39 ford tick/rattle when cruising not on accel

[Mikewatson]

39 ford flathead sounds normal idleing ,free reving , and low rpm driving.
Drive it at 50 in 3rd the motor rattles when barely on the gas to mantain speed . Push the gas a bit and it goes away . Any ideas?

[Lanny]

Possibly a loose fan ?



.

[ford38v8]

Without more specific information, the only thing that comes to mind is a possibility of the air cleaner not being mounted correctly to the carburetor.

[SoCalCoupe]

Could be just about anything. I had a metallic "tick" that drove me nuts for a year and half. Finally noticed that the "tick" was synchronized with the vibration of the ammeter. Very likely one of the voltage regulator cutouts cycling on and off. Replaced the voltage regulator and that fixed it.

Originally Posted by ford38v8

Without more specific information, the only thing that comes to mind is a possibility of the air cleaner not being mounted correctly to the carburetor.

Had a "rattle" too and just like Alan says, it was the air cleaner not tightened to the carb. Had fiddled with it, put it back on and forgotten to tighten the screws.


Banged around lightly under the hood with my fist and found that yet another "rattle" was one of the inner fenders rattling against the frame. Found a hole on the frame aligned with a hole on the inner fender but no fastener. Added a fastener and that was the end of that "rattle".

[Mikewatson]

It’s a loud noise rpm dependent , sounds like a rod knock but odd that it only higher rpm and hard on the gas it’s doesn’t make any noise .

[SoCalCoupe]

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Originally Posted by Mikewatson

It’s a loud noise rpm dependent , sounds like a rod knock but odd that it only higher rpm and hard on the gas it’s doesn’t make any noise .

Good information that it's RPM dependent. In that case, doesn't sound like any of my suggestions apply.


Another possibility. Had a small block Chevy several years ago with a RPM dependent tick. Thought it was valves but it turned out to be an exhaust manifold that wasn't sealing tightly to the head.


Again, could be just about anything. Any other clues? Good luck.

[Brian]

rod bearings

[Kube]

Originally Posted by Mikewatson

It’s a loud noise rpm dependent , sounds like a rod knock but odd that it only higher rpm and hard on the gas it’s doesn’t make any noise .

Rod knock is very distinctive and typically more pronounced upon deceleration.

[md8810]

Had a similar noise in an 8BA. Highway Cruising with no load or engine "floating" with a neutral throttle, the noise would come in and out.
Clyde of C&G suggested that the piston to head clearance might too tight. As usual, he was correct.
The late Dode Martin slightly reshaped the heads combustion chambers and the noise issue was solved.
Under the floating conditions, the rod/crank clearance as added to the length of the piston and rod length just a few thousands and can be enough for the piston to kiss the head combustion chamber.
I never would have figured that out..