Overheated fresh rebuild

[jwrmach1]

I am looking to the experts here for a little advice.  I have been lurking here for years as I assembled my 428.  Things did not go well this past weekend.  I finally finished my 70 Mach 1 and got it registered and it was time to take it for its first ride.  The 428 was run on the dyno at my local machine shop and it ran great with no issues.  In any event, for the first test drive, I headed down the road about three miles.  All was working great, good oil pressure, normal temp.  I turned around and headed back home but I hit the throttle a little and took off.  Little did I know at the time, a freeze plug popped out and I lost all coolant.  About half mile down the road I noticed the temp starting to rise.  I continued home, but the temp kept climbing and it started to knock.  I made it home the 2.5 miles home not knowing I had lost all coolant as the temp gauge was not in any coolant any more.  In hindsight, not a good decision.  I let it cool off for a few hours and did some troubleshooting and found the freeze plug missing.  Car seems to run ok,  I changed the oil and oil pressure is still great, but I'm worried so I pulled the plugs and stuck a borescope in all 8.  Piston tops all look good.  Cylinder walls all still show crosshatching with no vertical lines.  Of course it is all magnified with the borescope I used so little things look big.  There were some brown spots in cylinder 4 and oil in cylinder 8.  Cylinder 6 looked like it might have had oil in it too, not much though.  Compression is between 160 and 180 on all 8.  This seems like a big spread to me.  Should I pull the heads for a better look and replace the head gaskets?  What causes the freeze plug to pop out?  I did use the 1 49/64" brass plugs.  I hadn't planned on driving 6 miles before I had to tear it down again.  What to do next???
Thanks
Jack
70 Mach 1

[Joe-JDC]

I would do a compression test with all plugs removed, throttle blades wired open, and count even number of compression strokes for each cylinder.  If that looks to be acceptable, replace freeze plug, change oil and filter, and give it another try.  If the rings didn't get too hot, you may have dodged a bullet with the short/hot drive.  Joe-JDC

[dcm0123]

Try a compression check to see if you burned any valves. If it is running good you probably did not damage the engine.

Did you push the outer edge of the plug in just past the edge of the hole or the chamfer if one is present? I try to go about 1/32" further in.
Did you use a sealant around the plug before installing? I typically use Permatex #1 which is a hardening sealant.

I would replace your radiator cap unless it is new.
Never reinstall a plug. If it goes in to far, remove and throw it away.

They make expandable rubber plugs if you can not access the plug without pulling the engine.

[centredautomag]

Make sure you have the right size plug.can t remember size but someone here will tell you.

[My427stang]

I think given that it isn't doing bad now, I'd probably get it to hold water and let it run for a while.  You may have got lucky.

[BigBlueIron]

The 1 49/64" plug is the correct size. Maybe just didn't get it installed just right, stuff happens. Sounds like its not fatally wounded so I would repair and run it. Good advise below about the rad cap and rubber expansion plug. The rubber plug isn't considered a "true repair" by some but they do work.

The only thing I would do is re torque the heads. Loosen one bolt at a time and bring to torque in one swing. If you mark a few bolt heads I bet you will find they move a little, especially on new gaskets that have a little time to settle and have been hot. Also double check gasket orientation, its easy to but one on backwards. 

Drive it awhile and then inspect and compression test again if you think something is amiss.

[oldiron.fe]

       at one time dorman made a copper plug with a t-bar insert with nut ( possibly acorn style ) bar inside block and expanded cup never could come loose dont know if still available -mid 60s/70s dirt tracking - watch/ replace the rest- when seating the last 1/8 inch drive the center not the edge to expand to hold better-good luck -oldiron

[jwrmach1]

I took a walk down the road where I lost the freeze plug.  I found it.  It looks as though I did not install it far enough as there is blue paint on the edge.  Checking the others and all look like they are in correctly.  Tonight, I am going to put plugs back in and give it go to see what happens.
Jack
70 Mach 1

[Phil Brown]

       at one time dorman made a copper plug with a t-bar insert with nut ( possibly acorn style ) bar inside block and expanded cup never could come loose dont know if still available -mid 60s/70s dirt tracking - watch/ replace the rest- when seating the last 1/8 inch drive the center not the edge to expand to hold better-good luck -oldiron

I've also seen back in the day where guys racing would drill and tap two small ( 6-32 or maybe 8-32 holes across from each other real close to the edge of the core plug. Then install a small screw with a large button head that would overhang the edge of the core plug to keep it from pushing out.
But I think that with the 49/64 plug installed just below the chamfer you should be fine

[Barry_R]

We don't do it on a normal basis - but I have heard some racers that use epoxy as a plug installation lubricant/sealer.  Once in and hardened it ain't coming out....

[My427stang]

How did you make out?  Running again?

[jwrmach1]

Update - Crisis adverted.  All tests were positive, compression, and borescope.  The only issue that concerned me was the oil on top of piston #8.  I inspected the valve seals visually as much as I could see and poked them with a screwdriver to see if they were still soft and pliable and they were.  I figured if I had an oil consumption problem, running it would not hurt it and I would see the smoke.   I then put the plugs back in, started it up and took it for a ride.  I did put a new radiator cap on though.  No noises, no smoke, no skipping.  plenty of power.  So I put some more miles on it yesterday.  30 miles and still runs fine.  More "testing" today!!!  Thank you everyone for your help!
JWR

[HarleyJack17]

Good to hear!