1962 394ci

There is a random loud knock from the pass side of engine. Sounds like it's under the valve cover but not sure.
It's more of a high pitch knock like thin metal instead of a deeper sound like a thicker, heavier piece.

It has happened a few times at idle but always cleared up after a minute or so. Never on start up always after running a few minutes.
Yesterday on the way home it started at about 55mph. I stopped and let it sit, checked oil and it was still full.
Eased her home the last 3 miles and by the time I got home it was gone.

I do not have a oil pressure gauge but the idiot light works. Not sure about sensor but I'm assuming it does since idiot light goes off on start up and the motor hasn't grenaded yet.

Any ideas where to start?
I'm assuming valve cover removal since it's the easiest but what do I look for? Are these motors known for an issue I should check?

Thanks

 

My initial internet diagnosis would be a lifter bleeding down, since it comes and goes. Of course, it could be a handful of things, but changing up to a heavier weight oil may help without getting invasive.
Original engine and camshaft points to flat tappets that require proper lubrication. I recommend 15w-40, but I'm also an idiot. Shoot for a formula designed for flat tappet cams like Lucas Hot Rod, Valvoline VR1, Penngrade 1, or Driven.

 

Thanks

I'm running 20w50 VR1

 

Well, I guess that ain't it! 🤣🤣

 

I suspect you need to use a mechanic stethoscope or a make-shift stethoscope on that valve cover. Make-shift stethoscope could be a piece of rubber hose held against the valve cover at one end and held against your ear at the other end. Sometimes a wooden dowel rod works well.
Remove the offending valve cover & let engine idle for a look-see.

You might try a bottle of Rislone.

 

yeah that was the 1st thing I tried.
Sometimes you get lucky and sometimes ya dont

 

Gonna have to keep a piece of hose handy.
Never know when it's gonna do it or for how long

 

Stethoscope X2...

​​​​​​@Charlie Jones, Anything common about this on a 394?

 

I had a 394 that would make a helluva racket, but then purr like a kitten. I chalked it up to a piece of carbon rattling around that finally worked its way out the exhaust.

 

A slight exhaust leak can sound like lifter.

 

It is very steady knock that changes as the rpms change.
Thinking about it like that it's gotta be a.valve train issue wouldn't it?

Next time it does it I'll try to get a video

 

Check the fuel pump. Use a wooden dowel pressed against the top of fuel pump with engine running and see if you feel the clunk. Sometimes if you push down on the pump top you can feel the noise intensify. Have a helper rev the engine slightly during the test. Be careful of the running belts.

 

Keep in mind 394 have rocker shafts. Check to make sure all the rocker arms are in proper position and the cotter pins at the end of the shafts haven't broken off allowing movement.

 

I had the same issue on a knock on the passenger side that would come and go, usually at start up. Turned out to be two worn rocker arms that were the issue.

Rich

 

Interesting- I came here because I get a tick that sounds like a lifter on my 1964 394 if I let it sit at idle too long. If I shut it off, start it up again and go for a drive, noise is gone. It's only happened once or twice, but it makes me nervous. I'll have to go to a heavier oil. I'm using a conventional 10W-30.

 

Two sources of intermittent engine noise have been mentioned, lifter bleed down and carbon breaking loose rattling on top of a piston. I'd try Rislone for the lifters and perhaps Techron or GM Top Engine Cleaner if it seems more like carbon.