Hi everyone.

This '73 developed an engine knock after a good amount of oil seeped past a broken valve cover gasket on an interstate run. The oil was replaced but the knock persisted.

I know this is something big, my limited experience says a rod bearing at cylinder four or five, where the knock seems to be coming from listening with the hood up. It only knocks when I would give it more than half throttle.

What I want to know is, how safe is it to still drive the car? Will a connecting rod go flying through the hood eventually? Is there any way to diagnose which exact cylinder has developed the knock? Is it really a rod bearing?

Thanks for any help.

That's probably exactly what it is. And that is probably exactly where it is coming from. Sometimes you can pull the spark plug wires, one at a time, and determine which cylinder it is.
I wonder if disconnecting that wire would make it live any longer? I guess there's probably no way of knowing that.

_________________
'66 Cuda 225/4spd
'66 Dart GT convertible 225/auto
'64 Dart GT 340/4spd

Is it safe to drive the car? How bad is the emergency...

I've heard of people driving cars with a knocking rod for weeks. You might add some heavy(ier) oil like 20w-50 -- it'll help (some). Some times ya just gotta do what ya gotta do...

But, yeah, you've nailed it on the head with the "ticking time bomb" statement. It will eventually break on you. Will it throw a rod through the hood? Not likely. It'll probably just seize the crank. The last slant I saw with a thrown rod, it just wedged the remainder of the rod between the crank and the block & broke up the rod.

Without knowing how bad the damage is, there's know way I (or anyone else) could tell you how long you've got. I will say this: The longer you run it this way, the more damage you're going to do. If you have any plans to re-use that crank, you don't want to run it. I just helped rebuild an engine which had a rod-knock; and, by the time we got to it (it had been driven for a while with the knock) the scoring on the rod journal was over .040" deep -- new crank time.

You might get lucky and find you can just drop in a new bearing set, now, before the damage gets any worse.

_________________
My truck is a Frankenstein creation
Built from the dead carcasses of others
And brought BACK TO LIFE!

I've seen lots of rod problems in these motors, some not mine...

My '74 greased the rod bearings on 3 rods, luckily I got out of traffic and shut it off before the 'thunking' turned into a 'screeechh'...

My buddy drove his dad's '76 Brougham and blew #5 clean through the side of the block, the cap, detached and put a fist sized hole through the oil pan...I-5 had a nice oil slick in the slow lane for a week after that...

My buddy owns a tow lot and we 'torture tested' a 1963 Valiant with a 225 on it's last legs, 6 minutes and 54 seconds of brick on the accelerator it blew the #5 through the head and valve cover, and the bottom came out the oil. We lifted the hood and you could see the grass of the lawn through the bore hole...oddly my buddy reached in and fired tht slant back up and it ran rough for another 3 minutes or so before finally 'giving up'....

I'd be searching for a replacement mill, or checking into some options before you are 20 miles from home and 'BLAM'...

-D.Idiot

A "knocking" time bomb it is.
Every time it knocks, you are "pounding-out" the crank and con. rod journal. At some point the parts seize or break which can cause a lot of damage. You can most likely put some heavy oil in it and move the car around at low engine speed but it's not going to get "better" and can let loose at any time.
DD
http://www.dutra.org/pictures/engine/bo ... pieces.jpg