I have a 390 FE in my 76 Highboy. It has a performance CAM. Not sure the brand or specs. The engine has a valve train tap/knock. It seems to fade when I rev it or shift to a higher gear with medium load. I tested the compression, all are within 95 to 120 lbs. Oil pressure is decent. Seems to drop as engine warms. Spent the last 2 Saturday's replacing all the lifters thinking it was definitely a lifter problem. But, its still making noise. Not sure where to go from here. Only thing I noticed is when I remove the #4 spark plug wire. The sound doubles. Not louder, just sounds like two clicks instead of just one. Any comments or help would be greatly appreciated.


Here's a link to a video:

https://www.facebook.com/photo.php?v...66305494036531

 

How much is your oil pressure dropping when warm?

 

It's the factory gauge. Oil pressure starts around 2/3 and drops to about 1/3.

 

If you think you know what cylinder is causing it, i would pull the sparkplug and both the intake and exhaust pushrods for that cylinder and let the valve cover off. That will let you know if its a drivetrain noise, or somthing worse. That sounds like a loud noise to be a lifter.

are your valvesprings ok? The lobes on the cam look ok?

 

The valve springs look ok. The cam looks ok. A friend of mine who is a mechanic, thinks I might be missing some teeth on my timing chain gear. He says these are plastic. I've never dealt with the timing chain on a 390.

 

It could be, but i would think that they all would have stipped by now if it was skipping a few teeth and grabbing again.

Anyway, here is a vid of what i found on the last FE i tore down.

 

Mustang GT 350, did you mean take the spark plug out or just remove the spark plug wire?

 

sorry for the confusion. I was meaning this.

If you pull the pushrods both the intake and exhaust pushrods and the spark plug from the cylinder you think it is (since you think you know what cylinder is causing the noise) and start it you should be able to tell if its a valve train noise if it doesnt make the noise with the engine running since there would be no load on the lifters, valves, or cam lobes for that cylinder

The reason for pulling the plug is to relieve the pressure from that cylinder to make it turn over easier since both valves will be closed. And with both pushrods out of that cylinder there will be no load on those 2 lobes, and lifters. So that will let you know that somthing under load is making noise in that section of the valve train. Now, I'm assuming that if somthing is going on with the cylinder itself that it would still make that noise even without that cylinder firing. So theres a chance if it still does the noise and you have tried all the cylinders that you think are causing the problem that it could be rotating assembly related.

Now on another note. I'm wondering if you remove all of the plugs (to make it spin faster) and turn it over starter speed if the rotation of the starter would be fast enough to cause the noise you are hearing? If so you could just do that and narrow it down without having to fire the engine while its partially torn apart.

These are just brainstorms and i'm not a engine pro like some guys in here, but i have found with most things the best way to find a problem is by removing parts of the equation a piece at a time if there is a realistic way of doing so.

EDIT
I forgot to mention i would NOT rev the engine while the pushrods are pulled. I'm pretty sure they should stay in their homes at idle and even a little higher, since they sit pretty deep in the bores, but i have never tried this so proceed with caution.

 

Are your valve covers dented anywhere? Could be rocker arms hitting them if they are dented. If not then I think its a wrist pin noise. The noise is to low of a pitch to be a valve train noise. I had a wrist pin bushing go bad sounded just like that. Try pulling one plug wire at a time then replace while running. Be careful doing so use a pair of insulated pliers to remove to reduce the risk of shock. Also partialy loosen wires prior to starting helps. Listen to the engine as you pull wires if the noise goes away or gets louder the cause of the noise is coming from that cylinder. If it is a wrist pin the noise should go away or not be as loud. Do to not as big of load on pin bushing.

 

Hello phantomtruck68, already tried removing spark plug wires. The sound doesn't go away. It only doubles when I pull the wire from cylinder #4. I sure hope its not a wrist pin. That would suck.

 

Hello, Yeah I hated hearing it when it was mine. What condition are your valve covers in? Could the rocker arms be hitting them?

 

Valve covers are fine. I ran the engine with both valve covers off and it was still clicking. But, I have a funny feeling it is the wrist pin. I'm still gonna try what mustang GT 350 said and do another compression test.

 

I'm leaning towards internal, and not valvetrain related. Thats a nasty noise to be a cam/lifter issue

 

Thanks for all the feedback. I'll post my findings as soon as I can get back to it.

 

Have you had the valve covers off and started after you discovered the noise??/ and watched the side of the engine where the noise was coming from??/ Reason being is that my 390 had a lifter noise after removing the valve cover, started and watching the valve train I discovered that one of my rocker arms was falling off the valve(none adjustable valves), you probably won't have that problem if you have adjustable rocker set up,the only thing that keeps the rocker separated are a set of weak springs between the rockers!!/ correction to the problem was at then either Summit or Jeg's auto parts carried a set of aluminum spacers that replace the weak spring that separate the rockers (sleeves) that fit over the rocker shaft!!/ They work but you won't know if thats the problem until you remove the valve cover and start the engine??/