Coolant Drain on a 1968 427 Block

[Russ T.]

I am doing a coolant changeout on a 1968 L71 block and have a clearance issue
on the driver's side drain plug. There's no easy way to get it out.
Fortunately, the RH plug is easily accessible.

It looks like the only way to remove this plug is to remove the engine mount nut
and bolt ... or at least remove the nut and drive the bolt back until it's flush with the engine mount.
This will give me the clearance to get a 1/2" breaker bar in there. Right now I'm going
with the breaker bar, coupled to a reducing adapter and a 3/8" hex socket.
The engine was completely rebuilt 10 years ago, so I'm hoping it won't be too difficult.

Assuming I have to take the weight of the motor off of the mount to
do this, how is the best way to support the motor? This is a new one for
me and I'd appreciate any advice on doing this safely and securely.

Thanks!
Russ Trotter
NCRS #15444

[Mark E.]

Re: Coolant Drain on a 1968 427 Block

This isn't a direct answer but I thought I'd share what I do. Virtually every engine drain plug I've dealt with is solidly rusted in the block, to the point of risking breaking it. So my routine is to thoroughly flush the block without draining it. This may not be the best method for engines with considerable sludge and rust, but works great in most cases.

[Stephen L.]

Re: Coolant Drain on a 1968 427 Block

A box end 6 point wrench used with a short pipe "simulating a breaker bar extension" would do the trick. If it is frozen in place, then just forget draining that side. Flush plenty of water thru the system, with the engine running for circulation, leaving the other plugs open. Keep the radiator full thruout the process with your garden hose............

[Russ T.]

Re: Coolant Drain on a 1968 427 Block

Solution:

1) Take a 3/8" drive 1/4" hex socket and cut off all but 3/8" of the hex piece. It is hardened steel,
so you have to cut it with a grinder and file it afterwards. This fits 1/4" deep into the cast iron
internal hex plug.
2) Remove the engine mount bolt nut on the driver's side and tap it back flush with the engine mount.
(see photo). I was surprised that the bolt was relatively free enough that I didn't have to raise the motor.
3) Using a 1/2" ratchet (or breaker bar) and a reducing adaptor, I was barely able to get the hex bit into the
plug and align it properly. The plug is in the middle of the block above the oil gallery plugs. I was able
to break it loose without too much trouble. I drained about 2.5 gallons of coolant into a bucket on each side.
4) Next, coat a brass 1/4" X 0.75 NPTF hex pipe plug with Loctite 5113 thread sealant (with PTFE) and torque the plug to 15 ft./lbs.
Tap the motor mount bolt back in place and tighten to the proper torque. The RH side is straight forward
with no obstacles to deal with. It is next to the oil dipstick tube at the middle of the block.
5) The hex head on the LH plug and the pipe sealant will make it easier to remove with a box wrench next time,
As Stephen suggested. I plan on draining the block every 3-5 years.

LH Drain Plug.jpg

Russ Trotter
NCRS #15044

[Mark E.]

Re: Coolant Drain on a 1968 427 Block

Very creative. I'm glad it broke loose for you. But is it worth the risk of breaking/stripping the plug and the work to gain access to it?