady]

yeah, it's always the one behind the motor mount that goes bad. I've done two that I used the rubber ones on. you have to grind two notches in the big washer to clear the mount and an excessive amount of swearing, but you can get them in & I never had one leak or come out.

[CaptCobrajet]

Thanks for the confidence Mr. Doug.  Most average Street driver engines might not experience it, but there are situations where the plugs WILL blow out, and silicone does not help......green Loctite will.  One case being a high rpm-capable engine, on the starting line, for example......with a mechanical water pump.  Let's just say we are at 2500, then the tree comes down....then it goes to 6500-7000 immediately........ Nice cooler water pumps right in, not so nice thermostat shuts right down.  Pressure IN THE BLOCK goes waaaay up and the plugs push out.  I have seen it more than once in my life.  Spirited runners should use a restriction ring......not a thermostat.... or an electric pump!  I just use the green on all of them.  I take a little 80 grit paper to the block and the plug to give the Loctite a place to live.....then it won't leak.  If you have a sound block and plug, and it drips a little, just run straight water for a few days and the sediment will seal it.  If I did run a thermostat, I wouldn't want silicone stuck in it, or in my radiator......just my thoughts and my methods.......not saying it is the only right answer in a sea of possibilities.  There is often more than one way to get to the desired results.

[My427stang]

Green bearing set Loctite  is good stuff, unlike a lot of the Loctite stuff, it is designed to expand and really bite.  I actually had a "temporary" fix for a spun race in my F100 front wheel bearing.  I dimpled it, then used green loctite and it's been 9 years.   I will be inside it soon as I am changing over to a disk brake front axle, but that stuff holds well.

That being said, I hope EVERYONE has a good reason for posting what they post and I hope people don't think that because one person has a technique that we mean everyone else is wrong

A brass plug in a 7000 rpm motor, with the shock of hard launches and motor rapidly changing temp, I'd buy that it needs some help,and green loctite sounds like a great fix.  I'll also add, those guys who insist 1 3/4 plugs are right, might want to consider Loctite too. 

I'd also add that I use right steel plugs with antifreeze, they go in a lot harder, and I haven't seen one get rusty in a long time (different with water of course) and they work great on a street machine.  Last set of brass plugs I put in felt like they sort of fell in there and I wasn't happy with them, but lot's of guys have success

[blykins]

I don't think anyone was calling anyone else out, we were all just relaying our experience.  We all do things a little differently.  It's the whole "forum thing" where no one can hear the inflection in each other's voices, but if we were all sitting in the same room, we'd understand exactly. 

Blair has obviously had one pop out before, and once you have one pop out, you start changing your assembly procedures to try and eliminate that ever happening again.  I've never had a freeze plug pop out, even on drag race stuff, but something tells me that my time is now coming....LOL  If it happens, then I'll remember how Blair did the fix and will implement that.

Every guy here that builds a bunch has a list of things that they check off as they assemble, based on years and years of putting them together and dodging things that have bit them in the hindend.   

One that could have bit me in the hindend happened this morning:  putting rings on a 460ci SBF and noticed that the oil rail support ends were touching. 

Another one that could have bit me in the hindend a few weeks ago:  custom 391 crankshaft that had been modified 10 ways to Sunday, but the front face of the thrust surface had about .005" of run-out in it.  You could lay the crank in the block, push it forward up against the rear thrust bearing surface, rotate the crank, and watch the gap get smaller and bigger between the front thrust surface and the front side of the thrust bearing.  Just glad I caught it, but it cost me a few weeks as I had to drop it off at my local crank grinder's shop and have it trued up. 

That's why our assembly checklists keep getting longer and longer....

[cjshaker]

I knew that that's what Blair was probably referring to. The high water pressures exerted on a colder, high RPM engine have been brought up before, and I pictured that happening. If I had the proper tap, I'd go that route and be done with it forever.

The water in the small town that I live near, has a high calcium content. I'm not the only one who's ran straight water for a bit to seal up a small leak. The calcium doesn't take long to migrate to the leak, and will stop it in short order. I've "fixed" a couple of radiators that way.

Ross, I'm not sure what caused this plug to rust out, when all the others looked pretty good. Just a bad plug of steel would be my guess.

[babybolt]

Even with a daily driver engine, the coolant pressure inside the block can spike up to 60 psi briefly when the thermostat is closed. 

[Phil Brown]

I remember seeing years ago at the machine shop they were doing some work on blocks for the local circle track guys using FE's (them days are long gone) and they would drill and tap two small screws next to the core plug and use a screw with a large head that would overlap the core plug to keep it from popping out. The screws were small, like a 6-32 or 8-32 but with a large dia. head

[Pentroof]

I use Indian Head gasket shellac. It won't squeeze out and end up somewhere I don't want it and antifreeze doesn't phase it. A very thin swab around the plug, and another around the rim of the block. Wait a couple minutes and pop it it.

My junk mostly stays on the street. I think if I ever were to get serious at the strip, I'll take Blair's experience to heart.

[cammerfe]

I remember seeing years ago at the machine shop they were doing some work on blocks for the local circle track guys using FE's (them days are long gone) and they would drill and tap two small screws next to the core plug and use a screw with a large head that would overlap the core plug to keep it from popping out. The screws were small, like a 6-32 or 8-32 but with a large dia. head

That's an old sbc trick. At least the early blocks were known to 'squirm' a bit and pop the 'freeze' plugs. screws kept the plugs in place.

KS

[427Fastback]

Seen more than a few 392 Hemi's with straps across the plugs.They had the flat dish plugs..